Biological Approach

Assumptions of the Biological Approach

The most basic assumption is that there are biological correlates of behavior. Biologists study the role that neurotransmitters, hormones, brain structure, and genetics may play in behavior. 

A second assumption of the biological approach is that behaviors can be inherited. Psychologists argue that there is not a single gene for a behavior, but rather that a combination of genetic expression may lead to physiological processes that result in a behavior.

A final assumption is that animal research can provide insight into human behavior; as a result, a significant amount of research is undertaken using animals. 

Structural: create static images of the structure of the brain - do not show activity - research is therefore correlational

CT - Computed Tomography, MRI- Magnetic Resonance Imaging

Functional: series of images that show activity - may conduct limited experiments while participants undergo scan

PET- Positron Emission Tomography, fMRI- Functional Magnetic Resonance Imaging

anterograde amnesia

no longer having the ability to transfer information from short-term memory to long-term memory

Scoville and Milner (1957) HM Case Study

Use of method triangulation to study HM:

• IQ testing: HM’s results were slightly above average with an IQ of 104 before the operation and a slightly improved IQ of 112 after the operation due to the reduction in seizures. 

• Direct observation of his behavior:

  • He would read the same magazines day after day

  • He would forget that he had eaten lunch 30 minutes later

• Interviews with both HM and with family members

• Cognitive testing: memory recall tests and learning tasks - such as the star tracing task (using the image in a mirror)

Findings:

• HM had the short term working memory to hold a conversation, but he could not transfer any new episodic knowledge (memory for events) or  semantic knowledge (general knowledge about the world) into his long term memory.

• He retained procedural memories (motor skills and muscle memory) such as mowing a lawn (but never remembered where the lawnmower was). He also showed improvement on the performance of new hand-eye coordination skills such as the star tracing task. (But he had no memory of his daily practice sessions.)

• H.M. could retain many long term memories from before the surgery.

• This suggests that the hippocampus (which was mostly removed during his surgery) plays critical role in converting memory from short term to long term storage, but it does NOT store:

  • Long term memory

  • Procedural memory

  • Short term (working) memory

Corkin (1992) - HM

• Aim: to confirm missing and damaged areas of HM's brain

• Procedure:

  • MRI scans were used to determine the extent of brain damage

• Results:

  • discovered parts of temporal lobe were missing, including much of the hippocampus and amygdala, but damage not as extensive as originally believed

• Findings:

  • Confirmed Milner’s findings about the hippocampus:

    • plays critical role in converting memory from short term to long term storage

    • not permanent long term or short term or procedural memory store

    • H.M. could learn procedural memories, so those are not stored in hippocampus

    • brain has several complex memory systems supported by distinct brain regions

MRI

• Began to be used in 1970s

• detailed pictures of internal structures in the body - radio frequency transmitter produces an electromagnetic field

• distinguishes between hemoglobin that has given up its oxygen to active neurons and hemoglobin that has not

• strengths:

  • shows blood flow in the brain - circulation problems

  • safe - no radioactive material used - non invasive

  • individuals can be tested repeatedly

• limitations:

  • static picture of brain activity

  • very expensive

  • movement affects pictures - can lead to inaccuracies

  • not for everyone: claustrophobics, people with pacemakers

fMRI

• Invented in 1990s

• improves on MRI by showing blood oxygen-level response over time

• now the dominant method used in brain scanning

• provides three-dimensional pictures of brain structures, using magnetic fields and radio waves.

• Shows actual brain activity - measures changes in blood flow - and indicates which areas of the brain are active when engaged in a behavior.

• strengths:

  • can record activity in all regions of the brain

  • Higher resolution than PET

  • safe - no radioactive material - non invasive

• limitations:

  • focuses on localized functioning in the brain - does not take into account the distributed nature of processing in neural networks

  • Results can be difficult to interpret because of limited spatial resolution

Harris and Fiske (2006)

• Aim:

  • Harris & Fiske wanted to observe the role of the prefrontal cortex and the amygdala in reacting to what they called "extreme out-groups" - that is, homeless and addicts. The researchers wanted to see the biological correlates of a "contemptuous stereotype."

• Procedure:

  • sample of 22 Princeton University undergraduates randomly allocated to two conditions - with 10 participants seeing images of people and 12 seeing images of objects.

  • Once in the fMRI, participants were shown six sets of ten photographs. These photos included people with disabilities, rich businessmen, older people, American Olympic athletes, and homeless people. 

  • The participants were shown a response screen after each image and then, using a joystick, were asked to choose which of the four emotions that they felt toward the image

• Results:

  • Regardless of the emotion that was chosen, the participants in the "objects" group did not show any activity in the medial prefrontal cortex. However, in the images of people, this part of the brain was active.  Or, at least in most cases.

