Walter S. Pritchard

Faster P300 latency after smoking in visual but not auditory oddball tasks

In two separate experiments, P300 was recorded from overnight-abstaining smokers before and after smoking. In the first experiment, 32 subjects counted forward by ones and counted backwards by threes upon presentation of a rare tone burst (20%) in a stream of standard tones. There were no changes in P300 amplitude or latency pre- to post-smoking (1.1-mg FTC nicotine-yield cigarette). In the second experiment, 29 subjects completed auditory and visual oddball tasks before smoking, after smoking a low nicotine-yield cigarette (0.05 mg), after smoking a higher nicotine-yield cigarette (1.1-mg), and after smoking a second 1.1-mg cigarette. In the visual oddball task, P300 latency decreased after smoking the first higher-yield cigarette relative to both pre-smoking and post smoking the lower-yield cigarette. This effect was maintained after smoking the second higher-yield cigarette. In the visual task, P300 amplitude increased after smoking the first higher-yield cigarette (from a lower baseline level) in a group of subjects with larger changes in tidal-breath CO but not in a group with smaller changes in CO. There were no effects of smoking on P300 amplitude or latency in the auditory tasks of either the first or second experiment.

The relationship between impulsiveness subtraits, trait anxiety, and visual N100 augmenting/reducing: A topographic analysis☆

Abstract The relationship between impulsiveness subtraits assessed by the Barratt Impulsiveness Scale (BIS-10), the trait anxiety subscale of the State-Trait Personality Inventory (STPI), and the topographic distribution of visual N100 augmenting/reducing (AR) was examined. Topographic event-related potential (ERP) data were collected from an array of 14 electrodes covering the left side of the head while subjects counted the total number of light flashes presented at two different but equiprobable intensities. Principal components analysis of the ERP data yielded a factor accounting for 13.9% of the total variance around the grand mean waveform that corresponded to the N100 wave clearly visible in the raw waveforms. For each subject by scalp locus combination, an AR score was computed by subtracting the factor score associated with the bright flashes from the factor score associated with the dim flashes. The correlations between AR scores and scores on the BIS-10 cognitive impulsiveness subscale were significant (P

Visual augmenting/reducing and P300 in autistic children

Visual event-related potentials were recorded from five male autistics and five matched controls. Sensory effects were investigated by having subjects passively view flashes of three different but equiprobable intensities (augmenting/reducing paradigm). Cognitive effects were examined by having subjects count infrequent, target, flashes of one intensity embedded within a series of frequent, nontarget, flashes of a different intensity (oddball paradigm). In the augmenting/reducing paradigm, the sensory N100 wave of autistic but not controls showed a significant increase in amplitude (augmenting) as flash intensity increased. The cognitive P300 wave of autistics did not differ from controls in the oddball paradigm. Unlike controls, autistics had an equally large P300 in the no-task augmenting/reducing paradigm. It is concluded that autistics may experience a degree of stimulus overload in the visual modality.

No effect of chronic fenfluramine on the P300 component of the event-related potential.

Five autistic children were administered a visual version of the oddball paradigm under both drug (chronic fenfluramine) and placebo conditions. The P300 component of the event-related potential (ERP) was not affected by fenfluramine, although the drug significantly lowered blood concentrations of serotonin. It was concluded that serotonin as a neurotransmitter does not play a major role in production of P300. This conclusion fits with the facts that: (1) the general functional role of serotonin in the nervous system is to globally inhibit the overt expression of behavior, and (2) P300 is generally insensitive to response selection processes.

The effects of neonatal androgenization of female hamsters on adult preference for female hamster vaginal discharge

The effects of neonatal exposure of hamsters to androgen on the development of an adult preference for female hamster vaginal discharge (FHVD) were investigated. Three groups treated on Days 2-3 postpartum (females administered testosterone propionate (TP) in a peanut oil base, females administered oil alone, and males administered oil alone) were combined factorially with four sequential adult conditions (intact, post-gonadectomy, post-gonadectomy plus TP therapy, and post-gonadectomy) to produce twelve experimental conditions. Statistical analysis indicated that neonatal oil females did not show a significant FHVD preference in any adult condition. Neonatal TP females displayed a significant FHVD preference only in the post-gonadectomy plus TP condition. Males retained a significant FHVD preference in all the adult conditions, although the preference shown in the two adult hormonal conditions (intact and post-gonadectomy plus TP) was significantly higher than the preference shown in the two nonhormonal conditions.

