Cerebral blood flow activation and functional lesions in schizophrenia

Microvascular anomaly conditions in psychiatric disease. Schizophrenia - angiogenesis connection

Schizophrenia (SZ) is a severe mental disorder with unknown etiology and elusive neuropathological and neurobiological features have been a focus of many theoretical hypotheses and empirical studies. Current genetic and neurobiology information relevant to SZ implicates neuronal developmental and synaptic plasticity abnormalities, and neurotransmitter, microglial and oligodendrocytes dysfunction. Several recent theories have highlighted the neurovascular unit as a potential contributor to the pathophysiology of SZ. We explored the biological plausibility of a link between SZ and the neurovascular system by examining insights gained from genetic, neuroimaging and postmortem studies, which include gene expression and neuropathology analyses. We also reviewed information from animal models of cerebral angiogenesis in order to understand better the complex interplay between angiogenic and neurotrophic factors in development, vascular endothelium/blood brain barrier remodeling and maintenance, all of which contribute to sustaining adequate regional blood flow and safeguarding normal brain function. Microvascular and hemodynamic alterations in SZ highlight the importance of further research and reveal the neurovascular unit as a potential therapeutic target in SZ.

Executive attention deficits in schizophrenia: putative mandatory and differential cognitive pathology domains in medicated schizophrenia patients

Executive attention (EA) is a core-construct of working memory (WM) capacity. EA performance is directly related to dorsolateral prefrontal cortex (DLPFC) activation, a neural mechanism that is dysfunctional in schizophrenia. We examined the differences in particular types of EA failure in schizophrenia patients and healthy controls. We evaluated executive attention in 60 medicated schizophrenia patients and 60 matched healthy individuals. We used a standard WM task, a verbal n-Back task, to measure executive attention (WM accuracy). Our standard-version WM task (control block, 10min long) was designed to examine baseline executive attention function and was followed by one out of three different experimental blocks (revised n-Back tasks). Baseline executive attention performance was significantly related to psychosis severity and functional capacity in the psychiatric group. In both healthy and psychiatric groups, experimental-block conditions revealed that domain-general recall had a differential effect on WM scores, and was related to the patient's clinical condition. Only in the psychiatric group domain-specific recall impairments were mandatory, most severe, and independent of baseline WM scores. The results revealed the importance of domain-general recall WM scores in the evaluation of executive attention deficits in patients and controls. Disruption in domain-specific recall may represent a specifier of cognitive impairment in schizophrenia spectrum disorders.

Cell and receptor type-specific alterations in markers of GABA neurotransmission in the prefrontal cortex of subjects with schizophrenia

Impairments in cognitive control, such as those involved in working memory, are associated with dysfunction of the dorsolateral prefrontal cortex (DLPFC) in individuals with schizophrenia. This dysfunction appears to result, at least in part, from abnormalities in GABA-mediated neurotransmission. In this paper, we review recent findings indicating that the altered DLPFC circuitry in subjects with schizophrenia reflects changes in the expression of genes that encode selective presynaptic and postsynaptic components of GABA neurotransmission. Specifically, using a combination of methods, we found that subjects with schizophrenia exhibited expression deficits in GABA-related transcripts encoding presynaptic regulators of GABA neurotransmission, neuropeptide markers of specific subpopulations of GABA neurons, and certain subunits of the GABA(A) receptor. In particular, alterations in the expression of the neuropeptide somatostatin suggested that GABA neurotransmission is impaired in the Martinotti subset of GABA neurons that target the dendrites of pyramidal cells. In contrast, none of the GABA-related transcripts assessed to date were altered in the DLPFC of monkeys chronically exposed to antipsychotic medications, suggesting that the effects observed in the human studies reflect the disease process and not its treatment. In concert with previous findings, these data suggest that working memory dysfunction in schizophrenia may be attributable to altered GABA neurotransmission in specific DLPFC microcircuits.

Integration of emotional and cognitive aspects of theory of mind in schizophrenia and its relation to prefrontal neurocognitive performance

INTRODUCTION

There is substantial evidence that patients with schizophrenia present with impaired Theory of Mind (ToM). Whereas previous studies have focused on general ToM abilities, the present study is aimed at testing the underlying behavioural and neurocognitive mechanisms of the impaired integration of affective and cognitive aspects of ToM (the integration of emotional information with mentalising) in patients with schizophrenia.