  • There was a clear difference in brain activity when participants rated pictures of addicts or homeless people:

    •  in addition to activation of the amygdala, their brains set off a series of reactions associated with disgust. The insula was activated, which is usually a response to non-human objects such as garbage and human waste. 

    • Even more surprising, the part of the brain that is activated when we think about other people or ourselves – the medial prefrontal cortex – was not activated.

• Findings:

  • Their brains reacted to the homeless people as objects rather than people.

  • Small sample size may be due to cost of fMRI

  • fMRI does not allow for demand characteristics

Localization of Function

• Localization of function is the theory that specific parts of the brain are primarily responsible for specific behaviors or cognitive processes.

amygdala

Plays a role in the formation of emotional memory and fear responses

basal ganglia

plays a role in habit forming and procedural memory

hippocampus

responsible for transfer of short term memory to long term memory, the function of transferring STM to LTM is localized in the hippocampus

Squire (1992) Eugene Poly Case Study

Eugene Poly suffered from viral encephalitis which caused cognitive impairment, he has lesions on his medial temporal lobe which is responsible for the formation of long-term memory, the hippocampus and the amygdala were completely destroyed, he still has procedural memory

• Aim:

  • to carry out a case study that would deepen our understanding of how memory works.

• Procedure:

  • A case study triangulates methods in order to establish the credibility of the findings. 

    • Interviews with EP and his family; for example, EP was unable to describe how he would travel from his home to locations in his neighborhood that he visits with his wife

    • Psychometric testing: for example, IQ testing - which proved no impairment of intelligence.

    • Observational studies - watching how EP solved problems or behaved on memory tasks.  For example, EP could not  remember a string of numbers

    • MRI: found that the anterior temporal lobe was the most damaged - including the amygdala and hippocampus.

• Results:

• Structured interview that asks for detailed information about three periods of life: childhood, early adult life, and recent life. Within each of these periods EP’s memory was tested for both personal semantic knowledge (e.g., What was your home address while attending high school?) and autobiographical memory (e.g., Describe an incident that occurred while you were attending elementary school). The accuracy of all his responses was verified by at least two family members.

  • recent time period - performed extremely poorly

  • early adult life - did better at answering questions, but his scores were still below the control scores

  • childhood - performed normally, scoring nearly as high as the highest-scoring control subjects

• Experiment in which Squire took 16 different objects, glued them on cardboard rectangles, and organized them into 8 pairs. On the bottom of one of the objects in each pair was written the word "correct."  EP had to choose between the two with the goal that with rehearsal, he would be able to consistently choose the "correct" object. The experiment was repeated twice a week for months. 

  • After 28 days he was choosing the correct object 85% of the time; after 36 days he was right 95% of the time. 

  • He would even turn the objects over on his own, even though he didn't remember that there would be a sticker there, as he could not recall ever doing the task.

  • Squire wanted to see if this was true learning - that is, that Pauly actually remembered the objects, or whether there was something else happening. He then asked EP to put all the "correct" objects in a pile.  He was unable to do so.  He could only select the correct object from the consistent pairings.

• MRI indicated that EP's basal ganglia were undamaged.

  • This explains why EP could find the kitchen and the bathroom.  It also explained why he was able to make breakfast and other tasks that were "routine." Of course, this also explains Squires experiment with the pairing of objects.

  • It also explains another phenomenon which EP's wife reported. EP was able to take a walk around the block by himself, since his wife had taken him on a daily walk around the block after his surgery. She would even follow him around the block to make sure that he was ok, but he was able to find his way home without any problems. When he was asked from any point on his walk where he lived, he would say he didn't know, but since the task was associative - or a habit - he was able to simply walk home. However, occasionally there was a problem.  If the sidewalk was being repaired and he had to leave his familiar path, EP would get lost.  Returning to our example of driving a car - even when we drive a long time, bad weather or heavy traffic forces us to concentrate more. The task reverts from associative to cognitive.  When this happened to EP, he did not have the capacity to solve the problem as his memory was only procedural. Once the familiar pattern was changed - as when Squire asked him to put the objects in piles - he was unable to complete the task.

• The conclusions of this case study show us that memory is more complex than initially believed and that the creation of memories is not solely dependent on the hippocampus.  Even with hippocampal damage, tasks may be learned - even though the individual may not remember learning the task.  In the case of HM, he was taught to draw using a mirror, but he never remembered learning this. This was the result of the role of the basal ganglia.

• However, the research also showed that habits need to be triggered.  A cue leads to a routine.  When EP was cued to play the object identification game, the routine was triggered, telling the brain to go into automatic mode.

Neuroplasticity

• Neuroplasticity is the term used to describe the changes in neural pathways and synapses due to changes in behavior, environment, thinking, emotions, as well as changes resulting from bodily injury.

