Richard Coppola - Academia.edu (original) (raw)
Papers by Richard Coppola
Archives of Neurology, 1991
Psychiatry Research: Neuroimaging, Aug 1, 2016
Functional neuroimaging techniques including magnetoencephalography (MEG) have demonstrated that ... more Functional neuroimaging techniques including magnetoencephalography (MEG) have demonstrated that the brain is organized into networks displaying correlated activity. Group connectivity differences between healthy controls and participants with major depressive disorder (MDD) can be detected using temporal independent components analysis (ICA) on beta-bandpass filtered Hilbert envelope MEG data. However, the response of these networks to treatment is unknown. Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, exerts rapid antidepressant effects. We obtained MEG recordings before and after open-label infusion of 0.5mg/kg ketamine in MDD subjects (N=13) and examined networks previously shown to differ between healthy individuals and those with MDD. Connectivity between the amygdala and an insulo-temporal component decreased post-ketamine in MDD subjects towards that observed in control subjects at baseline. Decreased baseline connectivity of the subgenual anterior cingulate cortex (sgACC) with a bilateral precentral network had previously been observed in MDD compared to healthy controls, and the change in connectivity post-ketaminewas proportional to the
Advances in Alcohol & Substance Abuse, 1988
Imaging in vivo aspects of brain structure and function hold great promise for the study of alcoh... more Imaging in vivo aspects of brain structure and function hold great promise for the study of alcoholism. Computerized axial tomography and magnetic resonance imaging have been used successfully to demonstrate structural abnormalities in alcoholic patients. Positron emission tomography and topographic images of electrical and magnetic activity are useful measures of brain function that could be applied more rigorously to the study of alcoholism. Interrelating various types of imaging data is an important area that is still in the developmental stage.
Neuropsychobiology, 1996
In elderly subjects there is a vigilance decrease from morning to noon which was used in a clinic... more In elderly subjects there is a vigilance decrease from morning to noon which was used in a clinical pharmacological model as a state condition to verify vigilance-enhancing effects of an antidementia drug. In this model the effects of Memantine (20 mg, single-dose application) on the quantified EEG were investigated in 16 elderly (mean age: 65 ± 5 years), healthy subjects
Neuropsychobiology, 2008
In a double-blind fourfold crossover design, 11 subjects were randomly assigned to placebo, 10 mg... more In a double-blind fourfold crossover design, 11 subjects were randomly assigned to placebo, 10 mg diazepam, 75 mg amitriptyline, and 75 mg chlorpromazine. During a simple vigilance task, 12 midline and left hemisphere leads were recorded before and 3 h after drug administration. The EEG was quantified by spectrum analysis, the topographic structure displayed by brain mapping techniques, and the results compared with earlier studies which used the same design and drugs. Diazepam showed the expected increase in beta; however, fast beta was increased as much as slow beta. Amitriptyline showed an increase of slow wave power and a reduction of alpha. In contrast to earlier studies, a decrease of fast beta was found. In addition, the spatial pattern of alpha changed from an occipital to a parietal maximum. Chlorpromazine showed an increase in the theta band. In occipital regions, there was a small decrease of fast beta; however, centrally there was an increase of both slow and fast beta. These results were confirmed by a multivariate analysis of variance.
Archives of General Psychiatry, 1987
Several topographic mapping studies of electroencephalographic (EEG) power spectra have reported ... more Several topographic mapping studies of electroencephalographic (EEG) power spectra have reported increased slow (delta) activity in the frontal regions of schizophrenic patients. Using supraorbital and lateral canthus electrodes to detect eye movement, we deleted EEG epochs during eye movement in 15 medication-free patients with schizophrenia and in 13 normal control subjects. Power spectral analysis of the 28-channel EEG demonstrated a diffuse mild increase in delta activity in schizophrenic patients compared with normal control subjects but no tendency for frontal localization of this slow activity. There were no differences between schizophrenic patients and normal control subjects in other frequency bands. These results, which replicate earlier findings of increased delta activity in schizophrenia, emphasize the importance of excluding the slow activity due to eye movement in the comparisons of summed EEG spectra. This emphasis can best be ensured by equating the summed spectra from extraocular movement channels of experimental and control groups.
