Localization

Brain Structure

• The nervous system is a system of neurons— cells that perform the function of communication in the body.

• The central nervous system consists of the spinal cord and the brain.

• The major parts of the human brain are the cortex, the cerebellum, the limbic system, and the brain.

• The cortex is the layer of neurons with a folded surface covering the brain on the outside. It is the most significant part of the human brain associated with higher-order functions such as abstract thought or voluntary action. Evolutionarily, this part of the brain developed the latest. The cortex is divided into four sections called “lobes”.

• The frontal lobes are associated with reasoning, planning, thinking and decision-making, voluntary action, and complex emotions.

• The parietal lobe is associated with movement, orientation, perception, and recognition.

• The occipital lobe is associated with visual processing.

• The temporal lobes are associated with processing auditory information, memory, and speech.

• There is a deep furrow along the cortex that divides it into the left and right hemispheres. A structure of neurons that connects these two hemispheres is known as the corpus callosum.

• The limbic system is an evolutionarily older subcortical structure. It consists of: the thalamus which has mostly sensory functions, the hypothalamus which is below the thalamus in the brain and is involved in functions of emotion, thirst, and hunger, and the amygdala which is involved in memory, emotion, and fear. and the hippocampus which is important for learning, memory, and transferring short-term memory to a more permanent store, spatial orientation.

• The brain stem is underneath the limbic system and its main function is to regulate breathing or heartbeat. It connects the brain to the spinal cord.

Research supporting strict localization

• The first research studies that inspired psychologists to investigate the idea of strict localization of function were performed with patients with brain damage. These studies showed that a person with damage to a very specific brain area may demonstrate a very specific malfunction in behavior.

  Tan’s Case study

• One of the earliest discoveries in this sphere was the discovery of a speech center by Paul Broca (1861) in the case study of “Tan”.

• Tan lost the ability to speak when he was 30. Later, Tan developed gangrene and was admitted for surgery which was to be performed by Paul Broca.

• By that time “tan” was the only syllable that Leborgne could pronounce. His inability to speak (or write) was the only malfunction: his intelligence was intact, he understood everything he was asked and tried to communicate back.

• Broca described Tan’s condition as Broca’s aphasia (the loss of articulated speech).

• An autopsy of Tan’s brain was carried out and it revealed a lesion in the frontal area of the left hemisphere. This region is now known as Broca’s area.

Wernicke’s Area

• Wernicke’s area was discovered by Carl Wernicke in 1874.

• It is an area located in the temporal lobe of the dominant hemisphere.

• Wernicke’s area is responsible for the comprehension of written and spoken language.

• People with Wernicke’s aphasia have a general impairment of language comprehension, while at the same time speech production is intact. As a result, when they speak they sound really fluent and natural, but what they say is in fact largely meaningless.

Research opposing the idea of strict localization

• Karl Lashley used the technique of measuring behavior before and after a specific carefully controlled induced brain damage in the cortex of rats.

• Procedure - In a typical study, he would train a rat to run through a maze without errors in search of food. After learning occurred, he would remove an area from the cortex. Then, he placed the rat back at the start of the maze and registered the change in behavior. He removed varying portions of the cortex in different rats.

• Hypothesis - The idea was that if the memory of the maze is localized somewhere, then by removing area after area you will finally be able to pinpoint the specific region in the cortex responsible for it. This search turned out to be a failure, so Lashley abandoned his own initial hypothesis.

• Conclusion - He concluded that memory was distributed rather than localized; a conclusion supported by the following observations: The principle of mass action is based on a correlation observed between the percentage of cortex removed and learning abilities. The less cortex, the slower and more inefficient the learning. The key idea here is that performance deterioration depends on the percentage of cortex destroyed but not on the location of the destroyed cells. Equipotentiality—this refers to the ability of one part of the cortex to take over the functions of another part of the cortex. These observations led Lashley to conclude that memory is widely distributed across the cortex.

• Relative localization - admits localization for some functions under some conditions, but it also clearly outlines the limits of localization.

Relativity of Localization: The split-brain research

• Lateralization—the division of functions between the two hemispheres of the cortex. Lateralization is a special case of localization.

• Research in this field was conducted by Roger Sperry.

• He published the results of the first research with human split-brain patients.

• Procedure - Four of the ten patients who had undergone this surgical procedure by that time agreed to participate. The patients were examined thoroughly over a long time period with various tests. The researchers devised a technique where the participant had to sit in front of a board and look at the dot in the middle of it. Visual stimuli would then be presented for one-tenth of a second either to the left or the right visual eld. Optic nerves from the left eye are connected in our brain to the right hemisphere, and vice versa. So, by presenting the stimulus to the left visual field the researcher “sends it” to the right hemisphere, and stimuli from the right visual field go to the left hemisphere. Also, a variety of objects were placed behind the screen so that participants could feel them with their hands.

• Aims - The aims of the study were to test the theory of lateralization and to see if the two hemispheres have uniquely different functions.

• Results - When shown the picture of a spoon to the left visual field (connected to the right hemisphere) and asked to name or describe what they saw, the patients said nothing. However, when asked to pick a corresponding object from a group of objects behind the screen, they felt around and picked a spoon (with their left hand, because it is controlled by the right hemisphere). Patients could not explain why they picked the spoon. The right hemisphere saw the spoon and picked it from behind the screen using the left hand, but the center of speech is in the left hemisphere so the patients were unable to explain what they saw and what they did. This supports the lateralization of language in the left hemisphere.

Neuroplasticity

Definitions

• Neuroplasticity is the ability of the brain to change throughout the course of life. The change occurs through the making and breaking of synaptic connections between neurons. In this process, neural networks in the brain literally change their shape. The reasons for such changes are both genetic and environmental.

• Neuroplasticity can be observed on different scales. On the smallest scale, at the level of a single neuron, it takes the form of synaptic plasticity: the ability of the neuron to form new synaptic connections and break up the old ones. On the largest scale, neuroplasticity takes the form of cortical remapping: the phenomenon when brain area X assumes the functions of brain area Y, for example, due to injury.

• Synaptic plasticity depends on the activity of neurons. If two nearby neurons are frequently activated at the same time, a synaptic connection between them may gradually form. Similarly, if two neurons are rarely activated together, the existing connection may gradually fall apart.

Remapping of the sensory cortex

A study of neuroplasticity on the level of cortical remapping was done by Merzenich et al (1984).

Procedure

• Researchers studied the cortical representation of the hand in eight adult owl monkeys.

• Sensory inputs from all fingers were mapped in the cortex. To do this, electrodes were inserted in the cortical area known to be responsible for sensation from the hand, then researchers stimulated various areas on all the fingers and noted which electrode was responding to the stimulation.

• The the middle finger was amputated.

• Sixty-two days later a remapping was done to see how the cortical area responsible for sensitivity from the hand changed after amputation.

Results

• Results of the first mapping showed that there were five distinct areas in the brain, each responsible for one finger, and adjacent fingers were represented in adjacent areas in the cortex.

• It was found that the adjacent areas (those responsible for sensitivity from digits 2 and 4) spread and occupied parts of the now unused area. The areas responsible for digits 2 and 4 became larger while the areas responsible for digits 1 and 5 stayed the same.