• These changes occur in the structure of the brain as a result of learning or experience - changes in our environment. Every time we learn something new, the neurons connect to create a new trace in the brain.

How does neuroplasticity work?

• Neural networks are formed through this process of dendritic branching; the dendrites of the neurons grow in numbers and connect with other neurons.

• When a neuron is stimulated, an action potential (an electrical charge) travels down the axon. Neural networks are created when a neuron or set of neurons are repeatedly stimulated.  This repeated firing of the neurons, called long term potentiation, results in gene expression which causes the neurons to sprout new dendrites (dendritic branching).  This increases the number of synapses available for the behavior. These synapses are all linked to a certain type of receptor site, so these receptor sites will play a role in a specific behavior.

Neural pruning

which is a decrease in the number of synapses as a result of the removal of dendritic branches. Pruning can be the result of neuron cell death, hormones such as cortisol, or the lack of use of a neural pathway.  The exact mechanism of synaptic pruning is not yet fully understood.

Maguire - Quasi Experiment

• Aim:

  • to investigate whether full licensed taxi drivers in London would have a different hippocampi structure in their brains due to their exceptional knowledge of the city and the hours spent navigating the streets

• Procedure:

  • quasi experiment - no manipulation of IV - IV occurred naturally

  •  London taxi drivers must do a two-year training course where they end up being able to find their way around the city without a map.

  • MRI scans were used to scan the structure of the hippocampi of 16 right-handed male London taxi drivers who had completed the "Knowledge" test and had their license for at least 1.5 years.

  • These scans  were compared to MRI scans of 50 right-handed males  (from an MRI database)

  •  It was also a single-blind study - that is, the researcher did not know whether she was looking at the scan of a taxi driver or a control.

• Results:

  • Posterior hippocampi of taxi drivers were significantly larger relative to those of control subjects (non taxi drivers)

  • the anterior hippocampi were significantly smaller in the taxi drivers

  • the volume of the right posterior hippocampi correlated with the amount of time spent as a taxi driver.

  • No differences were observed in other parts of the brain.

• Findings:

  • argues that this demonstrates that the hippocampus may change in response to environmental demands.

  • concluded that there was probably a redistribution of grey matter in the hippocampi of taxi drivers due to the regular use of the spatial memory skills required to remember roads; the neurons are stronger in areas of the brain which are used most.

  • more synapses are created in the posterior hippocampus which also means more acetylcholine receptor sites which play a role in the creation of memories.

  • Some might argue that those with larger hippocampi might be more spatially talented and thus chose to be taxi drivers; however, this is disproven by the correlation between the size of the hippocampus and the number of years driving.

Bremner

• aim: 

  • to measure the volume of the hippocampus after prolonged stress

• procedure:

  • 33 women participated in this study, including 

    • women who experienced early childhood sexual abuse and were diagnosed with PTSD (N=10)

    • women who experienced early childhood sexual abuse without PTSD diagnoses (N=12)

    • Control group of women without any experience of abuse or PTSD (N=11)

  • MRI to measure the volume of the hippocampus in all of the participants

  • PET scan to measure its level of function during a verbal declarative memory test (remembering a story or list of words)

• results:

  • Women who were abused and showed symptoms of PTSD were found to have 

    • 16% smaller volume of the hippocampus compared to women who were abused but did not have PTSD.

    • 19% smaller hippocampal volume relative to control group

    • a lack of activity in the hippocampus when carrying out the memory task.

• findings:

  • clear correlation between number of years of abuse (based on trauma test), memory problems, and hippocampal volume

  • Reduction of hippocampus may also be explained by depression, which is associated with PTSD.

  • Study has small sample but has been replicated many times.

• Can also work for hormones

action potential

the electrical impulse that travels along the body of of the nueron

neurotransmitters

released into the synaptic gap and go to the receptor sites

Excitatory

activate the neuron - like stepping on a gas pedal. 

inhibitory

• prevents a neuron from firing - like putting on the brakes.

agonists

• Agonists

  • An agonist is a chemical that causes an action; it activates the receptor to produce a biological response.

  • All neurotransmitters are agonists for receptor sites.  

    • They are endogenous agonists since they are biologically already part of our nervous system.  

    • So, acetylcholine is an agonist for AcH receptor sites. 

  • Drugs can also be agonists.  

    • Since they are external to our system, they are exogenous agonists.  

    • Nicotine is an agonist for AcH receptor sites and short-term appears to have some positive effects on memory. 

Antagonists

• An antagonist blocks the action and decreases the effect of the neurotransmitter

• Some antagonists are drugs that block the receptor site on the post-synaptic neuron and do not allow the neurotransmitter to do its job.

  • For example, scopolamine is an antagonist for AcH. 

• Other antagonists block receptor sites on the pre-synaptic neuron and prevent the reuptake process, leaving more of the neurotransmitter available. 