METHODS

Twenty-six patients with schizophrenia and 35 healthy controls were tested on two ToM tasks involving the integration of affective and cognitive ToM abilities: "Faux Pas" and "reading the mind in the eyes" tasks. To assess the neurocognitive bases of impaired ToM, the ID/ED test (intradimensional/extradimensional shifting test from the CANTAB) was administered.

RESULTS

Patients performed poorly on both the cognitive-affective integration ToM tasks and the ID/ED task as compared to controls. Furthermore, patients' ToM scores were selectively correlated with the reversal trials, which are believed to be associated with orbitofrontal functioning. In addition, more than 50% of the variance in recognising and understanding Faux Pas could be explained by patients' symptomatology. Performance on orbitofrontal related tasks was correlated with subjects' Faux Pas scores in the patients group, but not in the healthy control group.

CONCLUSIONS

Schizophrenic patients appear to have considerable impairment in affective and cognitive ToM integration, which may be related to orbitofrontal dysfunction. These results are in line with previous findings regarding empathy and the importance of the orbitofrontal area in the integration of cognition and affect.

A single 20 mg dose of the full D1 dopamine agonist dihydrexidine (DAR-0100) increases prefrontal perfusion in schizophrenia

Dopamine D1 receptors play an important role in memory and cognition in non-human primates. Dopamine D1 agonists have been shown to reverse performance deficits in both aged non-human primates and in primates with lesions to dopamine systems. This study explored whether a single dose of the first full D1 agonist dihydrexidine (DAR-0100) would cause changes in brain activity (perfusion) in dopamine-rich brain regions. We used a new gadolinium-contrast magnetic resonance perfusion scanning technique to measure brain activity. A within-subject cross-over double-blind randomized design was used in 20 adults with SCID-diagnosed schizophrenia. Each morning at 0800 h, they were scanned on a 3.0 T MRI scanner for perfusion. They then received either 20 mg of dihydrexidine, or placebo, subcutaneously over 15 min. Over the next 45 min, they had intermittent MRI scans. Two days later, they had a repeat of the Day 1 schedule, but received the opposite treatment from that given on the first day. Within-day, as well as between-day, comparisons were made to test for perfusion effects of dihydrexidine. Analysis revealed that dihydrexidine induced a significant increase in both prefrontal and non-prefrontal perfusion compared to placebo. The greatest increases occurred approximately 20 min after dihydrexidine infusion, consistent with the short pharmacokinetic half-life of dihydrexidine. These data are consistent with the hypothesis formulated from studies of non-human primates that dihydrexidine and other D1 agonists may be able to modulate prefrontal dopaminergic function.

Dissociation of cognitive from affective components of theory of mind in schizophrenia

Patients suffering from schizophrenia show impaired emotional and social behavior, such as misinterpretation of social situations and lack of theory of mind. However, there is conflicting evidence regarding their ability to perform on theory of mind tasks. Based on previous findings with patients suffering from prefrontal damage, the present study suggests that the behavioral deficit of schizophrenic patients may be due to impaired 'affective theory of mind' abilities, rather than to a general impairment in theory of mind. To test this hypothesis we assessed the ability of 22 schizophrenic patients and 55 age-matched healthy controls, to judge first and second order affective vs. cognitive mental state attribution, based on eye gaze. The relationships between negative and positive symptoms of schizophrenia, and affective and cognitive theory of mind were also assessed. Results indicated that while healthy controls made fewer errors on affective as compared to cognitive theory of mind conditions, schizophrenic patients showed a less prominent trend. Although the pattern of reaction time did not differ significantly between groups, the patients made significantly more errors in the affective conditions, as compared to controls. Furthermore, correlation analysis indicated that impaired affective theory of mind in these patients correlated with their level of negative symptoms. These results indicate that individuals with high level of negative symptoms of schizophrenia may demonstrate selective impairment in their ability to attribute affective mental states. These findings offer new insight into the affective facets of social behavior that may underlie the profound behavioral disturbances observed in schizophrenia.

