Cerebral glucose metabolism in childhood onset schizophrenia

Brain glucose metabolism in schizophrenia: a systematic review and meta-analysis of 18FDG-PET studies in schizophrenia

BACKGROUND

Impaired brain metabolism may be central to schizophrenia pathophysiology, but the magnitude and consistency of metabolic dysfunction is unknown.

METHODS

We searched MEDLINE, PsychINFO and EMBASE between 01/01/1980 and 13/05/2021 for studies comparing regional brain glucose metabolism using 18FDG-PET, in schizophrenia/first-episode psychosis v. controls. Effect sizes (Hedges g) were pooled using a random-effects model. Primary measures were regional absolute and relative CMRGlu in frontal, temporal, parietal and occipital lobes, basal ganglia and thalamus.

RESULTS

Thirty-six studies (1335 subjects) were included. Frontal absolute glucose metabolism (Hedge's g = -0.74 ± 0.54, p = 0.01; I2 = 67%) and metabolism relative to whole brain (g = -0.44 ± 0.34, p = 0.01; I2 = 55%) were lower in schizophrenia v. controls with moderate heterogeneity. Absolute frontal metabolism was lower in chronic (g = -1.18 ± 0.73) v. first-episode patients (g = -0.09 ± 0.88) and controls. Medicated patients showed frontal hypometabolism relative to controls (-1.04 ± 0.26) while metabolism in drug-free patients did not differ significantly from controls. There were no differences in parietal, temporal or occipital lobe or thalamic metabolism in schizophrenia v. controls. Excluding outliers, absolute basal ganglia metabolism was lower in schizophrenia v. controls (-0.25 ± 0.24, p = 0.049; I2 = 5%). Studies identified reporting voxel-based morphometry measures of absolute 18FDG uptake (eight studies) were also analysed using signed differential mapping analysis, finding lower 18FDG uptake in the left anterior cingulate gyrus (Z = -4.143; p = 0.007) and the left inferior orbital frontal gyrus (Z = -4.239; p = 0.02) in schizophrenia.

CONCLUSIONS

We report evidence for hypometabolism with large effect sizes in the frontal cortex in schizophrenia without consistent evidence for alterations in other brain regions. Our findings support the hypothesis of hypofrontality in schizophrenia.

Enhanced Prefrontal Regional Homogeneity and Its Correlations With Cognitive Dysfunction/Psychopathology in Patients With First-Diagnosed and Drug-Naive Schizophrenia

Background: Schizophrenia, regarded as a neurodevelopmental disorder, is characterized by positive symptoms, negative symptoms, and cognitive dysfunction. Investigating the spontaneous brain activity in patients with schizophrenia can help us understand the underlying pathophysiologic mechanism of schizophrenia. However, results concerning abnormal neural activities and their correlations with cognitive dysfunction/psychopathology of patients with schizophrenia were inconsistent. Methods: We recruited 57 first-diagnosed and drug-naive patients with schizophrenia and 50 matched healthy controls underwent magnetic resonance imaging. The Positive and Negative Syndrome Scale (PANSS) and the MATRICS Consensus Cognitive Battery were used to assess the psychopathology/cognitive dysfunction. Regional homogeneity (ReHo) was used to explore neural activities. Correlation analyses were calculated between abnormal ReHo values and PANSS scores/standardized cognitive scores. Lastly, support vector machine analyses were conducted to evaluate the accuracy of abnormal ReHo values in distinguishing patients with schizophrenia from healthy controls. Results: Patients with schizophrenia showed cognitive dysfunction, and increased ReHo values in the right gyrus rectus, right inferior frontal gyrus/insula and left inferior frontal gyrus/insula compared with those of healthy controls. The ReHo values in the right inferior frontal gyrus/insula were positively correlated with negative symptom scores and negatively correlated with Hopkins verbal learning test-revised/verbal learning. Our results showed that the combination of increased ReHo values in the left inferior frontal gyrus/insula and right gyrus rectus had 78.5% (84/107) accuracy, 85.96% (49/57) sensitivity, and 70.00% specificity, which were higher than other combinations. Conclusions: Hyperactivities were primarily located in the prefrontal regions, and increased ReHo values in the right inferior frontal gyrus/insula might reflect the severity of negative symptoms and verbal learning abilities. The combined increases of ReHo values in these regions might be an underlying biomarker in differentiating patients with schizophrenia from healthy controls.

