Kasamatsu And Hirai Evaluation Essay

Using one or more examples, explain effects of neurotransmission on human behaviour

If you need a reminder of how neurons and synapses function, then re-read the section on the 'principles' page

Study 1 - Kasamatsu and Hirai (1999)

Martinez-Kessner et al (1991)

This study contains a few intimidating new words (including the names of the drugs used on the rats), and requires a clear understanding of the process of neurotransmission. The pictures below may help you as you read the description of the study.
Don't forget the question you're answering!! It says "Using one or more examples, explain effects of neurotransmission on human behaviour"... That's HUMAN behaviour! Just talking about mice and mazes all the time won't help you to answer the question. You need to take the lessons from the study and to apply them to humans.
The video below goes into much more detail on synapses and synaptic transmission. 

Focus on Command Term - Explain

"Give a detailed account including reasons or causes"

Level 2

When writing an 'explain' essay (8 marks) make sure you give reasons and causes for a behaviour or psychological phenomenon (e.g. detailed reasons and causes linking neurotransmission to behaviour... IN HUMANS!)

Vocab check

Can you define the following terms?
  • neurotransmission
  • synapse
  • excitatory
  • inhibitory
  • action potential

Assignment 1 - Mouse Party

Mouse party is a great website from the University of Utah which shows the effect of various drugs on synapses. Follow the link to the website and have a play around with the program.

  • Produce a summary of the action of any two drugs. Make sure you are really clear on the effect they have at the synapse (on neurotransmission)
We know that sensory deprivation can lead to hallucinations, as this video clearly shows. Katamatsu and Hirai linked this to changes in serotonin levels.

Is it so simple?

The points below relate specifically to the Kasamatasu and Hirai study, but it is important to realise that many of them apply to most other studies of neurotransmission as well!

  • The sample for the study is rather unusual, and so may be unrepresentative of everyone else! Monks are somewhat peculiar people in the first place, and findings from a small sample of Buddhist monks probably can't be generalized to the rest of humanity.
  • There is an issue with the direction of causality (what causes what). Does serotonin cause the hallucinations or do the hallucinations lead to an increase in serotonin? Might there have been a third factor which caused both hallucinations and increased serotonin level? We can't pinpoint a cause-and-effect relationship with absolute certainty.
  • Neurotransmitters have complex jobs in the brain, and will be involved in multiple functions in multiple areas of the brain. It is therefore much too simplistic to conclude that this neurotransmitter is solely 'responsible' for a certain behaviour, or indeed that this is the neurotransmitter's 'main job'.
Kasamatsu and Hirai (1999) studied how sensory deprivation affects the brain by studying a group of Buddhist monks on a 72-hour pilgrimage to a mountain. Specifically they looked at the effect of the neurotransmitter serotonin on their experiences. Serotonin is active in the hypothalamus and the frontal cortex. Low levels of serotonin are linked with antisocial and impulsive behaviour; serotonin also regulates sleep, arousal levels and emotion. 

Aim - to study the role of serotonin in conditions of sensory deprivation. 

Method - Field experiment. Exposed to harsh weather conditions, the monks didn't eat, drink, or speak. After 48 hours, the monks reported hallucinations; researchers took blood samples both before monks ascended the mountain and right after pilgrimages.

Results - They found higher serotonin levels in the blood of the monks after the pilgrimage than before. 

Conclusion - The higher levels of serotonin may have been related to the hallucinations experienced by the monks. The study seems to show that that levels of neurotransmitters can change in response to the environment, and that these levels may have an influence on behaviour.
The acetylcholine or 'cholinergic' synapse studied by Martinez-kessner et al
The synapse with scopolamine added...
The synapse with physostigmine added...
To determine the role of the neurotransmitter, acetylcholine on memory.

