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The Biochemical Explanation of Mental Illness

To think, feel or make a decision/act on it, our brain cells must transmit information in the form of electrical impluses around the brain - there is a gap/synapse at the end of each cell leading to the other brain cell, for information to pass on chemical called neurotransmitters must pass across the synapse, they are important in different parts in the brain and are believed to regulate different mental processes. One explanation of Mental Illness' symptoms is that there are abnormal neurotransmitter levels or action.

The monoamine hypothesis of depression:

  • A group of neurotransmitters called monoamines appear to be involved in depression, including, Serotonin, Dopamine and Noradrenaline
  • Depression involves lowered mood and disruption to activity levels - leaving patients more or less active than normal
  • It is believed that Dopamine plays an important role in regulating our mood, Noradrenaline is implicated in activity levels and Serotonin may be important in controlling the activity of Dopamine and Noradrenaline
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The Biochemical Explanation of Mental Illness

  • One version of the monoamine hypothesis of depression says that reductions in serotonin levels(which follow stressful events) lead to a failure to regulate normal Dopamine/Noradrenaline function - which disrupts mood and activity levels
  • A different version to the monomine hypothesis says that the disruption to monoamine levels is the result of abnormally high levels of an enzyme that breaks down the monoamines - reducing their action and disrupting the passage of information around the brain
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Genetic Explanations for Mental Illness

Humans randomly inherit half our genetic material from our mother and the other half from father, the total genetic make-up of an individual is known as a 'genontype'. Genes are sections of DNA that contain th instructions for producing physical structures (the brain, organic chemicals - neurotransmitters/enzymes that break them down). It is probable that genes exert an influence on individual psychological characteristics - including mental illness, by influencing the nature of physical structures of chemical levels in th central nervous system. It is unlikely that mental illness is purely a result of genetic factors - but it does appear that some people are more vulnerable than others in developing a mental illness due to their genetic make-up. The extent of genetic vulnerablilty varies widely between mental illnesses. Depression in its minor and common forms appears to be only moderately affected by genetic factors (genes) but vulnerability to schizophrenia is much more heavily influenced by genetic variations.

Genetic Vulnerability to Depression:

  • No suggestion that most types of depression are only/primarily the result of genetic vulnerability
  • The strongest predictor of depression is experience of stressful life events - but we do not respond to stress in the same way - some people are more resilient
  • Possible that are genes have important effects on how resilient people are to life events
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Genetic Vulnerabilty to Depression

  • Rather than just look at whether there appears to be a genetic influence on conditions such as depression - modern researching is focusing on the influence of particular genes and how they may interact with the enviroment which then influences symptoms 
  • They have been particularly interested with the Serotonin transporter gene - responsible for producing Serotonin in the brain 
  • The gene comes in three forms varying in the length of the strands (long-long, long-short, short-short) - it is believed that the short form leads to insufficient Serotonin production 
  • It may mean people with the short-short combination are less resilient than others to the effects of stress and are more likely to respond to stress with depression 
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Brain Abnormality

The human brain is a complex system, its delicate chemistry can be disrupted, depression is associated with low monoamine levels and schizophrenia is linked to abnormally high or low levels of dopamine in parts of the brain. Structure and function are also associated with mental illness - e.g. certain structures in the brain may develop with a different size or shape and levels of electrical activity can be higher or lower in particular brain regions. Also evidence that shows are central nervous systems do not function normally when we suffer from certain conditions - particular areas of the brain seem to malfunction during mental disorder - but it is unclear whether is it due to the abnormal neurotransmitter levels or to a sperate phenomenon. 

