Behavioral Neuroscience

2.1 Introduction

In this module, you will take a closer look at the neurological basis of human behaviour. CBT practitioners are concerned with a client's actions, but it is helpful to understand how behaviour occurs at the neurological level. This module will provide you with an overview of the physiological functions associated with various mood states and behaviours. Why should you take an interest in behavioural neuroscience?

Science has made major advances in understanding how the brain structure and physiological aspects affect behaviour. For example, we now know that the frontal lobes of the brain are responsible for rational and logical thinking, problem-solving, planning and reasoning. An individual who suffers from damage to the frontal lobes may experience inability to process thoughts logically. Similarly, the 'amygdala' is an almond-shaped cluster of neurons that are known to be responsible for aggression, PTSD, phobias and anxiety.

The hypothalamus is thought to affect anger, mood and libido. The anterior cingulate cortex impacts  decision-making, impulse control and the ability to empathise. The Nucleus Acumens triggers fears, addiction and laughter. Many drugs like LSD etc simulate the effects of neurotransmitters and induce feelings of false ecstasy and happiness. Overall, it's most likely that our behaviour results from a complex interplay of brain chemistry, genetic make-up and external factors. 

Debate still rages on about 'insanity' pleas in case of murders and other heinous crimes. While one set of researchers claim that the internal make-up of the brain and impaired functioning of the nervous system drives our behaviour, opponents suggest that we are consciously responsible for our behavioural choices. CBT practitioners will not need to use this information on a day to day basis.

For example

It is possible to help a client overcome their depression with no knowledge of the physical mechanisms underlying a person's mood state. Clients do not generally ask their therapists for biology lessons!At the same time, acquiring a greater insight into how mental illness and distress 'works' can help you feel more confident as a mental health professional. You may also find that some clients are curious as to the biological mechanisms underlying their distress and will be grateful if you can provide a simple explanation. Your knowledge will also inspire trust in your clients.

What is meant by the term behavioural neuroscience?

Although the term sounds complex, it can easily be broken down into two components.Behavioural simply means 'of or relating to behaviour.' In other words, behavioural science aims to uncover the correlates of human actions.Neuroscience describes the study of the function, development and structure of the nervous system. Behavioural neuroscientists are interested in how the human nervous system causes behaviour - or at least, the extent to which is correlates with human behaviour.

Although contemporary behavioural neuroscience makes extensive use of modern technology such as MRI and CT scanning equipment, the field has a long history stretching back thousands of years. The ancient Egyptians practiced their own form of neuroscience. They would remove the brains from bodies prior to the mummification process, which provided them with an opportunity to draw links between certain forms of brain damage and abnormal symptoms they had noticed in the person when they were still alive.

2.2 The Key Principles and Assumptions of Behavioral Neuroscience

We need to understand the structure of the brain in order to understand behavior. Researchers maintain that it is pointless to try and put together any meaningful theory of human behaviour without possessing an in-depth understanding of the physical mechanisms responsible for producing or encouraging the behaviour.Brain function directly informs behaviour.

Behavioural neuroscience is clear on this point - the reason why we should invest so much time and effort into uncovering the structure of the brain is because the brain - and the brain alone - is responsible for the full spectrum of human behaviour. If one part of the brain becomes damaged or changes in any way, it is inevitable that the individual's behaviour will change as a direct result

The link between structural damage and behavioural change has been thoroughly documented over thousands of years. There can be no doubt that such a relationship exists. Behavioural neuroscience assumes that everyone's brains function in more or less the same way and that when they uncover a 'rule' or relationship that this will hold true for humans as a species.The nervous system informs behaviour, not vice versa The prevailing assumption is that the nervous system detects sensory input, reacts in a standardised way, then produces observable behaviour as a result.

2.3 Points of Controversy and Discussion Within the Field of Behavioural Neuroscience

Although this paradigm has yielded a significant amount of relevant, useful data, there are key limitations that are currently under discussion by researchers in the field. The most important question is the very nature of behaviour itself. In the context of neuroscience, what should 'behaviour' actually mean?

