- Human behaviour can be explained by looking at hormones, genetics, evolution, the nervous system, etc.
- If we can explain all behaviour using biological causes, unwanted behaviour can be modified or removed using biological treatments (e.g. medication).
- Experimental research conducted using animals can inform us about human behaviour.
Biological Research - Experiments
The biological approach uses a variety of research methods. One is experiments.
- Experiments try to establish cause and effect by comparing groups and analysing any differences between them.
- They can investigate possible biological causes of behaviour.
- Other variables must be tightly controlled to ensure they don't affect the results of the experiment.
- Example: Krantz et al. (1991) conducted a lab. experiment into the impact of stress on the heart.
Biological Research - Correlations
- Correlations describe the relationship between two variables.
- They do not show cause and effect.
- Useful for establishing relationships between variables and often lead to further research (possibly an experiment to establish cause and effect).
- Example: Holmes and Rahe (1967) found a positive correlation between the amount of stressful life events and ill health experienced.
Biological Research - Case Studies
- Case studies are used to investigate things that couldn't be investigated any other way.
- Useful for investigating a situation in great depth.
- They can't be generalised to other people as they're often unique situations.
- Example: Milner et al. (1957) reported a case study study of a man who suffered memory loss after having part of his brain removed to reduce his epilepsy.
Biological Research - Questionnaires and Interview
- Used to collect information from people directly.
- They rely on the honesty of the person.
- They rely on the person having insight into themselves.
- Can provide very detailed information.
- Example: Holmes and Rahe (1967) used these techniques to get people to rate how stressful individual events were to them.
Magnetic Resonance Imaging (MRI):
- Use magnetic fields to produce a detailed image of the brain that can show up abnormalities such as tumours and structural problems.
- It can show brain activity by monitoring blood flow to different areas.
Positron Emission Tomography (PET)
- Measure brain activity by using sensors placed on the head to track a radioactive substance that is injected into the person.
- PET scans can show which areas of the brain are more active when the person performs an activity such as counting.
- This helps us to understand about function and communication within the brain.
Both techniques are pretty expensive to use during research. However, it is useful to be able to see which parts of the brain are activated during certain activities, as different functions are performed in different parts of the brain.
Human Nervous System
Human Nervous System (2)
The human nervous system is divided into two main sub-systems:
- The central nervous system (CNS) which consists of the brain and spinal cord.
- The peripheral nervous system (PNS) which consists of millions of neurons that carry messages to and from the CNS. These neurons are known as motor, sensory and relay neurons.
Motor (Efferent) Neurons
Motor (Efferent) Neurons (2)
- Carry messages away from the brain and spinal cord (CNS) to effectors such as muscles and glands.
- Has a cell body with many dendrites branching off it.
- These dendrites have a large surface area in order to connect with other neurons and and carry nerve impulses towards the cell body.
- The axon then carries the nerve impulse away from the cell body. Axon length varies.
- Schwann cells surround the axon to form an insulating layer called the Myelin sheath.
- At its end, the axon divides into a number of branches known as synaptic terminals.
- Between each neuron there is a gap known as a synapse.
- Short dendrites and long axons.
Sensory (Afferent) Neurons
- Carry messages from the receptors in the body (PNS) to the brain and spinal cord.
- Receptors such as sensory organs, muscles, skin or joints, detect physical and chemical changes in the body and relay these messages via sensory neurones to the brain or spinal cord.
- Long dendrites and short axons.
Relay (Interconnecting) Neurons
- Found in the visual system, brain and spinal cord.
- They receive messages from the sensory neurons and pass these messages on to other relay neurons or to motor neurons.
- Short dendrites and short or long axons.
- An example of a reflex arc.
- A response happens without conscious input.
Reflex Arc (2)
- A stimulus, such as a hammer hitting a knee, is detected by receptor cells in the PNS, which then conveys a message along a sensory neuron.
- The message reaches the CNS where it passes to a relay neuron.
- The relay neuron then transfers the message to a motor neuron.
- The motor neuron carries the message to an effector, such as a muscle, which causes the muscle to contract.
- Synapse: The gap between the end of one neuron and the dendrites of the next.
- Synaptic transmission: The transfer of electrical messages from one neuron to an adjacent neuron.
- When the nerve impulse travels down an axon, it arrives at pre-synaptic terminals, which triggers the release of neurotransmitters.