• Conclusion - It was concluded that cortical remapping of sensory inputs from the hand occurs within 62 days in owl monkeys.

Neuroplasticity as a mechanism of learning

Neuroplasticity is not confined to making up for damage. It occurs on a regular basis in our daily lives. For example, neuroplasticity is thought to be the brain mechanism of learning. When you learn, your brain gradually reshapes itself. Draganski et al (2004) conducted a study to find out whether the human brain can really change structure in response to environmental demands.

Procedure -

• The researchers used a random sampling design and a self-selected sample—they randomly allocated a sample of volunteers into one of two groups: jugglers and non-jugglers.

• They made sure that both groups had no experience of juggling before the start of the experiment. Thr first brain scan was performed at this point.

• Participants in the juggler group spent three months learning a classic juggling routin. The second brain scan was performed.

Then the participants spent another three months where they were instructed not to practise juggling. Finally, the third brain scan was performed after this nonpractice period. The control group lived their daily lives and had their brains scanned three times also.

Results

• Comparison of brain scans in the two groups prior to the start of the experiment showed no differences in brain structure.

• At the second scan, however, the juggler group had significantly more grey matter in the midtemporal area of the cortex in both hemispheres . These areas were known to be implicated in coordination of movement.

• At the time of the third scan these differences decreased, but the amount of grey matter in these areas in jugglers was still greater than at the time of the first scan.

• Conclusion - As you learn a simple juggling routine, certain areas of your brain grow. When you fail to practise, they shrink back significantly.

Another well-known study showing both localization of function and neuroplasticity for spatial memory is that of London taxi drivers. The value of this study is that it looks at human neuroplasticity in a natural setting.

• Maguire et al (2000) investigated the brains of London taxi drivers.

• Hypothesis - the structure of the hippocampus would be different because prior animal studies had shown the hippocampus to be involved in spatial abilities.

  Procedure

• Brain scans of control subjects were taken from the database of brain scans at the same unit where brain scans were performed with taxi drivers.

• The scans were obtained by magnetic resonance imaging (MRI). It was important to make the comparison groups as equivalent as possible in terms of potential confounding variables, so some exclusion criteria were applied to the control subjects. Subjects below 32 and above 62 years old were excluded, as well as subjects who were female, left-handed or had any health issues.

• This resulted in the selection of (brain scans of) 50 healthy right-handed male subjects who did not drive a taxi.

  Results

• Results indicated an increased brain matter volume in the brains of taxi drivers as compared to control subjects in the posterior hippocampus.

• At the same time, control subjects had greater volumes of grey matter in the anterior hippocampus. This meant there was no difference between the groups in terms of the general volume of the hippocampus, but there was significant redistribution of grey matter from the anterior to posterior hippocampus in the brains of taxi drivers.

• Brain matter “shifted” from the front to the back.

• Evaluation -

  • However, this study is a quasi-experiment. The researchers did not randomly assign people to be either taxi drivers or controls.

  • The results obtained are therefore essentially correlational and cause-and-effect inferences cannot be made. It seems plausible to suggest that driving a taxi in London leads to the redistribution of grey matter in the hippocampus, but we cannot be certain.

Practical Applications

• Sense substitution - The idea that other senses may be used to make up for the lost sense.

• Another application of neuroplasticity is human echolocation. Some blind people can acquire the ability to see around them with echoes: they produce clicking sounds with their mouths and analyze echoes as the sounds bounce off the objects in front of them.

• Another promising area is brain-machine interfaces. Include artificial sensory organs and bionic limbs that can be controlled by thought.

Neurotransmitters and Behavior

Nervous System Processes

• The nervous system is a system of neurons.

• A neuron consists of three parts: the body (soma), dendrites and axon.

  • Dendrites and axons are filaments that extrude from the soma.

  • The function of dendrites (and soma) is to receive signals from other neurons

  • The function of the axon is to transmit signals further.

  • Where the axon of one neuron approaches a dendrite or soma of another neuron, a synapse is formed. A synapse (or a synaptic gap) is a structure that connects two neurons.

• The nature of information transmission in the nervous system is partly electrical and partly chemical.

  • Every neuron has a certain threshold of excitation received from the other neurons, and if the sum excitation exceeds this threshold, the neuron generates an action potential that travels along the axon to other neurons, passing the excitation further.

  • The action potential is all-or-none: it either fires or not.

  • The pulse reaches the end of the axon and at the synaptic gap, the mechanism of transmission becomes chemical.

    • This happens as follows.

    • When the action potential reaches the end of the axon, a neurotransmitter is released from the axon terminal into the synaptic gap.

    • Neurotransmitters are chemical messengers. They are constantly synthesized in the neuron and moved to the axon terminal to be stored there.

    • A released neurotransmitter is available in the synaptic gap for a short period during which it may be destroyed, pulled back into the pre-synaptic axon terminal through reuptake, or reach the post-synaptic membrane and bind to one of the receptors on its surface.

    • If the neurotransmitter binds to a receptor in the post-synaptic membrane, this process changes the membrane potential and so contributes to activating an electric pulse in the post-synaptic neuron. Here the chemical mechanism becomes electrical again.

• All neurotransmitters are broadly divided into two groups: excitatory and inhibitory.

  • Excitatory neurotransmitters allow the impulse to cross the synapse. They produce stimulating effects on the brain.

  • Inhibitory neurotransmitters stop the impulse, preventing it from crossing the synapse. They produce calming effects on the brain.

• Neurotransmitters themselves are affected by agonists and antagonists.

  • Agonists are chemicals that enhance the action of a neurotransmitter.

  • Antagonists are chemicals that counteract a neurotransmitter and so prevent a signal from being passed further.

    • For example, a class of drugs known as SSRIs (selective serotonin reuptake inhibitors) selectively inhibit the reuptake of the neurotransmitter serotonin from the synaptic gap. This increases the concentration of serotonin in the synapse. SSRIs have been shown to be effective against depression.

Effect of serotonin on prosocial behavior

Crockett et al (2010) investigated the effect of serotonin on prosocial behavior. Serotonin is an inhibitory neurotransmitter that is involved in sustaining a stable mood and regulating sleep cycles.

Procedure

• The experiment followed a repeated measures design with two conditions.

• In condition 1, participants were given a dose of citalopram, a highly selective serotonin reuptake inhibitor (SSRI). In condition 2 (the control) participants were given a placebo.

• The design was counter-balanced, and this was a double-blind study.

• After taking the drug, participants were given a series of moral dilemmas that involved choosing between saving five lives and killing an innocent person. Harmful actions in the scenarios were of two types: personal (for example, pushing a man off a bridge to stop a train and prevent it from hitting people) and impersonal (for example, pressing a lever to divert a train off a track where it will hit ve people to a track where it will hit one).

Results

• Responses in the impersonal version were unaffected by citalopram.

• However, after receiving a dose of citalopram participants were less likely to push the man off the bridge in the personal scenario than participants in the placebo condition.

• Conclusion - Researchers concluded that serotonin reduces the acceptability of personal harm and in this way promotes prosocial behavior.

• Limitation - Citalopram intake induced slight nausea.

  • This might mean that participants could work out what condition they were in on that trial. However, it is not possible to estimate the extent to which this might have influenced the results.

