Biomedical subjects

Joseph H Callicott

Publications and source records attributed to Joseph H Callicott.

At least 19 recordsLinked to original sources

PubMed2006

Tolcapone improves cognition and cortical information processing in normal human subjects.

Prefrontal cortical dopamine (DA) regulates various executive cognitive functions, including attention and working memory. Efforts to enhance prefrontal-related cognition, which have focused on catecholaminergic stimulant drugs, have been unsatisfactory. Recently, the demonstration that a functional polymorphism in the catecholamine-O-methyltransferase (COMT) gene impacts prefrontal cognition raises the possibility of a novel pharmacological approach for the treatment of prefrontal lobe executive dysfunction. To explore in a proof of concept study the effects of tolcapone, a CNS penetrant specific COMT inhibitor, we performed a randomized, double blind, placebo controlled, and crossover design of this drug in normal subjects stratified by COMT (val158met) genotype. COMT enzyme activity was determined in peripheral blood. Forty-seven normal volunteers with no family history of psychiatric disorders underwent neuropsychological testing and 34 of those subjects underwent physiological measurement of prefrontal information processing assessed by blood oxygen level-dependent functional magnetic resonance imaging (fMRI). We found significant drug effects on measures of executive function and verbal episodic memory and a significant drug by genotype interaction on the latter, such that individuals with val/val genotypes improved, whereas individuals with met/met genotypes worsened on tolcapone. fMRI revealed a significant tolcapone-induced improvement in the efficiency of information processing in prefrontal cortex during a working memory test. This study demonstrates enhancement of prefrontal cortical function in normal human subjects with a nonstimulant drug having COMT inhibitory activity. Our results are consistent with data from animal studies and from computational models of the effects of selective enhancement of DA signaling in the prefrontal cortex.

Adult↗

PubMed2006

Prefrontal dysfunction in schizophrenia controlling for COMT Val158Met genotype and working memory performance.

Earlier studies with functional imaging in schizophrenia have demonstrated dysfunction of the dorsolateral prefrontal cortex during working memory. Controlling for behavioral performance and for catechol-O-methyltransferase (COMT) Val158Met genotype, we here demonstrate in a functional magnetic resonance imaging paradigm that patients recruit greater neuronal resources in prefrontal cortex during working memory, suggesting that this phenotype is a core functional trait of the disease. We also replicated earlier findings that the Val allele of the COMT polymorphism is associated with greater engagement of the prefrontal cortex.

Adult↗

PubMed2006

Neural mechanisms of genetic risk for impulsivity and violence in humans.

Neurobiological factors contributing to violence in humans remain poorly understood. One approach to this question is examining allelic variation in the X-linked monoamine oxidase A (MAOA) gene, previously associated with impulsive aggression in animals and humans. Here, we have studied the impact of a common functional polymorphism in MAOA on brain structure and function assessed with MRI in a large sample of healthy human volunteers. We show that the low expression variant, associated with increased risk of violent behavior, predicted pronounced limbic volume reductions and hyperresponsive amygdala during emotional arousal, with diminished reactivity of regulatory prefrontal regions, compared with the high expression allele. In men, the low expression allele is also associated with changes in orbitofrontal volume, amygdala and hippocampus hyperreactivity during aversive recall, and impaired cingulate activation during cognitive inhibition. Our data identify differences in limbic circuitry for emotion regulation and cognitive control that may be involved in the association of MAOA with impulsive aggression, suggest neural systems-level effects of X-inactivation in human brain, and point toward potential targets for a biological approach toward violence.

Alleles↗

PubMed2006

The G72/G30 gene complex and cognitive abnormalities in schizophrenia.