Mainstream researchers tend to adopt the view that if they identify a part of the brain that influences behaviour (or appears to do so) when it is stimulated or damaged, then the resulting change in a person's behaviour stands as proof of cause and effect. However, it is worth looking at the concept of behaviour more closely.

For instance, research with monkeys has demonstrated that certain neurons in their brains 'light up' or become more active when they show signs of recognising a face.But what does this actually mean? It does not mean that a collection of cells can, in themselves, recognise a face. Neuroscience has often been accused of overlooking the big picture, focusing on small details and forgetting that human experience is nebulous, qualitative and generally greater than the sum of its parts.

'Behaviour' is commonly used in reference to any action, both purposeful and unintentional, in this field. However, some authors have argued that if we want to devise a comprehensive overview of both the nervous system and behaviour, we need to focus on the latter asmuch as the former. We also need to gain some clarity with regards to whether we want to focus on the neural correlates of all physical actions, or those which are experienced as autonomous and goal-directed by those enacting them - or both.

Another consideration is neuroplasticity. In their bid to build clear, consistent models that show reliable links between the nervous system and behaviour, researchers have shown a tendency to overlook the role of neuroplasticity and how it may complicate this idea.

For example

Neural network X could result in neural network Y in response to external events.But we also know that the nervous system, especially the brain, is in a state of constant growth and change. How might this ability to change in terms of physical form - known as neuroplasticity - affect these theories? In short, although behavioural neuroscience is both interesting and useful in helping us draw linksbetween physiological events and human behaviour, it is not a fool proof paradigm that should be left to stand without criticism.

It is important to bear this in mind when learning about neuroscientific findings and how they mighthelp us understand both behaviour in general and mental illness in particular. Human behaviour cannot be reduced down to biological processes. It is a mixture of external and internal phenomena that shapes an individual's personality and behaviours.

2.4 Neurotransmitters

Behavioural neuroscientists are interested in how chemicals produced and used within the nervous system affect human behaviour. These chemicals are known as neurotransmitters. To appreciate their function, you need to have a basic understanding of how information is transmitted throughout the brain.

How information is transmitted through the human nervous system

The human brain contains over 80 billion neurons.These cells make up the information network within the brain and other components of the nervous system, including the spinal cord. Neurons are electrically excitable. This means that when they are exposed to an electrical impulse, they trigger nearby cells to act. The end result of a series of neural transmissions can range from hormonal secretion from a gland in the body to a muscle contraction.

There are many different types of neuron in the human body, including those that respond to external stimuli (sensory neurons) and those which receive messages from the spinal cord and brain that results in muscle movement (motor neurons). A neuron is made up of a cell body (called a soma), an axon and dendrites. Dendrites resemble branches of a tree emanating from the soma and are used to pick up signals from other neurons. When a neuron transmits a signal of its own, it sends the electrical impulse down the axon.

Neurotransmitters allow two neurons to communicate with one another. When a neuron receives an electrical signal, it releases neurotransmitters from the end of its axon. The neurotransmitter then 'jumps' to the next neuron to activate it or deactivate it, therefore continuing or discontinuing a chain of communication. The gap between two neurons is known as a synapse. Patterns of neuronal activity are associated with specific behaviours and feelings.

In this module, you will learn about three of the most significant neurotransmitters: Dopamine, Serotonin and Noradrenaline.

Activity: The Most Common Neurotransmitters

Estimated time: 5 minutes

Go online and run a search for 'neurotransmitters'. Skim over a few search results.

Which seem to be the most commonly mentioned?

2.5 The Role of Dopamine in Human Behaviour

Dopamine is implicated in feelings of reward and pleasure. It allows us to perceive potential rewards and then to take the necessary actions in order to obtain them. Compared with other species, including primates, humans have high levels of available dopamine. When an individual eats protein, they supply their body with an amino acid called tyrosine. Via a series of chemical interactions, tyrosine eventually becomes dopamine. Dopamine must be synthesised in the brain, because its molecules are too large to cross the blood-brain barrier. Not everyone has the same levels of dopamine in their brains and there is also variation with regards to dopamine sensitivity.