Attenuated resting-state functional connectivity in patients with childhood- and adult-onset schizophrenia

BACKGROUND

Childhood-onset schizophrenia (COS) is a rare, severe form of the adult-onset disorder (AOS). Our previous resting-state fMRI study identified attenuated functional connectivity in COS compared with controls. Here, we ask whether COS and AOS patients and their siblings exhibit similar abnormalities of functional connectivity.

METHODS

A whole-brain, data-driven approach was used to assess resting-state functional connectivity differences in COS (patients/siblings/controls, n: 26/28/33) and AOS (n: 19/28/30). There were no significant differences in age, sex, or head motion across groups in each dataset and as designed, the COS dataset has a significantly lower age than the AOS.

RESULTS

Both COS and AOS patients showed decreased functional connectivity relative to controls among a wide set of brain regions (P<0.05, corrected), but their siblings did not. Decreased connectivity in COS and AOS patients showed no amplitude differences and was not modulated by age-at-onset or medication doses. Cluster analysis revealed that these regions fell into two large-scale networks: one sensorimotor network and one centered on default-mode network regions, but including higher-order cognitive areas only in COS. Decreased connectivity between these two networks was notable (P<0.05, corrected) for both patient groups.

CONCLUSIONS

A shared pattern of attenuated functional connectivity was found in COS and AOS, supporting the continuity of childhood-onset and adult-onset schizophrenia. Connections were altered between sensorimotor areas and default-mode areas in both COS and AOS, suggesting potential abnormalities in processes of self-monitoring and sensory prediction. The absence of substantial dysconnectivity in siblings indicates that attenuation is state-related.

A Comprehensive Analysis of Nuclear-Encoded Mitochondrial Genes in Schizophrenia

BACKGROUND

The genetic risk factors of schizophrenia (SCZ), a severe psychiatric disorder, are not yet fully understood. Multiple lines of evidence suggest that mitochondrial dysfunction may play a role in SCZ, but comprehensive association studies are lacking. We hypothesized that variants in nuclear-encoded mitochondrial genes influence susceptibility to SCZ.

METHODS

We conducted gene-based and gene-set analyses using summary association results from the Psychiatric Genomics Consortium Schizophrenia Phase 2 (PGC-SCZ2) genome-wide association study comprising 35,476 cases and 46,839 control subjects. We applied the MAGMA method to three sets of nuclear-encoded mitochondrial genes: oxidative phosphorylation genes, other nuclear-encoded mitochondrial genes, and genes involved in nucleus-mitochondria crosstalk. Furthermore, we conducted a replication study using the iPSYCH SCZ sample of 2290 cases and 21,621 control subjects.

RESULTS

In the PGC-SCZ2 sample, 1186 mitochondrial genes were analyzed, among which 159 had p values < .05 and 19 remained significant after multiple testing correction. A meta-analysis of 818 genes combining the PGC-SCZ2 and iPSYCH samples resulted in 104 nominally significant and nine significant genes, suggesting a polygenic model for the nuclear-encoded mitochondrial genes. Gene-set analysis, however, did not show significant results. In an in silico protein-protein interaction network analysis, 14 mitochondrial genes interacted directly with 158 SCZ risk genes identified in PGC-SCZ2 (permutation p = .02), and aldosterone signaling in epithelial cells and mitochondrial dysfunction pathways appeared to be overrepresented in this network of mitochondrial and SCZ risk genes.

CONCLUSIONS

This study provides evidence that specific aspects of mitochondrial function may play a role in SCZ, but we did not observe its broad involvement even using a large sample.