Prefrontal abnormalities in patients with simple schizophrenia: structural and functional brain-imaging studies in five cases

Simple schizophrenia is an uncommon disorder with unknown pathophysiology, and its position in the current diagnostic system is ambiguous. Brain-imaging studies may help to elucidate its pathophysiology. Five patients fulfilling both ICD-10 criteria for simple schizophrenia and DSM-IV criteria for simple deteriorative disorder underwent computed tomography, magnetic resonance imaging, and single photon emission computed tomography. These scans were assessed individually by visual inspection as well as automatically by comparison with scans in normal controls or other schizophrenia subtype patients using voxel-based image analyses. Three of the five simple schizophrenia patients had findings of atrophy and reduced cerebral perfusion in the frontal areas. Voxel-based analyses also showed prefrontal grey matter deficits and hypoperfusion in simple schizophrenia patients compared with the controls. Although this study is limited by the small number of patients with simple schizophrenia, the results suggest that simple schizophrenia, or at least this subpopulation, may have rather homogeneous morphological and functional deficits in the prefrontal cortex. It is also suggested that simple schizophrenia may occupy an extreme position of the schizophrenic continuum where the prefrontal deficits and negative symptoms are most purely manifested.

The BOLD onset transient: identification of novel functional differences in schizophrenia

Blood oxygen level dependent (BOLD) signals characteristically exhibit an overshoot (transient signal increase) at the beginning of fMRI task blocks. This onset transient has often been overlooked as an independent measure of neuronal activity, but it may represent unique functional processes. We examined onset transient responses in normal subjects and individuals with schizophrenia performing three cognitive tasks. These analyses revealed a regionally specific and task specific attenuation of the onset transient in individuals with schizophrenia during performance of a working memory task. Furthermore, this attenuation was often not accompanied by a corresponding population difference in the sustained response, and is missed through conventional fMRI analysis techniques. Relevance of these findings to both an interpretation of the onset transient and the pathology of schizophrenia are discussed.

Schizophrenia and second language acquisition

Language acquisition involves brain processes that can be affected by lesions or dysfunctions in several brain systems and second language acquisition may depend on different brain substrates than first language acquisition in childhood. A total of 16 Russian immigrants to Israel, 8 diagnosed schizophrenics and 8 healthy immigrants, were compared. The primary data for this study were collected via sociolinguistic interviews. The two groups use language and learn language in very much the same way. Only exophoric reference and blocking revealed meaningful differences between the schizophrenics and healthy counterparts. This does not mean of course that schizophrenia does not induce language abnormalities. Our study focuses on those aspects of language that are typically difficult to acquire in second language acquisition. Despite the cognitive compromises in schizophrenia and the manifest atypicalities in language of speakers with schizophrenia, the process of acquiring a second language seems relatively unaffected by schizophrenia.

The cognitive neuroscience of creativity

This article outlines a framework of creativity based on functional neuroanatomy. Recent advances in the field of cognitive neuroscience have identified distinct brain circuits that are involved in specific higher brain functions. To date, these findings have not been applied to research on creativity. It is proposed that there are four basic types of creative insights, each mediated by a distinctive neural circuit. By definition, creative insights occur in consciousness. Given the view that the working memory buffer of the prefrontal cortex holds the content of consciousness, each of the four distinctive neural loops terminates there. When creativity is the result of deliberate control, as opposed to spontaneous generation, the prefrontal cortex also instigates the creative process. Both processing modes, deliberate and spontaneous, can guide neural computation in structures that contribute emotional content and in structures that provide cognitive analysis, yielding the four basic types of creativity. Supportive evidence from psychological, cognitive, and neuroscientific studies is presented and integrated in this article. The new theoretical framework systematizes the interaction between knowledge and creative thinking, and how the nature of this relationship changes as a function of domain and age. Implications for the arts and sciences are briefly discussed.

Selective alterations in prefrontal cortical GABA neurotransmission in schizophrenia: a novel target for the treatment of working memory dysfunction

RATIONALE

Disturbances in critical cognitive processes, such as working memory, are now regarded as core features of schizophrenia, but available pharmacological treatments produce little or no improvement in these cognitive deficits. Although other explanations are possible, these cognitive deficits appear to reflect a disturbance in executive control, the processes that facilitate complex information processing and behavior and that include context representation and maintenance, functions dependent on the dorsolateral prefrontal cortex (DLPFC). Studies in non-human primates indicate that normal working memory function depends upon appropriate GABA neurotransmission in the DLPFC, and alterations in markers of GABA neurotransmission are well documented in the DLPFC of subjects with schizophrenia.

OBJECTIVES

Thus, the purpose of this paper is to review the nature of the altered GABA neurotransmission in the DLPFC in schizophrenia, and to consider how these findings might inform the search for new treatments for cognitive dysfunction in this illness.