  • SSRIs like fluoxetine, for example, block receptors sites and prevent the reuptake of serotonin as a treatment for depression.

Acetylcholine

Plays a role in consolidation of memory in the hippocampus

• the most abundant neurotransmitter in the body

• promotes memory formation and consolidation by supporting hippocampal synaptic plasticity

• plays a role in motivation, arousal, attention, learning, and memory, and promoting REM sleep

• plays an excitatory role leading to the activation of muscles

Dopamine

Helps control the brain’s reward and pleasure centers.  Plays a key role in motivation; low levels are linked to addictive behavior.

Norepinephrine

Arousal and alertness

Serotonin

Sleep, arousal levels and emotion.

Rogers and Kesner

• Aim:

  • To determine role of neurotransmitter acetylcholine on memory, specifically memory formation.

• Procedure:

  • Rats were trained to go through maze and get to the end where they received food.

  • After rats were able to do this, he injected:

    • 1st group -scopolamine (an antagonist for AcH), which blocks Ach receptor sites - reduces available Ach

    • 2nd group - physostigmine, blocks production of cholinesterase (cleans up Ach from synapse and returns neuron to its 'resting state') - increases available Ach

    • 3rd group – control (saline  injections).

• Results:

  • 1st group - lower Ach levels - slower at finding way round maze and made more errors than control/physostigmine group.

  • 2nd group - higher Ach levels - ran faster compared to both groups and made fewer wrong turns.

• Findings:

  • Acetylcholine played an important role in creating a memory of the maze.

• Evaluation

  • Strengths:

    • Use of an experimental method with a control group made it possible to establish cause- and-effect relationship between levels of acetylcholine and memory.

  • Limitations:

    • Questionable to what extent these findings can be generalized to humans.

Antonova - True Experiment

• Aim: to investigate the role of acetylcholine in memory formation in humans 

• Procedure:

  • 20 healthy male adults randomly allocated to one of two conditions

    • 10 injected with Scopolamine (antagonist for AcH)  to block Ach receptors & decrease available Ach

    • 10 injected with placebo

  • double blind study

  • put into fMRI while playing virtual "Arena task"

    • the researchers are observing how well the participants are able to create spatial memories

    • complex virtual reality game  where participants learn how to navigate arena and find a pole

    • After they have learned where the pole is located, the screen would go blank for 30 seconds.  

    • During this time, the participants were told to actively rehearse how to get to the pole in the arena. 

    • When the arena reappeared, the participant was now at a new starting point in the arena. 

    • The participants would have to use their spatial memory to determine how to get to the location of the pole.

  • The participants' brain activity was measured for six trials.

  • Repeated measures design: participants returned 3 - 4 weeks later and redid the test - receiving the opposite injection  

• Results:

  • the participants injected with scopolamine had lower Ach levels

    • had a significant reduction in the activation of the hippocampus compared to the placebo group

    • took longer on average to find the pole (but not a significant difference)

• Findings:

  • Ach seems to play a key role in encoding of spatial memories in humans as well as rats

Key Issues with Neurotransmitters

• Research on neurotransmission can only be done indirectly, using fMRI technology.

• One of the key strengths of neurotransmission theories is that they have led to successful treatments for certain behaviors. Successful drug treatments have been developed for psychological disorders.

• There is experimental research that supports the role of neurotransmitters in behavior. These experiments can be replicated to establish reliability.

• However, many of these studies are on animals. This means that we cannot guarantee that the neurotransmitter plays the same role in human behavior.

• Much of the research on humans in correlational in nature. This means that we cannot establish a cause and effect relationship. For example, in the case of depression, bidirectional ambiguity is a problem. We do not know if a deficit in dopamine and serotonin causes depression or whether these deficits are a result of depression.

• The argument that neurotransmitters are the cause of behaviour is reductionist. 

Hormones

chemicals produced by glands that make up the endocrine system, released directly into the bloodstream

Cortisol

Secreted by the adrenal glands; helps control blood sugar levels, regulate metabolism, reduce inflammation and assist with memory formation

• Produced by adrenal cortex in response to stress

• Chronic stress may result in prolonged cortisol secretion with impairment of learning and memory

• Cortisol is a steroid hormone made in the cortex of the adrenal glands and then released into the blood, which transports it all round the body.

• Almost every cell contains receptors for cortisol and so cortisol can have lots of different actions depending on which sort of cells it is acting upon.

  • These effects include controlling the body’s blood sugar levels and thus regulating metabolism, acting as an anti-inflammatory, influencing memory formation, controlling salt and water balance, influencing blood pressure and helping development of the fetus.

Oxytocin

Produced by the hypothalamus and secreted by the pituitary gland.  When it affects the brain, it acts as a neurotransmitter.  Plays a role in mother-child attachment; believed to play a role in social bonding and trust between people.