Magnetic Resonance Spectroscopy in Schizophrenia: Evidence for Glutamatergic Dysfunction and Impaired Energy Metabolism

In the past couple of decades, major efforts were made to increase reliability of metabolic assessments by magnetic resonance methods. Magnetic resonance spectroscopy (MRS) has been valuable for providing in vivo evidence and investigating biomarkers in neuropsychiatric disorders, namely schizophrenia. Alterations of glutamate and glutamine levels in brains of schizophrenia patients relative to healthy subjects are generally interpreted as markers of glutamatergic dysfunction. However, only a small fraction of MRS-detectable glutamate is involved in neurotransmission. Here we review and discuss brain metabolic processes that involve glutamate and that are likely to be implicated in neuropsychiatric disorders.

Mitochondrial dysfunction in schizophrenia: an evolutionary perspective

Schizophrenia (SCZ) is a severe psychiatric illness with a lifetime prevalence of 0.4 %. A disturbance of energy metabolism has been suggested as part of the etiopathogenesis of the disorder. Several lines of evidence have proposed a connection between etiopathogenesis of SCZ and human brain evolution, which was characterized by an increase in the energy requirement, demanding a co-evolution of the mitochondrial system. Mitochondria are key players in brain energy homeostasis and multiple lines of evidence suggest that the system is disrupted in SCZ. In this review, we will describe the current knowledge on pathways/system involved in the human brain evolution as well as the main theories regarding the evolutionary origin of SCZ. We will furthermore discuss the role of mitochondria in the context of brain energy metabolism and its role in the etiopathogenesis of SCZ. Understanding SCZ in the context of human brain evolution opens a new perspective to elucidate pathophysiological mechanisms involved in the origin and/or portions of the complex symptomatology of this severe mental disorder.

Abnormalities in the tricarboxylic acid (TCA) cycle in the brains of schizophrenia patients

Images of brain metabolism and measurements of activities of components of the electron transport chain support earlier studies that suggest that brain glucose oxidation is inherently abnormal in a significant proportion of persons with schizophrenia. Therefore, we measured the activities of enzymes of the tricarboxylic (TCA) cycle in dorsolateral-prefrontal-cortex from schizophrenia patients (N=13) and non-psychiatric disease controls (N=13): the pyruvate dehydrogenase complex (PDHC), citrate synthase (CS), aconitase, isocitrate dehydrogenase (ICDH), the alpha-ketoglutarate dehydrogenase complex (KGDHC), succinate thiokinase (STH), succinate dehydrogenase (SDH), fumarase and malate dehydrogenase (MDH). Activities of aconitase (18.4%, p<0.05), KGDHC (26%) and STH (28.2%, p<0.05), enzymes in the first half of the TCA cycle, were lower, but SDH (18.3%, p<0.05) and MDH (34%, p<0.005), enzymes in the second half, were higher than controls. PDHC, CS, ICDH and fumarase activities were unchanged. There were no significant correlations between enzymes of TCA cycle and cognitive function, age or choline acetyl transferase activity, except for aconitase activity which decreased slightly with age (r=0.55, p=003). The increased activities of dehydrogenases in the second half of the TCA cycle may reflect a compensatory response to reduced activities of enzymes in the first half. Such alterations in the components of TCA cycle are adequate to alter the rate of brain metabolism. These results are consistent with the imaging studies of hypometabolism in schizophrenia. They suggest that deficiencies in mitochondrial enzymes can be associated with mental disease that takes the form of schizophrenia.

Findings of proton magnetic resonance spectometry in the dorsolateral prefrontal cortex in adolescents with first episodes of psychosis

Knowledge of the neurobiology of early onset psychosis is limited. We used proton magnetic resonance spectroscopy to investigate the possible existence of dorsolateral prefrontal brain biochemical abnormalities in adolescents with psychosis and to determine possible differential effects related to specific psychotic diagnoses. We measured the ratios of N-acetyl-aspartate (NAA), choline (Cho), and creatine (Cr) to water in two groups of adolescents with a first episode of psychosis (schizophrenia n=8; non-schizophrenia n=15) and in 32 healthy controls matched for age, gender, and years of education. Proton magnetic resonance spectroscopy at 1.5 T was used to study two 6.75-cc voxels placed in the left and right dorsolateral prefrontal region. The schizophrenia patients presented statistically significant reductions in NAA/water levels in the left dorsolateral prefrontal voxel as compared with non-schizophrenia patients and healthy controls. No significant differences were detected between groups for NAA/water in the right dorsolateral prefrontal voxel or for Cho/water and Cr/water levels in any hemisphere. A reduction of the NAA/water level in the left dorsolateral prefrontal region may be selectively present at the onset of psychosis during adolescence in patients who later progress to schizophrenia, but not in those who later progress to other psychotic disorders.

