BIO SAQS

Caspi et al (2003): Theory

A gene is a distinct series of nucleotides within chromosomal DNA that may code for the formation of a specific protein.

An allele is a different version of the same gene.

Psychologists believe that serotonin plays a role in mood and therefore plays a role in human depression.

The 5-HTT is a gene thought to be related to depression, and is known as the "serotonin transporter" gene, which regulates the level of serotonin in the synapse.

Diathesis-stress theories of depression predict that an individual’s responses to stressful events depend on their genetic makeup and the nature of the stress.

The long allele is the "normal" allele; the short allele is the mutation. A study that investigates genetics is Caspi et al (2003)

Caspi et al (2003): Study

Aim: The aim of this study was to test if people who inherit two versions of the 5-HTT gene are more likely to develop major depression after a stressful life event than people with two long alleles.

Sample: Caspi used an opportunity sample of over 847 Caucasian New Zealand 26-year-olds who were also taking part in another study. 17% had the two short 5-HTT alleles, 51% had one short allele, and 32% had two long alleles.

Procedure: The investigation was a correlational study. Participants were divided into 3 groups. Group 1 had two short alleles. Group 2 has one short and one long allele. Group 3 had two long alleles. The participants were asked to fill in a ‘stressful life events questionnaire’ about the frequency of 14 different events, such as unemployment and relationships. They were also assessed for depression.

Findings: People who had the two short versions of the allele and had three or more stressful life events were the most likely to have depression. Simply inheriting the gene was not enough to lead to depression; rather, the gene’s interaction with stressful life events increased one’s likelihood of developing depression.

Newcomer et al (1999): Theory

Hormones are chemicals that affect human behavior. They are secreted by glands in the endocrine system, and are released into the bloodstream.

Hormones can only produce reactions in certain target cells that have appropriate receptor sites for these specific hormones.

An example of a hormone that influences human behavior is cortisol.

Cortisol is secreted by the adrenal gland, and is responsible for regulating blood sugar levels, metabolism, and its levels rise during periods of stress.

A study that investigates the effects of hormones is Newcomer et al (1999).

Newcomer et al (1999): Study

Aim: The aim was to investigate whether high levels of cortisol interfere with verbal declarative memory.

Sample: The study consisted of 51 healthy participants aged 18-30 years old.

Procedure: It was a double blind lab experiment. Participants were matched for age and gender to one of 3 conditions.

Condition 1: high levels of cortisol, where the participants were given a tablet containing 160g of cortisol on each day of the four day experiment, which are similar cortisol levels to people experiencing a major stress event.

Group 2: low levels of cortisol, where the participants were given a tablet containing 40g of cortisol, a similar amount to people experiencing a low level stressor.

Condition 3: Placebo group, where they were given placebo tablets hence no cortisol. All participants were asked to listen to and recall parts of a prose paragraph. This tested their verbal declarative memory over a period of 4 days.

Findings: The results indicated that high cortisol levels impaired performance in the memory task, since the participants who received the highest level of cortisol also showed the worst performance in verbal declarative memory.

Although, this effect was not permanent, and the performance of participants in the high cortisol condition returned to normal after they stopped taking the hormone tablet.

Lundstrom and Olsson (2005): Theory

A pheromone is a chemical substance produced in the glands of animals and released into the environment, affecting the behaviour of other members of its own species.

Most commonly, pheromones affect sexual and mating behaviours.

Although many pheromones have a smell, pheromonal information in the brains of animals is not processed in the same brain regions as ordinary 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. 

Humans do not have either the VNO or accessory olfactory bulb, however, it is suggested that humans may have the accessory olfactory bulb, but it regresses and disappears after birth. 

There is research showing that some chemicals under controlled conditions may lead humans to show behaviours similar to what has been seen in animals.

One potential human pheromone is androstadienone. A study that investigates this is Lundstrom and Olsson (2005).

Lundstrom and Olson (2005): Study

Aim: The aim was to investigate the effect of androstadieone on the mood of women in the presence of men.

Sample: The study consisted of 37 heterosexual women, with a mean age of 25, with a normal menstrual cycle.

Procedure: A trial test was done to firstly ensure that the participants could not consciously tell the difference between the androstenedione and the control solution. The female participant’s mood was studied in a 2×2 experimental design. Then assessed after being exposed to either androstadienone or control solution, and in the presence of either a male or female experimenter. The experimenter carried out a number of measurements including several questionnaires, where one questionnaire measured mood. The experimenter was either a 28 year old female of a 30 year old man.

Findings: It was found that androstadienone increased women’s mood in the presence of a male experimenter, but not the female experimenter.