Effect of dopamine on romantic love

• Fisher, Aron, and Brown (2005) conducted a study of the neural mechanisms of romantic love.

• This study suggested the central role of dopamine in the brain's response to loved ones.

Dopamine is an excitatory neurotransmitter that is involved in our desire to get things done (motivation), in controlling the brain’s reward and pleasure centers and in regulating emotional responses.

Procedure

• Men and women who were currently “intensely in love” were recruited for the study.

• The mean reported duration of being in love was 7 months.

• All participants were placed in a functional magnetic resonance imaging (fMRI) scanner and engaged in a standardized procedure involving looking at photographs while their brains were being scanned. There were four stages.

• For 30 seconds each participant viewed a photograph of his or her beloved person.

• Participants were given a 40-second filler activity which was to count back from a given number.

• For 30 more seconds, participants viewed a photograph of an emotionally neutral acquaintance.

• The final stage was another 20 seconds of counting back from a number.

Results

• Results showed a specific pattern of activation in the brains of participants in response to the photographs of their loved ones: activation was observed in dopamine-rich neural systems.

The role of dopamine in Parkinson’s disease

• Freed et al (2001) studied the role of dopamine in Parkinson’s disease. Parkinson’s disease is a degenerative disorder that mainly affects the motor functions of the nervous system.

  Procedure

• The sample consisted of 40 patients who were 34–75 years old and had severe Parkinson’s disease, with the mean duration of 14 years.

• The sample was randomly divided into two groups: the experimental group received a transplant of nerve cells and the control group underwent sham surgery. I

• In the transplant group, nerve tissue containing dopamine-producing neurons was taken from embryos and transplanted into the patient's putamen.

• Four holes were drilled through the frontal bone, after which the tissue was transplanted through long needles.

• In the sham surgery group, holes were drilled in the skull but the dura was not penetrated. Otherwise, the procedure was identical.

• Clinical observations and interviews, and brain scans— positron emission tomography (PET) were conducted. All patients were followed up longitudinally for one year.

Results

• Irrespective of the age group, PET scans revealed increased growth of dopamine-producing cells in the putamen. ●

A reduction of symptoms by 28% was found in the patients in the transplant group, but only the younger ones (aged 60 or younger). No improvement was registered in the older subgroup of patients (aged over 60).

Conclusion

• Transplantation of dopamine-producing neurons in the putamen of patients with severe Parkinson’s disease results in some clinical benefits in younger but not older patients.

• Less response to treatment in older patients despite successful growth of dopamine neurons may be attributed to lower neuroplasticity of the brain.

The role of serotonin in depression

• Serotonin has been shown to be involved in the symptoms of major depressive disorder.

• The serotonin hypothesis states that low levels of serotonin in the brain play a causal role in developing depression.

• Studies have mainly involved clinical trials with two groups of patients.

  • The experimental group would be given a drug that affects levels of serotonin in the brain and the control group would be given a placebo, after which the symptoms of depression would be compared.

• If a drug known to affect serotonin (for example, an SSRI) leads to a reduction of symptoms in the experimental group, it is concluded that the level of serotonin is the cause of depression.

Techniques used to study the brain and behaviour

The commonly used techniques to study the brain and behavior are:

• Computerized axial tomography (CAT)

• Magnetic resonance imaging (MRI)

• Functional magnetic resonance imaging (fMRI)

• Positron emission tomography (PET)

• Electroencephalography (EEG)

CAT

Computerized axial tomography (CAT) works on the principle of differential absorption of X-rays.

Method

• The subject lies on a table that slides inside a cylindrical apparatus, where a moving source of X-rays scans the subject’s head.

• After passing through the head, the X-ray beam is picked up by a detector and analyzed. Bone and hard tissue absorb X-rays better than soft tissue.

As multiple X-ray beams go through the head, the structural features of the brain are revealed.

Advantages

• The strength of this technique is that it is a quick non-invasive method of studying brain structure.

• It has an advantage over standard X-rays because CAT records images of hard and soft tissue and blood vessels simultaneously.

• Unlike some other techniques, CAT scans can be made for people who have implanted medical devices

Disadvantage

• The limitation is that CAT scans involve some level of radiation exposure.

MRI

Principle

• MRI is based on the principle that some atomic nuclei—in particular those of hydrogen atoms—can emit energy when placed in an external magnetic field.

• When these pulses of energy are detected by the scanner, the relative distribution of hydrogen atoms in the brain can be mapped. Hydrogen atoms exist naturally in the body, but their concentration in different tissue is different.

• Analyzing the pattern of emission of energy in response to magnetic fields, we can see inside the brain.

• After excitation by the magnetic field, each tissue returns to its equilibrium state—and the time required to do differs in different tissue. This information is also analyzed. Therefore, it is necessary to transform the parameters of the magnetic eld and switch it on and off repeatedly.

Advantages

• It allows non-exposure to radiation and, as a result, less risk of radiation-induced cancer.

• MRI has a better resolution. This makes it particularly useful for detecting abnormalities in soft tissue—such as the brain.

Disadvantages

• People with metal in their body, for example, cardiac pacemakers or shrapnel, cannot undergo the procedure because metal will attract to the magnetic field.

• An MRI scan can be an issue for claustrophobic people because it requires being placed in a narrow tube. Also, longer scan times are required.

• Lying still for a long time may be problematic for young children, especially since the procedure is new and may be frightening.

• An MRI scan is more expensive than a CAT scan.

• Sometimes the scan will pick up slight abnormalities in the brain structure that are not actually related to the symptoms being investigated. This may create anxiety and cause patients to seek unnecessary treatment.

fMRI

• fMRI can show the ongoing brain processes.

• In a typical fMRI study, the subject is required to carry out some task in which periods of activity are alternated with periods of rest.

Principle

• The principle at work is that when a brain region is active during performing a task, the flow of oxygenated blood in that region increases.

• The response of blood to transforming magnetic fields differs depending on the bow and the level of oxygenation.

• The signal that is analyzed by the fMRI scanner to reconstruct brain activity is known as BOLD (blood-oxygen-level-dependent) signal.

• The flow of oxygenated blood directly correlates with the energy used by brain cells, and this directly corresponds to the level of activity in a specific brain region.

• An fMRI scan is characterized by spatial resolution and temporal resolution.

• Spatial resolution is the ability to discriminate between nearby locations. The resolution of an fMRI scanner is measured in voxels.

• Temporal resolution is the smallest time period in which changes in brain activity can be registered. Think about it as the rate at which snapshots of the brain are taken—“frames per second”.

• Currently, the temporal resolution achieved in fMRI is about 1 second.

Advantages

• It offers excellent spatial resolution (up to 1–2 mm).

• Unlike structural imaging techniques, it allows us to see brain processes.

Disadvantages

• There is poor temporal resolution when using fMRI as compared to electromagnetic techniques such as EEG.

• Claustrophobia, cost, lengthy procedure, and inability to use it with medical implants.

PET

• Positron emission tomography (PET) uses blood flow as an indicator of brain activity.

  Principle

• A radioactive tracer is used that binds itself to molecules naturally used in the brain, such as glucose.