- Neurotransmitter: A chemical substance released from a synaptic vesicle that affects the transfer of an impulse to another nerve or muscle.
- The neurotransmitter must be taken up immediately by the post-synaptic neuron otherwise it will either be reabsorbed by the synaptic terminals from which it was released, or be chemically broken down by enzymes in the synaptic cleft therefore making the neurotransmitter inactive.
- If successfully transmitted, the nerve impulse is then carried along the post-synaptic neuron until it reaches the next synaptic terminal where the message will continue to pass on via electrical impulses.
- Neurotransmitters such as dopamine, acetylocholine or serotonin can either influence the post-synaptic neuron to respond in an inhibitory way (decreases the firing of a cell) or an excitatory way (increases the firing of the cell).
- In Schizophrenia, it is thought that neurons that respond to dopamine fire too often. Therefore, anti-psychotic drugs that are designed to block the receptor sites for dopamine can be prescribed to control the symptoms.
Localisation of Cortical Function
- Localisation: Specific areas of the cerebral cortex are associated with particular physical and psychological functions.
- Lateralisation: The dominance of one hemisphere of the brain for particular physical and psychological functions.
The human brain can be viewed as being formed of three concentric layers:
- The central core which regulates our most primitive and involuntary behaviours.
- The limbic system which controls our emotions.
- The cerebrum which regulates our higher intellectual processes.
Map of the Brain
This is a lateral view of the human brain showing some of the major structures and divisions.
The Central Core
- Known as the brain stem and controls most of our primitive behaviours such as sleeping, breathing or sexual behaviour, as well as our involuntary behaviours, such as sneezing.
- Includes structures such as the hypothalamus.
- The hypothalamus is located in the midbrain and regulates our eating, drinking and sexual behaviour, as well as regulating the endocrine system in order to maintain homeostasis.
- Homeostasis: The process by which the body maintains a constant physiological state.
The Limbic System
- The limbic system is around the central core of the brain, and is closely interconnected with the hypothalamus.
- It contains key structures such as the hippocampus, which is thought to play a key role in memory.
- HM had their hippocampus surgically removed in order to treat severe forms of epilepsy. Upon recovery, HM suffered from a severe form of anterograde amnesia.
- Has an outermost layer known as the cerebral cortex.
- The cortex appears grey because of the location of cell bodies (hence why it's known as 'grey matter').
- Beneath the cortex lie myelinated axons which appear white (known as 'white matter').
- Each of our sensory systems sends messages to and from this cerebral cortex.
- The cerebrum is composed of the right and left hemispheres which are connected by the corpus callosum.
- The corpus callosum enables messages that enter one hemisphere to be conveyed to the other.
The Four Lobes
Each hemisphere is further divided into four lobes:
- The Frontal Lobe - Awareness of what we are doing within our environment (consciousness).
- The Parietal Lobe - Sensory / motor movements.
- The Temporal Lobe - Auditory ability and memory acquisition.
- The Occipital Lobe - Vision.
The Motor Area and the Somatosensory Area
The Motor Area:
- Located in the parietal lobe and is responsible for controlling our voluntary movements.
- Movements on the right side of the body are controlled by the left hemisphere and vice versa.
- Damage to the motor cortex results in impaired movements.
The Somatosensory Area:
- Located in the parietal lobe, and separated from the motor area by the central sulcus.
- It responds to heat, cold, touch, pain and our sense of body movement.
- The amount of somatosensory area associated with a particular part of the body is related to its use and sensitivity.
The Visual Area and the Auditory Area
The Visual Area:
- The occipital lobe is located at the back of the brain. It's primary function is vision.
- Predominately, nerve fibres from the inner half of the retina of each eye cross at the optic chiasm (the point at which the nerve fibres from both eyes converge) and travel to opposite sides of the brain.
- Damage to the left hemisphere can produce a loss of vision to the right side of our environment.
- nerve fibres from the outer edge of each retina do not cross at the optic chiasm, and so damage to the left optic nerve can affect the left eye.
The Auditory Area:
- Located in the temporal lobe and is responsible for the analysis of speech-based information.
- Within this area is 'Wernicke's area'. He discovered that damage to the left temporal lobe resulted in linguistic deficits. Individuals who experience difficulties in language comprehension suffer from Wernicke's aphasia.
