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D Brandeis

Publications and source records attributed to D Brandeis.

30 records · Page 2Linked to original sources
PubMed1994

The effect of D-amphetamine, clonidine, and yohimbine on human information processing.

Twelve subjects were tested with D-amphetamine, yohimbine, clonidine, and a placebo on a task with two levels of stimulus and two levels of response complexity. The purpose of this study was to test the hypothesis that noradrenergic drugs affect early stimulus processes. D-amphetamine speeded reaction time (RT), clonidine slowed it, and yohimbine had no effect. D-amphetamine and yohimbine decreased N1 latency and clonidine increased it. D-amphetamine and yohimbine decreased P3 latency and clonidine increased it but, in each case, only when latency estimates were based on single trials, not on averages. D-amphetamine's effect on RT, not P3, as measured by the average, is consistent with previous results. Single trial measures appear more sensitive. Speeding of N1 and single-trial P3 data indicate that noradrenergic drugs affect processing of early (visual) information. D-amphetamine's speeding of single-trial P3 estimates was attributed to its noradrenergic actions. Yohimbine's speeding of P3 without changing RT is consistent with neural net (parallel) simulations but not with a serial model. These findings support the assumption that different neurotransmitters modulate specific cognitive processes.

Adult↗
PubMed1994

Mapping brain electric micro-states in dyslexic children during reading.

An important issue in current research on dyslexia is to what extent the reading deficits of dyslexic children are related to processing deficits at the sensory-visual level, at the cognitive-linguistic level or at both levels. Event-related potential mapping distinguishes the split-second processing stages during reading as brief brain-electric micro-states and can address this issue directly. Previously, conventional studies have yielded inconsistent patterns of event-related potential differences between dyslexic and control children, but most of these discrepancies could result from the widely differing methodologies. We used event-related potential mapping during silent reading of correct and incorrect sentence endings to examine the neurophysiology of sensory and cognitive processes in dyslexic and control children (n = 12/group). Selected findings from spatio-temporal analyses of map strength (global field power), map latency and map topography measured in three dimensions are presented. Both sensory-visual processes in a P110 micro-state and cognitive-linguistic processes in an early N400 micro-state were affected in dyslexic children, and processing delays, as well as qualitatively different patterns of neural activation, were found. Our findings also indicated that the use of specific cognitive tasks and of appropriate spatio-temporal analyses of event-related map series are critical factors for successful identification of specific processing deficits in brain mapping studies.

Adolescent↗
PubMed1993

Localization of sources of brain alpha/theta/delta activity and the influence of the mode of spontaneous mentation.

A method is described that accounts for multichannel brain field data (EEG) epochs, after transformation into the frequency domain, by a single oscillating dipole source in terms of phase angles. The method produces a potential distribution for each frequency point ('FFT dipole approximation'). These maps can be subjected to conventional equivalent dipole source fittings in terms of amplitudes. We studied the equivalent source locations for the different temporal EEG frequency bands (delta/theta/alpha) in 12 normal subjects during the collection of reports of spontaneous thoughts. Some of the thought reports were classed into two modes, 'visual imagery' and 'abstract', and the associated equivalent source locations during the 2 s immediately prior to these reports were computed. Different equivalent source locations were found for the different spectral components of the EEG, implying that different neural generator populations generate the different frequencies. Further, the different types of spontaneous thought, i.e. different modes of cortical functioning, were found to be associated with the activity of different neuronal generator sources that operated at the same frequency at different source locations.

Alpha Rhythm↗
PubMed1992

Localization of the sources of EEG delta, theta, alpha and beta frequency bands using the FFT dipole approximation.

FFT dipole approximation and 3-dimensional dipole modelling were used to determine the locations of the equivalent dipole model sources of the delta, theta, alpha, beta-1 and beta-2 frequency bands in 13 normal subjects during resting. From each subject, 2 successive data sets were analysed, each consisting of 10 epochs of 2 sec randomly collected during 30 min. ANOVAs showed that over subjects, the source locations of EEG frequency bands differed significantly in the vertical and antero-posterior dimensions. Results of data set 2 confirmed those of data set 1. The source of delta was deepest and most anterior, theta more posterior and less deep, alpha most posterior and highest on the vertical dimension, beta-1 deeper and slightly more anterior than alpha, and beta-2 again more anterior and deeper than beta-1. Thus, the depth of source location was not linearly related to temporal frequency. The sources of all 5 bands were oriented in the sagittal direction; delta mean fields had steeper gradients anteriorly, alpha and beta-1 posteriorly. The power map for any frequency was well described by a single phase angle. The results indicate that the different EEG frequency bands during a given EEG epoch are generated by neural populations in different brain locations.