A recently discovered gene complex, G72/G30 (hereafter G72, but now termed DAOA), was found to be associated with schizophrenia and with bipolar disorder, possibly because of an indirect effect on NMDA neurotransmission. In principle, if G72 increases risk for psychosis by this mechanism, it might impact with greater penetrance those cortically based cognitive and neurophysiological functions associated with NMDA signaling. We performed two independent family-based association studies (one sample contained more than 200 families and the other more than 65) of multiple SNPs in the G72 region and of multiple SNPs in the gene for D-amino acid oxidase (DAAO), which may be modulated by G72. We examined the relationship between select cognitive measures in attention, working memory, and episodic memory and a restricted set of G72 SNPs in over 600 normal controls, schizophrenic patients, and their nonpsychotic siblings using mixed model ANOVAs. We also determined genotype effects on neurophysiology measures in normal controls using the fMRI BOLD response obtained during activation procedures involving either episodic memory or working memory. There were no significant single G72 SNP associations and clinical diagnosis in either sample, though one approached significance (p=0.06). Diagnosis by genotype interaction effects for G72 SNP 10 were significant for cognitive variables assessing working memory and attention (p=0.05), and at the trend level for episodic memory, such that in the schizophrenia group an exaggerated allele load effect in the predicted directions was observed. In the fMRI paradigms, a strong effect of G72 SNP 10 genotype was observed on BOLD activation in the hippocampus during the episodic memory paradigm. Tests of association with DAAO were consistently nonsignificant. We present evidence that SNP variations in the G72 gene region increase risk of cognitive impairment in schizophrenia. SNP variations were not strongly associated with clinical diagnosis in family-based analyses.

Adult↗

PubMed2006

Brain regions underlying response inhibition and interference monitoring and suppression.

Response inhibition and interference monitoring and suppression are two important aspects of cognitive control. Previous functional imaging studies have suggested a common network of brain regions underlying these cognitive processes; the dorsolateral prefrontal cortex (DLPFC), the ventrolateral prefrontal cortex (VLPFC), the dorsal cingulate (dACC), and the parietal cortex (PC). The relative contribution of these regions to these cognitive subprocesses, however, has not been determined. Based on previous findings supporting a role for dACC in the monitoring of conflicting information within a stimulus, we hypothesized greater activity in this cortical region during interference monitoring and suppression relative to response inhibition. On the other hand, as response inhibition is characterized by differential cognitive processes such as control implementation, top down modulation of the response, expectancy, and inhibition of behavioural response, we hypothesized increased activity in the other cortical nodes of the cognitive control network relative to interference monitoring and suppression. To this end, we conducted an event-related functional magnetic resonance imaging (fMRI) study in 57 healthy volunteers using a task preferentially involving either interference monitoring and suppression or response inhibition. Accuracy for response inhibition was lower than for interference monitoring and suppression. Imaging data showed activation in DLPFC, dACC, VLPFC, PC for both conditions. Comparisons between the two conditions indicated greater activation bilaterally in DLPFC, VLPFC and PC during response inhibition, and greater activation in the dACC during interference monitoring and suppression. These results extend previous findings by suggesting regional functional specialization within a cortical network supporting cognitive control.

Adult↗

PubMed2006

Instability of prefrontal signal processing in schizophrenia.

OBJECTIVE: Prefrontal dysfunction is considered a fundamental characteristic of schizophrenia. Recent electrophysiological evidence points to a major instability of signal processing in prefrontal cortical microcircuits because of reduced phase-synchronization (i.e., an increased stimulus-related variability [noise] of single-trial responses in the spatial and time domain). The authors used functional magnetic resonance imaging (fMRI) during a visual two-choice reaction task in order to measure, with higher topographic accuracy, signal stability in patients with schizophrenia and its relationship to more traditional measures of activation. METHOD: Twelve clinically stable inpatients with schizophrenia and 16 matched comparison subjects were evaluated. Event-related blood-oxygen-level-dependent responses were subjected to an analysis of residual noise variance and to independent data dimension independent component analysis in the medial prefrontal cortex. RESULTS: In patients with schizophrenia, the authors found increased residual noise variance of the blood-oxygen-level-dependent response that predicted the level of prefrontal activation in these subjects. In the left hemisphere, residual noise variance strongly correlated with psychotic symptoms. Independent component analysis revealed a "fractionized" and unfocussed pattern of activation in patients. CONCLUSIONS: These findings suggest that unstable cortical signal processing underlies classic abnormal cortical activation patterns as well as psychosis in schizophrenia.