• Produced by hypothalamus after being stimulated by pituitary gland

• Released with touches and hugs – “the love hormone” or "the cuddle hormone"

• The hormone causes uterine contractions during labor and helps shrink the uterus after delivery. When an infant suckles at his or her mother's breast, the stimulation causes a release of oxytocin, which, in turn, orders the body to "let down" milk for the baby to drink.

• Oxytocin also promotes mother-child bonding. Studies show that female rats find pups to be aversive if [the females are] virgins, but once they give birth, the brain is transformed, so they find the pups irresistible.

• In men, as in women, oxytocin facilitates bonding. Dads who got a boost of oxytocin via a nasal spray played more closely with their 5-month-old babies than dads who didn't get the hormone zap, a 2012 study found.

• oxytocin may be making social information more salient:

  • This anti-social effect of a social hormone brings some nuance to the story of oxytocin. In one study, researchers found that Dutch students given a snort of the hormone became more positive about fictional Dutch characters, but were more negative about characters with Arab or German names. The finding suggests that oxytocin's social bonding effects are targeted at whomever a person perceives as part of their in-group.

  • In another study, men were given a dose of oxytocin and asked to write about their mothers. Those with secure relationships described their moms as more caring after the hormone dose. Those with troubled relationships actually saw their mothers as less caring. The hormone may help with the formation of social memories, according to the study researchers, so a whiff strengthens previous associations, whether good or bad.

Scheele - True Experiment

• Aim: to investigate whether oxytocin may promote fidelity in men

• Procedure:

  • participants were 86 heterosexual men, some single and some in stable monogamous relationships

  • using a double-blind independent measures design, a research administered either oxytocin or a placebo intranasally

  • participants were positioned at one end of the room with an attractive female experimenter on the other side of the room

  • participant was required to move slowly towards the female experimenter and stop at a distance that made him feel slightly uncomfortable

• Results:

  • placebo group: both single males and those in relationships stopped at a mean of 57 cm away from the female experimenter

  • oxytocin group: single males stopped at a mean of 59 cm away from her; those in relationships stopped at a mean of 71 cm away

• Findings:

  • oxytocin stimulated men in monogamous relationships, but not single men, to keep a greater distance between themselves and an attractive woman

  • oxytocin levels could promote fidelity by influencing men to keep greater distance from attractive women they do not know

  • Single men didn't see any effect from the hormone, suggesting oxytocin may work as a fidelity booster for guys who are already bonded with another woman.

Pheromones

A pheromone is a chemical substance produced and released into the environment by an animal affecting the behavior or physiology of others of its own species. 

• In animals, we see two types of pheromones.

  • Primer pheromones that cause slow, long-term physiological changes, such as hormonal effects

  • signaling pheromones that produce rapid behavioral effects, such as mating. 

    • for mammals, one of the most important forms of messages they carry are communiqués about reproductive status and availability

    • androstenone, a pig pheromone, turns a sow's attention to mating and nothing else, and induces her to assume the sexually ready position.

    • This automatic reaction has been exploited by pig farmers wishing to spare the expense of keeping male studs.

    • There is a commercially available spray of androstenone called "Boar-Mate" that given to a sow, eases the process of artificial insemination. 

Vomeronasal Organ (VNO)

A small organ located in the nasal cavity of many animals, responsible for detecting pheromones and influencing social and reproductive behaviors.

Doucet

• Aim: investigate the role of secretion of the areolar glands in suckling behavior in 3-day-old infants. 

• Procedure:

  • 16 infants (8 male; 8 female - 8 breast fed; 8 bottle fed)

  • double blind experiment

  • administered different secretions to the infants by passing a glass stick one centimeter under their noses

  • measured their heart rate and breathing rate and mouth movement (rooting, munching, tongue or lips protrusions, licking, and sucking)

  • compared the infants' reactions to seven different stimuli

    • secretions of areolar glands (located near the nipple) from non-related women

    • human milk from their mothers, human milk from other women,  unpasteurized cow milk, formula milk, and vanilla

• Results:

  • found that the infants began sucking only when exposed to the secretions of the areolar glands

  • In addition, there was a significant increase in their breathing rate.

• Findings:

  • this stimulus of the aerolar odor may initiate a chain of behavioral and physiological events that lead to the progressive establishment of attachment between the mother and the infant

  • effect appears to be species-specific (aerolar gland had more effect than cow milk) rather than individual-specific (secretions were not from their own mothers)

  • However, more research is necessary to definitively draw these conclusions

Wedekind

• Background:

  • Major Histocompatibility Complex (MHC) genes play an important role in the immune system by making molecules that enable the immune system to recognize pathogens

    • more diverse MHC genes of the parents = stronger immune system of the offspring

    • we inherit the MHC alleles from both of our parents and they are expressed equivalently

    • It would be beneficial, therefore, to have evolved systems of recognizing individuals with different MHC genes and preferentially selecting them to breed with to maximize immune responses.