NeuroImage, Sep 1, 2015
Functional magnetic resonance imaging (fMRI) studies have revealed the existence of robust, inter... more Functional magnetic resonance imaging (fMRI) studies have revealed the existence of robust, interconnected brain networks exhibiting correlated low frequency fluctuations during rest, which can be derived by examining inherent spatio-temporal patterns in functional scans independent of any a priori model. In order to explore the electrophysiological underpinnings of these networks, analogous techniques have recently been applied to magnetoencephalography (MEG) data, revealing similar networks that exhibit correlated low frequency fluctuations in the power envelope of beta band (14-30Hz) power. However, studies to date using this technique have concentrated on healthy subjects, and no method has yet been presented for group comparisons. We extended the ICA resting state MEG method to enable group comparisons, and demonstrate the technique in a sample of subjects with major depressive disorder (MDD). We found that the intrinsic resting state networks evident in fMRI appeared to be disrupted in individuals with MDD compared to healthy participants, particularly in the subgenual cingulate, although the electrophysiological correlates of this are unknown. Networks extracted from a combined group of healthy and MDD participants were examined for differences between groups. Individuals with MDD showed reduced correlations between the subgenual anterior cingulate (sgACC) and hippocampus in a network with primary nodes in the precentral and middle frontal gyri.
Brain connectivity, Aug 1, 2015
In typical magnetoencephalography and/or electroencephalography functional connectivity analysis,... more In typical magnetoencephalography and/or electroencephalography functional connectivity analysis, researchers select one of several methods that measure a relationship between regions to determine connectivity, such as coherence, power correlations, and others. However, it is largely unknown if some are more suited than others for various types of investigations. In this study, the authors investigate seven connectivity metrics to evaluate which, if any, are sensitive to audiovisual integration by contrasting connectivity when tracking an audiovisual object versus connectivity when tracking a visual object uncorrelated with the auditory stimulus. The authors are able to assess the metrics' performances at detecting audiovisual integration by investigating connectivity between auditory and visual areas. Critically, the authors perform their investigation on a whole-cortex all-to-all mapping, avoiding confounds introduced in seed selection. The authors find that amplitude-based connectivity measures in the beta band detect strong connections between visual and auditory areas during audiovisual integration, specifically between V4/V5 and auditory cortices in the right hemisphere. Conversely, phase-based connectivity measures in the beta band as well as phase and power measures in alpha, gamma, and theta do not show connectivity between audiovisual areas. The authors postulate that while beta power correlations detect audiovisual integration in the current experimental context, it may not always be the best measure to detect connectivity. Instead, it is likely that the brain utilizes a variety of mechanisms in neuronal communication that may produce differential types of temporal relationships.
Science, 1996
Tourette syndrome, a chronic tic disorder with autosomal dominant inheritance, exhibits considera... more Tourette syndrome, a chronic tic disorder with autosomal dominant inheritance, exhibits considerable phenotypic variability even within monozygotic twin pairs. The origins of this variability remain unclear. Recent findings have implicated the caudate nucleus as a locus of pathology, and pharmacological evidence supports dopaminergic involvement. Within monozygotic twins discordant for Tourette syndrome severity, differences in D2 dopamine receptor binding in the head of the caudate nucleus predicted differences in phenotypic severity (r = 0.99); this relation was not observed in putamen. These data may link Tourette syndrome with a spectrum of neuropsychiatric disorders that involve associative striatal circuitry.
Biological Psychiatry, 1993
The authors performed spectral analysis of electroencephalograms (EEG), recorded awake, with eyes... more The authors performed spectral analysis of electroencephalograms (EEG), recorded awake, with eyes closed, in 13 patients with schizophrenia and 9 age-matched individuals without psychiatric diagnosis. We tested several possible parameterizations of the data, and two datareduction strategies; these yielded similar results. Comparison of the two groups revealed a relative increase in alpha frequency activi~ in the frontal regions in the patient group. The authors believe that this finding is consistent with data from neuropsychologic tests, metabolic imaging studies, and evoked potential studies that suggest impaired activation of frontal brain areas in patients with schizophrenia.