FDG-PET in never-previously medicated psychotic adolescents treated with olanzapine or haloperidol

We acquired Positron emission tomography with 18-F-deoxyglucose (FDG-PET) and anatomical MRI in 30 never-previously medicated psychotic adolescents (ages 13-20). (FDG-PET) was obtained at baseline and after 8-9 weeks of a randomized double-blind trial of either olanzapine or haloperidol. Neuropsychological tests of executive function were also obtained. Patients carried out the serial verbal learning task, a modification of the California Verbal Learning Test, during the uptake of the FDG. PET scans were coregistered with spoiled gradient MRI (TR=24, TE=5, flip angle 40 degrees, slice thickness 1.2 mm, field of view 230 mm) for accurate anatomical identification of regions of interest traced on the MRI. Twenty-two of the thirty patients completed the second PET and clinical evaluation. Individuals treated with olanzapine increased relative metabolic rates in the frontal lobe more than the occipital lobe while patients treated with haloperidol failed to increase frontal metabolic rates and did not show an anteroposterior gradient in medication response. Haloperidol increased striatal metabolic rate more than olanzapine. Both drugs increased thalamic metabolic rates and this increase was significantly larger in younger (age 13-15) than older (16-21) patients.

Neural correlates of working memory dysfunction in first-episode schizophrenia patients: an fMRI multi-center study

Working memory dysfunction is a prominent impairment in patients with schizophrenia. Our aim was to determine cerebral dysfunctions by means of functional magnetic resonance imaging (fMRI) in a large sample of first-episode schizophrenia patients during a working memory task. 75 first-episode schizophrenia patients and 81 control subjects, recruited within a multi-center study, performed 2- and 0-back tasks while brain activation was measured with fMRI. In order to guarantee comparability between data quality from different scanners, we developed and adopted a standardized, fully automated quality assurance of scanner hard- and software as well as a measure for in vivo data quality. After these quality-control measures had been implemented, 48 patients and 57 controls were included in the final analysis. During attention-related processes, even when the performance between patients and controls was comparable, there was a recognizable emergence of cerebral dysfunctions with hypoactivations in the ventrolateral prefrontal cortex (VLPFC), in the superior temporal cortex and in the thalamus. During working memory performance, parietal hypoactivations, especially in the precuneus, were prominent and were accompanied by poorer performance in patients. A hyperfrontality emerged in the ventrolateral prefrontal cortex. Hence, results point to a dysfunctional ventrolateral prefrontal-parietal network during working memory in patients, suggesting impairments in basic functions such as retrieval, storage and maintenance. The brain activation pattern of this large and significant sample of first-episode schizophrenia patients indicates an imbalanced system failing to adjust the amount of brain activity required in the cerebral network involved in attention and working memory.

Study of childhood onset schizophrenia (COS) using SPECT and neuropsychological assessment

BACKGROUND

In recent years, the development of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging has enhanced our understanding of the physiological functioning of the intact brain.

AIM

To study cerebral cortical perfusion defects in patients with childhood onset schizophrenia (COS) and to assess their neuropsychological functioning.

METHODS

This cross-sectional study comprised 14 patients with COS with onset at or before 14 years of age, diagnosed as per ICD-10 DCR criteria, attending a tertiary care centre in North India. All the patients were assessed on sociodemographic, clinical profile sheet, Positive and Negative Symptom Scale (PANSS) and Edinburgh Handedness Inventory (EHI). The Wisconsin Card Sorting Test (WCST) was used to assess their neuropsychological functioning. All patients underwent SPECT. A control group of 10 healthy subjects was studied with SPECT for comparison.

RESULTS

Nine patients (64.3%) showed perfusion anomaly on SPECT scan specifically in the left temporal and frontal areas of the brain. On WCST score these 9 patients showed a higher percentage of total errors (64.49%+/-9.42%) as compared to the other 5 patients (48.54%+/-12.70%) who showed no abnormality on SPECT scan. All normal control subjects showed no abnormality on SPECT.