    • Evolutionary psychologists argue that our “smell” is the sign of our MHC.

Aim:  to determine whether the relative similarity of MHC genes would affect mate choice

• Procedure:

  • sample was made up of 49 female and 44 male students from the University of Bern, Switzerland.

  • Each participant was “typed” for their MHC, and a wide variance of MHCs were included in the sample. It was noted if the women were taking oral contraceptives.

  • The students probably did not know each other – as they were from different courses: women from biology and psychology; men from chemistry, physics, and geography.

  • The men were asked to wear a T-shirt for two nights and to keep the T-shirt in an open plastic bag during the day. 

    • They were given perfume-free detergent to wash clothes and bedclothes, and perfume-free soap for showering. 

    • They were asked not to use any deodorants or perfumes, to refrain from smoking tobacco or drinking alcohol, to avoid all spicy foods, and to not engage in any sexual activity.

  • Two days later, the women were asked to rank the smell of 7 t-shirts, each in a cardboard box with a “smelling hole.” 

    • The women were tested whenever possible in the second week after the beginning of menstruation, as women appear to be most odor-sensitive at this time. 

    • The women were also asked to prepare themselves for the experiment by using a nose spray for the 14 days before the experiment to support regeneration of the nasal mucous membrane and to protect against colds or flu.

  • Independent Variable:

    • Three of the seven boxes contained T-shirts from men harboring MHC similar to the woman's own

    • three contained T-shirts from MHC-dissimilar men

    • one contained an unworn T-shirt as a control

  • Alone in a room, every woman scored the odors of the T-shirts for intensity (range 0-10) and for pleasantness and sexiness (range 0-10, 5 = neutral).

• Results:

  • Women scored male body odors as more pleasant when they differed from the men in their MHC than when they were more similar.

  • This difference in odor assessment was reversed when the women rating the odors were taking oral contraceptives.

• Findings:

  • This suggests that a pheromone carrying a message about MHC genes influence human mate choice.

  • The study has been successfully replicated by Jacob et al (2002). Yamazaki et al. (1976) showed this to be the case for male mice, which show a preference for females of different MHC.

  • The contraceptive pill seems to interfere with natural mate choice. If the pill changes preferences for familiar as well as unfamiliar body odors, then starting on the pill after developing a relationship could have an influence on the stability of the relationship by influencing odor preference.

  • Research shows that couples who suffer from repeated miscarriages often share a higher proportion of their MHC than control couples in many different populations (Beer et al. 1985). Also, newborn babies of such couples often have a reduced birth mass (Reznikoff-Etievant etal. 1991). So the ability to detect MHC could play a key role in a woman’s search for the “best mate.” Of course, such a “decision” is not a conscious one.

  • Miscarriages in mice can be experimentally induced by the odor of a male which genetically differs only in his MHC from the fathering male (Yamazaki et al. 1983).

  • Some argue that the theory is too reductionist – that is, it over-simplifies the behavior of human mate selection by bringing it down to the MHC – ignoring cognitive and socio-cultural factors.

This was a double-blind quasi-experiment. Neither the researchers nor the participants were aware of which t-shirt they were being exposed to at any point in the study. This was done in order to minimize demand characteristics

Arguments for Pheromones

• Other mammals have them.

• We also secrete scents like other mammals.

• Some mammals detect pheromones using their olfactory system (sense of smell), so it is possible that we do, too.

• Doucet showed that babies respond to pheromones in order to find their mother's breast and engage in rooting behavior.

• Sobel showed that air-borne chemicals can affect the nervous system without being consciously detected.

Arguments against pheromones

• Human mating behavior is influenced by cognitive and sociocultural factors - including learned experience and social norms.

• Studies on pheromones have often not been replicated and tend to have small sample sizes.

• Humans do not appear to have a functional VNO which most animals use to detect pheromones.

• Smells are not necessarily pheromones. 

  • The human scent is complex and made up of many different molecules.  

  • We have about 400 different kinds of odor receptors, each with genetic variations (Axel & Buck).

  • Many body odors are actually not caused by secretions but by bacteria that mix with our secretions - for example, in the armpits.  However, about 20% of the population does not have this bacteria and thus does not create the same scent.  

Culture plays a key role in our sense of smell - we learn what smells bad and what smells good.  This could be a confounding variable when trying to determine the role of pheromones on behavior.

Epigenetics

• argues that in order for a behavior to occur, genes must be “expressed.” 

• Genetic expression is a complex chemical reaction to environmental or physiological changes that allow a gene to “do its job.” 