Adult↗

PubMed2006

Dysfunctional prefrontal regional specialization and compensation in schizophrenia.

OBJECTIVE: It has been suggested that in healthy persons higher-order cognitive processing engaged by incremental working memory load hierarchically employs more dorsal than ventral prefrontal resources in healthy individuals. Given that working memory performance is impaired in schizophrenia, especially at higher executive loads, the authors investigated how this prefrontal functional organization might be altered in disease, independent of performance deficits. METHOD: Using N-back working memory functional magnetic resonance imaging (fMRI) data, the authors studied 15 patients with schizophrenia and 26 healthy comparison subjects. Subgroups based on median performance accuracy at 2-back were analyzed; high performers included eight schizophrenia patients and 14 comparison subjects, and low performers included seven patients and 12 comparison subjects. RESULTS: High-performing but not low-performing comparison subjects responded to incremental working memory executive load with disproportionately greater dorsal but not ventral prefrontal cortex activation, which also predicted performance accuracy. In the high- and low-performing patient groups, incremental working memory load caused a disproportionate increase in ventral but not dorsal prefrontal cortex activation relative to the respective comparison group, which also correlated with accuracy. Functional connectivity between the ventral prefrontal cortex and posterior parietal cortex was relatively greater in patients, whereas comparison subjects had greater functional connectivity between the dorsal prefrontal cortex and posterior parietal cortex. CONCLUSIONS: The hierarchical organization of the prefrontal cortex may be compromised in schizophrenia, resulting in loss of functional specialization and integration at the dorsal prefrontal cortex and in compensatory activation from the ventral prefrontal cortex, which may ultimately affect working memory and executive cognition.

Humans↗

PubMed2005

Neurophysiological correlates of age-related changes in working memory capacity.

Cognitive abilities such as working memory (WM) capacity decrease with age. To determine the neurophysiological correlates of age-related reduction in working memory capacity, we studied 10 young subjects (<35 years of age; mean age=29) and twelve older subjects (>55 years of age; mean age=59) with whole brain blood oxygenation-level dependent (BOLD) fMRI on a 1.5 T GE MR scanner using a SPIRAL FLASH pulse sequence (TE=24 ms, TR=56 ms, FA=60 degrees , voxel dimensions=3.75 mm(3)). Subjects performed a modified version of the "n" back working memory task at different levels of increasing working memory load (1-Back, 2-Back and 3-Back). Older subjects performed as well as the younger subjects at 1-Back (p=0.4), but performed worse than the younger subjects at 2-Back (p<0.01) and 3-Back (p=0.06). Older subjects had significantly longer reaction time (RT) than younger subjects (p<0.04) at all levels of task difficulty. Image analysis using SPM 99 revealed a similar distribution of cortical activity between younger and older subjects at all task levels. However, an analysis of variance revealed a significant group x task interaction in the prefrontal cortex bilaterally; within working memory capacity, as in 1-Back when the older subjects performed as well as the younger subjects, they showed greater prefrontal cortical (BA 9) activity bilaterally. At higher working memory loads, however, when they performed worse then the younger subjects, the older subjects showed relatively reduced activity in these prefrontal regions. These data suggest that, within capacity, compensatory mechanisms such as additional prefrontal cortical activity are called upon to maintain proficiency in task performance. As cognitive demand increases, however, they are pushed past a threshold beyond which physiological compensation cannot be made and, a decline in performance occurs.

Adult↗

PubMed2005

Variation in DISC1 affects hippocampal structure and function and increases risk for schizophrenia.