Higher dopamine levels are correlated with greater aggression and impulse control, meaning that those with greater levels of this neurotransmitter are in a better position to plan what they want. They are in a position to meet their goals and ignore distractions along the way. Excessively high and abnormally low dopamine levels both come with their individual set of problems.

Too much dopamine can trigger psychosis, a state in which a person loses contact with reality. They may become paranoid, experience hallucinations and start to believe things that are not true (delusions). The reason cocaine, amphetamines and chemically similar recreational drugs are so popular is that they trigger the release of dopamine, which can give rise to feelings of intense happiness and a strong desire for sex.

How does dopamine work in the brain?

Dopamine is synthesised within two areas of the brain, the substantia nigra and the ventral tegmental area. From there, it activates neurons in several areas of the brain, two of which are outlined below. The pathway between the frontal cortex and the ventral tegmental area: These areas facilitate the higher cognitive functions such as planning, motivation, some aspects of normal emotional responses and prioritisation. People with ADHD and depression often show a lack of dopamine activity in these areas. 

The pathway between the ventral tegmental area and parts of the limbic system, which includes the hippocampus and the frontal cortex: Appropriate levels of dopamine activity in these parts of the brain is essential for the urges and sensations associated with reward and emotional regulation.

For instance

Without dopamine, we would not be able to understand that a bar of chocolate is likely to trigger pleasurable feelings and a sense of reward if we were to eat it. Abnormal levels of dopamine in this part of the brain are thought to be a key cause of addiction and psychotic experiences. Schizophrenia, a mental illness characterised by psychosis, responds well to drugs that lower dopamine levels.

Dopamine works in complex ways to initiate and maintain addiction. When someone first ingests a recreational drug, such as cocaine, they will experience a 'hit'. This encourages them to continue. However, as time goes on, the user will report that their behaviour is no longer driven by a desire to feel pleasure, but a compulsion to avoid feeling 'flat' or a sense that they are missing something crucial by not taking it.

This is because when high dopamine levels - the abnormal highs generated by recreational drugs - become the norm, the brain will compel the individual to do whatever it takes to restore them when the effect of the drug wears off. This is why drugs provide less and less satisfaction over time.Not everyone reacts to dopamine in the same way. Genetics and experience literally shape the way in which a person's brain uses dopamine and this has a direct effect on their behaviour.

For instance, a study published in the journal Neuropsychopharmacology summarised the findings of research into the differences in dopamine receptors in the brains of people who had died from suicide and healthy controls, who had died from other causes.

There was a clear difference - those who had died from suicide and lived with severe depression showed abnormalities in D1 and D2 receptors, which are responsible for the healthy transmission of dopamine throughout the brain. This lends support to the notion that depression and suicidal behaviour have roots in biological abnormalities. This kind of research supports the idea that depression and other mood disorders are genetic. They tend to affect multiple generations within the same family.

2.6 The Role of Serotonin in Shaping a Person's Behaviour

Before continuing please complete the activity below.

Activity: What do you know about serotonin?

Estimated time: 5+ minutes

Serotonin is one of the best-known neurotransmitters. It is often mentioned in popular psychology articles.

What do you already know about the function of serotonin and how do you think it may play a role in mental health?

Much like dopamine, serotonin is implicated in feelings of wellbeing. It is sometimes nicknamed 'thehappy chemical'. Recreational drugs such as ecstasy and LSD, which are taken for their mood-enhancing effects, trigger the release of serotonin. It is found not only in the brain, but also in the blood and the bowel.

Serotonin is vital in the regulation of basic bodily functions (including blood clotting and muscle movement) and the maintenance of a normal sleep-wake cycle. Its effects are vast and varied.