Kindler et al (2006): Theory

A gene is a distinct series of nucleotides within chromosomal DNA that may code for the formation of a specific protein.

An allele is a different version of the same gene.

Twin studies are commonly used to estimate the heritability of a disorder. Where, heritability refers to the proportion of variation in a trait for example depression, that can be attributed to genetic differences among a population.

These studies may compare monozygotic twins, who develop from a single fertilized egg and have the same genome, to dizygotic twins, who develop from two separately fertilized eggs, and would be the genetic equivalent to siblings. A study that investigates this is Kindler et al (2006).

Kindler et al (2006): Study

Aim: The aim of Kindler et al (2006) was to investigate the following:

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 seen in major depression?

Is there evidence that genetic and environmental factors in major depression differ over time?

Sample: The sample was made up of 15,493 complete twin pairs listed in the national Swedish twin registry. Only twins whose zygosity was verified were used in the study.

Procedure: Telephone interviews were carried out between March 1998 and January 2003.

The interviews assessed lifetime major depression by using a modified DSM-IV criteria.

In addition to this, the interviewers also asked questions about the twins shared environment, so when they were living in the same household, as well as their individual-specific environment, meaning personal life events.

Results: The results indicate that the heritability of major depression was significantly higher in women than men.

In addition, the correlations were significantly higher in monozygotic than in dizygotic twins.

The estimated heritability of depression was 0.38, in line with previous research.

It was found that there was no correlation between the number of years that the twins had lived together and lifetime major depression.

There were also no significant differences seen in the roles of genetic and environmental factors in major depression in the three cohorts spanning birth years 1900-1958.

Fessler et al (2005): Theory

Evolution is the change of heritable characteristics in a species over time.

It is theorized that certain human behaviors are a result of evolution by natural selection, which is where the behaviors/traits that are better adapted to the environment, are passed more readily onto offspring, and thus become more prevalent within the species.

An example of this is the behavior of disgust, which is the emotion motivating avoidance of contact and refusal to eat something.

Disgust is elicited with many stimuli associated with pathogen transmission, which suggests that disgust may be a behavioral adaption that serves to guard against disease.

A study that investigates the evolution of disgust is Fessler et al (2005)

Fessler et al (2005): Study

Aim: The aim of this study was to investigate whether disgust sensitivity varies across pregnancy in a manner that compensates for changes in vulnerability to disease.

Sample: The sample consisted of 691 pregnant women recruited through pregnancy related web sites, where no compensation was offered, with a median age of 28 years.

Procedure: It used an online survey consisting of a 31-item questionnaire asking to rate current nausea levels on a 16 point scale.

Questions tested disgust sensitivity in eight different areas: food, contact with animals, body products, dead animals, hygiene, and contact with toilets.

Findings: Overall, it was found that participants in the first trimester reported a greater overall disgust sensitivity than participants in the second and third trimesters, and also experienced more nausea.

Techniques to study the brain

One technique used to study the brain is magnetic resonance imaging (MRI); which is a non-invasive imaging technique that employs a magnetic field in conjunction with radio waves in order to map the activity of hydrogen molecules, and thus produce a visual representation of the participant’s brain.

By aligning the hydrogen atoms' polarity in the body with a strong magnetic field and then perturbing them with radio waves, an MRI machine is able to detect the signals emitted as these atoms return to their original alignment.

Different types of tissues in the brain emit distinct signals, allowing for the creation of detailed images that can reveal abnormalities when compared to a standardized group. An MRI machine is static in nature and is thus unable to reveal any functional differentiations.

Maguire (2000): Study

Aim: to investigate the neural plasticity in conjunction with localization of function in the brain,

Sample: It was a correlational study where the MRI brain scans of 16 right handed London Taxi drivers faced observation.

Procedure: The Taxi drivers were required to have been certified for a minimum of 1.5 years prior to their MRI and had completed a ‘knowledge’ test. 50 right-handed males who were not taxi drivers were brain-scanned in the MRI which served as a control group, the investigation was a single-blind study, thus the MRI’S were not labelled, the participants status of taxi driver, or not a taxi driver, not revealed to the researcher.

Maguire (2000): Findings

The study found that the taxi drivers had a larger posterior hippocampus than the non-taxi drivers, however, the taxi drivers additionally had a smaller anterior hippocampus.

The MRI was able to investigate this firstly via pixel counting, which clearly exhibited size differences between the posterior and anterior hippocampus between the brain scans observed.

