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Biomedical subjects

B Porjesz

Publications and source records attributed to B Porjesz.

At least 73 records · Page 4Linked to original sources
PubMed1994

Multivariate composite estimators: new ways to track signals with application to human cerebral potentials.

In this paper, we propose new multivariate composite estimators (MCE) to track multiple channel potential waves of individual and grand averages of recorded potentials at the scalp from a number of trials in a group of subjects. The advantages of these estimators over simple averages used in the literature are that they have larger signal to noise ratios (SNR), and that they have taken into account variations and correlations of the recorded potentials at the electrode sites as well as differences among subjects. Multivariate techniques and composite concept are used for deriving the estimators. We also provide an application to human event-related potentials in a memory for faces experiment.

Adult↗
PubMed1994

Surface energy, its density and distance: new measures with application to human cerebral potentials.

In this paper, we propose three new measures for topographic studies of event related potentials (ERP) called the surface energy (SE), its density (SED) and the distance of surface energy density fields (DSED) based on the entire scalp current density (SCD) field. These measures have a specific physical meaning, are free of the reference electrode and any physical conductive model of the head. They capture not only spatial properties, but also continuous time elements present and smeared in the original scalp potential records. They provide a common base for comparisons of recorded potentials among different time points, subjects, regions on the scalp, or experimental conditions. We also construct a statistical inference based on these new measures, and provide an application to human event-related potentials in a visual short-term memory experiment.

Adult↗
PubMed1994

P300 from an auditory oddball task: inter-laboratory consistency.

Event-related potentials (ERPs) were recorded from normal subjects for the purpose of evaluating measurement consistency among six laboratories located in different cities within the United States. At each laboratory location 15 male subjects were tested using a simple auditory stimulus discrimination task and identical electrophysiological equipment and recording methods. Assessment of the N1, P2, N2, and P3(00) potentials from both the target and standard stimuli resulted in no reliable differences among laboratories for component amplitudes, latencies, and scalp distributions. Quantitative evaluation of overall waveform and specific component morphology yielded good to excellent agreement across laboratories. The findings suggest that large-scale inter-laboratory human electrophysiological studies are feasible and may prove of value when using ERPs to evaluate cognitive function in humans.

Adult↗
PubMed1994

Event-related potentials to faces: the effects of priming and recognition.

Short-term visual memory, as in both implicit priming and explicit recognition tasks, can be demonstrated by decreased reaction times, the ability to preferentially select previously presented objects from lists and the ability to more readily complete previously exposed words from fragmented letters. The visual processing of faces occurs separately from the visual processing of non-face stimuli, within discrete areas of bilateral posterior inferotemporal cortices. While visual recognition and memory of faces are independent of those for non-faces, their processing appears to be similar. We have demonstrated an electrophysiologic correlate of short-term visual memory in a face-matching paradigm. We have observed a series of evoked potential components consisting predominantly of a C140, C180 and C240 with a posterior, bitemporal distribution. The priming effect is reflected by a diminution of C240 amplitude in the response to repeated pictures of faces compared to novel pictures of faces. These data reflect a previously unreported set of neurophysiological observations on short-term visual memory for faces.

Adult↗
PubMed1993

The effects of ethanol on EEG activity in males at risk for alcoholism.

The present investigation examined the effects of placebo (P), low dose (LD) and high dose (HD) ethanol on EEG activity in two groups of males. One group consisted of individuals at high risk for the development of alcoholism (HR, N = 21) while the other consisted of matched, low risk (LR, N = 21) controls. Only one condition (P, LD or HD) was presented each day and condition order was randomized. For each subject, both blood alcohol level(s) (BAL) measured via breathalyzer and EEG activity, using the entire 10/20 international system, were recorded prior to and at intervals of 35, 70, 105 and 140 min after P, LD or HD administration. The Fast Fourier Transform (FFT) was used to calculate power spectral densities (PSD). Measures of relative area under the power spectral curve were obtained for each of the following frequency bands: slow alpha (SA, 7.5-10 Hz), fast alpha (FA, 10.5-13.0 Hz), slow beta (SB, 13.5-19.5 Hz) and fast beta (FB, 20-26 Hz) at electrodes: F3, F4, C3, C4, P3, P4, O1 and O2. The results of repeated measures MANOVA conducted on the normalized values of relative areas revealed that at each electrode examined, ethanol elicited significant changes only in SA activity. Risk group differences in SA activity were observed only at electrodes F3, F4 and P4. These differences were the consequence of differential ethanol effects rather than differences in baseline SA levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

A neurophysiologic correlate of visual short-term memory in humans.