For instance

Some researchers now believe that a deficiency in serotonin may cause Sudden Infant Death Syndrome (SIDS), sometimes known as cot death. It is responsible for producing and controlling the human sex drive. Drugs that increase the levels of serotonin in the body sometimes cause an individual's libido to drop, suggesting that healthy levels of serotonin are important in the maintenance of a healthy sex drive.

How is serotonin produced in the body?

The body makes serotonin from tryptophan, an amino acid. It is found in foods that are rich in protein, iron, vitamin B-6 and riboflavin such as salmon, turkey and some types of nuts and seeds. Serotonin is then produced in the brain and intestines. Tryptophan can cross the blood-brain barrier, but serotonin cannot. This means that all serotonin used by the brain must be created within the organ itself.

Gut serotonin and mood

Although it is primarily associated with the brain and mood in popular science and psychology, the majority of serotonin is produced in the digestive system. Research with mice has demonstrated that the amount of serotonin produced in the intestines may depend on the presence of particular gut microbes and that the amount of serotonin produced in this part of the body may have a direct or indirect impact on animal behaviour.

Even though serotonin and dopamine cannot cross the blood-brain barrier, scientists are increasingly interested in the so-called 'brain-gut axis'. It is a well-known fact that strong negative emotions such as anxiety can trigger digestive problems such as stomach pains and diarrhoea. Therefore, it may be the case that this communication is a two-way system and that the gut can 'talk' to the brain. The neurotransmitters produced by the digestive system may send signals to the brain, which in turn may alter mood and behaviour. Research into the potential benefit of taking in good bacteria (in the form of probiotics) is ongoing. So far, the results of clinical trials have been mixed.

Fact

90% of serotonin found in the body is produced in the intestines.

Source: www.caltech.edu

Serotonin and depression

The mainstream view within contemporary psychiatry is that depression is caused by abnormally low levels of serotonin within the brain. However, no one is quite sure why an individual's brain might not be able to make much use of serotonin.

Four possible reasons are given below. Note that they might not be mutually exclusive:

*A person's brain cells may not produce sufficient serotonin

*The serotonin might not be able to reach the neuron receptor sites, for reasons unknown

*An individual might not be consuming sufficient tryptophan

*A person's brain might not have sufficient neuronal receptor sites

Doctors prescribe drugs called Selective Serotonin Reuptake Inhibitors (SSRI) for depression, on the assumption that if brain levels of serotonin are increased, the patient will experience a reduction in symptoms. Research has found that people with depression typically have levels of blood serotonin that are lower than average.

However, there is no definitive proof that low serotonin levels in the brain cause depression and therefore it is not clear whether increasing levels of serotonin in the brain is a particularly effective treatment. At the moment, researchers do not have the technology to measure levels of serotonin in a living, working human brain.

Moreover, although they appear to help some people feel less depressed; it appears that the placebo effect is responsible for a large proportion of this improvement. It is also important to note that even if we were to draw a definitive link between serotonin levels in the brain and symptoms of depression, it does not mean that a drop in serotonin leads to depression.

It may be the other way around - perhaps depression leads to a reduction in serotonin levels. There is evidence showing that exercise is just as effective as antidepressants in treating mild to moderate depression. A single workout can be enough to significantly improve mood. Neuroscientists are not certain how this works. In short, there is still much research to be done before we understand serotonin's exact mechanism of action. At the moment, it is safe to say that they certainly have some part to play in human behaviour and emotions, but it is not clear precisely how they work within the human brain.

Fact

An adult human's body holds between 5-10 mg of serotonin.

Source: www.vitamins-supplements.org

Sex differences and serotonin

Although men are more likely to commit suicide than women, depression is more common in the latter. One explanation for this gender difference may lie in the way men and women respond to changes in serotonin levels. Following tryptophan depletion - a process that is thought to reduce available serotonin in the brain- behavioural changes are observed in both sexes.