• This radioactive tracer is administered into the subject’s bloodstream. It has a short half-life period

• The scanner then registers radio frequencies emitted by the decaying tracer.

• Brain areas that are more active require more blood supply, so the distribution of the tracer in the brain will depend on what regions are mostly in use at the time of the scan.

• PET has a decent spatial resolution of about 4 mm throughout the brain. However, its temporal resolution is only 30–40 seconds, so quick processes are not easily detected.

Advantages

• The biggest advantage of PET scans is their good spatial resolution, but they are used less and less these days given the existence of non-invasive alternatives (fMRI) which do not require administration of a radioactive chemical.

• PET is useful for detecting tumors and metastases, as well as other diffuse brain diseases so that it becomes clear what areas are affected by the spreading disease. It is often helpful in diagnosing the causes of dementias.

• Scanners can be small.

EEG

• Electroencephalography (EEG) measures electric potentials generated by neural circuits.

• Neurons communicate with each other by sending electrical impulses along their axons.

• An impulse fired in an individual neuron is “invisible” to any device outside of the skull because the impulse is too tiny. However, when large groups of neurons fire synchronously, electric potentials generated by these impulses become detectable at the head surface.

  Principle

• Electrodes are attached to the scalp at predetermined points and pick up the changes in the electric potential of the scalp areas.

• This information is used to generate an electroencephalogram.

• EEG has a perfect temporal resolution. It can detect changes in brain activity within milliseconds.

• However, its spatial resolution is a weakness: EEG is not used to establish the origin location of the electrical signal.

• EEG is good for measuring brain activity “on the whole”.

Use - EEG is commonly used to diagnose such conditions as epilepsy and sleep disorders.

Advantages

• It is a low-cost technique.

• Unlike PET and fMRI, EEG measures neuronal activity directly.

• EEG can be offered as a mobile service because the apparatus can be manually transported.

• EEG is silent, which is an advantage because responses to auditory stimuli can be studied.

• EEG is completely non-invasive compared to most other neuroimaging techniques.

Disadvantages

• EEG offers extremely low spatial resolution, so it only gives a very crude picture in terms of localization.

• EEG is good for measuring electric activity in the cortex, but not so good for detecting activity in subcortical areas. The farther away from the surface of the scalp, the weaker the signal.

• It takes experience to interpret an encephalogram correctly because several artifacts contribute to noise in the data, and the signal-noise ratio is quite low.

Hormones and Behavior

The function of hormones

• Hormones are released into the bloodstream and travel with blood to reach their destination. Conversely, neurotransmission is communication along nerve cells.

• The nervous system regulates rapid processes (movement, emotion, decisions, and so on), whereas hormones can regulate long-term ongoing processes such as growth, metabolism, digestion, or reproduction.

• The degree of voluntary control over neural regulation is higher than over hormonal regulation.

• The nervous system and the endocrine system are interdependent. These two systems interact and can influence each other. Also, some chemicals may be both hormones and neurotransmitters, for example, adrenaline.

• Hormones can only influence cells that have receptors for this particular hormone. Such cells are called target cells.

  • When a hormone binds to a receptor it launches a sequence of changes, some of which are genomic: gene activation or gene suppression.

  • Hormones do not influence behavior directly. Instead, they change the probability that a certain behavior will occur in response to a certain environmental stimulus.

• The most well-known hormones include adrenaline, noradrenaline, cortisol, oxytocin, insulin, testosterone, and oestrogen.

Oxytocin

• Oxytocin is produced in the hypothalamus and released into the blood by the pituitary gland.

• It plays a role in sexual reproduction, childbirth, and social bonding. It has been referred to as “the love hormone”, “the bonding hormone” and “the cuddle chemical”

• Romero et al (2014) demonstrated that oxytocin promotes social bonds in mammals in nonreproductive contexts.

  • Procedure - Dogs were sprayed intra-nasally either with oxytocin or a placebo (in a repeated measure, double-blind counterbalanced design).

    • They were placed with their owner and another dog in the same room and their behavior was recorded by four cameras for one hour.

    • The room was empty except for a chair on which the dog owner sat.

    • The owner was instructed to move the chair in pre-designated positions every 10 minutes, but otherwise sit quietly and not actively interact with the dog.

  • Results -

    • The dogs sprayed with oxytocin showed higher affiliation towards their owner.

    • Affiliation was operationalized as sniffing, licking, gentle touching with the nose or paw, play bouts, and body contact.

    • They also spent significantly more time in close proximity to the owner.

    • Similar results were observed for the dog partner (the other dog present in the room): affiliation and approach behaviors were more frequent in the oxytocin condition.

    • Furthermore, the effect of oxytocin was found to be bidirectional: subsequent blood tests showed that the more often the dog interacted with the owner and the dog partner, the higher the levels of endogenous oxytocin it had.

• Conclusion - The researchers concluded that oxytocin performs the function of maintaining close social bonds in mammals

The role of oxytocin in interpersonal trust

Kosfeld et al (2005) claimed that oxytocin increases trust in humans.

Procedure

• Participants were 128 healthy male students.

• Subjects were randomly allocated into either the oxytocin group or the placebo group. Substances were administered via an intra-nasal spray.

• For the purposes of the experiment, the researchers designed a trust game with real monetary stakes. In this game, subjects were paired anonymously and played the role of either an investor or a trustee. Each round of the game (each with a new partner) consists of three steps

• Step 1 - the experimenter gives both the investor and the trustee an endowment of 12 monetary units.

• Step 2 - the investor needs to decide how much of that to send to the trustee (there are four options: 0, 4, 8, 12). The experimenter triples whatever is sent to the trustee: if the investor sends 4 units, the trustee receives 12, if the investor sends 12 units the trustee receives 36, and so on.

• The trustees have their own endowment, which is added to their total.

• Step 3 - the trustee decides how much of the now available money to send back to the investor. Participants played the game four times in the same role, each time paired randomly with a new partner. At the end of the experiment, the total earned monetary units were exchanged for real money

  Results

• The level of trust in those participants who received a dose of oxytocin was higher than in the control group. The median transfer of investors was 10 in the oxytocin group and 8 in the control group. Forty-five percent of subjects in the oxytocin group showed the maximum trust level (12 monetary units), whereas only 21% in the placebo group showed the maximum trust level.

• The authors suggested two alternative explanations for this finding. ● Oxytocin reduces risk aversion in general. ● Oxytocin increases people’s trust in other humans.

• In order to clarify, they designed a follow-up study in which an independent group of subjects played a similar trust game, but this time against software. The algorithm in the software was modeled after the decisions of real people (trustees) in the previous experiments, so the investors faced exactly the same risks as in the “human” experiment, only this time they knew they were playing against machines.

• No difference was observed in this experiment between the oxytocin and placebo groups. The median transfer was eight monetary units in both conditions.

• Conclusion - The researchers concluded that oxytocin specifically affects trust in interpersonal interactions.

The role of oxytocin in fidelity

Scheele et al (2012) showed that oxytocin modulates social distance between men and women.

Procedure

• The researchers studied heterosexual men. Some of them were single and others were in a stable monogamous relationships.

• Using a double-blind independent measures design, a researcher administered either oxytocin or a placebo intranasally.

