Neural and behavioral correlates of aberrant salience in individuals at risk for psychosis

The "aberrant salience" model proposes that psychotic symptoms first emerge when chaotic brain dopamine transmission leads to the attribution of significance to stimuli that would normally be considered irrelevant. This is thought to occur during the prodromal phase of psychotic disorders, but this prediction has not been tested previously. In the present study, we tested this model in 18 healthy volunteers and 18 unmedicated individuals at ultra-high risk of psychosis. Subjects performed the Salience Attribution Test, which provides behavioral measures of adaptive and aberrant motivational salience, during functional magnetic resonance imaging to assess neural responses to relevant and irrelevant stimulus features. On a separate occasion, the same subjects were also studied with [(18)F]fluorodopa positron emission tomography to measure dopamine synthesis capacity. Individuals at ultra-high risk of psychosis were more likely to attribute motivational salience to irrelevant stimulus features (t(26.7) = 2.8, P = .008), and this bias was related to the severity of their delusion-like symptoms (r = .62, P = .008). Ventral striatal responses to irrelevant stimulus features were also correlated with delusion-like symptoms in the ultra-high risk group (r = .59, P = .017). Striatal dopamine synthesis capacity correlated negatively with hippocampal responses to irrelevant stimulus features in ultra-high risk individuals, but this relationship was positive in controls. These data are consistent with the hypothesis that aberrant salience processing underlies psychotic symptoms and involves functional alterations in the striatum, hippocampus, and the subcortical dopamine system.

[Some questions about the essence of delusions in the light of recent neurobiological findings]

Formation of delusions in the phase of acute psychosis is based on two subsequent processes. The first one is dopamine hyperactivity in mesolimbic neural pathways, the second one is a cognitive process of up-down attribution of meanings of this subjectively perceived state of mind by the higher levels of brain. After the successful antipsychotic treatment, the subjectivity of patients changes. When the state of acute psychosis resolves patients must re-interpret this new emerging subjective experience. These interpretations are often incorrect and bizarre. In most cases they are regarded as delusions (sometimes "chronic delusions"). The question asked in the presented paper is whether they are truly delusions. The essence of delusion must include in the same time an active neurobiological basis of delusion (hyperdopaminergic state) and its cognitive level. It's not clear what is the proper term for the phenomenon when only incorrect or bizarre cognitive convictions are present after successful treatment of psychosis, but without dopaminergic hyperactivity.

Parasitosis, dopaminergic modulation and metabolic disturbances in schizophrenia: evolution of a hypothesis

Recent meta-analyses have provided a comprehensive overview of studies investigating Toxoplasma gondii antibodies in schizophrenic patients, thus attempting to clarify the potential role these infections might play in causing schizophrenia. Issues for further research have been suggested. Associations and theories that may enrich the current level of knowledge with regard to this significant subject deserve attention. Anti-parasitic agents as well as antipsychotics are effective in treating parasitosis. Both classes of drugs have been shown to exert dopaminergic activity. Parasites and human organisms have a long history of mutual contact. The effect of parasitosis on the host and the host's response to infection are undoubtedly the product of a long evolutionary process. The neurochemical background of delusions of parasitosis is potentially similar to ancient evolutionary traces of altered neurotransmission and neuropeptide gene expression caused by parasites; these include fungal and viral infections. This is very unique in medicine if a class of drugs is effective in the treatment of an illness but also cures the delusion of the same disorder as well. Furthermore, metabolic disturbances such as hyperglycemia and insulin resistance were reported several decades before the antipsychotic era. Toxoplasmosis may also be linked to insulin resistance. Schizophrenia research can benefit from understanding this evolutionary link. New chemical entities that are liable to alter neurochemical changes related to the brain's perception of the risk of predation secondary to parasites may result in new approaches for the treatment of psychosis. These findings suggest that further research is needed to clarify this evolutionary link between parasite infection and delusions of parasitosis. We believe this model may well open up new avenues of research in the discovery of drugs to counteract schizophrenia.

A neuropsychiatric model of biological and psychological processes in the remission of delusions and auditory hallucinations

This selective review combines cognitive models and biological models of psychosis into a tentative integrated neuropsychiatric model. The aim of the model is to understand better, how pharmacotherapy and cognitive-behavior therapy come forward as partners in the treatment of psychosis and play complementary and mutually reinforcing roles. The article reviews the dominant models in literature. The focus in this review is on one hand on neural circuits that are involved in cognitive models and on the other hand on cognitive processes and experiences involved in biological models. In this way, a 4-component neuropsychiatric model is tentatively constructed: (1) a biological component that leads to aberrant perceptions and salience of stimuli, (2) a cognitive component that attempts to explain the psychic abnormal events, (3) a mediating component with psychological biases which influences the reasoning process in the direction of the formation of (secondary) delusions, and (4) a component of psychological processes that maintains delusions and prevents the falsification of delusional ideas. Remission consists actually of 2 processes. Biological remission consists of the dampening of mesolimbic dopamine releases with antipsychotic medication and decreases the continuous salient experiences. Psychological remission consists of the reappraisal of primary psychotic experiences. Both forms of remission are partially independent. We expect that a full remission including biological and psychological remission could prevent relapse.