- Split-brain patients have undergone a corpus callosoptomy (a large part of the corpus callosum is cut.
- As a result of the surgery, the two hemispheres are unable to communicate effectively.
- In the 1960s, Roger Sperry and Michael Gazzaniga conducted research on split-brain patients by testing various cognitive and perceptual processes. They administered tasks known to be associated with each hemisphere of the brain to the patients. They discovered that the two halves of the brain were able to function quite independently.
- Considered to be an invasive method of investigating cortical specialisation as it involves manipulating structures within the brain. It is performed in two main ways - ablation (areas of the brain are removed) and lesions (certain neural connections are cut).
- Hubel and Wiesel (1950s-1960s) inserted a microelectrode into the visual cortex of a cat. they projected patterns of dark and light onto a screen in front of the cat and found that some neurons within the cat's brain fired quickly when the lines were presented at a certain angle compared to other angles. Hubel and Wiesel called these neurons 'simple cells'.
- They also discovered that 'complex cells' respond best to lines of a certain angle that move in one direction.
- Hubel and Wiesel therefore showed how the visual system in the brain builds up an image from a simple to a more complex representation.
- Strengths: Allows for a great deal of specificity and control in the location of damage.
- Limitations: Problem of cause and effect - does lesioning one area of the brain cause damage to other areas?
Electrical and Chemical Stimulation
- In 1954, James Olds and Peter Milner were testing the effects of reticular formation (a complex network of fibres involved in maintaining functions vital to life) in rats when they accidentally placed an electrode in the septal area.
- They found that this part of the limbic system was associated with pleasure as the rats, who soon learned that they could control the electrical stimulation, would press the lever that initiated the pleasure repeatedly.
- The WADA test is a chemical test used to establish which cortical functions are located to which hemisphere. The procedure is often done on patients prior to surgery to establish which side of the brain is responsible for speech and and memory so that damage to these structures can be minimised during surgery.
- During the WADA test, the patient is kept awake and an anaesthetic is injected into one hemisphere at a time in order to 'shut down' any language or memory functions in that hemisphere so that a thorough evaluation of the other hemisphere can be carried out.
- Strengths: Stimulating the brain is a less harmful procedure than surgery and therefore more ethical.
- Limitations: Problems in extrapolating research conducted on animals to explaining human cortical function.
- The brain of a patient, who has usually been the subject of a longitudinal study because of some rare affliction, is examined after death.
- The area of the brain that is damaged is then attributed to the affliction suffered by the person.
- Before the introduction of scanning methods, it was one of the few ways to study the relationship between the brain and behaviour.
- Paul Broca used post-mortem studies to investigate the location of speech production. 'Tan' could only say the word 'tan'. In the post-mortem of his brain, Broca discovered that Tan had a lesion in left cerebral hemisphere. This area became known as 'Broca's area'.
- Strengths: Provides a greater understanding of rare afflictions in individuals.
- Limitations: Obtaining a person's brain, even if they have been the subject of a longitudinal study, can be very difficult.
- A non-invasive measurement of electrical activity of the brain by recording from electrodes placed on the scalp.
- The EEG represents an electrical signal from a large number of neurons within the brain and the voltage differences between different parts of the brain are recorded.
- The filtered signal is displayed on a computer screen which is used to monitor situations such as the categorisation of different types of epileptic seizures.
- EEG patterns recorded during sleep sessions have contributed significantly to theories of sleep behaviour.
- Strengths: No intervention is necessary and therefore allows for natural measurements of brain activity.
- Limitations: Electrodes are not sensitive enough to pick out individual action potentials of single neurons.
Computerised Axial Tomography (CAT)
- Is a procedure where a narrow X-ray beam is sent through the patient's head and the amount of radiation absorbed is measured.
- They are fed into a computer where a cross-section of the brain can be displayed.
- They are useful for evaluating the amount of swelling due to tissue damage in the brain, or assessment of the size of the ventricles located deep within the brain.
Positron Emission Tomography (PET)
- Is a procedure whereby different levels of neural activity, in various locations of the brain, are assessed whilst the brain is active.
- A small amount of radioactive glucose is injected into the person's bloodstream and, after a few minutes, the brain begins to use the radioactive glucose in the same way as it uses glucose which provides the brain with energy.