Archives of Neurology, 1991
A high-affinity muscarinic receptor antagonist, 123IQNB (3-quinuclidinyl-4-iodobenzilate labeled ... more A high-affinity muscarinic receptor antagonist, 123IQNB (3-quinuclidinyl-4-iodobenzilate labeled with iodine 123), was used with single photon emission computed tomography to image muscarinic acetylcholine receptors in 14 patients with dementia and in 11 healthy controls. High-resolution single photon emission computed tomographic scanning was performed 21 hours after the intravenous administration of approximately 5 mCi of IQNB. In normal subjects, the images of retained ligand showed a consistent regional pattern that correlated with postmortem studies of the relative distribution of muscarinic receptors in the normal human brain, having high radioactivity counts in the basal ganglia, occipital cortex, and insular cortex, low counts in the thalamus, and virtually no counts in the cerebellum. Eight of 12 patients with a clinical diagnosis of Alzheimer's disease had obvious focal cortical defects in either frontal or posterior temporal cortex. Both patients with a clinical diagnosis of Pick's disease had obvious frontal and anterior temporal defects. A region of interest statistical analysis of relative regional activity revealed a significant reduction bilaterally in the posterior temporal cortex of the patients with Alzheimer's disease compared with controls. This study demonstrates the practicability of acetylcholine receptor imaging with 123IQNB and single photon emission computed tomography. The data suggest that focal abnormalities in muscarinic binding in vivo may characterize some patients with Alzheimer's disease and Pick's disease, but further studies are needed to address questions about partial volume artifacts and receptor quantification.
Archives of General Psychiatry, 1990
To the Editor.— Posner and colleagues 1 have made considerable strides studying how the parietal ... more To the Editor.— Posner and colleagues 1 have made considerable strides studying how the parietal lobe controls covert shifts of attention in the visual-spatial domain. They have recently used the methods developed from using tasks that have simple separable cognitive components in the study of hemispheric control of attention in schizophrenia. 2 As part of this study, 12 schizophrenic patients were compared with 30 normal control subjects in a spatial-orienting task. Mean reaction time (RT) was measured as a function of cue condition (no cue, valid, or invalid), cue to target interval (100 or 800 milliseconds), and visual field (VF) (left or right). The normal subjects showed the expected RT advantage for a valid cue that was independent of VF but slightly elevated for the shorter cue interval. The schizophrenic subjects showed no significant difference between the VFs for the valid cue but a strong difference between VFs in
Frontiers in Computational Neuroscience, 2013
Complex networks have been observed to comprise small-world properties, believed to represent an ... more Complex networks have been observed to comprise small-world properties, believed to represent an optimal organization of local specialization and global integration of information processing at reduced wiring cost. Here, we applied magnitude squared coherence to resting magnetoencephalographic time series in reconstructed source space, acquired from controls and patients with schizophrenia, and generated frequency-dependent adjacency matrices modeling functional connectivity between virtual channels. After configuring undirected binary and weighted graphs, we found that all human networks demonstrated highly localized clustering and short characteristic path lengths. The most conservatively thresholded networks showed efficient wiring, with topographical distance between connected vertices amounting to one-third as observed in surrogate randomized topologies. Nodal degrees of the human networks conformed to a heavy-tailed exponentially truncated power-law, compatible with the existence of hubs, which included theta and alpha bilateral cerebellar tonsil, beta and gamma bilateral posterior cingulate, and bilateral thalamus across all frequencies. We conclude that all networks showed small-worldness, minimal physical connection distance, and skewed degree distributions characteristic of physically-embedded networks, and that these calculations derived from graph theoretical mathematics did not quantifiably distinguish between subject populations, independent of bandwidth. However, post-hoc measurements of edge computations at the scale of the individual vertex revealed trends of reduced gamma connectivity across the posterior medial parietal cortex in patients, an observation consistent with our prior resting activation study that found significant reduction of synthetic aperture magnetometry gamma power across similar regions. The basis of these small differences remains unclear.