Delusional thoughts and regional frontal/temporal cortex metabolism in Alzheimer's disease

OBJECTIVE

Delusional thoughts are common in patients with Alzheimer's disease and contribute prominently to morbidity. The pathophysiologic underpinnings for delusions in Alzheimer's disease are not well understood. In this study the authors examined the relationship between delusional thoughts and regional cortical metabolism in patients with Alzheimer's disease.

METHOD

Twenty-five patients with probable Alzheimer's disease were included. None was taking psychotropic medication. Severity of delusions and other neuropsychiatric symptoms was assessed by using a semistructured interview and the Neurobehavioral Rating Scale just before the imaging procedure. [(18)F]Fluorodeoxyglucose positron emission tomography was used to measure resting cerebral glucose metabolic rates in the cortical lobes and in anatomically defined subregions of the frontal and temporal cortexes.

RESULTS

A linear regression model, controlling for the effects of cognitive deficits, revealed a significant relationship between severity of delusional thought and the metabolic rates in three frontal regions: the right superior dorsolateral frontal cortex (Brodmann's area 8), the right inferior frontal pole (Brodmann's area 10), and the right lateral orbitofrontal region (Brodmann's area 47). Bivariate partial correlation analysis indicated that severity of delusions was associated with hypometabolism in additional prefrontal and anterior cingulate regions. Robust relationships with metabolism in regions of the temporal cortex were not apparent.

CONCLUSIONS

Dysmetabolism in specific regions of the right prefrontal cortex may be associated with delusional thought in Alzheimer's disease. Delusions appear to reflect the pathophysiologic state of particular cortical regions. Activity across distributed neuronal networks and the specific content of delusional thoughts may modulate these relationships.

Delusions associated with elevated muscarinic binding in dementia with Lewy bodies

The relation between disturbances of cholinergic neurotransmission and delusions (DELs) has not been investigated in degenerative dementias such as dementia with Lewy bodies (DLB). A cohort of dementia patients were assessed with standardized clinical evaluations (including the Columbia University Scale for Psychopathology in Alzheimer's Disease), which were repeated annually until death. DLB was confirmed neuropathologically in 21 patients. Neurochemical evaluation included M1 receptor autoradiography (pirenzepine binding), biochemical measurement of choline acetyltransferase (ChAT), and acetylcholinesterase (AChE) histochemistry in brain regions hypothesized to be involved in the genesis of psychosis. Compared with 11 age-matched controls, CHAT and pirenzepine levels were most extensively reduced in the temporal and parietal neocortex of DLB patients. In Brodmann area 36, DELs were significantly associated with elevated pirenzepine binding (131.0 vs 93.5, t = 2.7), whereas visual hallucinations were associated with significant reductions in ChAT (1.7 vs 2.5, t = 2.5). There were no significant associations with other areas or with cholinesterase. Although DELs and visual hallucinations were both linked with disturbances in cholinergic neurotransmission, the nature of the associations was different. Upregulation of the postsynaptic muscarinic receptor may be central in the genesis of DELs, with important treatment implications.

Prolactin secretion in response to haloperidol challenge in delusional (psychotic) and non-delusional depression

Certain studies on measures related to central neurotransmitter activity have demonstrated that in delusional (psychotic) depression there is a dopaminergic dysregulation which distinguishes it from non-psychotic depression. A neuroendocrinologic method to check the degree of DA receptor responsivity is by measuring the prolactin responses to acute intramuscular administration of haloperidol. We studied this possibility by applying the haloperidol test in seven delusional and ten non-delusional depressed patients. All patients met DSM-IV criteria for a major depressive episode, single or recurrent, with or without psychotic features. After a three-week washout period, 5 mg of haloperidol were injected i.m. and blood samples were taken at 0, 30, 60, 90 and 120 minutes. In both trials, significant time effects were observed (elevated prolactin levels, F = 11.36, P = 0.000). However, the prolactin responses to haloperidol did not differ significantly between the two patient groups (F = 0.12, P = 0.97). These data do not show a difference in D(2) receptor responsivity, at least at the hypothalamus-pituitary level, between psychotic and non-psychotic depression.

Alteration of regional cerebral glucose utilization with delusions in Alzheimer's disease

The authors examined 65 patients with Alzheimer's disease for delusions and explored the relationship of delusions with regional cerebral glucose metabolism determined by [18F]fluorodeoxyglucose PET. In patients with delusions (n = 26), normalized glucose metabolism was significantly increased in the left inferior temporal gyrus and significantly decreased in the left medial occipital region as compared with those without delusions (n = 39). The two groups were similar in age, sex, and dementia severity. These results suggest that delusions in Alzheimer's disease are attributable to a dysfunction in specific brain areas rather than a simple reaction to intellectual deficits.

Delusional depression in Parkinson's disease

A 72 year-old female patient is presented in whom delusional depression, a possible distinct subtype of depressive illness characterized by a selective decrease of cerebrospinal fluid (CSF) norepinephrine (NE) metabolism, preceded the onset of Parkinsonism by several years. The report suggests that delusional depression may be a particular manifestation of depressive illness in Parkinsonian patients. In addition, since the activity of plasma and cerebrospinal fluid (CSF) dopamine beta-hydroxylase (DBH) is genetically determined, the co-occurrence of delusional depression and Parkinsonism in this patient may be related to a common underlying genetic defect that expresses itself biochemically by reduced cerebral NE metabolism.