CONCLUSION

The results from WCST show that COS patients have difficulty in executive functioning. Also, patients had perfusion anomaly in the left temporal, frontal and parietal areas. Deficits found in COS are similar to those found in adult onset schizophrenia (AOS). In view of the findings, the nature of COS and its relationship with AOS are discussed.

GAD1 (2q31.1), which encodes glutamic acid decarboxylase (GAD67), is associated with childhood-onset schizophrenia and cortical gray matter volume loss

Postmortem brain studies have shown deficits in the cortical gamma-aminobutyric acid (GABA) system in schizophrenic individuals. Expression studies have shown a decrease in the major GABA-synthesizing enzyme (glutamic acid decarboxylase (GAD67) mRNA levels in neurons in dorsolateral prefrontal cortex in schizophrenics relative to controls. In the present study, SNPs in and around the GAD1 gene, which encodes the protein GAD67, were tested on a rare, severely ill group of children and adolescents with childhood-onset schizophrenia (COS) (n=72), in a family-based association analysis. Compared to adult-onset samples, the COS sample has evidence for more salient familial, and perhaps genetic, risk factors for schizophrenia, as well as evidence for frontal cortical hypofunction, and greater decline in cortical gray matter volume on anatomic brain MRI scans during adolescence. We performed family-based TDT and haplotype association analyses of the clinical phenotype, as well as association analyses with endophenotypes using the QTDT program. Three adjacent SNPs in the 5' upstream region of GAD1 showed a positive pairwise association with illness in these families (P=0.022-0.057). Significant transmission distortion of 4-SNP haplotypes was also observed (P=0.003-0.008). Quantitative trait TDT analyses showed an intriguing association between several SNPs and increased rate of frontal gray matter loss. These observations, when taken together with the positive results reported recently in two independent adult-onset schizophrenia pedigree samples, suggest that the gene encoding GAD67 may be a common risk factor for schizophrenia.

PET in pediatric diseases

FDG-PET is being increasingly applied to pediatric conditions, particularly in oncology. PET and PET/CT scanning in children are not currently supported by Centers for Medicare and Medicaid Services unless the disease condition coincides with a reimbursed adult condition. The recent merger of the Children's Cancer Group and the Pediatric Oncology Group to form the Children's Oncology Group creates an opportunity to examine the use of FDG-PET in the management of childhood tumors in multi-institutional, cooperative efforts. The interest in incorporating PET imaging technology in pediatric medicine has been evidenced by several recent review articles summarizing the ongoing progress in this area. Future data will show that FDG-PET provides useful diagnostic information and can play a pivotal role in the clinical management and care of children with disease.

Differential psychostimulant-induced activation of neural circuits in dopamine transporter knockout and wild type mice

Dopamine (DA) is a neurotransmitter that has been implicated in a wide variety of psychiatric disorders that include attention deficit-hyperactivity disorder (ADHD), schizophrenia, and drug abuse. Recently, we have been working with a mouse in which the gene for the DA transporter (DAT) has been disrupted. This mouse is hyperactive in the open field, displays an inability to inhibit ongoing behaviors, and is deficient on learning and memory tasks. Psychostimulants such as amphetamine and methylphenidate attenuate the hyperlocomotion of the mutants, but stimulate activity of the wild type (WT) controls. The objective of the present study is to examine the neural basis for the differential responses to psychostimulants in these mice. WT and DAT knockout (KO) animals were given vehicle or methylphenidate, amphetamine, or cocaine and brain sections were immunostained for Fos. In WT mice, methylphenidate induced Fos-like immunoreactivity (Fos-LI) in the mesostriatal and mesolimbocortical DA pathways that included the anterior olfactory nucleus, frontal association cortex, orbitofrontal cortex, cingulate cortex, caudate-putamen, globus pallidus, claustrum, lateral septum, nucleus accumbens, basolateral and central nuclei of the amygdala, bed nucleus of stria terminalis, subthalamic nucleus, substantia nigra, ventral tegmental area, and dorsal raphe. Additional areas of activation included the granular dentate gyrus, Edinger-Westphal nucleus, and periaqueductal gray. While the mutants showed little response in most of these same areas, the anterior olfactory nucleus, caudal caudate-putamen, lateral septum, basolateral and central nuclei of the amygdala, and bed nucleus of stria terminalis were activated. Amphetamine and cocaine produced similar changes to that for methylphenidate, except these psychostimulants also induced Fos-LI in the nucleus accumbens of the KO animals. Since the DAT gene is disrupted in the KO mouse, these findings suggest that dopaminergic mechanisms may mediate the WT responses, whereas non-dopaminergic systems predominate in the mutant. In the mutants, it appears that limbic areas and non-dopaminergic transmitter systems within these brain regions may mediate responses to psychostimulants. Inasmuch as the KO mouse may represent a useful animal model for ADHD and because psychostimulants such as cocaine are reinforcing to these animals, our results may provide some useful insights into the neural mechanisms-other than DA-that may contribute to the symptoms of ADHD and/or drug abuse in human patients.