  • Rats were trained to go through a maze and get to the end
  • One group of rats was injected with scopolamine (blocks acetylcholine receptors) (Making less ACh available)
  • A second group of rats was injected with physostigmine, which blocks the production of cholinesterase. Cholinesterase “cleans up” the acetylcholine from the synapse (Making more ACh available).
  • The third group were not injected with anything.
  • The rats injected with scopolamine were slower at finding their way around the maze and made more errors than the control and physostigmine group.
  • The physostigmine group ran through the maze and found the food more quickly than the control group and took fewer wrong turns.
  • Acetycholine played an important role in creating a memory of the maze.
  • The use of control group and the direct manipulation of the chemicals made it possible to establish a cause and effect relationship between levels of acetylcholine and memory. We can be more certain of the relationship here than we can for Katamatsu and Hirai.
  • It is questionable to what extent these findings can be generalized to humans as they use animal models. However, memory processes are assumed to be the same for all animals.

Assignment 2 - test your memory

From memory, write down the three conditions of Martinez-Kessner et al's experiment, including details of the drugs used and their effect on neurotransmission.

Bringing both studies together

Triangulating evidence...
It is important that you think about both of the studies here holistically, working out what they can tell us together, as well as individually. For example:

They illustrate the need for triangulation to discover relationships... Martinez-Kessner et al found a cause and effect relationship in very controlled conditions and directly manipulating chemicals in the brain. This is great, but it would be totally unethical in humans (!), and the use of animal models means that we are not sure that humans would react the same way. Kasamatsu and Hirai looks at neurotransmitters at work in a less controlled, but more ecologically valid and ethical setting, and in humans...

TOGETHER, therefore, each study helps to cover some of the weaknesses of the other one. The evidence is more powerful as a result.

Scopolamine - the world's scariest drug?

In a rather less scientific usage of the substance, scopolamine is sometimes used recreationally as a drug. 

CHALLENGE - can you link the effects mentioned in this video to the chemical effects of the drug at the synapse? At the very least it might help you to understand why the rats didn't do so well at the maze!

Assignment 3 - 8 mark essay question

Try to write about 2/3 of a page minimum from memory to answer the following question:

Using one or more examples, explain the effects of neurotransmission on human behaviour (8)

Other triangulating evidence


  • State what you are doing in the essay
    • This essay will explain the effects of neurotransmission on human behaviour. 
  • Introduce topic
    • One of the most important discoveries that have influenced psychology is the role of neurotransmission in behaviour, thought and emotion.
    • To understand the effect of neurotransmission on human behaviour, the physiology or method of neurotransmission should be understood.
  • Define Neuron 
    • Neurons are nerve cells - one of the building blocks of behaviour.
    • Send electrochemical messages to the brain so that people can respond to stimuli:
      • Either from external stimuli (environment) 
      • From internal changes in the body 
    • This transferral of messages is known as neurotransmission. 
  • Define Neurotransmission 
    • Neurotransmission is the method by which messages are sent through the central nervous 
  • Explain Neurotransmission
    • When an electrical impulse travels down the axon (body of neuron), it releases neurotransmitters which cross the gap between two neurons known as a synapse.
  • Define Neurotransmitters
    • Neurotransmitters are the body’s natural chemical messengers which transmit information from one neuron to another.
    • They are stored in the neurons' terminal buttons.
    • After crossing synapse, neurotransmitters fir into receptor sites on the post synaptic membrane (like a key in a lock).
    • Once the message has been passed on, they are either broken down or reabsorbed by terminal buttons known as reuptake.
  • So what is the significance of neurotransmitters in the BLA? 
    • Neurotransmitters have been shown to have a range of different effects on human behaviour. 
    • Neurotransmission underlies behaviour as varied as mood, memory, sexual arousal and mental illness.
  • State examples of some neurotransmitters 
    • There are various types of neurotransmitters, such as serotonin, dopamine, acetylcholine and noradrenaline that influence behaviour.
    • Several studies have been undertaken to demonstrate the effects of neurotransmission on human behaviour. 
  • Outline and state which neurotransmitters will be explained 
    • Serotonin and acetylcholine will be explained in the following essay.