The 26th Annual International Conference of the IEEE Engineering in Medicine and Biology Society
The interpretation of MEG/EEG data in terms of brain connectivity is largely obscured by artefact... more The interpretation of MEG/EEG data in terms of brain connectivity is largely obscured by artefacts of volume conduction, i.e. by the fact that a single source is observable in many channels. Here, we analyze a measure which is insensitive to spurious connectivity arising from volume conducted "self-interaction". For rhythmic data such a measure can be given by the imaginary part of the cross-spectrum between EEG/MEG channels. For the derivation we essentially exploit that a signal is not time-lagged to itself. To localize the sources of this observed interaction we fit a model cross-spectrum consisting of N interacting dipoles to the sample cross-spectrum. The relation to the maximum likelihood estimator will be discussed in detail. The method is illustrated for MEG data of human alpha rhythm in eyes closed condition. The eigenvalues of the imaginary cross-spectrum clearly indicate the presence of at least 4 necessarily interacting sources. Fits of 2 to 6 dipoles in a realistic volume conductor all resulted in locations scattered in the mesial part of the occipital lobe.
Schizophrenia Research, 2001
Previous studies have suggested that schizophrenic patients show resting EEG changes such as freq... more Previous studies have suggested that schizophrenic patients show resting EEG changes such as frequency-slowing and decreased coherence in the frontal and temporal area. We sought to determine whether these findings are also found in clinically unaffected siblings of schizophrenics and estimate heritability by calculating relative risk. We investigated two independent data sets: (1) from the NIMH St. Elisabeths campus (59
European Neuropsychopharmacology, 1996
European Neuropsychopharmacology, 1999
Breier A et al. (1994). Effects of clozapine on positive and negative symptoms in outpatients wit... more Breier A et al. (1994). Effects of clozapine on positive and negative symptoms in outpatients with schizophrenia. Am J Psychiatry, 151: 2&26.
Archives of Neurology, 1991
Psychiatry Research: Neuroimaging, Aug 1, 2016
Functional neuroimaging techniques including magnetoencephalography (MEG) have demonstrated that ... more Functional neuroimaging techniques including magnetoencephalography (MEG) have demonstrated that the brain is organized into networks displaying correlated activity. Group connectivity differences between healthy controls and participants with major depressive disorder (MDD) can be detected using temporal independent components analysis (ICA) on beta-bandpass filtered Hilbert envelope MEG data. However, the response of these networks to treatment is unknown. Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, exerts rapid antidepressant effects. We obtained MEG recordings before and after open-label infusion of 0.5mg/kg ketamine in MDD subjects (N=13) and examined networks previously shown to differ between healthy individuals and those with MDD. Connectivity between the amygdala and an insulo-temporal component decreased post-ketamine in MDD subjects towards that observed in control subjects at baseline. Decreased baseline connectivity of the subgenual anterior cingulate cortex (sgACC) with a bilateral precentral network had previously been observed in MDD compared to healthy controls, and the change in connectivity post-ketaminewas proportional to the
Advances in Alcohol & Substance Abuse, 1988
Imaging in vivo aspects of brain structure and function hold great promise for the study of alcoh... more Imaging in vivo aspects of brain structure and function hold great promise for the study of alcoholism. Computerized axial tomography and magnetic resonance imaging have been used successfully to demonstrate structural abnormalities in alcoholic patients. Positron emission tomography and topographic images of electrical and magnetic activity are useful measures of brain function that could be applied more rigorously to the study of alcoholism. Interrelating various types of imaging data is an important area that is still in the developmental stage.