- The PET scan then detects and measures the amount of radioactivity emitted when individuals are asked to perform tasks such as solving problems.
Magnetic Resonance Imaging (MRI)
- A powerful technique where scanners use strong magnetic fields and radio waves to produce a high quality image of an individual's brain.
- During the procedure, the individual lies in a tunnel surrounded by a large magnet which produces a strong magnetic field.
- When a certain area of the body is exposed to a radio-frequency pulse, the tissues in the body give out a signal that is then measured.
- Hundreds of measurements can be made to produce precise images of the brain.
- MRI scans have been particularly useful in diagnosing diseases of the brain and spinal cord, e.g. multiple sclerosis, which is not detectable with a CAT scan.
- Provides detailed knowledge of areas of the brain that are active whilst completing tasks such as problem solving. They can study the brain in action.
- Non-invasive, and much less harmful than other methods.
- Some scans are time consuming, so therefore unable to record spontaneous behaviour.
- Ethical issues surrounding the injection of radioactive glucose (PET scan).
The Autonomic Nervous System
The peripheral nervous system has two divisions:
- The somatic nervous system, which controls skeletal muscles and receives information to and from sensory receptors.
- The autonomic nervous system, which maintains homeostasis by controlling glands and vital muscles such as the heart, stomach, blood vessels etc.. It is known as 'autonomic' because the system operates involuntarily.
The autonomic nervous system has two divisions:
- The sympathetic nervous system
- The parasympathetic nervous system
Their actions are usually antagonistic (work in opposition to each other).
Actions of the Sympathetic and Parasympathetic Ner
- Sympathetic: Dilates pupils.
- Parasympathetic: Constricts pupils.
- Sympathetic: Inhibits saliva production.
- Parasympathetic: Stimulates saliva production.
- Sympathetic: Dilates bronchi.
- Parasympathetic: Constricts bronchi.
- Sympathetic: Inhibits digestion.
- Parasympathetic: Stimulates digestion.
The Sympathetic Nervous System
- Typically, the sympathetic nervous system functions when quick action is required, e.g. during a threatening situation - 'fight or flight'.
- If you heard a loud noise behind you late at night, your body would divert blood away from the stomach to your muscles in order for you to stay and confront the potential attacker (fight) or run away (flight). Heart rate increases and other sympathetic responses are activated.
The Parasympathetic Nervous System
- The parasympathetic nervous system does not require immediate action.
- Considered to be the 'rest and digest' system. It stores the body back to its normal state.
- Using the previous example of walking home late at night, the parasympathetic nervous system comes into play when the threat leaves.
- For example, after a short while, you realise that the loud noise was in fact a cat. You feel a sense of relief, your breathing slows and your palms stop sweating - your parasympathetic nervous system is now acting to restore your bodily functions back to their normal state.
- Even though the threat has gone away, you may still find yourself shaking as the hormones in your bloodstream (e.g. adrenaline) take longer to disperse.
The Endocrine System
- Composed of a number of glands that release hormones directly into the bloodstream.
- Acts more slowly than the nervous system.
- One of the major endocrine glands is the pituitary gland, as it controls the release of hormones from all other endocrine glands in the body.
- During a threatening / stressful situation, the pituitary gland releases ACTH, which is the body's major stress hormone. ACTH is then carried around the bloodstream and stimulates the adrenal gland, in particular the adrenal medulla, which releases adrenalin into the bloodstream.
- In conjunction with the sympathetic nervous system, the adrenalin aids in the fight or flight response by constricting blood vessels in the stomach which inhibits digestion and increasing the heart rate.
Effects of the Stress Response
- The 'fight or flight' response is very useful in a threatening or stressful situation, however prolonged exposure to these stress hormones can be damaging both physically and psychologically.
- Common side-effects include disruption to one's sex life, digestion problems and heart disease (more severe cases).
- The autonomic nervous system is thought to be involuntary, however Zen Buddhists appear to be able to control a number of autonomic functions such as their heart rate and oxygen consumption.
Genotype and Phenotype
Genotype: Refers to an individual's genetic make-up, that is the particular set of genes that the individual possesses.
Phenotype: The characteristics shown by an individual that are a result of both genes and the environment.
Genotype + Environment = Phenotype
- If identical twins, who share the same genotype, were separated at birth and raised in different environments, they may have completely different phenotypes.