Disrupted-in-schizophrenia 1 (DISC1) is a promising schizophrenia candidate gene expressed predominantly within the hippocampus. We typed 12 single-nucleotide polymorphisms (SNPs) that covered the DISC1 gene. A three-SNP haplotype [hCV219779 (C)-rs821597 (G)-rs821616 (A)] spanning 83 kb of the gene was associated with schizophrenia in a family-based sample (P = 0.002). A common nonconservative SNP (Ser704Cys) (rs821616) within this haplotype was associated with schizophrenia (P = 0.004). Based on primary expression of DISC1 in hippocampus, we hypothesized that allelic variation at Ser704Cys would have a measurable impact on hippocampal structure and function as assayed via specific hippocampus-related intermediate phenotypes. In addition to overtransmission in schizophrenia, the Ser allele was associated with altered hippocampal structure and function in healthy subjects, including reduced hippocampal gray matter volume and altered engagement of the hippocampus during several cognitive tasks assayed with functional magnetic resonance imaging. These convergent data suggest that allelic variation within DISC1, either at Ser704Cys or haplotypes monitored by it, increases the risk for schizophrenia and that the mechanism of this effect involves structural and functional alterations in the hippocampal formation.

Adult↗

PubMed2005

Effect of catechol-O-methyltransferase val158met genotype on attentional control.

The cingulate cortex is richly innervated by dopaminergic projections and plays a critical role in attentional control (AC). Evidence indicates that dopamine enhances the neurophysiological signal-to-noise ratio and that dopaminergic tone in the frontal cortex is critically dependent on catechol-O-methyltransferase (COMT). A functional polymorphism (val158met) in the COMT gene accounts for some of the individual variability in executive function mediated by the dorsolateral prefrontal cortex. We explored the effect of this genetic polymorphism on cingulate engagement during a novel AC task. We found that the COMT val158met polymorphism also affects the function of the cingulate during AC. Individuals homozygous for the high-activity valine ("val") allele show greater activity and poorer performance than val/methionine ("met") heterozygotes, who in turn show greater activity and poorer performance than individuals homozygous for the low-activity met allele, and these effects are most evident at the highest demand for AC. These results indicate that met allele load and presumably enhanced dopaminergic tone improve the "efficiency" of local circuit processing within the cingulate cortex and thereby its function during AC.

Adult↗

PubMed2004

The brain-derived neurotrophic factor val66met polymorphism and variation in human cortical morphology.

A variation in the BDNF gene (val66met) affects the function of BDNF in neurons, predicts variation in human memory, and is associated with several neurological and psychiatric disorders. Here, we show that, in magnetic resonance imaging scans of a large sample of normal individuals, this polymorphism affects the anatomy of the hippocampus and prefrontal cortex, identifying a genetic mechanism of variation in brain morphology related to learning and memory.

Adolescent↗

PubMed2004

Variation in GRM3 affects cognition, prefrontal glutamate, and risk for schizophrenia.

GRM3, a metabotropic glutamate receptor-modulating synaptic glutamate, is a promising schizophrenia candidate gene. In a family-based association study, a common GRM3 haplotype was strongly associated with schizophrenia (P = 0.0001). Within this haplotype, the A allele of single-nucleotide polymorphism (SNP) 4 (hCV11245618) in intron 2 was slightly overtransmitted to probands (P = 0.02). We studied the effects of this SNP on neurobiological traits related to risk for schizophrenia and glutamate neurotransmission. The SNP4 A allele was associated with poorer performance on several cognitive tests of prefrontal and hippocampal function. The physiological basis of this effect was assessed with functional MRI, which showed relatively deleterious activation patterns in both cortical regions in control subjects homozygous for the SNP4 A allele. We next looked at SNP4's effects on two indirect measures of prefrontal glutamate neurotransmission. Prefrontal N-acetylaspartate, an in vivo MRI measure related to synaptic activity and closely correlated with tissue glutamate, was lower in SNP4 AA homozygotes. In postmortem human prefrontal cortex, AA homozygotes had lower mRNA levels of the glial glutamate transporter EAAT2, a protein regulated by GRM3 that critically modulates synaptic glutamate. Effects of SNP4 on prefrontal GRM3 mRNA and protein levels were marginal. Resequencing revealed no missense or splice-site SNPs, suggesting that the intronic SNP4 or related haplotypes may exert subtle regulatory effects on GRM3 transcription. These convergent data point to a specific molecular pathway by which GRM3 genotype alters glutamate neurotransmission, prefrontal and hippocampal physiology and cognition, and thereby increased risk for schizophrenia.