The structure of human attention: Evidence for separate spatial and verbal resource pools

Recent evidence has suggested that human limited-capacity information-processing resources do not reside in a unitary, undifferentiated pool. Rather, multiple and at least partially independent pools appear to exist. The present investigation addressed this issue. Subjects performed a spatial memory load secondary task in conjunction with either a spatial or a verbal primary task. The two primary tasks were structurally highly similar. Results indicated that performance of the spatial memory load secondary task was significantly poorer when it was paired with the spatial primary task than when it was paired with the verbal primary task. The results are interpreted as indicating the existence of at least partially independent spatial and verbal resource pools.

Individual differences in visual event-related potentials: P300 cognitive augmenting/reducing parallels N100 sensory augmenting/reducing

In a visual event-related potential experiment, both N100 augmenting/reducing data and oddball paradigm P300 data were collected from the same subjects. A significant correlation was obtained between augmenting/reducing and the degree to which stimulus probability affected P300 amplitude. Subjects who augment/reduce in response to increased stimulus brightness in the sensory domain also appear to augment/reduce in response to low probability in the cognitive domain.

PCAVR: A portable laboratory program for performing varimax-rotated principal components analysis of event-related potentials

A portable laboratory computer program for performing varimax-rotated principal components analysis (PCA) of event-related potentials (ERPs) is described. The program is written in FORTRAN 77; its compiled version requires 429, 140 bytes of memory. The program reads a matrix of numbers from an input file. The PCA can be performed on either the variance/covariance or the correlation matrix. The program computes the first six principal components. The user is given the option of rotating as many of the principal components as desired based upon the percentages of variance that they account for. Eigenvalues, percentages of variance, cumulative percentages of variance, factor loadings, and factor scores are written to an output file. Description of the program is preceded by a conceptual overview both of PCA as a factor analytic technique and of the application of PCA to ERP data analysis.

NONLINEAR PREDICTION AND COMPLEXITY OF ALPHA EEG ACTIVITY

Two prediction techniques were used to investigate the dynamical complexity of the alpha EEG; a nonlinear method using the K-nearest-neighbor local linear (KNNLL) approximation, and one based on global linear autoregressive (AR) modeling. Generally, KNNLL has more ability to predict nonlinearity in a chaotic time series under moderately noisy conditions as demonstrated by using increasingly noisy realizations of the Henon (a low-dimensional chaotic) and Mackey–Glass (a high-dimensional chaotic) maps. However, at higher noise levels KNNLL performs no better than AR prediction. For linear stochastic time series, such as a sine wave with added Gaussian noise, prediction using KNNLL is no better than AR even at very low signal-to-noise ratios. Both prediction techniques were applied to resting EEGs (O2 scalp recording site, 10–20 EEG system) from ten normal adult subjects under eyes-closed and eyes-open conditions. In all recordings tested, KNNLL did not yield a lower root mean squared error (RMSE) than AR prediction. This result more closely resembles that obtained for noisy sine waves as opposed to chaotic time series with added noise. This lends further support to the notion that these EEG signals are linear-stochastic in nature. However, the possibility that some EEG signals, particularly those with high prediction errors produced by a noisy nonlinear system cannot be ruled out in this study.

Effects of fenfluramine on EEG and brainstem average evoked response in infantile autism

The effects of fenfluramine on electrophysiological activity in autistic children were assessed by computerized EEG power analysis and brainstem evoked responses (BSER). Prolonged administration of fenfluramine resulted in a decrease of relative share of alpha-waves in the EEG power spectrum and in corresponding increase in slow activity. No effects of the drug on BSER latencies were observed. The spectral EEG pattern of fenfluramine identified in this sample was compared to the spectra reported for normal volunteers on an acute dose of fenfluramine. The implications of these findings for EEG classification of fenfluramine and neurochemical mechanisms of autism are discussed.