• Subjects participated in two independent tasks. In the first task—“stop-distance paradigm”— subjects were positioned at one end of the room with their toes on the mark on the floor, while an attractive female experimenter was positioned on the other side of the room. The subject was then required to move slowly towards the female experimenter and stop at a distance that made him feel slightly uncomfortable (too close).

• In the second task—“approach/avoidance task”— subjects viewed a series of pictures on a screen with their head positioned on a chin rest at the viewing distance of 50 cm.

• Pictures were flashed for two seconds each. There were four types of pictures, shown in random order: positive social (attractive women), positive non-social (beautiful landscapes), negative social (mutilations) and negative non-social (dirt).

• All participants had a joystick, and if they liked the picture they were instructed to pull the joystick, which resulted in an increase in the picture’s size. Conversely, if they did not like what they saw, they pushed the joystick and this reduced the picture’s size.

  Results

• In the first task, it was shown that oxytocin stimulated men in monogamous relationships, but not single ones, to keep a greater distance between themselves and an attractive woman. It was concluded that oxytocin caused men in a relationship to “stay away from” an attractive woman who was not his partner.

• Results of the experiment in the second task showed that the only group of pictures affected by oxytocin and relationship status was the positive social group (pictures of attractive women).

• Specifically, participants who received oxytocin had a slower reaction time in response to these pictures, but only if they were in a relationship.

• It was concluded that oxytocin selectively inhibits the approach to certain stimuli—attractive women—in men who are in a stable relationship, but not in single men. From the results of these trials, it is seen that by selectively influencing men in a relationship to keep a greater distance from attractive women they do not know, oxytocin may promote fidelity.

The role of oxytocin in inter-group conflict

De Dreu et al (2012) looked at the role of oxytocin in inter-group conflict—more specifically, defense-motivated non-cooperation.

Procedure

• This was a double-blind experiment using the independent measures design.

• The sample consisted of 102 males and they self-administered either a dose of oxytocin or placebo through nasal spray.

• Participants were randomly assigned to three-person groups and told that they would need to compete against another group of three people. Following this, each participant was paired with a member of another three-person group and played a modied version of the “Prisoner’s dilemma”.

• The two participants were asked to choose, simultaneously and independently, whether they want to cooperate or compete. Although the decision is made independently, both players see the pay-off matrix. They can see the following possible outcomes.

  • If I (the participant) cooperate and he (the outgroup player) also cooperates, I win 7 points, the members of my group win 7, he wins 7 and the members of his group win 7.

  • If I compete and he competes, we only win 6— both I and my group members and he and his group members. This is less attractive than outcome A for all of us.

  • If I cooperate but he competes, he and the members of his group win 8—the largest possible pay-off. At the same time, I only win 5, and the members of my group only win 1. This means that I am vulnerable to my opponent’s non-cooperation, but my group members are even more vulnerable.

  • D If he cooperates but I compete, outcome C is reversed.

• Participants were asked to make a choice between cooperation and non-cooperation five times.

• The numeric rewards were varied in these five trials. The pay-offs from the game were converted to real money and given to the participants.

  Results

• A player’s defense-motivated non-cooperation:

  • is more likely if the vulnerability of the player’s group is high (for example, suppose we change 1 to 0 in the pay-off matrix)

  • does not depend so much on the player’s own vulnerability

  • is more likely in the oxytocin condition.

• The researchers concluded that oxytocin-induced non-cooperation is motivated by the desire to protect vulnerable group members (and not so much by the desire to protect oneself). This reinforces the role of oxytocin in creating bonds with the members of your ingroup but also shows how oxytocin has a reverse, negative side—defensiveness and non-cooperation with others.

The role of oxytocin in human ethnocentrism

De Dreu et al (2011) found that oxytocin promotes human ethnocentrism, a type of inter-group bias where one’s own ethnic group is perceived as more important than or superior to others. When exaggerated, ethnocentrism may lead to xenophobia.

Procedure

• De Dreu et al (2011) conducted a series of experiments all of which used double-blind placebo-control independent measures designs.

• Participants in the studies were indigenous Dutch males. They self-administered either oxytocin or a placebo intra-nasally.

• Experiments involved exposing subjects to images of people belonging either to their ingroup (Dutch males) or outgroup (immigrants from the Middle East and German citizens).

• Experiments used “moral-choice dilemma” tasks, such as the famous trolley problem. Participants in the oxytocin and placebo groups were given a series of moral choice dilemmas where a decision had to be made as to whether one person should be killed in order to save five other people.

• In some of these tasks the target person (the one who had to be killed) was a member of the participants’ ingroup, and in other tasks a member of their outgroup. This was achieved by manipulating the name of the target person: either a typically Dutch, Arab, or German name.

• The other five individuals were unnamed and so their identity or ethnic background was not indicated. The question was, in a task like this, would a Dutch person prefer to sacrifice a non-Dutch person, and how does this depend on oxytocin?

Results

• Under oxytocin, males were more likely to sacrifice an outgroup target than an ingroup target, while under the placebo there was no significant difference.

• There are two alternative explanations for this finding.

  • Oxytocin promotes ingroup favoritism.

  • Oxytocin promotes outgroup derogation.

Pheromones and behavior

Localization of processing pheromonal behavior information in the brain

• processed differently from regular smells. Mammals have a separate structure called the vomeronasal organ (VNO) which is located in the anterior nasal cavity.

• Nerves from the VNO in animal brains connect to a special region called the accessory olfactory bulb. This region is adjacent to but separate from, the main olfactory bulb.

• A major difculty with extrapolating animal research to human behavior is linked to the fact that humans do not have either the VNO or the accessory olfactory bulb.

Search for human sex pheromone: laboratory experiments

Lundstrom and Olsson (2005) studied the effects of androstadienone—a derivative of testosterone and one of the chemical components of sweat.

Procedure

• The study involved studying a woman’s mood after being exposed to: either androstadienone or control solution; and in the presence of either a male or a female experimenter.

Results showed that androstadienone increased women’s mood in the presence of a male experimenter and had no effect when the experimenter was female.

Limitations

• The concentration of androstadienone used in the study was much higher than the normal amount found in male sweat—which is a common feature of pheromone studies.

It is hard to separate the effects of the pheromone from the effects of the experimenter.

Hare et al (2017) investigated whether androstadienone (AND) and estratetraenol (EST)—the best-known candidates for human sex pheromones—signal gender and affect mate perception.

Procedure

• The experiment used a repeated measures design.

• Heterosexual participants completed two computer-based tasks twice on two consecutive days.

• While completing the task, on one of the days they were exposed to the putative pheromone (AND or EST) masked with clove oil, and on the other days they were exposed to a control scent (clove oil only).Substances were administered by a cotton ball taped under the nose throughout the task.

• The design was counterbalanced (some participants had the pheromone on the rst day and the control substance on the second day, some vice versa).

• The first computer-based task involved showing the participants ve “gender-neutral facial morphs”, and participants had to indicate the gender (male or female). In the second task participants were shown opposite-sex photographs and asked to rate them for attractiveness on a scale from 1 to 10.

The study was double-blinded. There were two experimenters—a male and a female—and they alternated for different sessions.

Results

• No difference in gender was assigned to the morphed faces in the pheromone versus control condition.