Neurophysiological investigations in non-human primates and neuropsychological studies in patients with lesions indicate that the inferotemporal cortex is critically involved in visual object recognition. We have recorded event-related potentials from 31 electrodes in a group of healthy normal individuals performing a modified delayed matching to sample task. We have identified a visual memory potential (VMP) which indexes visual short-term memory in humans. This component of the event-related brain potential occurs as early as 170 msec, is maximal at 240 msec, and is generally located in the temporal region. Both the temporal and spatial characteristics of the VMP in humans are in keeping with single cell studies in monkeys.

Adult↗
PubMed1993

Ethanol-induced alterations in electroencephalographic activity in adult males.

The present investigation examined the effects of placebo (P), low-dose (LD), and high-dose (HD) ethanol on electroencephalographic (EEG) activity in 21 healthy, adult males (X = 22.7 years). Only one condition (P, LD, or HD) was presented per day and the condition order was randomized. For each subject, blood-alcohol levels measured via breathalyzer and EEG activity, using the entire 10/20 International System, were recorded both prior to and at intervals of 35, 70, 105, and 140 minutes after P, LD, or HD administration. The Fast Fourier Transform was used to calculate power spectral densities for each EEG recording. Measures of the relative areas under the power spectral curve were made for each of the following frequency bands: slow alpha (7.5 to 10 Hz); fast alpha (10.5 to 13.0 Hz); slow beta (13.5 to 19.5 Hz); and fast beta (20 to 26 Hz) at electrodes F3, F4, C3, C4, P3, P4, O1, and O2. Repeated-measures multivariate analysis of variance performed on normalized relative area values revealed that ethanol had significant effects on EEG activity at anterior sites: frontal (F3, F4) and central (C3, C4) that presented as increased activity in the slow alpha frequency band. These results suggest a differential responsivity of both cortical region and EEG frequency band to the effects of ethanol ingestion.

Adult↗
PubMed1992

The Tridimensional Personality Questionnaire in males at high and low risk for alcoholism.

Cloninger has proposed a tridimensional model as the basis for the classification of personality variants and has developed the Tridimensional Personality Questionnaire (TPQ) as an empirical test of this model. In this study, the TPQ was administered to two groups of young men. One group was comprised of nonalcoholic sons of male alcoholics; the other group consisted of nonalcoholic men with no family history of alcoholism. Since the sons of male alcoholics are considered to be at greater risk to develop alcoholism than the sons of nonalcoholics, it was hypothesized that the two groups would demonstrate differences with regard to one or more personality variants as measured by the TPQ. No statistically significant differences in the three TPQ-subscale scores of the two groups were found.

Adult↗
PubMed1991

EEG characteristics in males at risk for alcoholism.

Baseline EEG activity was recorded with eyes closed in 15 males, aged 19 to 24 at risk (HR = high risk) for the development of alcoholism and 15 matched controls (LR = low risk). Four EEG frequency bands were examined: slow alpha (7.5-10 Hz), fast alpha (10.25-12.75 Hz), slow beta (13-19.5 Hz) and fast beta (19.75-26 Hz). The HR and LR groups were compared on four measures of EEG activity for each frequency band: band power, absolute and relative area and laterality differences. Statistical analysis of the data via ANOVA revealed no significant difference between the HR and LR groups for any comparison. The results indicate that EEG measures prior to alcohol administration do not effectively discriminate between individuals at high and low risk for alcoholism.

Adult↗
PubMed1991

Neurophysiological factors in individuals at risk for alcoholism.

The literature dealing with electrophysiological research in individuals at risk for alcoholism is reviewed. Event-related potential (ERP) and electroencephalographic (EEG) differences between family-history-positive (FHP) and family-history-negative (FHN) men have been reported both prior to the ingestion of alcohol and following alcohol challenge doses. At present, the most robust of these electrophysiological findings is the lower P3 amplitude of the ERP, which has now been replicated in several laboratories. This perhaps provides a phenotypic marker, distinguishing those at risk for alcoholism. However, its specificity for alcoholism and the role of gene-environment interactions in the development of alcoholism remain to be determined.