Brain Abnormaility in Depression:

  • Some evidence of brain abnormaility in depression 
  • Studies have suggested the role of the frontal lobes (involved in thinking) 
  • Coffey et al (1993) compared the size of frontal lobes in depressed patients and non-depressed controls using MRI scanning technology - found that the mean frontal-lobe volume in DP was significantly smaller 
  • A PET-scan study by Milo et al (2001) also showed that frontal lobes in depressed patients do not draw on blood flow in the brain as they do normally (called 'hyperinfusion') - ECT success
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Brain Abnormality

Brain Abnormaility in Schizophrenia: 

  • Evidence that due to Schizophrenia the left hemisphere of the brain does not function normally
  • Purdon et al (2001) compared the force applied with the right and left hand in 21 patients with schizophrenia and in a control group 
  • 10 of the treatment group were given anti-psychotic medication and tested again - the untreated group were significantly weaker in their right hand, not the left 
  • The effect disappeared after treatment - suggesting that schizophrenia involves a problem with the left-brain and anti-psychotic drugs help this 
  • Evidence to show negative symptoms of schizophrenia e.g. loss of motivation (avolition) are associated with brain abnormalities, motivation is linked to the ventral striatum 
  • Juckel et al (2006) measured activity levells in the ventral striatum in schizophrenia and found a lower level of activity than the controls - also found a negative correlation between activity levels in the ventral striatum and severity of overall negative symptoms - suggests that this symptom is linked to abnormal function of the vental striatum 
  • Hallucinations arlso associated with abnormal brain function - Allen et al (2007) scanned the brains of patients with auditory hallucinations and compared them to controls 
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Brain Abnormality

  • While they identified segments of pre-recorded speech as either their own or other people 
  • Lower activation levels in two brain regions - the superior temporal gyrus and anterior cingulate gyrus - were found in the hallucination group (made more errors than the control) 
  • It can be concluded that abnoramal function in these areas is associated with hallucination in schizophrenia 
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Application: Biological Treatments

Depression can be treated biologically using drugs and/or eclectroconvulsive therapy (ECT)

Antidepressant Drugs:

  • Most people approaching their GP with depression have been prescribed antidepressants - number of different ones and work in different ways - they usually work by raising the level of monoamine neurotransmitters in the brain 
  • Monoamine oxidase inhibtors (MAOIs) prevent the brekadown of serotonin, noradrenaline and dopamine so that the three levels build up 
  • Tricyclics prevent serotonin and noradrenaline from being reabsorbed after crossing a synapse 
  • These 'old-fashioned' antideressants are effective in reducing symptoms as they interfere with neurotransmitters but they have serious side effects (Tricyclics can cause drowsiness, dry mouth and constipation) 
  • New antidepressants usually work on one monoamine only - Selective serotonin reuptake inhibitors (SSRIs) e.g. Prozac and Seroxat stop serotonin being reabsorbed and broken down after crossing a synapse and Noradrenaline reuptake inhibitors (NRIs) do the same with noradrenaline
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Application: Biological Treatments

  • Important to have a variety of antidepressants avaliable because indiiviuals respond to drugs differently in effects on symptoms and side effects 
  • People present with different symptoms and this influences the choice of drug (NRIs e.g. can be helpful in motivating patients whose depression has left them very inactive) 
  • Different types of antidepressants are prescribed in different circumstances: e.g. gender is an issuse women suffer more side effcts than men from Tricyclics, women tolerate MAOIs well but they are highly toxic so they are a not a good idea if the person is a suicide risk 

Electroconvulsive Therapy (ECT):

  • Is an alternative medical procedure for treating depression - involves administering an electric shock for a fraction of a second to the head - inducing a seizure that is similar to epilepsy 
  • The seizure generally lasts 15-60 seconds - in most cases the shock is bilateral (both sides of the head) which is considered more effective than unilateral but is more likely to lead to side effects - typical course treatment runs 2-3 weeks with ECT being repeated 6-12 times in total, ECT is a controversial treatment - in early use the shock was large and given without anaesthetic/muscle relaxants - resulting in fitting and broken bones and sometimes burns to the brain - modern ECT = small shocks for short periods (800miliamps) under anaesthetic and muscle relaxant drugs to try to prevent broken bones
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