Adult↗

PubMed2004

Functional lateralization of the sensorimotor cortex in patients with schizophrenia: effects of treatment with olanzapine.

BACKGROUND: Earlier cross-sectional studies with functional magnetic resonance imaging (fMRI) in treated patients with schizophrenia have reported abnormalities of cortical motor processing, including reduced lateralization of primary sensory motor cortex. The objective of the present longitudinal study was to evaluate whether such cortical abnormalities represent state or trait phenomena of the disorder. METHODS: Seventeen acutely ill, previously untreated patients were studied after 4 weeks and after 8 weeks of olanzapine therapy. Seventeen matched healthy subjects served as control subjects. All subjects underwent two fMRI scans 4 weeks apart during a visually paced motor task using a simple periodic block design. Functional magnetic resonance imaging data were analyzed in Statistical Parametric Mapping (SPM99). Region of interest analyses were used to determine a laterality quotient (an index of lateralization) of motor cortical regions. RESULTS: The fMRI data indicated that patients had reduced activation of the primary sensory motor cortex at 4 weeks but not at 8 weeks; however, the laterality quotient in the primary sensory motor cortex was reduced in patients at both time points. CONCLUSIONS: These results suggest that some cortical abnormalities during motor processing represent state phenomena, whereas reduced functional lateralization of the primary sensory motor cortex represents an enduring trait of schizophrenia.

Adolescent↗

PubMed2004

Interaction of COMT (Val(108/158)Met) genotype and olanzapine treatment on prefrontal cortical function in patients with schizophrenia.

OBJECTIVE: Deficits in working memory and in prefrontal cortical physiology are important outcome measures in schizophrenia, and both have been associated with dopamine dysregulation and with a functional polymorphism (Val(108/158)Met) in the catechol O-methyltransferase (COMT) gene that affects dopamine inactivation in the prefrontal cortex. The purpose of the present study was to evaluate in patients with schizophrenia the effect of COMT genotype on symptom variation, working memory performance, and prefrontal cortical physiology in response to treatment with an atypical antipsychotic drug. METHOD: Thirty patients with acute untreated schizophrenia were clinically evaluated with the Positive and Negative Syndrome Scale, underwent COMT Val/Met genotyping, and entered an 8-week prospective study of olanzapine treatment. Twenty patients completed two 3-T functional magnetic resonance imaging scans at 4 and 8 weeks during performance of N-back working memory tasks. RESULTS: There was a significant interaction of COMT genotype and the effects of olanzapine on prefrontal cortical function. Met allele load predicted improvement in working memory performance and prefrontal physiology after 8 weeks of treatment. A similar effect was found also for negative symptoms assessed with the Positive and Negative Syndrome Scale. CONCLUSIONS: These results suggest that a genetically determined variation in prefrontal dopamine catabolism impacts the therapeutic profile of olanzapine.

Adult↗

PubMed2003

Brain-derived neurotrophic factor val66met polymorphism affects human memory-related hippocampal activity and predicts memory performance.

BDNF plays a critical role in activity-dependent neuroplasticity underlying learning and memory in the hippocampus. A frequent single nucleotide polymorphism in the targeting region of the human BDNF gene (val66met) has been associated with abnormal intracellular trafficking and regulated secretion of BDNF in cultured hippocampal neurons transfected with the met allele. In addition, the met allele has been associated with abnormal hippocampal neuronal function as well as impaired episodic memory in human subjects, but a direct effect of BDNF alleles on hippocampal processing of memory has not been demonstrated. We studied the relationship of the BDNF val66met genotype and hippocampal activity during episodic memory processing using blood oxygenation level-dependent functional magnetic resonance imaging and a declarative memory task in healthy individuals. Met carriers exhibited relatively diminished hippocampal engagement in comparison with val homozygotes during both encoding and retrieval processes. Remarkably, the interaction between the BDNF val66met genotype and the hippocampal response during encoding accounted for 25% of the total variation in recognition memory performance. These data implicate a specific genetic mechanism for substantial normal variation in human declarative memory and suggest that the basic effects of BDNF signaling on hippocampal function in experimental animals are important in humans.

