Neuroimaging The first brain image of an individual with psychosis was completed as far back as 1935 using a technique called
pneumoencephalography (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). Both
first episode psychosis, and high risk status is associated with reductions in
grey matter volume (GMV). First episode psychotic and high risk populations are associated with similar but distinct abnormalities in GMV. Reductions in the right
middle temporal gyrus, right
superior temporal gyrus (STG), right
parahippocampus, right
hippocampus, right
middle frontal gyrus, and left
anterior cingulate cortex (ACC) are observed in high risk populations. Reductions in first episode psychosis span a region from the right STG to the right insula, left insula, and
cerebellum, and are more severe in the right ACC, right STG, insula and cerebellum. Another meta analysis reported bilateral reductions in insula, operculum, STG, medial frontal cortex, and ACC, but also reported increased GMV in the right
lingual gyrus and left
precentral gyrus. The
Kraepelinian dichotomy is made questionable by grey matter abnormalities in bipolar and schizophrenia; schizophrenia is distinguishable from bipolar in that regions of grey matter reduction are generally larger in magnitude, although adjusting for gender differences reduces the difference to the left
dorsomedial prefrontal cortex (dmPFC), and right
dorsolateral prefrontal cortex (dlPFC). During attentional tasks, first episode psychosis is associated with hypoactivation in the right middle frontal gyrus, a region generally described as encompassing the dlPFC. Altered Behavioral Inhibition System functioning could possibly cause reduced sustained attention in psychosis and overall contribute to more negative reactions. In congruence with studies on grey matter volume, hypoactivity in the right insula, and right inferior parietal lobe is also reported. During cognitive tasks, hypoactivities in the right insula, dorsal anterior cingulate cortex, and the left
precuneus, as well as reduced deactivations in the right
basal ganglia, right
thalamus, right
inferior frontal gyrus and left
precentral gyrus are observed. These results are highly consistent and replicable possibly except the abnormalities of the right inferior frontal gyrus. Decreased grey matter volume in conjunction with bilateral hypoactivity is observed in anterior insula, dorsal medial frontal cortex, and dorsal anterior cingulate cortex. Decreased grey matter volume and bilateral hyperactivity is reported in posterior insula, ventral medial frontal cortex, and ventral anterior cingulate cortex.
Hallucinations Studies during acute experiences of hallucinations demonstrate increased activity in primary or secondary sensory cortices. As auditory hallucinations are most common in psychosis, most robust evidence exists for increased activity in the left
middle temporal gyrus, left
superior temporal gyrus, and left
inferior frontal gyrus (i.e.
Broca's area). Activity in the
ventral striatum,
hippocampus, and ACC are related to the lucidity of hallucinations, and indicate that activation or involvement of emotional circuitry are key to the impact of abnormal activity in sensory cortices. Together, these findings indicate abnormal processing of internally generated sensory experiences, coupled with abnormal emotional processing, results in hallucinations. One proposed model involves a failure of feedforward networks from sensory cortices to the inferior frontal cortex, which normally cancel out sensory cortex activity during internally generated speech. The resulting disruption in expected and perceived speech is thought to produce lucid hallucinatory experiences.
Delusions The two-factor model of delusions posits that dysfunction in both belief formation systems and belief evaluation systems are necessary for delusions. Dysfunction in evaluations systems localized to the right lateral prefrontal cortex, regardless of delusion content, is supported by neuroimaging studies and is congruent with its role in conflict monitoring in healthy persons. Abnormal activation and reduced volume is seen in people with delusions, as well as in disorders associated with delusions such as
frontotemporal dementia, psychosis and
Lewy body dementia. Furthermore, lesions to this region are associated with "jumping to conclusions", damage to this region is associated with post-stroke delusions, and hypometabolism this region associated with caudate strokes presenting with delusions. The
aberrant salience model suggests that delusions are a result of people assigning excessive importance to irrelevant stimuli. In support of this hypothesis, regions normally associated with the
salience network demonstrate reduced grey matter in people with delusions, and the neurotransmitter
dopamine, which is widely implicated in salience processing, is also widely implicated in psychotic disorders. Specific regions have been associated with specific types of delusions. The volume of the hippocampus and parahippocampus is related to paranoid delusions in
Alzheimer's disease, and has been reported to be abnormal post mortem in one person with delusions.
Capgras delusions have been associated with occipito-temporal damage, and may be related to failure to elicit normal emotions or memories in response to faces.
Negative symptoms Psychosis is associated with the
ventral striatum (VS), which is the part of the brain that is involved with the desire to naturally satisfy the body's needs. When high reports of
negative symptoms were recorded, there were significant irregularities in the left VS. Anhedonia, defined as the inability to feel joy or pleasure, is a commonly reported symptom in psychosis; experiences with the condition are present in most people with schizophrenia. Previous research has indicated that a deficiency in the
neural representation in regards to goals and the motivation to achieve them, has demonstrated that when a reward is not present, a strong reaction is noted in the ventral striatum; reinforcement learning is intact when contingencies about stimulus-reward are implicit, but not when they require explicit neural processing; reward prediction errors are what the actual reward is versus what the reward was predicted to be. In most cases positive prediction errors are considered an abnormal occurrence. A positive prediction error response occurs when there is an increased activation in a brain region, typically the
striatum, in response to unexpected rewards. A negative prediction error response occurs when there is a decreased activation in a region when predicted rewards do not occur. The
anterior cingulate cortex (ACC) response, taken as an indicator of effort allocation, does not increase with reward or reward probability increase, and is associated with negative symptoms; deficits in dorsolateral prefrontal cortex (dlPFC) activity and failure to improve performance on cognitive tasks when offered monetary incentives are present; and dopamine mediated functions are abnormal.