- For example, if one twin were fed a more nutritious diet, it would be physically much taller and stronger than the other twin.
- Psychologists have referred to various disorders to try to explain the difference between genotype and phenotype.
- PKU is characterised by a deficiency in the enzyme PAH. PKU is a recessive genetic disorder, which means that each parent must have at least one defective gene for PAH which the child then inherits. A child who has two parents with PKU will always inherit two defective genes and therefore the disorder.
- If undetected and untreated at birth, individuals tend to fail to accomplish important developmental milestones. However, if PKU is diagnosed early, a newborn can develop normally if given a special diet for the rest of its life.
- The distinction between an individual's genotype and phenotype can also arise from studies of hereditary diseases, such as haemophilia.
- Haemophilia is a recessive, genetic illness that impairs the body's ability to control blood coagulation. The disease is more common in males than females.
- In the case of haemophilia, a heterozygous (the genotype consists of two different genes) individual is a carrier. The individual has a normal phenotype but has a 50:50 risk of passing the gene onto its offspring.
- A homozygous (the genotype consists of two genes that are the same) dominant individual has a normal phenotype and has no risk of passing the gene onto its offspring.
- A homozygous recessive individual has an abnormal phenotype and is guaranteed to pass the gene onto its offspring.
Mono-zygotic Twins (MZ)
- Identical twins.
- Occur when a single egg, which is fertilised to form one zygote (a fertilised cell), divides to form two separate embryos. These two embryos continue to develop into foetuses whilst sharing their mother's womb. They may or may not share a placenta / amniotic sac.
- Genetically identical - share exactly the same DNA.
- They generally look similar, but not the same due to a different phenotype (influence of the environment).
Di-Zygotic Twins (DZ)
- Non-identical or fraternal twins.
- Occur when two egg cells are fertilised by two different sperm cells.
- Unlike MZ twins who share the same DNA, DZ twins are no more genetically alike than ordinary siblings.
Psychologists are interested in studying MZ and DZ twins in order to investigate the genetic basis of behaviour.
If one set of MZ twins were separated at birth and raised in different environments, what is the likelihood of them both developing a mental disorder such as schizophrenia? If both twins were to develop it, it may lead psychologists to believe it is a genetic disorder.
- MZ twins are often used to try and work out whether certain traits are genetic or a result of the environment.
- If one MZ twin has a particular characteristic and so does the other twin, then the characteristic may be genetic as they share the same genotype: there should be 100% concordance between them.
- However, MZ twins often share the same environment, so the fact they share the same trait may be due to the shared environment rather than genetics. MZ twins that are reared apart are therefore of particular interest to psychologists.
- If the environment plays a significant role in determining behaviour, then MZ twins who have been raised apart should show a low concordance rate for traits such as intelligence.
Twin Studies - Intelligence
- Wilson (1978, 1983) conducted a longitudinal study and found that by the age of 18 months, MZ twins were more similar than DZ twins on tests of infant intelligence. The follow-up data over the next 13 years showed that the MZ twins were more similar in intellectual performance.
- Plomin (1990) tried to account for these intellectual differences in DZ twins by saying their different genotypes may have directed them along separate developmental paths, compared to MZ twins who share the same genotype.
- Bouchard and McGue (1981) conducted a meta-analysis of twin studies and IQ. He found that:
-MZ twins reared together had a correlation coefficient of 0.86
-MZ twins reared apart had a correlation coefficient of 0.72
-DZ twins reared together had a correlation coefficient of 0.60
-Siblings (including DZ twins) reared apart had a correlation coefficient of 0.24
Twin Studies - Sexual Orientation
There is some evidence from twin studies to suggest that homosexuality may be genetically determined.
- Bailey and Pillard (1991), in a study of male twins where at least one of the pair was gay, found that 52% of MZ brothers were concordant for homosexuality compared to 22% of DZ brothers.
- Bailey, Dunne and Martin (2000) obtained a sample of twins from an Australian twin registry. They found a 30% concordance for homosexuality in MZ twins.
- Criticisms of sexual orientation studies have included the way in which participants were recruited, e.g. through gay media, whose target audience is clearly homosexual. This would account for the high response rates to take part in such studies compared to the potential recruitment of homosexual people through more traditional forms of media.
