PubMed HealthSearch

Biomedical subjects

C Shagass

Publications and source records attributed to C Shagass.

At least 19 recordsLinked to original sources

Quantitative EEG in elderly depressives.

Thirty-one elderly depressive patients were evaluated with topographic, quantitative EEG using relative measures, absolute measures, and computations of interhemispheric asymmetry and interhemispheric coherence in four frequency bands: delta, theta, alpha and beta. Patients were found to have lower than normal delta, higher than normal theta, higher than normal alpha and lower than normal beta values. EEG values were greater over the left than the right hemisphere in theta, alpha and beta bands. Lower than normal anterior interhemispheric coherence was found in all four frequency bands.

Aged

Evoked potential topography in major depression. I. Comparisons with nonpatients and schizophrenics.

This study compared evoked potential (EP) topography in major depression (MD), schizophrenia and nonpatient controls. EPs to four kinds of stimuli were recorded from 15 locations. Patients were 69 MDs and 52 schizophrenics, currently unmedicated. EP waveforms of 195 controls were subjected to principal component factor analysis (PCA). The structures of 32 factors so extracted have been shown to encompass the data space of disparate groups; they were used to compute factor scores for all subjects. Age- and gender-matched groups were compared. Factor scores were normalized across leads (Z-transform) to distinguish between topographic and mean level differences. Topographic differences (P < 0.05) between MD and controls were demonstrated for scores of 8 factors, with 2 others at P = 0.053. Unlike those for schizophrenia/control comparisons, these topographic differences did not converge regionally in MD. EP findings were not related to duration of withdrawal from drugs. There were few differences between bipolar and unipolar patients. Topographies of 5 factors differed between MDs and schizophrenics; these involved all modalities and reflected long latency, cognition-related events, such as P300. These topographic differences were antero-posterior (AP); values were greater posteriorly in MDs and anteriorly in schizophrenics. Deviant AP gradients appear specific to MD; gradients were similar in schizophrenics and controls.

Adolescent

Evoked potential topography in major depression. II. Comparisons between subgroups.

Brief Psychiatric Rating Scale (BPRS) ratings of 69 patients with major depression (MD) were employed in an attempt to define subgroups of MD with more homogeneous evoked potential (EP) findings than the MD group as a whole. Correlations were computed between 6 BPRS ratings and scores for 32 EP factors; 14 correlations were significant. These indicated mainly that EP values were related to severity of depression. When age- and gender-matched groups of MDs with above- and below-median depressive mood (D) ratings were compared with controls, 3 of the 10 factors differing significantly between groups gave evidence of two different subgroups of MD. EPs of these subgroups differed from those of controls in opposite directions. Such bidirectional differences from normal suggest differing pathophysiology in the subgroups and support the multiple process view of depression.

Analysis of Variance

Evoked potential topography in unmedicated and medicated schizophrenics.

The main purposes were to determine whether: (1) evoked potential (EP) topography differs from normal in schizophrenics; (2) EP topography is altered by psychotropic drugs. Unmedicated (n = 72) and medicated (n = 57) schizophrenics were compared with age- and sex-matched non-patients and with one another. EPs to left and right median nerve, visual pattern and auditory stimuli were recorded from 15 leads. EP data were reduced by principal component analysis (PCA) of EP waveforms, with separate PCAs for later and earlier poststimulus times; 32 factors were extracted. Factor scores, based on factor structure of 195 non-patients, were computed for all subjects. Topographic effects were evaluated by ANOVAs on Z-transformed factor scores. The results were: (1) topographies differed between groups in about one-third of the factors, but variables yielding effects differed between comparisons; (2) topographic differences from normal in unmedicated patients converged at left temporoparietal (higher in schizophrenics) and right fronto-central-temporal areas (lower in schizophrenics); (3) similar convergence was absent in medicated patients; (4) most medicated vs unmedicated patient topographic differences persisted in groups matched for psychopathology. Results appear consistent with "focal cortical arousal" of the left posterior quadrant in schizophrenics (Morihisa and Duffy, 1986) and suggest that medication alters EP topography.