• Similarly, the results of the second task revealed no difference in the average attractiveness ratings of opposite-sex photographs.

• The authors concluded that AND and EST do not act as signals of gender or of attractiveness, which means that they do not qualify as sex pheromones. Incidentally, the gender of the experimenter had no effect on the results.

Search for a human sex pheromone: field experiments

Cutler, Friedmann, and McCoy (1998) investigated whether synthesized male pheromones increase the sociosexual behavior of men.

Procedure

• Participants were recruited through local press releases that invited volunteers to participate in an experiment with the aim to test whether a male pheromone added to aftershave lotion would increase the romance in their lives.

• There were a number of selection criteria: male, heterosexual, 25–42 years old, in good health, not taking any medication, with regular appearance (“neither unusually handsome nor unattractive”), shaving regularly, and having adequate social skills with women.

• To ensure that participants fitted the selection criteria they were screened with personality questionnaires and anyone with personality traits too strongly deviating from the average was excluded.

• Participants were randomly divided into two groups (in a double-blind manner).

• Each participant brought his aftershave lotion (which was examined by the researchers) and was asked to use it after every shave and at least three times a week throughout the study period.

• Participants were also given a behavioral calendar which they had to fill out daily indicating the incidence of six behaviors on that day.

• The behaviors were:

  • petting, affection, and/or kissing

  • sleeping next to a romantic partner

  • sexual intercourse

  • informal dates (that is, dates not arranged before that day)

  • formal dates (that is, dates that were prearranged)

  • masturbation.

• After a baseline period of two weeks, subjects returned to the laboratory and the technician (who was blinded to the conditions) added either ethanol or pheromone with ethanol to their aftershave lotion.

• The pheromone was a synthesized version of a pheromone naturally secreted by men.

Participants went on to use their aftershave lotion for a six-week trial period (so the total study time was eight weeks).

Results

• Results showed that there were significantly more men in the pheromone group (as compared to the placebo group) who had an increase over the baseline in the first four behaviors (petting, affection and/or kissing; sleeping next to a partner; sexual intercourse; and informal dates).

• For example, 47% of men in the pheromone condition reported an increase in the frequency of sexual intercourse, as compared to 9.5% in the placebo group

• . Differences were not observed for the last two behaviors (formal dates and masturbation).

• Conclusion - The researchers concluded that applying the synthetic pheromone resulted in an increase in sociosexual behaviors in which the willingness of a female partner plays a major role. In contrast, behaviors like masturbation did not increase. The researchers took it as evidence that the synthetic human pheromone did not just increase libido but actually increased the attractiveness of men to women.

McCoy and Pitino (2002) conducted a similar study with female subjects.

Procedure

• McCoy and Pitino (2002) conducted a similar study with female subjects.

• Participants were 36 regularly menstruating women.

• Either the synthesized pheromone or placebo was added to their perfume.

• Seven sociosexual behaviors were recorded weekly across three menstrual cycles—the same six as Cutler, Friedman, and McCoy (1998) used plus an additional category of “male approaches”.

• Similar to the previous study, a significant increase over the baseline was found in the pheromone group (as compared to the control group) in such behaviors as sexual intercourse; sleeping next to a partner; formal dates; petting, affection, and/or kissing.

• There was no increase in the other three behaviors (male approaches, informal dates, and masturbation). The authors concluded that the synthesized pheromone increased the sexual attraction of women to men.

Criticism of research into human Pheromones

• Population validity.

  The fact that most of the studies used self-selected samples (that is, volunteers who respond to posters or advertisements). This means that the majority of studies are performed with young, relatively educated participants.

• Participant bias (demand characteristics).

  • In most studies, researchers try not to disclose the true nature of the study to participants.

  • Mild deception is used and subjects are told that the study looks at the effects of “odors”. However, there are hints that may lead participants to guess the true aims of the study. Many volunteers participate in more than one psychological experiment and they may know that researchers use deception when it comes to revealing the aims of the study.

  • Participants are aware of the exclusion criteria (for example, women using contraceptive pills are not included in the sample).

  • Study surveys or interviews include questions about participants’ sexual orientation. ●

• Ecological validity.

  • Studies typically use a concentrated solution of the pheromone much higher than that found in natural sweat. As a result, some participants can identify the smell and report that the applied solution smells like “sweat”, “urine” and “clothes”

  • . This artificially high concentration can distort participants’ behavior in ways that do not occur naturally.

  • Researchers make efforts to mask the smell by adding a masking agent both to the pheromone and the control solution. This may partially solve the problem of demand characteristics, but not that of ecological validity.

• Internal validity.

  Other smells act as confounding variables, so it is important to control subjects’ odourlessness, which is difficult.

• Experimenter bias.

• Since the study of pheromones focuses on participants’ responses to other people, there are important sources of bias that are more crucial in pheromone research than anywhere else: the gender, the looks, and the behavior of the experimenter t conducting the study. This is difficult to control or keep constant in all the groups.

• Construct Validity

  • Even if the infuence of a chemical substance or a scent on the behavior of human subjects is demonstrated, this does not mean that the chemical substance is a pheromone.

  • There are many smells and substances that can have an effect on human behavior.

  • To be a pheromone, the substance must perform the function of communication between two individuals.

• Ethics

There may be some ethical issues involved.

Genes and Behavior, genetic similarities

Genotype and phenotype

• All cells in the human body that have a nucleus contain a set of chromosomes.

• A chromosome is a thread-like structure that contains a DNA molecule. The long DNA molecule is tightly coiled many times around supporting proteins.

• DNA (deoxyribonucleic acid) stores information. It is a code made up of a long sequence of four chemical bases (A = adenine, G = guanine, C = cytosine, T = thymine).

• The bases are paired up, making a sequence of base pairs. DNA has a characteristic structure of the double helix.

• Humans have 23 pairs of chromosomes, one of each pair from the mother, and the other from the father.

• A gene is a unit of heredity, a region of DNA that encodes a specific trait or function.

• Alleles are different forms of the gene. They can be dominant or recessive. The trait controlled by the recessive allele only develops if the allele is present in both chromosomes in the pair, whereas the trait controlled by the dominant allele will develop if at least one of the chromosomes in the pair contains it.

• The set of traits as coded in an individual’s DNA is called a genotype.

• The set of traits that actually manifest in an individual’s body, appearance or behaviour is called the phenotype. Phenotype comprises observable characteristics (eye color, height, and so on) and unobservable characteristics (blood type, immune system, and so on), as well as behavior.

The nature-nurture debate

Nature-nurture is the long-lasting debate in psychology that attempts to establish whether human behaviour is determined primarily by biological factors such as genetics and brain structure (that is, nature) or environmental factors such as education and friends (that is, nurture).

Methods of research

Twin studies.

The main principle is estimating the similarity between identical (monozygotic— MZ) twins and comparing it to the similarity between fraternal (dizygotic—DZ) twins.

MZ twins develop from the same egg and share 100% of the genotype. DZ twins develop from different eggs and share 50% of the genotype, just like regular siblings. If identical twins are more similar to each other than fraternal twins, we can attribute it to genetic influences.

Family studies.

This method also uses the principle of genetic relatedness, but compares relatives on a broader scale and across generations, for example, comparing children to parents, grandparents, siblings, cousins, uncles, and aunts.

