Psychosis principally consists of ‘reality distortions’. A person exhibiting psychosis has a skewed perception of reality - the result of faulty circuits in the brain which are involved in perception. Reality distortions are typically characterised by hallucinations and delusions.
Psychosis can occur in isolation, but usually occurs with other symptoms which together form a psychiatric syndrome. In a syndrome, patients exhibit a cluster of symptoms which individually could be seen as distinct disease states. Examples of such syndromes include bipolar depression, major depressive disorder and schizophrenia. Many patients do not exhibit the same set of symptoms. They probably share the same defining hallmarks of said disease, but also have other more variable symptoms alongside. These ‘extra’ symptoms complicate matters, as they usually arise from dysfunction in a different system of the brain, which could require a different course of therapy.
Schizophrenia is a psychotic syndrome. It is characterised by the presence of
‘positive symptoms’; The psychosis. Psychosis is one of the defining and more recognisable symptoms of schizophrenia
‘negative symptoms’; Social withdrawal, decreased spontaneous speech, apathy, self-neglect and decreased emotional expression (flat affect).
Many of the neural circuits involved in perception and attention use dopamine as their neurotransmitter. Dopamine is not exclusive to perception circuits, and neither are all perception circuits dopaminergic – but the point is there’s a lot of dopamine involvement.
There are 4 main dopamine pathways in the brain; mesocortical, mesolimbic, nigrostriatal and tuberoinfundibular.
The diagram hasn’t labelled the tuberoinfundibular pathway, though it is highlighted as the small pathway starting from the hypothalamus. Diagram from ‘Dopaminergic neurons’, Chinta & Anderson 2005, The International Journal of Biochemistry & Cell Biology
All of these tracts originate from roughly the same brain region. This region includes the structures involved in reward and motivation. The pathway of note in psychosis and perception is the mesolimbic (and to an extent, the mesocortical). In schizophrenia, the positive symptoms (psychosis) arise from excessive dopamine function in the mesolimbic pathway. Drugs which block dopamine neurotransmission are used to combat psychotic symptoms. Such drugs include haloperidol and aripiprazole; useful chemicals which bring perception back in tune with reality, removing hallucinations and bringing delusions down to a tolerable level.
chemical structure of Dopamine
A hallucination is a seemingly realistic perception which occurs without any sensory input; seeing something which isn’t actually there, but having no idea that it isn’t actually there. It is as real as your own two feet in your own thoughts, though objective evidence from the world around you would suggest it wasn’t there.
Hallucinations are thought to arise from impaired wiring in neural circuits involved in perception. One theory suggests that the neuronal networks involved in imagination are misconnected to the circuits involved in processing incoming sensory information into perception. As a result, thoughts which would be the domain of imagination are ‘perceived’ as information directly sensed from the environment. Electrophysiology studies using EEG to measure brain waves support this theory by showing aberrant electrical patterns from such sensory-to-perception circuits. The theory makes sense (and is one that has my backing, if it’s worth anything) given the nature of hallucinations, and it has reasonable evidence to back it up making it a strong candidate to explain, at least in part, how hallucinations occur. Neuroanatomical evidence to back this up is complex, with different regions involved depending on what sort of hallucination the person is undergoing. However, the impairments which give rise to hallucinations are only part of the story of psychosis.
A delusion is defined as a fixed belief derived by illogical reasoning or unjustified assumptions that cannot be explained by culture or religion. At the crux of a delusion is a premature conclusion - seeing a trend before enough information to rationally describe a trend has been presented. Delusions are generally culturally influenced, with delusions of old consisting of stories about ghosts and demons (stories which do still exist) to more modern delusions which involve government conspiracies and aliens. The cultural context of the story is variable, but rests on fixed, illogical conclusions which cannot be swayed by contrary evidence or reasoning. This sounds like a complex behaviour as opposed to a symptom of a disease state– but the real behavioural pathology here is the fixed misinterpretation of information to jump to early, and absolute conclusions.
The biological basis of delusions, which should hopefully begin to explain their role in psychosis, lies in a phenomenon termed by those in the field as ‘aberrant salience’. Normally at the level of neuronal computation, the brain makes predictions about events in the environment, and when such an event does not meet the prediction, dopamine is released in regions of the brain which drive reward and salience. There is a network of neuronal circuits in the brain called the Salience Network. The Salience Network is involved in influencing attention to environmental events. The salience network uses dopamine neurons (amongst others), and when the dopamine neurons in the salience network are active, they activate neuronal networks involved in drawing attention to this stimulus, and this begins analysis of the novel event – which will thus drive perception and thoughts of this new, interesting event.
Diagram showing regions of brain part of the Salience network and Central Executive Network. The Salience Network regions are highlighted in red and orange. Images obtained from fMRI neuroimaging. Diagram adapted from “Large-scale brain networks in cognition: emerging methods and principles”, Bressler & Mennon 2010, Trends in Cognitive Sciences
In a delusion, this dopaminergic system appears to be impaired, resulting in salience being attributed to irrelevant cues in the environment. This would imply excessive dopamine is being released. The theory put forward by Andreas Heinz and the various members of his research teams asserted that environmental stresses could induce ‘chaotic’ dopamine release in these systems, responding to irrelevant events as if they were relevant. This would lead to the formation of a thought or conclusion about a given event that was based on irrelevant or misleading information. This theory is supported by a wealth of evidence from rodent, primate and human studies. Such studies include verifying that social stress plays a role in dysregulating dopamine release in primates, and pharmacological and neuroimaging studies in humans has shown that ‘chaotic’ dopamine signalling can affect reward-prediction processing. In schizophrenia, there is already a malfunction leading to increased release of dopamine, so this would explain the existence of pathological delusions in the absence of environmental stressors in line with this theory. More research is needed to conclusively verify this hypothesis of chaotic dopamine, but the trend of evidence is very promising.
Transient psychotic symptoms can be induced by some recreational drugs as part of their action. Such drugs include cannabis, amphetamines and cocaine. There is verified experimental evidence for acute transient psychosis (psychotic symptoms brought on during drug use) from cannabis and amphetamine, and population based evidence for such symptoms from cocaine. Long term use of cannabis, amphetamine and cocaine is associated with the development of a psychotic disorder later in life, but the there is great debate as to what the causation to this correlation is.
Chronic use of cannabis is thought to inhibit the generation of new neurons in the brain so it is possible that cannabis usage can interfere with brain development, leading to some miswiring events involved in psychotic symptoms. With brain development occurring well into the teenage years, it is thought that cannabis use may precipitate schizophrenia or psychotic disorder in teens who have a genes which make them susceptible to such disorders. Amphetamines and cocaine interfere directly with the dopaminergic pathways, and their role in producing psychotic symptoms during drug use is much more straightforward. Amphetamines directly increase dopamine function so by looking at their very chemistry and pharmacology, their predicted effect would be something similar to psychosis.
Psychosis and the effects of drug use on the brain demonstrate just how material our thoughts, emotions, personalities and memories are. They can be seen as another part of our body. This line of thinking should hopefully allow us to understand those who suffer from mental health issues. It shows that mental health disorders are a very real phenomenon, and not just people trying to be awkward. Such disorders are leading scientists to question the very nature of free will itself. Psychosis and the predictable effects of drugs on the brain are striking evidence of just how chemical we are at the deepest level of what we see as our soul.