- Bearman and Bruckner (2002) argue against a genetic basis for sexual orientation. They say that such low concordance rates do not account for a genetic similarity in homosexual twins.
Most researchers suggest that it is unlikely that there's a single 'gay gene'. Instead, our sexual orientation is more likely to be the result of a combination of genetic and environmental factors.
- Gianoulakis, Krishnan and Thavundayil (1996) found that sons of alcoholic fathers were more likely to be alcoholics themselves compared to people selected at random.
- The researchers discovered that when sons of alcoholics drank alcohol, they tended to release more of the neurotransmitter endorphin compared to other people, therefore suggesting a biological predisposition towards alcoholism.
Family size and birth order:
- There is evidence to suggest that the environment plays a more significant role than genes in determining behaviour.
- Zajonc and Markus (1975) researched IQ data of 40000 Dutch males who were born in 1944. They found that IQ is related to birth order and family size.
- The researchers suggested that this was largely due to the degree of attention given by parents.
- Adoption studies are particularly useful for investigating the genetic basis of behaviour.
- They involve comparing a trait or characteristic between adopted children and their biological or adoptive parents.
- If a trait or characteristic has a genetic basis, then the adopted child should show the same trait as the biological parent.
- If the trait or characteristic is environmentally influenced, then the adopted child should show similar characteristics to their adoptive parent.
Adoption Studies - Age
- As children grow older, it is assumed that their cognitive and verbal abilities would develop to become more like their adoptive parents than their biological parents.
- However, Plomin, Fulker, Corley and DeFries (1997) found that, as adoptive children approached the age of 16, they became more similar to their biological parents in cognitive and verbal ability compared to their adoptive parents, therefore suggesting a genetic influence.
Adoption Studies - Intelligence
- In the Minnesota Adoption Study of black children, Scarr and Weinberg (1976) found evidence that intelligence was strongly linked to environmental influence.
- Black children from low socio-economic backgrounds were adopted into white middle-class families where the adoptive parents had at least one biological child.
- Scarr and Weinberg initially found that the black children were more intellectually similar to their adoptive parents (0.29) therefore supporting a genetic intelligence.
- However, they found that inter-racial siblings also showed intellectual similarities. as these inter-racial siblings have no genes in common, their similarities in intelligence may be due to the environment and not genetics.
Findings from adoption studies must be viewed with caution. Adoptive families are usually smaller, financially richer and may provide a more stimulating environment compared to some biological parents. This would therefore account for an increase in IQ scores.
One method of studying whether a trait or characteristic has a genetic basis is through selective breeding. This method involved artificially selecting male and female animals for a particular trait. These are then put together to breed and produce offspring.This method is a quick way to select for particular traits with effects of artificial selection being seen with just a few generations of breeding.
- Plomin (1989) suggests that if selective breeding does not alter the trait or characteristic, then we must assume that it is entirely dependent on environmental factors.
Selective breeding has been used to demonstrate how a number of behavioural characteristics may have a genetic basis.
- Fruit flies have been breed to be more or less sensitive to light.
- Mice have been bred to be more or less dependent on alcohol.
- Dogs have been bred to be excitable or lethargic.
- Chickens have been bred to be aggressive and sexually active.
Selective Breeding (2)
Tryon (1940) conducted an experiment with the aim of investigating whether genetics influenced learning in rats.
- He trained a large number of rats to run a complex maze. those that were the quickest and slowest were selected. The quickest were bred together, and the slowest were bred together.
- He continued the breeding process for a number of generations.
- The DV was the number of errors and speed with which the rats learned their way through the maze.
- The quicker rats learned to run the maze faster and made fewer errors. We can conclude from this that learning is a heritable characteristic which can be controlled and manipulated through selective breeding.
These findings suggest that learning has a genetic basis. However, humans interact very differently to rats, so the findings can not necessarily be applied to humans.
Selective Breeding (3)
Cooper and Zubeck (1958) conducted a similar study to Tryon but found very different results. They reared slow rats in one of two environments:
- An impoverished, or boring, environment consisting of an empty wire-meshed cage.
- A stimulating environment containing tunnels, ramps, etc.
When the rats reached maturity the slow rats that had been reared in a stimulating environment made the same number of learning errors as the fast rats in a stimulating environment.
This study therefore shows that the environment is also an important factor in determining behaviour.