Neurobiology Psychosis has been traditionally linked to the overactivity of the
neurotransmitter dopamine, in particular to its effect in the
mesolimbic pathway, spanning from the
ventral tegmental area to the ventral
striatum. Additionally, recent evidence suggests a crucial involvement of the pathway spanning from the
substantia nigra to the dorsal
striatum. The two major sources of evidence given to support this theory are that
dopamine receptor D2 blocking drugs (i.e.,
antipsychotics) tend to reduce the intensity of psychotic symptoms, and that drugs that accentuate dopamine release, or inhibit its reuptake (such as
amphetamines and
cocaine) can trigger psychosis in some people (see
stimulant psychosis). However, there is substantial evidence that dopaminergic overactivity does not fully explain psychosis, and that neurodegerative pathophysiology plays a significant role. This is evidenced by the fact that psychosis commonly occurs in neurodegenerative diseases of the dopaminergic nervous system, such as Parkinson's disease, which involved reduced, rather than increased, dopaminergic activity. The
endocannabinoid system is also implicated in psychosis. This is evidenced by the propensity of
CB1 receptor agonists such as
THC to induce psychotic symptoms, and the efficacy of
CB1 receptor antagonists such as
CBD in ameliorating psychosis. NMDA receptor dysfunction has been proposed as a mechanism in psychosis. This theory is reinforced by the fact that
dissociative NMDA receptor antagonists such as
ketamine,
PCP and
dextromethorphan (at large overdoses) induce a psychotic state. The symptoms of dissociative
intoxication are also considered to mirror the symptoms of schizophrenia, including
negative symptoms. NMDA receptor antagonism, in addition to producing symptoms reminiscent of psychosis, mimics the neurophysiological aspects, such as reduction in the amplitude of
P50,
P300, and
MMN evoked potentials. Hierarchical Bayesian neurocomputational models of sensory feedback, in agreement with neuroimaging literature, link NMDA receptor hypofunction to delusional or hallucinatory symptoms via proposing a failure of NMDA mediated top down predictions to adequately cancel out enhanced bottom up AMPA mediated predictions errors. Excessive prediction errors in response to stimuli that would normally not produce such a response is thought to root from conferring excessive salience to otherwise mundane events. Dysfunction higher up in the hierarchy, where representation is more abstract, could result in delusions. The common finding of reduced
GAD67 expression in psychotic disorders may explain enhanced AMPA mediated signaling, caused by reduced GABAergic inhibition. The connection between dopamine and psychosis is generally believed to be complex. While dopamine receptor D2 suppresses
adenylate cyclase activity, the
D1 receptor increases it. If D2-blocking drugs are administered, the blocked dopamine spills over to the D1 receptors. The increased adenylate cyclase activity affects
genetic expression in the nerve cell, which takes time. Hence antipsychotic drugs take a week or two to reduce the symptoms of psychosis. Moreover, newer and equally effective antipsychotic drugs actually block slightly less dopamine in the brain than older drugs whilst also blocking 5-HT2A receptors, suggesting the 'dopamine hypothesis' may be oversimplified. Soyka and colleagues found no evidence of dopaminergic dysfunction in people with alcohol-induced psychosis and Zoldan et al. reported moderately successful use of
ondansetron, a 5-HT3 receptor antagonist, in the treatment of
levodopa psychosis in
Parkinson's disease patients. A review found an association between a first-episode of psychosis and prediabetes. Prolonged or high dose use of
psychostimulants can alter normal functioning, making it similar to the manic phase of bipolar disorder. NMDA antagonists replicate some of the so-called "negative" symptoms like
thought disorder in subanesthetic doses (doses insufficient to induce
anesthesia), and
catatonia in high doses. Psychostimulants, especially in one already prone to psychotic thinking, can cause some "positive" symptoms, such as delusional beliefs, particularly those persecutory in nature.
Culture Cross-cultural studies into schizophrenia have found that individual experiences of psychosis and 'hearing voices' vary across cultures. In countries such as the
United States where there exists a predominantly biomedical understanding of the body, the mind and in turn, mental health, subjects were found to report their hallucinations as having 'violent content' and self-describing as 'crazy'. Such research creates pathways for social or community-based treatment, such as reality monitoring, for individuals with schizophrenia and other psychotic disorders, providing alternatives to, or supplementing traditional pharmacologic management. Cross-cultural studies explore the way in which psychosis varies in different cultures, countries and religions. The cultural differences are based on the individual or shared illness narratives surrounding cultural meanings of illness experience. In countries such as
India,
Cambodia and
Muslim majority countries, they each share alternative epistemologies. These are known as knowledge systems that focus on the connections between mind, body, culture, nature and society. Cultural perceptions of mental disorders such as psychosis or schizophrenia are believed to be caused by
jinn (spirits) in Muslim majority countries. Furthermore, those in
Arab-Muslim societies perceive those who act differently than the social norm as "crazy" or as abnormal behaviour. In Cambodia, hallucinations are linked with spirit visitation, a term they call "cultural kindling". These examples of differences are attributed to culture and the way it shapes conceptions of mental disorders. These cultural differences can be useful in bridging the gap of cultural understanding and psychiatric signs and symptoms. == Diagnosis ==