Neuropsychobiology, 1996
In elderly subjects there is a vigilance decrease from morning to noon which was used in a clinic... more In elderly subjects there is a vigilance decrease from morning to noon which was used in a clinical pharmacological model as a state condition to verify vigilance-enhancing effects of an antidementia drug. In this model the effects of Memantine (20 mg, single-dose application) on the quantified EEG were investigated in 16 elderly (mean age: 65 ± 5 years), healthy subjects
Neuropsychobiology, 2008
In a double-blind fourfold crossover design, 11 subjects were randomly assigned to placebo, 10 mg... more In a double-blind fourfold crossover design, 11 subjects were randomly assigned to placebo, 10 mg diazepam, 75 mg amitriptyline, and 75 mg chlorpromazine. During a simple vigilance task, 12 midline and left hemisphere leads were recorded before and 3 h after drug administration. The EEG was quantified by spectrum analysis, the topographic structure displayed by brain mapping techniques, and the results compared with earlier studies which used the same design and drugs. Diazepam showed the expected increase in beta; however, fast beta was increased as much as slow beta. Amitriptyline showed an increase of slow wave power and a reduction of alpha. In contrast to earlier studies, a decrease of fast beta was found. In addition, the spatial pattern of alpha changed from an occipital to a parietal maximum. Chlorpromazine showed an increase in the theta band. In occipital regions, there was a small decrease of fast beta; however, centrally there was an increase of both slow and fast beta. These results were confirmed by a multivariate analysis of variance.
Archives of General Psychiatry, 1987
Several topographic mapping studies of electroencephalographic (EEG) power spectra have reported ... more Several topographic mapping studies of electroencephalographic (EEG) power spectra have reported increased slow (delta) activity in the frontal regions of schizophrenic patients. Using supraorbital and lateral canthus electrodes to detect eye movement, we deleted EEG epochs during eye movement in 15 medication-free patients with schizophrenia and in 13 normal control subjects. Power spectral analysis of the 28-channel EEG demonstrated a diffuse mild increase in delta activity in schizophrenic patients compared with normal control subjects but no tendency for frontal localization of this slow activity. There were no differences between schizophrenic patients and normal control subjects in other frequency bands. These results, which replicate earlier findings of increased delta activity in schizophrenia, emphasize the importance of excluding the slow activity due to eye movement in the comparisons of summed EEG spectra. This emphasis can best be ensured by equating the summed spectra from extraocular movement channels of experimental and control groups.
NeuroImage, Sep 1, 2015
Functional magnetic resonance imaging (fMRI) studies have revealed the existence of robust, inter... more Functional magnetic resonance imaging (fMRI) studies have revealed the existence of robust, interconnected brain networks exhibiting correlated low frequency fluctuations during rest, which can be derived by examining inherent spatio-temporal patterns in functional scans independent of any a priori model. In order to explore the electrophysiological underpinnings of these networks, analogous techniques have recently been applied to magnetoencephalography (MEG) data, revealing similar networks that exhibit correlated low frequency fluctuations in the power envelope of beta band (14-30Hz) power. However, studies to date using this technique have concentrated on healthy subjects, and no method has yet been presented for group comparisons. We extended the ICA resting state MEG method to enable group comparisons, and demonstrate the technique in a sample of subjects with major depressive disorder (MDD). We found that the intrinsic resting state networks evident in fMRI appeared to be disrupted in individuals with MDD compared to healthy participants, particularly in the subgenual cingulate, although the electrophysiological correlates of this are unknown. Networks extracted from a combined group of healthy and MDD participants were examined for differences between groups. Individuals with MDD showed reduced correlations between the subgenual anterior cingulate (sgACC) and hippocampus in a network with primary nodes in the precentral and middle frontal gyri.