RESULTS AND CONCLUSIONS

Postmortem studies suggest that markers of reduced GABA neurotransmission in schizophrenia may be selective for, or at least particularly prominent in, the subclass of GABA neurons, chandelier cells, that provide inhibitory input to the axon initial segment of populations of pyramidal neurons. Given the critical role that chandelier cells play in synchronizing the activity of pyramidal neurons, the pharmacological amelioration of this deficit may be particularly effective in normalizing the neural network activity required for working memory function. Because GABA(A) receptors containing the a(2) subunit are selectively localized to the axon initial segment of pyramidal cells, and appear to be markedly up-regulated in schizophrenia, treatment with novel benzodiazepine-like agents with selective activity at GABA(A) receptors containing the a(2) subunit may be effective adjuvant agents for improving working memory function in schizophrenia.

Cortical motor activation in akinetic schizophrenic patients: A pilot functional MRI study

Akinesia is associated with supplementary motor area (SMA) dysfunction in Parkinson's disease. We looked for a similar association in patients with schizophrenia. Using functional magnetic resonance imaging (fMRI), we compared motor activation in 6 akinetic neuroleptic-treated schizophrenic patients and 6 normal subjects. Schizophrenic patients had a defective activation in the SMA, left primary sensorimotor cortex, bilateral lateral premotor and inferior parietal cortices, whereas the right primary sensorimotor cortex and a mesial frontal area were hyperactive. SMA was hypoactive in akinetic schizophrenic patients, emphasizing the role of this area in motor slowness. Other abnormal signals likely reflect schizophrenia-related abnormal intracortical connections.

Regulation of NMDA receptors by dopamine D4 signaling in prefrontal cortex

Increasing evidence has suggested that the interaction between dopaminergic and glutamatergic systems in prefrontal cortex (PFC) plays an important role in normal mental functions and neuropsychiatric disorders. In this study, we examined the regulation of NMDA-type glutamate receptors by the PFC dopamine D4 receptor (one of the principal targets of antipsychotic drugs). Application of the D4 receptor agonist PD168077 caused a reversible decrease of the NMDA receptor (NMDAR)-mediated current in acutely isolated and cultured PFC pyramidal neurons, an effect that was blocked by selective D4 receptor antagonists. Furthermore, application of PD168077 produced a potent reduction of the amplitude (but not paired-pulse ratio) of evoked NMDAR EPSCs in PFC slices. The D4 modulation of NMDA receptors in PFC involved the inhibition of protein kinase A, activation of protein phosphatase 1 and the ensuing inhibition of active Ca2+-calmodulin-dependent kinase II (CaMKII). Moreover, PD168077 reduced the surface expression of NMDARs and triggered the internalization of NMDARs in a manner dependent on CaMKII activity. These results identify a mechanistic link between D4 and NMDA receptors in PFC pyramidal neurons, suggesting that D4 receptors may play an important role in modulating synaptic plasticity and thus cognitive and emotional processes in PFC circuits.

Effect of the 5-HT6 receptor antagonists Ro04-6790 and Ro65-7199 on latent inhibition and prepulse inhibition in the rat: comparison to clozapine

In the present study, we have investigated the effects of two selective 5-HT6 receptor antagonists, Ro04-6790 and Ro65-7199, in three drug-induced models of PPI disruption and on latent inhibition (LI) utilizing a conditioned lick suppression (CLS) procedure. Clozapine was included in each experiment for comparison. Neither Ro04-6790 nor Ro65-7199 (both 30 mg/kg) affected the PPI disruption produced by PCP (1.5 mg/kg s.c.), apomorphine (0.1 mg/kg s.c.), or LSD (0.1 mg/kg s.c.). There was also no interaction between each drug and CS preexposure in the CLS test indicating a failure of each drug to facilitate LI. In contrast, clozapine (12 mg/kg) attenuated an apomorphine and PCP-induced PPI deficit, although the PPI disruption produced by LSD was not significantly affected. At a lower dose of 5 mg/kg, clozapine also facilitated LI. Since each of these tests bear some predictive validity for the detection of antipsychotic drugs, the present studies do not support a therapeutic potential of 5-HT6 receptor antagonists in this regard.