Adoption studies.

These compare adopted children to their adoptive parents, biological parents, adoptive siblings, and biological siblings. We can infer genetic influences if adopted children are more similar to their biological parents than to their adoptive parents.

Molecular genetics.

• Studies of molecular genetics are based on using modern technology for genetic mapping and identifying the alleles of particular genes in a particular individual.

• Genetic variants are then correlated with observed behavior. These methods are usually used to identify specific genes responsible for specific behavior—the “gene of depression”, “gene of aggression”, and so on.

The first three methods involve the use of genetic similarity as the principle of research.

Genetic heritability: the Falconer Model

Genetic heritability is the quantitative measure of the relative contribution of genetic factors to a trait or behavior.

• Estimation of genetic heritability is performed in twin studies and is based on the so-called Falconer model, which assumes that phenotype is comprised of three types of influence.

• These are:

  • genetics

  • shared environment

  • individual environment

• The shared environment is part of the environmental influences that are common to the two twins (such as similar schooling, and the same exposure to books and technology).

• The individual environment comprises environmental influences that are unique to each of the twins (different friends at school, different hobbies, and so on).

• This idea can be written in the following form: 1 = A + C + E (where A = genetic inheritance, C = shared or common environment, E = individual environment).

The influence of genetics on the environment: niche-picking

• Genes and environment are not completely independent: in many instances, genes influence the environment too.

• Niche-picking is the phenomenon when genetic predisposition causes individuals to select environments that, in turn, start to affect their behavior.

• Niche-picking may explain one interesting property of heritability coefficients: they change during life, typically becoming larger. of their genotype, much like regular siblings. In this way, in terms of their behavior, MZ twins become more and more similar with age. This phenomenon cannot be explained by the Falconer model.

Heritability of Intelligence: twin studies

Bouchard and McGue (1981) conducted a meta-analysis of 111 studies on IQ correlations between relatives.

Results

Results of the study demonstrate that intelligence is to a large extent (54%) genetically inherited.

• The assumption that similarity between MZ twins reared apart is solely due to genotype is limited, for these reasons.

  • Many twin pairs were not separated immediately after birth, so they experienced some formative months or years together

  • . Many twin pairs, even when separated, grew up in similar cultural and SES environments. They were not “randomly allocated” into different environments. Twins share a common prenatal environment.

• Moreover, the prenatal environment of MZ twins is more similar to that of DZ twins.

• Twin studies are usually small in sample size and rare due to the uniqueness of their target group. This implies fewer opportunities for replication.

• Twins might not be as representative of the general population as we would like them to be, so twin study findings might not be generalizable to a wider population.

• The similar physical features of the twins might elicit similar responses from the environment.

Heritability of intelligence: adoption studies

Adoption studies provide a direct test of environmental malleability of cognitive abilities.

• There are two aspects of adoption studies that may provide slightly different angles on the nature-nurture problem. These aspects are:

  • computing the correlation between cognitive abilities of the adopted child and the adoptive parents and comparing it to the correlation between cognitive abilities of the adopted child and the biological parents

  • comparing the cognitive abilities of adopted children to those of their siblings who were not adopted but raised by their biological parents. Interestingly, these two approaches yield contradictory results.

• In general, most of the existing studies support the idea that IQ is increased by adoption into more prosperous families. This is demonstrated by comparing the average IQ of children adopted into higher-SES families and the average IQ of their biological home-reared siblings.

• At the same time, the same studies demonstrate that adopted child– biological parent correlations are always higher than an adopted child–adoptive parent correlations, suggesting that the genetic component in cognitive abilities is strong. Together these two effects suggest the additive influence of genetics and environment on the development of intelligence: adopting into higher-SES family results in an increase in IQ, but this increase will be higher or lower depending on the genetic inheritance of the child.

• An example of a study that demonstrated this additive influence is Kendler et al (2015).

• Procedure

  • The researchers conducted a rigorously designed adoption study of a sample of sibling pairs in which one of the siblings was home-reared and the other one was adopted away.

  • IQ scores were taken from the Military Conscription Register. Available data also included the educational attainment of both biological and adoptive parents.

  • Demand for child adoption in Sweden was considerably larger than the number of children available for adoption, so potential adoptive parents were carefully screened. The mean educational level was significantly higher in the group of adoptive parents as compared to biological parents. There was a modest correlation (r = 0.18) between the educational levels of biological and adoptive parents, which may suggest some effects of selective placement.

  • Interpretation of these findings suggests that cognitive ability is environmentally malleable: there was a 5-point IQ increase on average by age 18.

  • The fact that there is a correlation between the cognitive ability of adopted children and the educational levels of adoptive parents supports this conclusion.

  • On the other hand, results also suggest the heritability of intelligence: this is evident from the correlation between the cognitive ability of adopted children and the educational level of biological parents. Results seem to suggest an additive influence of environment and genetics: the largest IQ scores were observed in adopted children from well-educated biological families adopted into well-educated families.

• Scarr and Weinberg (1983) reported on the results of two longitudinal studies launched in 1974, both of which investigated the malleability of intelligence. One of the studies—the Transracial Adoption Study—was designed to see if black children reared by white families performed on tests of IQ and school achievement as well as other adoptees. The other study—the Adolescent Adoption Study—looked at how differences in cognitive ability accumulate over years till adolescence. The Transracial Adoption Study sampled 101 adoptive families who had biological children but who also adopted transracially. Some of the adopted children were black and some white; some children were adopted in the first year of life and some after 12 months of age. All children were assessed on IQ and school achievement tests.

• Results of the study support the idea of the additive influence of genetics and the environment on the development of IQ. In this sense, it corroborated the findings of Kendler et al.

The influence of the environment on genetics: niche-picking

• Biologically, genotype becomes manifested as phenotype through a process called gene expression. Each gene contains instructions for the synthesis of a functional product—in most cases a protein—a molecule that will then influence the chemical composition of the cells that determine the trait.

• Proteins usually are a chain of amino acids. T

• The process of constructing a protein based on the plan encoded in the DNA involves two major steps: transcription and translation. In transcription, the sequence of the gene is copied to make an RNA (ribonucleic acid) molecule. In translation, the RNA molecule is decoded into a sequence of amino acids in a protein.

• In humans, transcription takes place in the nucleus of a cell, and translation takes place in cell structures known as ribosomes.

• A wide range of sophisticated mechanisms can be used by the body to increase or decrease the production of proteins based on the genetic code. Collectively these mechanisms are known as regulation of gene expression.

• The process when chemicals are added to the DNA molecule, and so repress gene transcription, is known as methylation.

• Regulation of gene expression results in epigenetic change-—deviation of phenotypes from the genetic code in the DNA sequence. Epigenetic changes can be attributed to environmental influences, and in this sense, it is a study of how nurture influences nature.

Behavioral epigenetics: regulating the response to stress

• Behavioral epigenetics was demonstrated in the pioneering research of Weaver et al (2004).

• They found that the type of nurturing rats receive from their mothers in the young ones’ early life affects the way their brain responds to stress later in life. More specifically, rats raised by mothers that were less nurturing were more sensitive to stress when they became adults. For example, when their movements were restricted, their adrenal glands produced more stress hormones.