Brain connectivity, Aug 1, 2015
In typical magnetoencephalography and/or electroencephalography functional connectivity analysis,... more In typical magnetoencephalography and/or electroencephalography functional connectivity analysis, researchers select one of several methods that measure a relationship between regions to determine connectivity, such as coherence, power correlations, and others. However, it is largely unknown if some are more suited than others for various types of investigations. In this study, the authors investigate seven connectivity metrics to evaluate which, if any, are sensitive to audiovisual integration by contrasting connectivity when tracking an audiovisual object versus connectivity when tracking a visual object uncorrelated with the auditory stimulus. The authors are able to assess the metrics' performances at detecting audiovisual integration by investigating connectivity between auditory and visual areas. Critically, the authors perform their investigation on a whole-cortex all-to-all mapping, avoiding confounds introduced in seed selection. The authors find that amplitude-based connectivity measures in the beta band detect strong connections between visual and auditory areas during audiovisual integration, specifically between V4/V5 and auditory cortices in the right hemisphere. Conversely, phase-based connectivity measures in the beta band as well as phase and power measures in alpha, gamma, and theta do not show connectivity between audiovisual areas. The authors postulate that while beta power correlations detect audiovisual integration in the current experimental context, it may not always be the best measure to detect connectivity. Instead, it is likely that the brain utilizes a variety of mechanisms in neuronal communication that may produce differential types of temporal relationships.
Science, 1996
Tourette syndrome, a chronic tic disorder with autosomal dominant inheritance, exhibits considera... more Tourette syndrome, a chronic tic disorder with autosomal dominant inheritance, exhibits considerable phenotypic variability even within monozygotic twin pairs. The origins of this variability remain unclear. Recent findings have implicated the caudate nucleus as a locus of pathology, and pharmacological evidence supports dopaminergic involvement. Within monozygotic twins discordant for Tourette syndrome severity, differences in D2 dopamine receptor binding in the head of the caudate nucleus predicted differences in phenotypic severity (r = 0.99); this relation was not observed in putamen. These data may link Tourette syndrome with a spectrum of neuropsychiatric disorders that involve associative striatal circuitry.
Biological Psychiatry, 1993
The authors performed spectral analysis of electroencephalograms (EEG), recorded awake, with eyes... more The authors performed spectral analysis of electroencephalograms (EEG), recorded awake, with eyes closed, in 13 patients with schizophrenia and 9 age-matched individuals without psychiatric diagnosis. We tested several possible parameterizations of the data, and two datareduction strategies; these yielded similar results. Comparison of the two groups revealed a relative increase in alpha frequency activi~ in the frontal regions in the patient group. The authors believe that this finding is consistent with data from neuropsychologic tests, metabolic imaging studies, and evoked potential studies that suggest impaired activation of frontal brain areas in patients with schizophrenia.
Archives of Neurology, 1991
A high-affinity muscarinic receptor antagonist, 123IQNB (3-quinuclidinyl-4-iodobenzilate labeled ... more A high-affinity muscarinic receptor antagonist, 123IQNB (3-quinuclidinyl-4-iodobenzilate labeled with iodine 123), was used with single photon emission computed tomography to image muscarinic acetylcholine receptors in 14 patients with dementia and in 11 healthy controls. High-resolution single photon emission computed tomographic scanning was performed 21 hours after the intravenous administration of approximately 5 mCi of IQNB. In normal subjects, the images of retained ligand showed a consistent regional pattern that correlated with postmortem studies of the relative distribution of muscarinic receptors in the normal human brain, having high radioactivity counts in the basal ganglia, occipital cortex, and insular cortex, low counts in the thalamus, and virtually no counts in the cerebellum. Eight of 12 patients with a clinical diagnosis of Alzheimer's disease had obvious focal cortical defects in either frontal or posterior temporal cortex. Both patients with a clinical diagnosis of Pick's disease had obvious frontal and anterior temporal defects. A region of interest statistical analysis of relative regional activity revealed a significant reduction bilaterally in the posterior temporal cortex of the patients with Alzheimer's disease compared with controls. This study demonstrates the practicability of acetylcholine receptor imaging with 123IQNB and single photon emission computed tomography. The data suggest that focal abnormalities in muscarinic binding in vivo may characterize some patients with Alzheimer's disease and Pick's disease, but further studies are needed to address questions about partial volume artifacts and receptor quantification.