Alcoholism↗
PubMed1990

Neuroelectric processes in individuals at risk for alcoholism.

The literature dealing with electrophysiologic research in alcoholics and individuals at risk for alcoholism is reviewed. Event-related potential (ERP) differences between family history positive (FHP) and family history negative (FHN) males have been reported both prior to the ingestion of alcohol and following alcohol challenge doses. At present, the most robust of these electrophysiological findings is the lower P3 amplitude of the ERP, which has now been replicated in several laboratories. This perhaps provides a phenotypic marker, distinguishing those at risk for alcoholism.

Alcohol Drinking↗
PubMed1987

Late positive component amplitude in schizophrenics and alcoholics in two different paradigms.

Abstinent alcoholics, unmedicated schizophrenics, and controls were tested in two paradigms designed to elicit the late positive component. Experiment A used frequent stimuli of differing incentive value and Experiment B used infrequent stimuli of differing perceptual discriminability. Alcoholics and schizophrenics showed late positive components that were significantly reduced in amplitude compared to controls. The patient groups were similar in their late component amplitudes. Control subjects showed a substantially wider response range than the patient groups. The narrow response range in both patient groups was manifested in diminished late component amplitudes to both stimuli in both experiments. The intraclass correlation coefficient of late component amplitudes for both patient groups was significantly greater than that of the controls.

Adult↗
PubMed1987

The N2 component of the event-related brain potential in abstinent alcoholics.

The latencies of the N2 component of the ERP and reaction time were manipulated in abstinent alcoholics and controls. The experimental design consisted of visual stimuli that differed in difficulty of discrimination. N2 latencies were found to be significantly delayed in alcoholics compared to controls, particularly for the easy discrimination. While controls manifested significantly earlier N2 latencies for the easy discrimination compared to the difficult discrimination, alcoholics did not manifest any significant difference in the latency of N2 as a function of the level of difficulty. There were no significant differences between groups in terms of RT or number of errors. In addition, alcoholics displayed significantly reduced P3 amplitudes to target stimuli compared to controls. These results suggest that match/mismatch processes are impaired in alcoholics and that they have difficulty evaluating the potential significance of a stimulus.

Adult↗
PubMed1987

The N2 component of the event-related potential in schizophrenic patients.

Event-related potentials (ERPs) to easy and difficult infrequent visual target stimuli were recorded in unmedicated schizophrenic patients and age-matched controls. N2 difference wave forms were computed by subtracting the ERP to a frequent non-target stimulus from the ERP to each target. The N2 component was identified in these difference wave forms. All subjects showed longer latency N2 and P3 peaks to the difficult target than to the easy target. Schizophrenic patients had longer latency N2 peaks than controls to both targets. Schizophrenic patients also showed reduced P3 amplitudes to both targets compared to controls. The prolonged N2 latency in schizophrenics accounts for a substantial portion of the delayed reaction time commonly observed in this group. N2 latency prolongation appears to be yet another evoked potential abnormality in schizophrenic patients.

Adult↗
PubMed1987

Auditory brainstem potentials in sons of alcoholic fathers.

With the use of event-related brain potentials we have observed sensory as well as cognitive deficits in abstinent alcoholics. By recording auditory brainstem potentials (BSP) from abstinent alcoholics we demonstrated significant delays in brainstem transmission time. We have also reported that P3 amplitudes are significantly reduced in abstinent alcoholics compared to control subjects. Although the neurophysiological deficits observed in abstinent alcoholics are presumed to be alcohol-related effects, it is possible that some of these deficits may exist prior to alcohol exposure, and may be present in subjects at high risk for alcoholism. We have recently observed significantly reduced P3 components in young sons of alcoholics similar to those observed in abstinent alcoholics. In the present study, we examined auditory BSPs in young boys at high risk for alcoholism and matched controls. We found no statistically significant difference in brainstem transmission time between high risk individuals and matched control subjects. These findings suggest that while some brain deficits observed in abstinent alcoholics may antecede the development of alcoholism (P3) and may represent a predisposing factor, other deficits (BSP) appear to be the consequence of alcohol and/or nutritional-related effects.

Adolescent↗