The presence of psychosis may be related to other mental health issues, but the condition is also caused by drugs of abuse, alcoholism and several disease conditions. This suggests that several pathological mechanisms within the brain are shared by individuals affected by these conditions.
One of the most common features of psychosis is hallucination which may involve seeing, hearing, smelling or tasting something that is not really present. Another common feature is delusional thinking or believing something that is not real or true. Delusions may be in the form of paranoid delusions or delusions of grandeur.
The initial studies performed in order to understand the pathology of the brain in psychosis date back to 1935 and involved the analysis of brain structures in people with psychosis using X-ray imaging.
Now obsolete, a procedure called pneumoencephalography where fluids from the brain were drained out and replaced with air, was used to study the X-ray pictures of the brain. It is known that the brain is the seat of emotions, sensations, and feelings of hunger, thirst and pain, for example, as well as being the control centre for perception and judgement.
All information that enters the brain via the sensory organs is processed by the brain to form coherent thoughts that help a person behave and react in a logical, coherent way. In people with psychosis, however, the sensory centres of the brain may produce spontaneous reactions without any stimuli which can then result in hallucinations.
The main problem in psychosis is not hallucination or delusions but the inability to distinguish between them and reality. Brain scans using PET (positron emission tomography) or fMRI (functional Magnetic resonance) imaging in people who have auditory hallucinations show that parts of the brain that process speech and hearing are affected.
Studies have also shown that transmitters in the brain called neurotransmitters (e.g. serotonin and dopamine) may play a role in psychosis, depression and other forms of mental illness. Some studies show that activation of the 5-HT2A receptor may lead to hallucination. In addition, drugs that block D2 receptors for dopamine can reduce the effects of psychosis.