Acoustic Stimulation

Replication of an evoked potential study of lateralized hemispheric dysfunction in schizophrenics.

Visual (VEP) and auditory (AEP) evoked potentials (EPs) were measured to replicate previous findings concerning lateralized hemispheric dysfunction in chronic schizophrenic patients in a new sample. Measures of EP waveform stability (Zr') showed greater hemispheric asymmetry in 26 unmedicated chronic schizophrenics than in 26 matched nonpatients, and relatively lower left and right hemisphere values in schizophrenics. Similar hemispheric differences were not found between medicated patients and matched nonpatients; medication was associated with higher left and lower right hemisphere stability. EP amplitudes were lower with medications, the lowest amplitudes found in patients receiving nonphenothiazine or nonpiperazines as opposed to phenothiazine-piperazine drugs. Medications were associated with amplitude asymmetries not observed in unmedicated patients. This study confirms greater than normal hemispheric asymmetry of VEP and AEP waveshape stability measures in chronic schizophrenics, and lower left than right hemisphere stability suggesting left hemisphere dysfunction. Alteration of EP asymmetries by antipsychotic medications suggests that medication effects may obscure evidence of lateralized dysfunction in schizophrenics.

Antipsychotic Agents

Early cognitive components of somatosensory event-related potentials.

Somatosensory event-related potentials (ERPs) were recorded during a selective attention task involving electrical stimuli delivered to index fingers or the left and right median nerves at the wrist. In 11 healthy, young subjects, ERPs were recorded from 6 scalp locations while they mentally counted the electrical stimuli designated as target. Sequential ERP events measured included N20 (negativity at 20 ms), P30, P45, N60, P100, N140, P180, and P400. Analysis of amplitude data indicated modifications of both early and late ERP events with selective attention. While electrical stimulation at the wrist yielded early ERP amplitudes that were larger overall and latencies that were generally shorter, the selection attention effects did not differ on the basis of site of stimulation. The early ERP selective attention effects had differing scalp topography, with the P30/P45 effect of maximal over postcentral gyrus and N60 effect maximal over prerolandic gyrus. The data further elucidate the temporal features and spatial distribution of somatosensory ERP processes involved in attentional activity.

Adult

Are gender differences in schizophrenia reflected in brain event-related potentials?

Numerous studies have reported relationships between gender and cerebral event-related potentials (ERPs) recorded from the human scalp. Recent studies have suggested that the influences of gender on ERPs may differ in persons with schizophrenia compared to healthy controls. In a further evaluation of the influences of this critical subject variable on ERP characteristics in schizophrenia, ERPs of age- and gender-matched groups (n = 72 each) of unmedicated schizophrenic patients and healthy controls were compared. ERPs elicited by left and right median nerve stimulation, checkerboard pattern visual flash, and auditory clicks were recorded from 15 scalp leads. The results confirm previous findings showing that: (1) number of comparable gender effects present in the ERP records of these two large study groups and (2) specific Diagnosis x Gender interactions suggesting that schizophrenic illness may modify normal gender influences on ERP characteristics. These data illustrate the point that matching schizophrenic patients and healthy control populations for gender is essential but not sufficient. Even in carefully matched groups, gender confounding can persist as a source of error variance because the influence can vary for different diagnostic groups.

Adolescent

Comparing principal components analyses of evoked potentials recorded from heterogeneous groups of subjects.