Neurotransmitter 1: Serotonin 
  • Introduce serotonin 
    • One example of a neurotransmitter is serotonin, which is commonly associated with depression and aggression. 
  • Outline serotonin 
    • Serotonin is a body regulator it controls bodily processes such as sleep, libido and body temperature.
    • It protects us from negative emotions such as anxiety and depression.
    • Serotonin stimulates neurotransmission in the post-synaptic neuron, increasing arousal, emotion and is also implicated in depression.
    • Secreted into the human body by the pineal glands.
    • Low levels of serotonin due to efficient re-uptake in the pre-synaptic neuron leads to low levels of arousal and lack of positive emotion, hence symptoms of depression

Supporting Study 1: Kasamatsu and Hirai (1999)

Introduce Study (Signpost):

  • One example of how the neurotransmitter serotonin can affect behaviour was seen by researchers, Kasamatsu and Hirai, 1999. 
  • To see how sensory deprivation affects the brain 
  • Also to see how the serotonin affects behaviour 


  • Studied a group of Buddhist monks who went on a 72-hour pilgrimage to a holy mountain in Japan. 
  • Monks did not consume water or food; did not speak and were also exposed to cold weather. 
  • Researchers took a blood sample before monks ascended into the mountain and immediately after they reported having hallucinations 


  • After about 48 hours, monks began to have hallucinations, seeing ancient ancestors or feeling their presence by their sides. 
  • They found that serotonin levels had increased in the monks? brainsthus the higher levels of serotonin activated the hypothalamus and frontal cortex resulting in the hallucinations. 


  • Researchers concluded that sensory deprivation triggered the release of serotonin, which altered the way that the monks experienced the world, a behaviour expressed by humans. 

Connection of study to question
    • Thus, this study shows that the neurotransmitter serotonin affects the human behaviour of increased arousal causing hallucinations (as demonstrated by monks after a spike in serotonin), therefore affecting human behaviour in terms of arousal and emotion.

Neurotransmitter 2:Acetylcholine (Ach) 

  • Introduce acetylcholine
    • Another example of a neurotransmitter is acetylcholine (Ach).
  • Outline Ach 
    • Serotonin is associated with the brain - in how it involved in learning and memory.
    • Present in the peripheral nervous system (PNS) and acetylcholine receptors are found widely throughout the body and brain.
    • Effects of Ach in the body include:
      • Effective deliverer of sodium ions stimulates muscle contractions; excites nerves 
    • An increase in Ach causes
      • Decreased heart rate 
      • Increased production of saliva 
      • High doses - convulsions and tremors 
      • Deficient levels - contribute to motor dysfunction 

Supporting Study 2: Martinez & Kesner (1991)

Introduce Study (Signpost):

  • One example of how the acetylcholine can affect behaviour was seen by researchers, Martinez & Kesner, 1991.

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

  • Methods: 
    • 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, which blocks acetylcholine receptor sites. 
      • 2nd group - physostigmine, blocks production of cholinesterase (does 'clean-up' of - acetylcholine from synapse and returns neuron to its 'resting state'). 
      • 3rd group – control (no injections). 

  • Results:

Results showed that:

    • Scopolamine - slower at finding way round maze and made more errors than control/physostigmine group.
    • Physostigmine - ran faster compared to both groups and made fewer wrong turns.

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

  • Evaluation
    • Strengths:
      • Design and application 
      • 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. (Possible tapply research on rats to human beings)
      • Assumed that memory processes are the same for all animals.
  • Connection of study to question
    • Thus, this study shows that the neurotransmitter acetylcholine affects the human behaviour of memory causing an increase in memory functions with higher amounts of Ach compared to lower levels of Ach, which decreases memory functioning.


  • Conclude with a few statements about the effect of neurotransmitters on behaviour:
    • Neurotransmission is an effective way to communicate messages through the brain.
    • Thus neurotransmitters such as Serotonin & Acetylcholine affect specific human behaviours such as mood and memory.
    • Overall, it can be seen that neurotransmitters do affect human behaviour in a variety of ways. 


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