• This increased production of stress hormones was linked to a fewer number of receptors for these hormones in the brain (specifically glucocorticoid receptors). In its turn, the smaller number of glucocorticoid receptors in the brain was linked to the suppression of the glucocorticoid receptor gene.

• The gene itself did not differ in the groups of rats receiving different nurturing, but rats raised by less-nurturing mothers had more chemicals that inhibited the transcription of the glucocorticoid receptor gene. As a result, fewer receptors were produced; more stress hormones were released, and the organism suffered more consequences of stress.

• Miller et al (2009) studied gene expression in people raised in poverty versus wealthy environments. The researchers expected to find increased concentrations of chemicals that suppress the glucocorticoid receptor genes, as predicted by Weaver et al’s research with rodents, but they didn’t. However, they measured these chemicals in white blood cells, and arguably epigenetic changes in brain and blood cells might not be the same.

McGowan et al (2009) conducted post-mortem examinations of the brains of 24 individuals who had committed suicide. Half of these people had been abused in childhood. Examination revealed epigenetic changes in brain cells similar to those in the rodent study: people who had been abused as children had more chemicals in their brain cells suppressing the expression of the glucocorticoid receptor gene.

Behavioral epigenetics: personality traits

• MZ (identical) twins are 100% similar in terms of their DNA sequence.

• However, certain phenotypical differences between MZ twins are observed. Traditionally these differences have been attributed to individual environments.

• However, some recent studies suggest that measurable environmental differences cannot explain all the discordance in identical twins’ phenotypes. There may exist other factors over and above what was suggested in the Falconer model. One such possible factor is epigenetics.

• Kaminsky et al (2008) conducted an extensive case study of a pair of identical twins using cognitive and personality tests as well as genetic and epigenetic tests.

• Procedure - Epigenetic testing was performed on DNA extracted from blood cells.

  • Participants were two female MZ twins, one of them a war journalist and the other an office manager in a law firm.

  • When they were young they were very close to each other and their parents tried to raise them in the same way and ensure they were indistinguishable.

  • At age 17 the “war twin” left home, traveled a lot, and ended up choosing the career of a war journalist working in multiple war zones in Africa, the Middle East and the Balkans. She was exposed to atrocities of war, saw people killed, and lost close colleagues. She married in her forties and never had children. Occasionally she drank alcohol in excess.

  • Her sister’s life turned out to be quite different. She settled down early with a career in law, married young, and soon had two children. She drank alcohol occasionally, but never in excess.

  • Despite living far from each other, the “war twin” and the “law twin” remained emotionally close and met as often as they could.

  • Personality questionnaires showed a difference in that whereas the war twin’s profile appeared normal, the law twin had a tendency to overreact to minor problems with a high degree of anxiety and tension.

  • According to tests, the law twin also was more risk-aversive than the warring twin. Variations in gene expression were examined by comparing methylation pairwise in 12,192 DNA regions (genes).

  • Results showed that one particular gene was differentially methylated in the warring twin and in the law twin. This was the DLX1 gene. This gene is known to be involved in the production of neurons that form a part of the stress center of the brain. The authors suggest that this discordance in DLX1 gene methylation can explain the reduced overall level of anxiety in the warring twin as compared to the law twin.

  • Limitations - A cause-effect relationship in the study should be inferred with caution because differences in DLX1 methylation may themselves have been caused by the environment.

    • The researchers also recognize that one twin pair is not enough to make definitive statements about the role of DLX1 methylation in the development of stress responses in MZ twins.

    • Another important limitation of the study is that DNA was obtained from blood cells and, as you know, gene expression in blood and brain cells may be different.

Evolutionary Explanations for Behavior

The theory of evolution

The modern theory of evolution is based on the following premises.

• Biological organisms are driven by the need to survive and reproduce

• There is considerable variation in the traits of individual organisms from the same population. Organisms having different traits are adapted to their environment to varying degrees—some better, some worse. This is called “differential fitness”.

• Those organisms that are well adapted to the environment have higher chances of surviving and producing offspring. Organisms that are less adapted die out or are unable to produce offspring. This is called “survival of the fittest”.

• Gradually as those organisms that are less adapted do not pass on their genes, those genes disappear from the population gene pool. More adapted organisms produce more offspring, so their genes in the gene pool get stronger. This is called “natural selection”.

• As the environment changes, organisms need to adapt to this change.

Scarce resources (such as food and mates) make organisms fight for survival. The theory of evolution has great explanatory power. It explains the variety of species and their modifications that we observe in the world by placing all these species into a developmental historical perspective. It also traces back common ancestors for all organisms, including humans.

The evolutionary explanation for disgust

Curtis, Aunger, and Rabie (2004) published a study suggesting that disgust evolved as protection from the risk of disease. Researchers reasoned that if this was true, then the following conditions have to be fulfilled.

• Disgust should be felt more strongly when faced with a disease-salient stimulus as opposed to a similar stimulus with less salience.

• Disgust should operate in a similar way across cultures.

• Disgust should be more pronounced in females since they have to protect their babies in addition to themselves.

• Disgust should become weaker as the individual’s reproductive potential declines with age (there is less responsibility to care about offspring).

• Disgust should be stronger in contact with strangers than with close relatives because strangers potentially can carry novel pathogens.

Procedure

• To test their hypotheses, Curtis, Aunger, and Rabie (2004) used a survey placed on the BBC Science website. The survey was advertised in a BBC documentary. It was completed by over 77,000 people from 165 countries.

• First, respondents were asked a set of demographic questions on their age, sex, country, and so on.

Then they were asked to rate 20 photographs for disgust on a scale from 1 (not disgusting) to 5 (very disgusting). Of these photographs, 14 comprised 7 pairs of disease-salient versus less salient stimuli.

Results

• Results showed support for all five hypotheses.

• First, disease-salient stimuli were rated as more disgusting than less salient ones.

• Second, the results were consistent across cultures.

• Third, females rated the disease-salient pictures as more disgusting than men. This was true for all the disease-salient pictures used in the study.

• Fourth, as predicted, there was an age-based decline in the sensitivity to disease-salient stimuli.

• There was one question in the survey that asked participants to choose with whom they would be less likely to share a toothbrush. The average responses ranged in the following order: postman (least likely), the boss, the weatherman, a sibling, a best friend, the spouse, or a partner. This shows that disgust is felt more strongly in contact with strangers than with relatives.

• Therefore, all five tests supported the evolutionary explanation of disgust as a response that reduces the risks of disease.

The role of animal research in human understanding

The value of animal models in psychology research

• An animal model is a concept that refers to using animal research to test a certain cause-effect hypothesis about a certain human behavior.

• There are four major types of experimental manipulation used in animal models (Shapiro, 1998).

• These four types are:

  • genetic manipulation (when animals are bred in a certain way)

  • invasive manipulations with the nervous system (parts of the brain are stimulated with electrodes, lesioned, or removed)

  • invasive manipulations with other body parts (parts may be stimulated by substances or damaged)

  • behavioral and environmental manipulations (such as electric shocks for rats depending on their performance in a maze-learning task).

• Using animal research to inform our understanding of human behavior relies on the assumption that animal and human brains are similar.

.