Principal components analysis of evoked potentials differing between groups presents an interpretive problem, particularly in psychiatric research. Two sets of principal components and associated factor scores may appear to differ. The issue is to determine the extent to which visually differing principal components and resultant factor scores span the same factor space. Sets of evoked potentials from controls and from schizophrenics were each subjected to principal components analysis, from which factor score coefficients were computed for all subjects. This allowed determination of the extent to which (1) the two sets of basis waves were similar and (2) the factor scores resulting from the set of basis waves derived from principal components analysis of the control subjects' evoked potential data adequately represented those of the schizophrenics and vice-versa. Canonical correlation analyses indicated substantial similarities between the principal component structures (sets of basis waves). Multiple correlational analyses confirmed that the basis waves from either group spanned the other group's factor space. Factor scores from either set of basis waves were highly correlated. These results suggest that principal component structures derived from evoked potentials of a control group may be used in computing evoked potential factor scores of psychiatrically diverse populations even though the average evoked potentials of the groups may differ in several ways.

Evoked Potentials

Dealing with differential gender and age effects in evoked potential studies of psychopathology.

Data selected from comprehensive EP studies of a large sample of psychiatric patients and nonpatients illustrate the point that matching patient and control populations for age and gender is essential, but not sufficient, to control for these subject variables. It is necessary to test for the interactions resulting from different relationships between EP measures and gender and/or age in different diagnostic groups and to examine differences between subgroups defined by gender and age.

Adolescent

Somatosensory evoked potential correlates of schizophrenic subtypes identified by the Millon Clinical Multiaxial Inventory.

Evoked potentials (EPs) of schizophrenic patients differ from those of normal controls and some other diagnostic groups, but EP measurements of the comparison groups often overlap considerably. This suggests that schizophrenics are heterogeneous with respect to EP measurements and that additional methods for clinical subtyping are needed to account for the heterogeneity. This study used criteria based on the Millon Clinical Multiaxial Inventory to partition 20 patients, who were all schizophrenic by three diagnostic systems, into two subgroups. Somatosensory EP measurements of these two subgroups differed, suggesting that neurophysiological heterogeneity within the total sample of schizophrenics was associated with corresponding heterogeneity of the clinical features in the Millon scales.

Adult

A sensory evoked potential comparison of persons 'at risk' for Huntington's disease and hospitalized neurotic patients.

Scalp-recorded sensory evoked potentials (EPs) elicited by left and right median nerve stimulation (LSEP and RSEP), checkerboard pattern flash (VEP) and acoustic click (AEP) were obtained in 22 individuals 'at risk' (AR) for Huntington's disease and 22 hospitalized neurotic patients matched for age, gender and intelligence. EPs of AR subjects were generally similar to those of the neurotic comparison group, in terms of overall configuration; however, mean amplitudes were significantly lower for ARs. While the general amplitude reduction for ARs was seen in all three modalities, the somatosensory modality yielded the most abnormal findings.

Adult

Evoked potential correlates of intelligence in nonpatient subjects.

To evaluate possible influences of intelligence on evoked potential (EP) characteristics in nonpatients. EPs of age and gender matched groups (N = 19 each) of 'high', 'medium', and 'low' IQ groups were compared. EPs elicited by left and right median nerve stimulation, checkerboard pattern visual flash, and acoustic clicks were recorded from 15 scalp leads. The results confirmed previous findings showing that higher IQs are associated with higher EP amplitudes. An unexpected finding was a trend towards higher IQ/EP correlations for left than right recording sites. It appears that intelligence is an important subject variable to be controlled in any EP investigation, and furthermore that EP topography should be considered in seeking IQ/EP correlations.

Adult

Some quantitative EEG findings in unmedicated and medicated major depressives.

To confirm previous quantitative EEG findings in major depressive disorder and to assess effects of medication, EEGs were recorded under eyes closed and open conditions in 68 patients (34 unmedicated and 34 medicated) and nonpatients matched for age and sex. Time series analyses of amplitude, frequency and wave symmetry were performed; differences between eyes open and closed were adjusted for eyes closed values to obtain measures of reactivity. These reactivity measures yielded the main differences between unmedicated patients and nonpatients; depressives were more reactive. Reactivity differences were eliminated or reversed in medicated patients. The EEGs of unmedicated depressives appear to be overreactive, while medications decrease EEG reactivity.