• environmental factors such as stress, exercise or diet, may result in genetic expression, or the lack of genetic expression.

• an individual may have a gene that could lead to a behavior, but if the gene is never expressed, then this behavior will not occur.

Caspi

• Aim:

  • to determine whether there is evidence for a gene-environment interaction (G x E) for a mutation of the serotonin transporter gene - 5-HTT, involved in the reuptake of serotonin in brain synapses

• Procedure

  • Caspi and his team looked at a sample of 847 New Zealand 26-year-olds. All were members of a cohort that had been assessed for mental health on an every-other-year basis until they were 21.

  • They were divided into three groups based on their 5-HTT alleles: Group 1 had two short alleles; Group 2 had one short and one long allele; Group 3 had two long alleles. The mutation of the 5-HTT gene has the shorter alleles. Roughly 43% of people have the shorter alleles.

  • The participants were asked to fill in a "Stressful life events" questionnaire which asked them about the frequency of 14 different events - including financial, employment, health and relationship stressors - between the ages of 21 and 26.  They were also assessed for depression.

• Results

  • concluded that people with one or two copies of this short allele exhibited more depressive symptoms, diagnosable depression and suicidal ideation in relation to stressful life-events than individuals who carried the long allele of 5-HTT.

• Findings:

  • correlational, so no cause and effect relationship can be determined.

  • makes an assumption that low serotonin levels are directly linked to depression.

  • Information about life-events was self-reported.  It may be the salience of the negative life events which plays a role in depression - that is, those that recalled them more easily (ruminate on them) may have a tendency toward depression.  Those who are more resilient, may not recall negative life events as easily.

  • This holistic approach acknowledges the interaction between biological and environmental factors in depression. 

  • Later studies have been able to show similar results.  It appears that the study has high reliability.

  • There were some participants who did not carry the gene mutation who became depressed; therefore, we cannot say that gene expression alone can cause expression.

Kendler - twin study on MDD (Correlation)

• Aim: 

  • Kendler and his team wanted to investigate three questions in their study:

    • Past studies suggest a 35 - 45% heritability of major depression. Would this be true in a large Swedish sample?

    • Are there significant gender differences in the heritability of major depression?

    • Is there evidence that genetic and environmental factors in major depression differ over time?to investigate prevalence of MDD in twins

• Procedure:

  • The sample was made up of 15,493 complete twin pairs listed in the national Swedish Twin Registry. The twins were born between 1886 and 1958. Only twins whose zygosity could be verified were used in the study.

  • In order to gather their data, the researchers used a team of trained interviewers to carry out telephone interviews.  Interviews were carried out between March 1998 and January 2003. The interviewers assessed lifetime major depression by using modified DSM-IV criteria. 8056 twins met the criteria for a diagnosis of major depression at some point in their life - and 322 twins voluntarily discussed a history of antidepressant treatment.

  • In addition to this information, the interviewers also asked questions about the twins "shared environment" - that is, when they were living in the same household - and their "individual-specific environment" - that is, adult personal life events that may make members of the twin pair more susceptible to depression.

• Results:

Sex and Zygosity Number of Complete Twin Pairs  Concordance for Lifetime MDD

Female-Female, MZ 2317 0.44

Female-Female, DZ 3185 0.16

Male-Male, MZ 1774 0.31

Male-Male, DZ 2584 0.11

Male-Female, DZ 5633 0.11

• results indicate that the heritability of major depression was significantly higher in women than men

• monozygotic twins had a higher concordance rate for MDD than dizygotic twins

• estimated heritability of major depression was 0.38, in line with previous research

• no correlation between the number of years that the twins had lived together and lifetime major depression

• Findings:

  • large sample size increases the internal reliability of the study

  • results mirror what is seen in society – women have a higher rate of depression than males

  • This study seems to show that there is a genetic link for depression; however, no specific genes are actually identified.  Also, we cannot know if the twins may have the gene but that it is not expressed.

  • Research on gender differences in depression argue that women are subject to more environmental stressors than men, which could lead to gene expression and account for the differences in concordance rates.

Evolutionary Psychology

• genes mutate, those that are advantageous are passed down through a process of natural selection. Evolutionary psychologists attempt to explain how certain human behaviors are the result of the development of our species over time. It is important to remember that natural selection cannot select for a behavior; it can only select for the genes that may produce behavior.  

Disgust

Disgust is thought to be universal in humans and has an associated facial expression that is recognizable across cultures. 

Its physiological manifestations include lowered blood pressure and galvanic skin response, nausea and actions including stopping, dropping the object of disgust and shuddering. 

MRI studies have located a neurological substrate for perceiving facial expressions of disgust in the anterior insula cortex.