Secondly via implementation of voxel-based morphology (VBM), which concluded that the quantity of grey matter in the right posterior hippocampus was in direct correlation with the amount of time the subject had spent as a taxi driver.

Thus, the study through an inclusion of MRI technology was able to support its investigational theory of neuroplasticity, as the brain exhibited change in response to environmental stimuli.

Localization

Localization is the theory that specific parts of the brain have specific functions that are related to specific behaviors. 

The limbic system is a major focus of psychological research for its role in memory and emotion. The hippocampus is a key component of the limbic system.

The hippocampus is a bilateral brain structure, meaning there is a hippocampus on the left and on the right. The hippocampus helps us navigate; that is, to find our way around both familiar and new environments. This area plays an important part in our spatial memory.

Brain plasticity refers to the brain’s ability to rearrange the connections between its neurons - that is, the changes that occur in the structure of the brain as a result of learning or experience, where high levels of stimulation lead to an increase in the density of neural connections.

Neural Networks

The process by which neural networks are formed is called neuroplasticity.  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 – known as dendritic branching. 

This increases the number of synapses available for the behavior. The branching of neurons in the brain is called grey matter

Neural pruning

Neuroplasticity is the process by which our brains adapt to changes in the environment. 

One of the ways that our brains change is through the creation of neural networks. This happens because of long-term potentiation - that is, the repeated firing of neurons. 

This leads to an increase in dendritic branching which leads to an increase in the number of synapses.  Another way that our brain can change is through 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 neural pruning is not yet fully understood.

Agonists

Neurotransmission is the process where neurons communicate with other neurons. 

This is done when the presynaptic neuron releases chemicals called neurotransmitters to cross the gap between two neurons called the synapse.

These neurotransmitters then bind to specific receptor sites on the postsynaptic neuron creating an electrical signal called the action potential.

An agonist is any chemical that binds to a receptor site on a postsynaptic neuron, causing the neuron to fire.

Acetylcholine is a neurotransmitter that plays a role in the formation of memories, and is an example of an endogenous agonist.

Antonova (2011): Study

Aim: to investigate the effect of using scopolamine on hippocampal function during an allocentric memory task.

Sample: Participants were 20 male volunteers.

Procedure: The study used a repeated measures design wherein half the participants were injected with the placebo first and then Scopolamine (acetylcholine antagonist), and the other half vice versa.

It was a randomized double blind experiment in that the participants and the experimenters didn’t know who had been allocated to which group. 

The maze needed to be completed via virtual reality as they used a fMRI and was navigated by the participant, using a joystick. Participants navigated around the arena to find the pole.

Once they found it the scene went black for 30 seconds. The participants were told to actively rehearse and remember the position of the pole.

The maze moved them to a different starting position, to ensure allocentric memory was being tested and asked them to navigate to the pole again. Single trial lasted 2.5 minutes with six trials during a single fMRI experiment 15 minutes. The interval between the two conditions and the scanning sessions was 3-4 weeks.

Antonova (2011): Findings

There was no significant difference in the number of errors made between the groups. However, when the participants had scopolamine they demonstrated a significant reduction in the activation of the hippocampus compared to when they received a placebo.

Antagonists

Neurotransmission is the process where neurons communicate with other neurons.  This is done when the presynaptic neuron releases chemicals called neurotransmitters to cross the gap between two neurons called the synapse.

These neurotransmitters then bind to specific receptor sites on the postsynaptic neuron creating an electrical signal called the action potential. 

An antagonist is any substance that fits into a receptor site on the postsynaptic neuron, inhibiting the neuron.  This means that the neuron will not fire and therefore a behavior will not happen. 

Acetylcholine is a neurotransmitter that plays a role in the formation of memories, scopolamine is an example of an exogenous antagonist.

Neurotransmitter

Neurotransmission is the process where neurons communicate with other neurons.  This is done when the presynaptic neuron releases chemicals called neurotransmitters to cross the gap between two neurons called the synapse.

These neurotransmitters then bind to specific receptor sites on the postsynaptic neuron creating an electrical signal called the action potential. A neurotransmitter can sometimes have either an excitatory or an inhibitory effect, depending on the receptor sites that it binds to.

An example of an excitatory endogenous neurotransmitter is acetylcholine.

Excitatory synapses

Neurotransmission is the process where neurons communicate with other neurons.  This is done when the presynaptic neuron releases chemicals called neurotransmitters to cross the gap between two neurons called the synapse.

These neurotransmitters then bind to specific receptor sites on the postsynaptic neuron creating an electrical signal called the action potential.

A neurotransmitter can sometimes have either an excitatory or an inhibitory effect, depending on the receptor sites that it binds to