However, women are more likely to feel low and take fewer risks, whereas men commonly become impulsive. These differences might also go some way in explaining the sex differences in ADHD and alcoholism, both of which more commonly affect males than females. Women also experience more fluctuations in levels of sex hormones compared to men. Oestrogen may interact with serotonin and this may explain why women experience changes in mood throughout their menstrual cycle. By contrast, a man's sex hormones remain largely unchanged until his forties or fifties. At this point, they begin to drop at a slow, steady pace.

2.7 How Noradrenaline Affects Human Behaviour

Noradrenaline, also known as norepinephrine, is classified as both a neurotransmitter and a hormone.It is manufactured and released by the adrenal glands, which are positioned above the kidneys. Its precursor is an amino acid called tyrosine, which is found in high-protein foods. When an individual encounters a surprise, their adrenal glands release noradrenaline. It increases blood sugar levels and blood pressure. This allows the body to get ready to respond to external threats. It is an adaptive system that has kept humans safe for hundreds of thousands of years. Whenthe body is under stress and releases noradrenaline, the result is heightened awareness and sensitivity.However, this system cannot readily tell the difference between the danger posed by a physical threat that requires immediate resolution and an ongoing source of stress that is not a danger to life, but is still problematic.

For example

Working long hours or getting into fights with a partner or other family member do not usually present any physical danger, but they still trigger the release of norepinephrine. Ongoing stress causes the ongoing release of norepinephrine. This can cause physical and psychological damage. Living in a state of chronic stress is a risk factor for depression, anxiety, exhaustion and burnout. These problems can have long-lasting effects.

Norepinephrine levels may be an important factor in explaining why work for some depressed people but not others. In the 1960s, the catecholamine theory of mood disorders was developed by psychiatrist Joseph Schildkraut. He thought that depression was caused by a deficiency of norepinephrine, whereas manic states (such as those seen in bipolar disorder) arose when a person's adrenal glands became over-active. For this reason, some doctors prescribe drugs that increase levels of both norepinephrine and serotonin, or drugs that boost levels of norepinephrine and dopamine.

Norepinephrine is responsible for the symptoms an individual experiences when they have a panic attack. When norepinephrine is released, the body goes into a state of 'fight or flight', which results in symptoms such as heart palpitations, sweating, a feeling of unreality, nausea, dizziness and a feeling of being choked. Once this reaction has started, there is no way of reversing it - it must be allowed to run its course. Some clients find this explanation helpful in removing the mystery of extreme anxiety. It is reassuring to know that there is a good reason for their symptoms.

MODULE SUMMARY

Behavioural neuroscience is a discipline concerned with uncovering links between the nervous system and observable behaviours. Although biological knowledge is not necessary to carry out CBT, a working knowledge of the link between mental health and the nervous system is interesting and useful background information. It may also be reassuring for a client to learn that there is a scientifically validated reason for their symptoms.

Neurotransmitters are particularly interesting in the context of mental health. These chemicals are an important component within the nervous system. They facilitate the transmission of electrical impulses between two or more neurons, or prevent a signal from travelling further.Three neurotransmitters that play a role in human behaviour are dopamine, serotonin and noradrenaline.

Dopamine is essential for the proper functioning of the human reward system. It facilitates addiction and is also implicated in psychosis. Serotonin is another neurotransmitter implicated in positive feelings. A versatile neurotransmitter, it is produced in the brain and the intestines before regulating and promoting normal bodily functions.

Finally, although norepinephrine does not receive as much attention as dopamine or serotonin, it also plays a major role in mood and concentration.The catecholamine theory of depression states that a lack of norepinephrine, rather than a lack of serotonin, is responsible for the symptoms of major depression. Some antidepressant medications increase norepinephrine along with dopamine or serotonin.

Norepinephrine is also implicated in panic attacks. When it is released from the adrenal glands, it triggers physical sensations such as nausea, dizziness and feelings of being choked. Clients suffering from panic disorder can find it helpful to understand how and why their symptoms arise.