Archives of General Psychiatry, 1990
To the Editor.— Posner and colleagues 1 have made considerable strides studying how the parietal ... more To the Editor.— Posner and colleagues 1 have made considerable strides studying how the parietal lobe controls covert shifts of attention in the visual-spatial domain. They have recently used the methods developed from using tasks that have simple separable cognitive components in the study of hemispheric control of attention in schizophrenia. 2 As part of this study, 12 schizophrenic patients were compared with 30 normal control subjects in a spatial-orienting task. Mean reaction time (RT) was measured as a function of cue condition (no cue, valid, or invalid), cue to target interval (100 or 800 milliseconds), and visual field (VF) (left or right). The normal subjects showed the expected RT advantage for a valid cue that was independent of VF but slightly elevated for the shorter cue interval. The schizophrenic subjects showed no significant difference between the VFs for the valid cue but a strong difference between VFs in
Frontiers in Computational Neuroscience, 2013
Complex networks have been observed to comprise small-world properties, believed to represent an ... more Complex networks have been observed to comprise small-world properties, believed to represent an optimal organization of local specialization and global integration of information processing at reduced wiring cost. Here, we applied magnitude squared coherence to resting magnetoencephalographic time series in reconstructed source space, acquired from controls and patients with schizophrenia, and generated frequency-dependent adjacency matrices modeling functional connectivity between virtual channels. After configuring undirected binary and weighted graphs, we found that all human networks demonstrated highly localized clustering and short characteristic path lengths. The most conservatively thresholded networks showed efficient wiring, with topographical distance between connected vertices amounting to one-third as observed in surrogate randomized topologies. Nodal degrees of the human networks conformed to a heavy-tailed exponentially truncated power-law, compatible with the existence of hubs, which included theta and alpha bilateral cerebellar tonsil, beta and gamma bilateral posterior cingulate, and bilateral thalamus across all frequencies. We conclude that all networks showed small-worldness, minimal physical connection distance, and skewed degree distributions characteristic of physically-embedded networks, and that these calculations derived from graph theoretical mathematics did not quantifiably distinguish between subject populations, independent of bandwidth. However, post-hoc measurements of edge computations at the scale of the individual vertex revealed trends of reduced gamma connectivity across the posterior medial parietal cortex in patients, an observation consistent with our prior resting activation study that found significant reduction of synthetic aperture magnetometry gamma power across similar regions. The basis of these small differences remains unclear.
The 26th Annual International Conference of the IEEE Engineering in Medicine and Biology Society
The interpretation of MEG/EEG data in terms of brain connectivity is largely obscured by artefact... more The interpretation of MEG/EEG data in terms of brain connectivity is largely obscured by artefacts of volume conduction, i.e. by the fact that a single source is observable in many channels. Here, we analyze a measure which is insensitive to spurious connectivity arising from volume conducted "self-interaction". For rhythmic data such a measure can be given by the imaginary part of the cross-spectrum between EEG/MEG channels. For the derivation we essentially exploit that a signal is not time-lagged to itself. To localize the sources of this observed interaction we fit a model cross-spectrum consisting of N interacting dipoles to the sample cross-spectrum. The relation to the maximum likelihood estimator will be discussed in detail. The method is illustrated for MEG data of human alpha rhythm in eyes closed condition. The eigenvalues of the imaginary cross-spectrum clearly indicate the presence of at least 4 necessarily interacting sources. Fits of 2 to 6 dipoles in a realistic volume conductor all resulted in locations scattered in the mesial part of the occipital lobe.
Schizophrenia Research, 2001
Previous studies have suggested that schizophrenic patients show resting EEG changes such as freq... more Previous studies have suggested that schizophrenic patients show resting EEG changes such as frequency-slowing and decreased coherence in the frontal and temporal area. We sought to determine whether these findings are also found in clinically unaffected siblings of schizophrenics and estimate heritability by calculating relative risk. We investigated two independent data sets: (1) from the NIMH St. Elisabeths campus (59
European Neuropsychopharmacology, 1996
European Neuropsychopharmacology, 1999
Breier A et al. (1994). Effects of clozapine on positive and negative symptoms in outpatients wit... more Breier A et al. (1994). Effects of clozapine on positive and negative symptoms in outpatients with schizophrenia. Am J Psychiatry, 151: 2&26.