Temporal modulation of cerebral hemodynamics under prefrontal challenge in schizophrenia: a transcranial Doppler sonography study

Transcranial Doppler sonography (TCD) is a non-invasive method to assess cerebral blood flow velocity (CBFV) and hence cerebral blood flow during cognitive activation. Major cognitive dysfunctions have been consistently reported in patients with schizophrenia, and important deficits have been observed with respect to prefrontal functions. However, prefrontal activation in schizophrenics has not been investigated with TCD despite its potential to examine short-term changes of cerebral blood flow. The Wisconsin Card Sorting Test (WCST) and the Tower of Hanoi puzzle were administered to 11 right-handed schizophrenics and 20 healthy controls. The middle and anterior cerebral arteries were pairwise insonated. Schizophrenics showed decreased CBFV during the initial phase of both prefrontal functions and the steady-state phase of the Tower of Hanoi. In healthy controls, there was a succession of three significantly different phases of mean CBFV during the Tower of Hanoi, and there was no such modulation in schizophrenics. Immediately after category shift in the WCST, there was an increase of mean CBFV in healthy controls, but not in schizophrenics. In conclusion, transcranial Doppler sonography was able to detect differing specific alterations of CBFV during two prefrontal tasks in healthy controls and patients with schizophrenia. Importantly, the results of this study imply a degraded pattern of CBFV changes over time in schizophrenia during prefrontal activation.

Neural correlates of memory organization deficits in schizophrenia. A single photon emission computed tomography study with 99mTc-ethyl-cysteinate dimer during a verbal learning task

Regional cerebral blood flow (rCBF) during a verbal learning task was measured using 99mTc-ethyl-cysteinate dimer and single photon emission computed tomography in 10 patients with schizophrenia and nine normal controls. Verbal repetition was used as a control task. The schizophrenic patients showed failure to spontaneously utilize implicit category information to learn the word lists. In the normal controls, rCBF in the left inferior frontal and left anterior cingulate regions was significantly increased during the verbal learning task, compared with the verbal repetition task. In contrast, there was no significant frontal lobe activation by the verbal learning in the schizophrenic patients. The patients had lower rCBF during the verbal learning task than the controls in the bilateral inferior frontal, left anterior cingulate, right superior frontal, and bilateral middle frontal regions. Activation in the left inferior frontal region was significantly positively correlated with categorical clustering in the task in the controls, but no such correlation was found in the patients. These results indicate that memory organization deficits in schizophrenia may be related to dysfunction in the prefrontal areas, especially in the left inferior frontal region.

Evidence for a compromised dorsolateral prefrontal cortical parallel circuit in schizophrenia

Evidence is reviewed that one of the cognitive-affective parallel circuits in the brain, the dorsolateral prefrontal circuit, is compromised at the level of anatomical, neuropathological and transmitter-related molecules in a subgroup of schizophrenic patients. The dorsolateral prefrontal cortex (DLPFC) comprises a key structure in this circuit. Data supporting a compromised DLPFC includes cognitive deficits, decreased regional metabolism and blood flow activation; disruption of cortical subplate activity (inferred from maldistribution of neurons from the cortical subplate which are required for the orderly neuronal migration during the second trimester and for connectivity of the thalamocortical neurons); decrease in major components of the cortical inhibitory neurotransmitter system; and alterations in the molecules critical for NMDA-receptor mediated neural transmission. Thus a great deal of evidence accumulated over the last decade has definitively implicated the dorsolateral prefrontal cortex in the pathophysiology of schizophrenia. Emerging data also confirms neuropathology in the mediodorsal nucleus of the thalamus that projects to the DLPFC. There is currently a consensus that schizophrenia involves epigenetic factors interacting with genetic information in the cells to produce abnormal molecules which when they are associated with abnormal circuits such as the DLPFC, may result in abnormal behavior. Thus, abnormal cortical connections and or altered neurotransmitter related molecules in the DLPFC could explain some of the prominent frontal cognitive disruptions seen in schizophrenia.

Spontaneous oscillations of cerebral blood flow velocity in the middle cerebral arteries of normal subjects and schizophrenic patients

Although many regional cerebral blood flow (rCBF) studies of schizophrenic patients have been carried out, only a few studies have investigated real-time hemodynamic changes in schizophrenic patients. In the present study, we used long-term monitoring of the middle cerebral artery (MCA) by non-invasive transcranial Doppler ultrasonography to obtain real-time CBF data in 55 schizophrenic patients and 20 normal comparison subjects. The mean blood flow velocity and pulsatility index (PI) of the MCA were not constant during long-term monitoring. They showed sinusoidal oscillations similar to those described in previous reports. The amplitude variations of these oscillations in both drug-naive and medicated schizophrenic patients were significantly decreased compared with findings in normal control subjects. The averaged PI values were found to be decreased in patients with illness durations of more than 10 years. After withdrawal of antipsychotic medication, both the amplitude variations of oscillations and the PI values in the drug-withdrawn patients were significantly decreased relative to findings in normal control subjects. Our results show a decreased adjustment ability of cerebral vessel resistance not only in neuroleptic-naive schizophrenic patients but also in patients with longer illness duration. Neuroleptics could affect the adjustment ability of vessel resistance.