The more vulnerable the individual is to infection, the greater the importance of disease avoidance and being careful about what you eat. Therefore we would expect people with lowered immune systems to be the most sensitive to disgust and therefore the most protected from accidental infection.

Relative to later stages, the first trimester (first three months) of pregnancy involves substantial suppression of the maternal immune response, and both maternal and fetal vulnerability to pathogens are greatest during this phase; food-borne illnesses, in particular, pose a threat during the first trimester. 

Curtis

• Aim: 

  • to investigate whether people are more disgusted by potential threats to immune system

• Procedure:

  • online survey on the BBC Science website

  • Began with 77,000 participants in 165 countries – after removing improbable data and responses from those who had already seen a BBC TV show that alerted them to the hypothesis, just under 40,000 respondents were counted

  • Respondents were asked to rate 20 photographs, which appeared one-by-one on separate web pages, for disgust on a scale of 1–5. 

  • Randomly placed among the 20 photographs were seven pairs: one depicting something potentially harmful to the immune system and another visually similar but non-infectious

    • For example, one image was a plate of bodily fluid and its pair was a plate of blue viscous liquid.

  • A final question on the Web site asked respondents to choose with whom they would least like to share a toothbrush

• Results:

  • Disgust reaction was strongest for images that threatened immune system

  • All seven of the disease-salient images were rated as more disgusting by females than by males 

  • Feelings of disgust were higher for younger people

  • with whom would participants least like to share a toothbrush?

    • the postman (59.3%)

    • the boss at work (24.7%)

    • the weatherman (8.9%)

    • a sibling (3.3%)

    • a best friend (1.9%)

    • spouse/partner (1.8%)

• Findings:

  • Natural selection may have helped human ancestors to be more disgusted at things which threatened the immune system to avoid things that could potentially lead to diseases or sickness.

  • This would allow them better chances of survival and reproduction to pass on their genes.

  • The decline with age is explained by the fact that older people have finished their reproductive life and are therefore evolutionarily disposable.

  • This gender-bias in the result is consistent with women’s enhanced evolutionary role in protecting the next generation.

  • The preference for toothbrush-sharing with a partner rather than a stranger is explained thus: sharing a person’s bodily fluids becomes more disgusting as that person becomes less familiar because strangers are more likely to carry new diseases and present a greater threat to another person’s immune system.

  • This study supports the role of disgust in aiding reproduction, and thus, as an evolutionary behavior.

Fessler

• Aim: 

  • To investigate whether disgust sensitivity is adjusted as a function of the immune system, by testing the hypothesis that disgust sensitivity varies across pregnancy in a manner that compensates for changes in the vulnerability to disease.

• Procedure:

  • web-based study of 496 healthy pregnant women ages 18 – 50 (mean age of 28)

  • researchers compared the disgust sensitivity of participants in the first trimester with those in later stages of pregnancy

    • 155 participants were in the first trimester

    • 341 participants in the second trimester (183) and third trimester (158)

  • participants rated current level of nausea (morning sickness) using 16 point scale

  • 31-item questionnaire with both true/ false and three-point Likert-type responses, measures disgust sensitivity in eight domains:

    • contact with animals (questions concern cockroaches, rats, worms, etc.)

    • body products (items address mucous, excreta, etc.)

    • sex (topics include bestiality, incest, and age disparate unions)

    • body envelope violations (questions concern wounds, exposed organs, etc.)

    • death (contact with corpses, dead animals, cremated remains, etc.)

    • hygiene (items address contact with toilets, personal cleanliness, etc.)

    • magical contagion (beliefs concerning contagion at a distance, contagion due to similarity, etc.)

    • food (items include “might be willing to try eating monkey meat, under some circumstances” and “You are about to drink a glass of milk when you smell that it is spoiled”).

• Results:

  •  A simple correlational analysis revealed that overall disgust sensitivity was positively related to the current level of nausea throughout pregnancy.

  • Women in their first trimester scored higher in disgust sensitivity (and experienced more nausea)  than women in the second and third trimesters.

  • controlling for the effects of nausea, the first trimester elevation in disgust sensitivity in the food domain remained significant

• Findings:

  • Natural selection may have helped human ancestors to be more disgusted at things which threatened the immune system to avoid things that could potentially lead to diseases or sickness.

  • This would allow them better chances of survival and reproduction to pass on their genes.

  • The decline with age is explained by the fact that older people have finished their reproductive life and are therefore evolutionarily disposable.

  • This gender-bias in the result is consistent with women’s enhanced evolutionary role in protecting the next generation.

  • The preference for toothbrush-sharing with a partner rather than a stranger is explained thus: sharing a person’s bodily fluids becomes more disgusting as that person becomes less familiar because strangers are more likely to carry new diseases and present a greater threat to another person’s immune system.

  • This study supports the role of disgust in aiding reproduction, and thus, as an evolutionary behavior.