Neurotransmitters & Their Effect on Behaviour (HL IB Psychology)

Neurotransmitters & Their Effect on Behaviour

What are neurotransmitters?

• Neurotransmitters are chemicals that are transported via electrical impulses from the presynaptic neuron to the post-synaptic neuron across the synaptic cleft

• An action potential begins the process of neurotransmission at the dendrites of the neuron: this comes in the form of an electrochemical impulse which travels down the axon to the terminal buttons containing the synaptic vesicles holding the neurotransmitter which is then released into the synaptic cleft 

• Synapses can be excitatory in the presynaptic neuron: this increases the probability of an action potential occurring in the post-synaptic neuron i.e. the neuron ‘fires’

• Synapses can be inhibitory in the presynaptic neuron: this decreases the probability of an action potential in the post-synaptic neuron

• Molecules of the neurotransmitter which are not passed across the synaptic cleft are taken back up into the axon of the presynaptic neuron (known as reuptake)

• Examples of neurotransmitters include dopamine and serotonin

The process of neurotransmission

What is dopamine and what effect does it have on behaviour?

• Dopamine is one of a group of neurotransmitters known as monoamines

• Brain regions and structures associated with dopamine production include the ventral tegmental area, the nucleus accumbens, the caudate nucleus and the basal ganglia

• Dopamine (as is the case with all neurotransmitters) acts a chemical messenger, communicating between cells (from the brain to the rest of the body)

• Dopamine has been strongly associated with reward, motivation, intense pleasure and, by association, addiction

• Dopamine has strong associations with the function of movement and motor skills as seen in dopamine deficiency in Parkinson’s disease

• Irregular levels of dopamine have also been linked to the symptoms of schizophrenia (known as the dopamine hypothesis)

Roller coasters provide a dopamine boost for some people!

What is serotonin and what effect does it have on behaviour?

• Serotonin is also a monoamine, specifically known as 5-HT as it can also act as a hormone (but for the purposes of your IB studies only refer to it in its role as a neurotransmitter)

• Serotonin plays a crucial role in regulating functions such as sleep, mood, body temperature

• Low or irregular levels of serotonin have been linked to affective disorders such as depression and anxiety

• Some drugs prescribed for depression (antidepressants) are known as SSRIs (Selective Serotonin Reuptake Inhibitors) as they prevent the reuptake of serotonin, ensuring that it is passed onto the post-synaptic neuron

• Serotonin is made from an amino acid called tryptophan which can be found in foods such as turkey, eggs, cheese and tofu

Which studies focus on the effect of neurotransmitters on behaviour?

• Fisher et al. (2005) in her study of the link between romantic love and dopaminergic activity in the brain

• Brunner et al. (1993) in his case study of abnormal, anti-social behaviour in one family explained by a dysfunctional MAOA gene (linked to the 5-HT) gene

Fisher and Brunner’s studies are available as separate Key Studies – just navigate the Brain and Behaviour section of this topic to find them.