Cognition and neuropathology in schizophrenia

Clinical, neuropsychological and neuropathological avenues of research have advanced in concert to increase our understanding of schizophrenia. Progress in four general areas of investigation will be reviewed: (i) fronto-temporal-limbic dysfunction; (ii) abnormal connectivity or 'miswiring'; (iii) aberrant neurodevelopment; and (iv) neurodegeneration and neural injury. The challenge for post-mortem research is to identify the molecular pathways in which abnormalities culminate in the highly diverse features of the disorder. Candidate pathways must be able to account for the developmental and deteriorative clinical profiles and the global and focal neuropsychological deficits, as well as the various patho-anatomical abnormalities that indicate aberrant cytoarchitecture and connectivity in the absence of neurodegeneration or other obvious evidence of postmaturational neural injury.

A meta-analytic review of Wisconsin Card Sort studies in schizophrenia: general intellectual deficit in disguise?

A majority of studies show that schizophrenics perform poorly on so-called tests of executive or frontal lobe function--the paradigmatic case being the Wisconsin Card Sort Test (WCST). Nevertheless, the specific character of this deficit in schizophrenia remains underspecified. In particular, it seems premature to assume that schizophrenia is characterised by an executive dysfunction and/or a disorder of frontal lobe function before determining whether any deficit is: selective; disproportionate to the general level of intellectual functioning; or qualitatively comparable with that of frontal lobe patients. A meta-analysis was conducted on 29 studies comparing the performance of schizophrenics and normal controls on the WCST. This showed that the mean weighted effect size was large for categories achieved (d = 0.91), medium for absolute level of perseveration (d = 0.53), but only small for the proportion of perseverative errors (d = 0.18). By contrast, the effect size for Wechsler Adult Intelligence Scale Intelligence Quotient (WAIS IQ) in a subset of these studies (d = 1.23) was significantly larger than for any WCST measures. This pattern of findings challenges notions that schizophrenia is characterised by an executive dysfunction that is: selective; disproportionate to IQ level; and analogous to that found in frontal lobe patients. Rather, the poor WCST performance of schizophrenics appears to reflect a generalised intellectual deficit.

Interhemispheric EEG coherence in never-medicated patients with paranoid schizophrenia: analysis at rest and during photic stimulation

We assessed functional relationships between hemispheres by calculating interhemispheric EEG coherence at rest and during photic stimulation in 18 never-medicated patients with paranoid schizophrenia and 30 control subjects. Although no significant group differences were found in the resting EEG, the schizophrenic patients had significantly higher coherence on EEGs recorded during photic stimulation, compared to the control subjects. In this study, we also examined the changes in interhemispheric coherence from rest to the stimulus condition (i.e., stimulation-related coherence reactivity); the patients were found to show significantly greater coherence reactivity to photic stimulation. These findings provide further evidence that schizophrenic patients have a higher degree of interhemispheric functional connectivity and thus have less lateralized cerebral organization than normal subjects. Our results also suggest that schizophrenic patients have excessive functional reorganization between hemispheres in association with photic stimulation.

Dopamine D2 densities and the schizophrenic brain

Meta-analytic methods were used to test the D2 dopamine density hypothesis in schizophrenia. Post-mortem as well as in-vivo (i.e., PET and SPECT) neuroimaging studies that met criteria for inclusion into the meta-analysis were gathered from 1980 to 1996. The mean effect size across studies corresponds to an effect size of 1.47 (d). Although large, the effect size obtained does not meet heuristic benchmark criteria that would suggest D2 density increases to be a marker for schizophrenia. That is, roughly 30% of patients with schizophrenia could not be discriminated from normal healthy controls. Based on the findings, it is argued that D2 density receptor increases in patients with schizophrenia, although a reliable finding in many patients (i.e., approximately 70%), is not a specific or consistent marker for schizophrenia.

Images of psychopathology

Brain imaging continues to provide important data about brain structure, neurotransmitter function and the physiological basis of cognitive processes, as these relate to schizophrenia and mood disorders. A unifying theoretical perspective, however, that can clarify the precise nature of the biological basis of these diverse psychiatric conditions is lacking. It is becoming increasingly evident that a lesion model is inappropriate and that a more relevant characterisation will be found in terms of disorders of functional interconnections between brain regions.