Childhood-onset schizophrenia: research update

This review is a research update of recent literature related to childhood-onset schizophrenia (onset of psychotic symptoms by age 12 years). This subgroup of patients has attracted considerable research interest because patients with a childhood onset may represent a more homogeneous patient population in which to search for risk or etiologic factors. We examine data indicating that childhood-onset schizophrenia (COS) shares the same clinical and neurobiologic features as later-onset forms of the disorder. Compared with adults with schizophrenia, however, this subgroup of patients appears to have more severe premorbid neuro-developmental abnormalities, more cytogenetic anomalies, and potentially greater family histories of schizophrenia and associated spectrum disorders. While preliminary, these data indicate that a greater genetic vulnerability may be one of the underpinnings of COS. Future studies of this subgroup may provide important clues as to the genetic basis for schizophrenia and how gene products influence certain features of the disease, such as age of onset and mode of inheritance.

Mapping adolescent brain change reveals dynamic wave of accelerated gray matter loss in very early-onset schizophrenia

Neurodevelopmental models for the pathology of schizophrenia propose both polygenetic and environmental risks, as well as early (pre/perinatal) and late (usually adolescent) developmental brain abnormalities. With the use of brain mapping algorithms, we detected striking anatomical profiles of accelerated gray matter loss in very early-onset schizophrenia; surprisingly, deficits moved in a dynamic pattern, enveloping increasing amounts of cortex throughout adolescence. Early-onset patients were rescanned prospectively with MRI, at 2-year intervals at three time points, to uncover the dynamics and timing of disease progression during adolescence. The earliest deficits were found in parietal brain regions, supporting visuospatial and associative thinking, where adult deficits are known to be mediated by environmental (nongenetic) factors. Over 5 years, these deficits progressed anteriorly into temporal lobes, engulfing sensorimotor and dorsolateral prefrontal cortices, and frontal eye fields. These emerging patterns correlated with psychotic symptom severity and mirrored the neuromotor, auditory, visual search, and frontal executive impairments in the disease. In temporal regions, gray matter loss was completely absent early in the disease but became pervasive later. Only the latest changes included dorsolateral prefrontal cortex and superior temporal gyri, deficit regions found consistently in adult studies. These emerging dynamic patterns were (i) controlled for medication and IQ effects, (ii) replicated in independent groups of males and females, and (iii) charted in individuals and groups. The resulting mapping strategy reveals a shifting pattern of tissue loss in schizophrenia. Aspects of the anatomy and dynamics of disease are uncovered, in a changing profile that implicates genetic and nongenetic patterns of deficits.

Update on childhood-onset schizophrenia

Updated findings from the ongoing National Institute of Mental Health Child Psychiatry Branch longitudinal study of childhood-onset schizophrenia (COS) are presented, along with replications from collaborators at other sites. Clinical and neurobiologic continuities of COS with poor-outcome adult-onset schizophrenia suggests that their underlying pathophysiology is the same. However, these early-onset cases appear to have more striking genetic contributions to their etiology. Updated findings involve risk factors (birth complications, cytogenic abnormalities, early language and motor problems, and familial psychopathology), treatment trials, and brain magnetic resonance imaging studies.

