Neuroimaging The first brain image of an individual with<unk>  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<unk> , 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<unk>  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, and right dorsolateral prefrontal cortex. During attentional tasks, first episode<unk>  is associated with hypoactivation in the right middle frontal gyrus, a region generally described as encompassing the dorsolateral prefrontal cortex (dlPFC). 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, dACC, and the left precuneus, as well as reduced deactivations in the right basal ganglia, right thalamus, right inferior frontal and left precentral gyri 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 ACC. Decreased grey matter volume and bilateral hyperactivity is reported in posterior insula, ventral medial frontal cortex, and ventral ACC. Hallucinations Studies during acute experiences of hallucinations demonstrate increased activity in primary or secondary sensory cortices. As auditory hallucinations are most common in<unk> , 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,<unk>  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<unk>  is associated with ventral striatal (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, the inability to feel pleasure, is a commonly reported symptom in<unk> ; experiences are present in most people with schizophrenia. The impairment that may present itself as anhedonia derives from the inability to not only identify goals, but to also identify and engage in the behaviors necessary to achieve goals. Studies support a deficiency in the neural representation of goals and goal directed behavior by demonstrating that when the reward is not anticipated, there is a strong correlation of high reaction 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. 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<unk>  has been traditionally linked to the overactivity of the neurotransmitter dopamine. In particular to its effect in the mesolimbic pathway. 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<unk>  in some people (see stimulant<unk> . NMDA receptor dysfunction has been proposed as a mechanism in<unk> . 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<unk> , 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<unk>  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<unk> . 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<unk>  and Zoldan et al. reported moderately successful use of ondansetron, a 5-HT3 receptor antagonist, in the treatment of levodopa<unk>  in Parkinson's disease patients. A review found an association between a first-episode of<unk>  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
Psychosis
Anti-NMDA receptor encephalitis
Depression 
Dissociative identity disorder
Psychotic depression
Phobia
Depression and Anxiety
Collective depression