Adolescent

Relationship between evoked potential and neuropsychological findings in persons "at risk" for Huntington's disease.

Scalp-recorded evoked potentials (EPs) elicited by left and right median nerve stimulation (LSEP and RSEP), checkerboard pattern flash (VEP), and acoustic click (AEP) were obtained in 40 individuals "at risk" (AR) for Huntington's disease (HD) and 40 nonpatients matched for age, sex, and intelligence. EPs of AR subjects were generally similar to those of nonpatient's overall configuration; however, mean amplitudes were significantly lower for ARs. The lower amplitudes tended to occur primarily among a subgroup of ARs who manifested some degree of cognitive change, as defined by neuropsychological test criteria.

Acoustic Stimulation

Combinations of evoked potential amplitude measurements in relation to psychiatric diagnosis.

The purposes of this investigation were (1) to determine the extent to which single nonredundant measures, derived from optimal combinations of evoked potential (EP) amplitude measurements, could differentiate between various groups of psychiatric patients and between patients and nonpatients, and (2) to assess the replicability of such discriminations. Somatosensory, visual, and auditory EPs were recorded from 15 locations in 253 unmedicated patients and 99 nonpatients. Multivariate statistical methods were used to reduce the amplitude measurements to sets of factor scores that met specified criteria for entry into discriminant analyses between pairs of the following groups: nonpatients, neuroses, personality disorders, schizophrenias, schizotypal/borderlines, major depressives, and manics. Sensitivity, specificity, and predictive value were assessed for discriminant scores. The discriminant scores yielded many differences between groups, most of which were replicable in split-half analyses. Among these were differences between all six patient groups and nonpatients, and between schizophrenics and nonpsychotics. Split-half discriminant analyses were also performed with 12 measures that were obtained by taking the means of factor scores grouped by sensory modality, time, and spatial location; these variables, used without preselection, provided several replicable diagnostic discriminations.

Adolescent

Auditory and visual evoked potentials in Huntington's disease.

Auditory and visual evoked potentials elicited by acoustic click (AEP) and checkerboard pattern flash (VEP) were recorded from 15 locations in 21 patients with Huntington's disease (HD) and 21 controls matched for age and sex. Peak latencies were approximately the same for both groups, except that AEP peak N100 appeared earlier in HDs. The main deviation in HDs consisted of generally reduced amplitude of VEP and AEP components; these deviations can be considered non-specific. Early VEP and AEP peaks contained no specific abnormalities comparable to those found in early somatosensory evoked potentials, as previously reported for the same subjects. VEP and AEP amplitudes were lower in medicated than in unmedicated HD patients, but amplitudes for both medicated and unmedicated HDs deviated from normal. Drugs may act to further diminish the already lower than normal amplitudes in HDs.

Adult

Psychiatric drugs and the somatosensory P400 wave.

The effects of antipsychotic and antidepressant medications on the somatosensory evoked potential (SEP) late wave (P400) were investigated in a diagnostically heterogeneous group of 51 psychiatric patients. SEPs were recorded from five scalp locations while subjects counted electrical stimuli to one of four randomly stimulated fingers. In seven subjects, tested both on and off medication, no significant drug effects were observed. P400 amplitudes of 14 patients being treated with antipsychotic medication were greater than those of unmedicated patients matched for age, sex, and diagnosis. P400 amplitudes did not differ between eight patients being treated with antidepressants and eight unmedicated matched patients. Accuracy in stimulus counting (index of task performance) was significantly correlated with P400 amplitude; more accurate counting was associated with higher P400 amplitude. When 14 medicated and 14 unmedicated subjects, matched for task performance, age, sex, and approximate diagnoses, were compared, P400 amplitude did not differ. These findings suggest that higher P400 amplitudes associated with medication probably reflected improved task performance with medication, rather than a direct action of the drugs on P400. The results suggest the conclusion that lower P400 amplitude in psychosis is not secondary to psychiatric drugs.

Adult