NEUROPSYCHOLOGY

1. NEUROPSYCHOLOGY Dr. Malcolm Hughes

2. Watson defined psychology as the “science of the mind” and in that respect, the subject of psychology has focused on a range of topics which reflect the manner in which human subjects behave. Attempts to explain behaviour in terms of brain mechanisms is also expressed by the term “biological psychology”. The subject is sub-divided into disciplines which include: a) Neuro-anatomy b)Psycho-genetics c) Psycho-endocrinology d) Psycho-neuro-immunology e) Psychopharmacology

3. “Biological psychology” is defined as explaining behaviour in biological terms – considerable emphasis in placed on the brain structure at a cellular level and the associated processes e.g. chemical mechanisms. Now recognised that chemical energy within the brain can be converted into various kinds of brain activity; conversely, brain activity, e.g. cognitive processes and emotions, can instigate changes in the brain’s chemistry resulting in other mental and behavioural responses. Biological Explanations of Human Behaviour Example: some psychologists would advocate that anger in an experience that merely reflects a pattern of activity within a specific area of the brain, heightened by certain hormones. A further suggestion is that the brain is “programmed” by natural selection to enable such experiences to happen. This implies a “psychogenic” influence.

4. Within these areas of study, the understanding of the brain and its constituent parts have led to substantial contributions to the relationship between brain and behaviour. Included among these areas are the physiological mechanisms associated with thecentral nervous system. An overall understanding of the anatomy of the brain structure reflects the diversity of the individual’s mental processes and behaviour. Some structures can highlight these effects quite significantly. Among such structures are: a) The thalamus b) The hypothalamus c) The hippocampus and amygdala d) The corpus callosum e) The cerebral hemispheres

5. The midline structures of a human brain.

6. From the biological standpoint, there are two types of likely explanation: 1. Factors that “force” a behaviour to occur e.g. sweating, constriction of the pupil of the eye, knee-jerk reflex. 2. Factors that “enable” a behaviour to occur e.g. social or competitive motivation, “choice” of aggression, sexual motivation. Therefore, theories would suggest that human behaviour is a product of several different, but possibly integrated forces. The Mind-Brain Relationship Problem of definition – what is meant by the “Mind”? Various interpretations 1. MATERIALISTS: view the brain as a machine in which the consciousness was irrelevant to its functioning. 2. DUALISTS: consider the mind to exist independently of the brain, but could exact some control over it. Mind and body are separate but interactive. 3. IDENTITY POSITION: the mind is viewed as being the same as the brain except that it is described in different terms.

7. Neuro-transmitters These are chemicals released at the synapse separating two sections along a nerve fibre. It is now recognised that a large number of chemicals function as neurotransmitters within the brain. The three major categories of neurotransmitters are: a) Biogenic amines (contain an amine (NH2group) b) Amino acids – derived from the breakdown of proteins c) Peptides Each neurone has the capacity to synthesise its neurotransmitters from precursor molecules that reach the cell by way of the blood, derived originally from foods that the individual ate. Many neurotransmitters are synthesised both in the cell body and in the terminal, close to the point of release. Under normal circumstances, the brain maintains fairly constant levels of each neurotransmitter, even during periods of fasting.

8. Cell body Synthesis of neurotransmitter, formation of vesicles The major events in transmission at a synapse. Vesicles without neurotransmitter are transported back to cell body Transport of neuro-transmitter down axon Reuptake of neuro-transmitter to be recycled Release of neurotransmitter Separation of neuro-transmitter molecules from receptors Interaction with receptor exciting or inhibiting postsynaptic neuron Postsynaptic neuron

9. Diagram of a synapse: the end of the presynaptic axon swells to form the terminal which releases the neurotransmitters.

10. NEUROTRANSMITTERS BiogenicaminesAminoacidsPeptidesOthers (contain NH2 gp.) (glutamate, G.A.B.A.) (endorphins) (adenosine) Acetylcholine Monoamines Serotonin Catecholamines Dopamine Norepinephrine Epinephrine (Nor-adrenaline) (Adrenaline) The above diagram illustrates the different types of neurotransmitters and their synthesis pathway.

11. Drug effects on Pre-synaptic Neurones Certain drugs exert their effects by altering the synthesis of a neurotransmitter e.g. A.M.P.T. (α – methyl para-tyrosine) – has the effect of blocking the synthesis of: Dopamine Adrenaline Nor-adrenaline These effects are due to the similarity in the chemical structure of tyrosine to A.M.P.T. A.M.P.T. blocks the enzyme from attaching to tyrosine, therefore very little tyrosine is converted into DOPA. Amphetamines have the capacity to release neurotransmitters from storage in the pre-synamptic neurones: Results in: a) increase in the release of adrenaline and nor- adrenaline. b) increases the alertness and arousal of the individual.

12. After some hours, the individual can enter a “rebound” state of depression. This is due to the brain’s inability to re-synthesise new nor-adrenaline in sufficient quantities to replace that released as a result of amphetamine intake. Effects of caffeine Adenosine (a neurotransmitter) acts at many pre-synaptic receptors to inhibit the release of excitatory transmitters e.g. glutamate. Caffeine can block the effects of adenosine (Silinsky, 1989) – this results in an increase in the release of glutamate. Therefore the nervous system becomes stimulated.

13. Effects on Post-synaptic Receptors Some drugs have similar chemical structures to the neuro-transmitter; therefore both substances can fit into the same receptor site. e.g. acetylcholine has certain synapses referred to as “nicotinic synapses” (are naturally stimulated by the drug nicotine). Therefore, nicotine acts as an acetylcholine agonist. Has the effects of: increasing heart rate increasing cerebral cortex activity Other drugs are capable of slotting into receptor sites but do not necessarily stimulate it: e.g. Haloperidol – blocks the DOPA synapses. Is thus defined as a DOPA antagonist. N.B. this is now take as evidence that dopamine activity in excess of normal, contributes to schizophrenia.

14. Neuro-anatomical and neuro-chemical influences: These can impact on a diverse range of cognitive, emotional and behavioural outcomes. • At a cognitive level, there are implications in terms of thought processes, memory and learning and the way the individual can perceive. • In emotional terms, the impact of stress can bring about changes in the neuro-endocrine system. Can in turn impact on other elements of the brain’s biochemistry and the immune system, thereby affecting both mental and physical health. • Behavioural outcomes, often associated with psychogenetic conditions and physical trauma to the brain, including lesions.

15. Therefore, in conclusion, it is important to recognise that the brain is a complex organ in terms of its function together with the way it can itself can be profoundly affected by events occurring elsewhere in the body: e.g. biochemical changes or electrolyte imbalance. In a similar manner, the brain can also be influenced by factors external to the body: e.g. events perceived by the individual, intensity of light Thus, when considering the processes which reflect on the overall functioning of the human individual, it is vital to remember that even the slightest changes can bring about alterations in how that individual may react emotionally and the nature of their behaviour, both at a psychological and physical level.