Medical understanding of psychosis
There are a number of possible causes for psychosis. Psychosis may be the result of an underlying mental illness such as Bipolar disorder (also known as manic depression), and schizophrenia. Psychosis may also be triggered or exacerbated by severe mental stress and high doses or chronic use of drugs such as amphetamines, LSD, PCP, cocaine or scopolamine. However, incidence of psychosis resulting from a single administration of any drug is rare, although cases have been reported in the medical literature suggesting a person's sensitivities to new compounds can be unpredictable. As can be seen from the wide variety of illnesses and conditions in which psychosis has been reported to arise (including for example, AIDS, leprosy, malaria and even mumps) there is no singular cause of a psychotic episode.
The division of the major psychoses into manic depressive insanity (now called bipolar disorder) and dementia praecox (now called schizophrenia) was made by Emil Kraepelin, who attempted to create a synthesis of the various mental disorders identified by 19th century psychiatrists, by grouping diseases together based on classification of common symptoms. Kraepelin used the term 'manic depressive insanity' to describe the whole spectrum of mood disorders, in a far wider sense than it is usually used today. In Krapelin's classification this would include 'unipolar' clinical depression, as well as bipolar disorder and other mood disorders such as cyclothymia. These are characterised by problems with mood control and the psychotic episodes appear associated with disturbances in mood, and patients will often have periods of normal functioning between psychotic episodes even without medication. Schizophrenia is characterized by psychotic episodes which appear to be unrelated to disturbances in mood, and most non-medicated patients will show signs of disturbance between psychotic episodes.
Psychotic episodes may vary in duration between individuals. In brief reactive psychosis, the psychotic episode is related directly to a specific stressful life event so patients may spontaneously recover normal functioning within two weeks. In some rare cases, individuals may remain in a state of full blown psychosis for many years, or perhaps have attenuated psychotic symptoms (such as low intensity hallucinations) present at most times.
Patients who are undergoing a brief psychotic episode may have many of the same symptoms as a person who is psychotic as a result of (for example) schizophrenia, and this fact has been used to support the notion that psychosis is primarily a breakdown in some specific biological system in the brain. The dopamine hypothesis of psychosis was an early, and still popular, example of a theory based on this assumption. However, it is controversial how much weight should be given to such exclusively biological theories as it has become clearer that a wide range of influences (including environmental, social and childhood development factors) may contribute to the final experience of psychosis.
It has also been argued that psychosis exists on a continuum as everybody may have some unusual and potentially reality-distorting experiences in their life. This has been backed up by research showing that experiences such as hallucinations have been experienced by large numbers of the population who may never be impaired or even distressed by their experiences10. In this view, people who are diagnosed with a psychotic illness may simply be one end of a spectrum where the experiences become particularly intense or distressing (see schizotypy).
Psychosis and brain function
The first brain image of person with psychosis was completed as far back as 1935 using a technique called pneumoencephalography1 (a painful and now obsolete procedure where cerebrospinal fluid is drained from around the brain and replaced with air to allow the structure of the brain to show up more clearly on an X-ray picture).
Pneumo- encephalogram of person with psychosis, 1935Modern brain imaging studies, investigating both changes in brain structure and changes in brain function of people undergoing psychotic episodes have shown mixed results.
A 2003 study investigating structural changes in the brains of people with psychosis showed there was significant grey matter reduction in the cortex of people before and after they became psychotic2. Findings such as these have led to debate about whether psychosis is itself neurotoxic and whether potentially damaging changes to the brain are related to the length of psychotic episode. Recent research has suggested that this is not the case3 although further investigation is still ongoing.
Functional brain scans have revealed that the areas of the brain that reacts to sensory perceptions are active during psychosis. For example, a PET or fMRI scan of a person who claims to be hearing voices may show activation in the auditory cortex, or parts of the brain involved in the perception and understanding of speech.
On the other hand, there is not a clear enough psychological definition of belief to make a comparison between different people particularly valid. Brain imaging studies on delusions have typically relied on correlations of brain activation patterns with the presence of delusional beliefs.
One clear finding is that persons with a tendency to have psychotic experiences seem to show increased activation in the right hemisphere of the brain4. This increased level of right hemisphere activation has also been found in healthy people who have high levels of paranormal beliefs5 or in people who report mystical experiences6. It also seems to be the case that people who are more creative are also more likely to show a similar pattern of brain activation7. Some researchers have been quick to point out that this in no way suggests that paranormal, mystical or creative experiences are in any way by themselves a symptom of mental illness, as it is still not clear what makes some such experiences beneficial whilst others lead to the impairment or distress of diagnosable mental pathology. However, people who have profoundly different experiences of reality or hold unusual views or opinions have traditonally held a complex role in society, with some being viewed as kooks, whilst others are lauded as prophets or visionaries.
Psychosis has been traditionally linked to the neurotransmitter dopamine. In particular, the dopamine hypothesis of psychosis has been influential and states that psychosis results from an overactivity of dopamine function in the brain, particularly in the mesolimbic pathway. The two major sources of evidence given to support this theory are that dopamine blocking drugs (i.e. antipsychotics) tend to reduce the intensity of psychotic symptoms, and that drugs which boost dopamine activity (such as amphetamine and cocaine) can trigger psychosis in some people (see amphetamine psychosis).
Nevertheless, the connection between dopamine and psychosis is generally believed to be complex. First of all, while anti-psychotic drugs immediately block dopamine receptors, they usually take a week or two to reduce the symptoms of psychosis. Moreover, newer and equally as effective antipsychotic drugs actually block slightly less dopamine in the brain than older drugs whilst also affecting serotonin function, suggesting the 'dopamine hypothesis' is vastly oversimplified.
Psychiatrist David Healy has criticised pharmaceutical companies for promoting simplified biological theories of mental illness that seem to imply the primacy of pharmaceutical treatments while ignoring social and developmental factors which are known to be important influences in the aetiology of psychosis8.
Some theories regard many psychotic symptoms to be a problem with the perception of ownership of internally generated thoughts and experiences9. For example, the experience of hearing voices may arise from internally generated speech that is mislabelled by the psychotic person as coming from an external source.http://en.wikipedia.org/wiki/Psychosis