Adult↗

PubMed2003

Neuronal pathology in the hippocampal area of patients with bipolar disorder: a study with proton magnetic resonance spectroscopic imaging.

BACKGROUND: The brain regions involved in the pathophysiology of bipolar disorder have not been definitively determined. Previous studies have suggested possible involvement of the hippocampus and of prefrontal regions. Proton magnetic resonance spectroscopic imaging ((1)H-MRSI) allows measurement of N-acetylaspartate (NAA, marker of neuronal integrity), choline-containing compounds (CHO), and creatine+phosphocreatine (CRE) in multiple brain regions. The objective of this study was to assess possible NAA reductions in hippocampus and prefrontal regions in patients with bipolar disorder. METHODS: We studied 17 patients with bipolar disorder and 17 age- and gender-matched healthy subjects on a 1.5-T nuclear magnetic resonance (NMR) machine. With (1)H-MRSI we measured ratios of areas under the metabolite peaks of the proton spectra (i.e., NAA/CRE, NAA/CHO, CHO/CRE) for multiple cortical and subcortical regions. RESULTS: Patients showed significant reductions of NAA/CRE bilaterally in the hippocampus. There were no significant changes in CHO/CRE or in NAA ratios in any other area sampled. CONCLUSIONS: This study shows that patients with bipolar disorder have a regional reduction of NAA relative signals, suggesting neuronal damage or malfunction of the hippocampus. As suggested by other studies, neuronal pathology in the hippocampus may be involved in the pathophysiology of bipolar disorder and in susceptibility to psychosis.

Adult↗

PubMed2003

Catechol O-methyltransferase val158-met genotype and individual variation in the brain response to amphetamine.

Monamines subserve many critical roles in the brain, and monoaminergic drugs such as amphetamine have a long history in the treatment of neuropsychiatric disorders and also as a substance of abuse. The clinical effects of amphetamine are quite variable, from positive effects on mood and cognition in some individuals, to negative responses in others, perhaps related to individual variations in monaminergic function and monoamine system genes. We explored the effect of a functional polymorphism (val(158)-met) in the catechol O-methyltransferase gene, which has been shown to modulate prefrontal dopamine in animals and prefrontal cortical function in humans, on the modulatory actions of amphetamine on the prefrontal cortex. Amphetamine enhanced the efficiency of prefrontal cortex function assayed with functional MRI during a working memory task in subjects with the high enzyme activity val/val genotype, who presumably have relatively less prefrontal synaptic dopamine, at all levels of task difficulty. In contrast, in subjects with the low activity met/met genotype who tend to have superior baseline prefrontal function, the drug had no effect on cortical efficiency at low-to-moderate working memory load and caused deterioration at high working memory load. These data illustrate an application of functional neuroimaging in pharmacogenomics and extend basic evidence of an inverted-"U" functional-response curve to increasing dopamine signaling in the prefrontal cortex. Further, individuals with the met/met catechol O-methyltransferase genotype appear to be at increased risk for an adverse response to amphetamine.

Amino Acid Substitution↗

PubMed2003

The BDNF val66met polymorphism affects activity-dependent secretion of BDNF and human memory and hippocampal function.

Brain-derived neurotrophic factor (BDNF) modulates hippocampal plasticity and hippocampal-dependent memory in cell models and in animals. We examined the effects of a valine (val) to methionine (met) substitution in the 5' pro-region of the human BDNF protein. In human subjects, the met allele was associated with poorer episodic memory, abnormal hippocampal activation assayed with fMRI, and lower hippocampal n-acetyl aspartate (NAA), assayed with MRI spectroscopy. Neurons transfected with met-BDNF-GFP showed lower depolarization-induced secretion, while constitutive secretion was unchanged. Furthermore, met-BDNF-GFP failed to localize to secretory granules or synapses. These results demonstrate a role for BDNF and its val/met polymorphism in human memory and hippocampal function and suggest val/met exerts these effects by impacting intracellular trafficking and activity-dependent secretion of BDNF.

Alleles↗