Steady-state visually evoked potential topography during the continuous performance task in normal controls and schizophrenia

OBJECTIVES

To examine the latency topography of the steady-state visually evoked potential (SSVEP) in patients diagnosed with schizophrenia and normal controls while undertaking a visual vigilance task.

METHODS

Twenty patients diagnosed with schizophrenia and 18 normal controls performed the A-X version of the continuous performance task (CPT A-X) where subjects are required to press a micro-switch on the unpredictable appearance of an 'X' that had been preceded by an 'A.' Brain electrical activity was recorded from 64 scalp sites and a 13 Hz spatially uniform visual flicker presented with the task was used to elicit a steady-state visually evoked potential (SSVEP).

RESULTS

Following the appearance of the 'A' and 'X,' the control group demonstrated a transient SSVEP latency reduction at parietal and prefrontal sites. By contrast, the patients group showed no such SSVEP latency reduction. The prefrontal SSVEP latency changes in the 500 ms interval following the appearance of the 'X' were correlated with mean individual reaction time in both populations.

CONCLUSIONS

We suggest that the SSVEP latency reduction may index excitatory processes and that the absence of prefrontal SSVEP latency reduction in schizophrenic patients may be a manifestation of reduced prefrontal activity or 'hypofrontality' observed with other neuroimaging modalities.

Functional neuroimaging in child psychiatry

Functional neuroimaging in child psychiatry presents unique scientific, ethical, and technical challenges. The study of childhood disorders presupposes knowledge of neurodevelopment and brain maturation. However, much of human brain science is based on inferences from animal work and indirect neurochemical measures from body fluids. Neuroimaging can examine brain development directly in humans. The benefits can be enormous for learning how and when to intervene to prevent or treat a disorder. These unprecedented potential gains are countered by complex and difficult ethical issues. Technical advances can reduce ethical concerns by minimizing risks. They also promise to enhance the sensitivity and specificity of the measures (eg, by improving spatial and temporal resolution). Judiciously designed investigations will permit the testing of a priori hypotheses built on rational models of neuropathology. Finally, it is the integration of scientific knowledge across the various fields of neuroscience and clinical research that will push the limits of our understanding of health and disease.

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.

Childhood-onset schizophrenia: rare but worth studying

Childhood-onset schizophrenia (defined by an onset of psychosis by age 12) is a rare and severe form of the disorder that is clinically and neurobiologically continuous with the adult-onset disorder. There is growing evidence for more salient risk or etiologic factors, particularly familial, in this possibly more homogeneous patient population. For the 49 patients with very early onset schizophrenia studied to date at the National Institute of Mental Health, there were more severe premorbid neuro-developmental abnormalities, a higher rate of cytogenetic anomalies, and a seemingly higher rate of familial schizophrenia and spectrum disorders than later onset cases. There was no evidence for increased obstetric complications or environmental stress. These data, while preliminary, suggest that a very early age of onset of schizophrenia may be secondary to greater familial vulnerability. Consequently, genetic studies of these patients may be particularly informative and may provide important etiologic information.

Integrating science and ethics in child and adolescent psychiatry research

Research to elucidate the biological bases of psychopathology in children and adolescents is needed to understand pathogenesis and to develop effective and safe treatment and preventive interventions. Because of the effect of development, data collected in adults are not always applicable to youth, and direct participation of children in research is necessary. Many medications are currently used in the community to treat children and adolescents with neuropsychiatric disorders without adequate data about their safety and efficacy. Conducting research in children requires attention to specific ethical and regulatory factors. In deciding whether minors can participate in a study with potential direct benefit to the research subjects, the most important variable to consider is the balance between risks and potential benefit, in the context of the severity of the child's condition and the available alternatives. Research with no potential benefit to the participants is guided by the concepts of minimal risk (which may apply more to normal children) and minor increase over minimal risk (perhaps more relevant to children affected by psychopathology). Recently conducted studies relevant to this issue are reviewed. Of paramount importance is the ratio of risk/scientific value of the proposed experiment. In fact, no research is justifiable, no matter how low the risk may be, unless the potential yield of the study is important and may help advance our understanding of normal functioning and mental illness.