Essay
IB SL/HL Psychology (biological approaches to behaviour): Explain effects of neurotransmission on behaviour (9 marks)
A level 7 short answer explaining the effects of neurotransmission on behaviour.
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Explain effects of neurotransmission on behaviour [8]- What is neurotransmission
- Serotonin/ Kasamatsu and Hirai
- Acetylcholine/ Martinez and Kesner
One of the principles of the biological level of analysis states that there are biological correlates to
behaviour. Many psychologists attempt to uncover this relationship between biological factors and
behaviour, and one of the main biological processes believed to play a role in behaviour is
neurotransmission. Neurotransmission is a physiological process that is vital to the normal functioning of
the human brain and body. Signalling molecules named neurotransmitters are released by a pre-synaptic
neuron into the space between neurons called the synaptic cleft. They bind to receptor proteins on the
post-synaptic neuron, triggering a nerve impulse. This process is used for communication between
neurons, and to pass messages via the nervous system to muscles and glands within the body, to cause a
certain physiological response. There are several different neurotransmitters which have different effects
on behaviour. The neurotransmitters which I will discuss in this essay are serotonin and acetylocholine.
Serotonin is a neurotransmitter responsible for constricting smooth muscle and contributes to wellbeing
and happiness. As the precursor for melatonin, it also helps to regulate the body’s circadian rhythms.
Kasamatsu and Hirai’s study [1999] demonstrates the effect of serotonin transmission on human
behaviour. The study aimed to uncover the effects of sensory deprivation on neurotransmission and
behaviour. Opportunity blood samples were taken from a group of Buddhist monks who went on a 72-hour
pilgrimage to a holy mountain in Japan. During this time, the monks did not eat, drink or have any human
contact, and they were exposed to cold, autumnal weather. After 48 hours, after the monks reported
hallucinations, blood samples were taken again and neurotransmitter levels were compared with the initial
samples. It was found that the serotonin levels in the monks’ brains had significantly increased over the 48-
hour period, and the hypothalamus and frontal cortex areas of the brain were activated. It was concluded
that sensory deprivation triggered the release of serotonin, which hence changed the way that the monks
had perceived their surroundings. Therefore, elevated levels of serotonin can induce hallucinations in
response to sensory deprivation, through causing emotional arousal.
Acetylcholine is a neurotransmitter associated with muscle contraction and the development of memory in
the hippocampus. It is also involved with many continuous unconscious functions such as breathing.
Martinez and Kesner’s study [1991] investigates the role of acetylcholine in spatial memory formation in
rats. Although this study investigates animals, to some extent the results can be generalised to human
behaviour, as the principles of the biological level of analysis state that the biological systems of animals
and humans are similar due to evolution from a common ancestor. Within this study, rats were trained to
run a maze and were rewarded at the end with food. Once the rats were able to do this, he injected one
group with scopolamine, a molecule which blocks acetylcholine receptor sites, thus decreasing available
acetylcholine. He then injected a second group with physostigmine, which blocks the production of
cholinesterase, the enzyme that is responsible for the clean-up of acetylcholine from the synapse and
returns the neuron to its resting state. The third group was a control, and received no injections. It was
found that the rats injected with scopolamine were slower at finding their way around the maze and made
more errors than either the control group or the physostigmine group. The physostigmine group ran
through the maze even quicker than the control group, making fewer mistakes. The study concluded that
acetylcholine played an important role in creating the memory of the maze, and therefore the
neurotransmitter plays a role in spatial memory.
These studies are useful in correlating neurotransmitter levels with specific behaviours to uncover the
biological correlates to human behaviour.
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