Adult↗
PubMed1992

Scopolamine effects on visual information processing, attention, and event-related potential map latencies.

We measured performance and event-related brain potential (ERP) map latencies in 12 subjects during four visual discrimination tasks to compare the timing of scopolamine effects on information processing and attention. "Topographic component recognition" found ERP map latencies at times of best fit with a component model map. This "common topography" criterion minimized topographic differences among conditions to facilitate latency interpretations. Scopolamine slowed N1 latency in all tasks, and P3 and reaction time in some tasks. The drug delayed responses to easy targets more than to hard targets. It also induced a disproportionate N1 delay for unilateral high spatial frequency gratings. Both effects reflect a scopolamine-induced impairment when processing targets that usually capture attention. Scopolamine also impaired accuracy for unilateral high spatial frequency gratings, and for gratings presented at probable locations, confirming and extending previous findings. Scopolamine-induced P1 and N1 delays showed that visual processing was affected. Several results were inconsistent with a serial stage model. We suggest that scopolamine both delays selected processes and impairs a processing mode based on automatic capture of attention, inducing more serial processing.

Adult↗
PubMed1991

Clonidine and scopolamine: differences and similarities in how they change human information processing.

1. Humans have been tested on a choice reaction time task designed to disclose interactions between stimulus complexity and drug effect. 2. Tests were carried out using oral scopolamine (1.2 mg) and clonidine (0.2 mg). 3. Reaction times and event related potentials were measured. 4. Both drugs slowed reaction time and the N1 component of the ERP. 5. SCOP slows RTs to easy-to-discriminate stimuli more than RTs to harder stimuli. Its effect on P3 is the same for both types of stimuli. 6. CLON tends to slow P3 latencies to easy stimuli more than P3 latencies to harder stimuli, while the RT slowing is almost identical for both types of stimuli.

Adult↗
PubMed1989

Segments of event-related potential map series reveal landscape changes with visual attention and subjective contours.

Changes of the event-related potential (ERP) map landscape with time and condition were used to identify qualitative changes in the ERP generating process which are indicative of a change in the functional microstate. Twelve subjects attended or ignored unilaterally presented visual stimuli with and without subjective contours. ERP map series from 16 electrodes were adaptively segmented to identify periods of stable map landscape, using topographic descriptions (map maxima and minima). Attention as well as the subjective contours changed the map topography and increased the map amplitude. From 170 to 380 msec, they had similar effects on the antero-posterior map topography. Topographic differences between the effects of attention and subjective contours were also present, but affected mainly the left-right topography. The results are in line with the notion of attentional involvement in subjective contour perception and show that global modulation of exogenous brain activity cannot account for topographic changes with attention or with subjective contours. They further establish space-oriented data reduction as a powerful tool to identify components and to distinguish among hypotheses about the underlying generator processes.

Adult↗
PubMed1986

Event-related potentials of the brain and cognitive processes: approaches and applications.

Event-related potentials (ERPs) are recordings of the electric field which the brain produces in fixed time-relation to an event. ERPs open a time and space window onto covert steps of brain information processing which need not be accompanied by overt behavior or private experiences. ERPs are the only noninvasive method which resolves the dynamic pattern of events in the human brain down to the millisecond range. Early ERP components are valuable tools in clinical testing of the afferent sensory systems in the absence of anamnestic or clinical pathology. Later components (e.g. the 'P300') index intermediate, covert steps of information processing and have clarified the time course and the contingencies of processes in attention, decisions and language. ERP waveshapes show electric potential differences between two recording points. Conventional analysis often ignores the fact that there is no unique voltage amplitude or signal latency for a single point, and interprets ambiguous results. Although important insights have emerged with such strategies, full utilization of ERP data requires unambiguous ERP assessment and converging evidence from neuropsychological and cognitive experimentation. Sequences of field distribution maps offer an unbiased display of ERP data. Spatial analysis yields unambiguous values for further comprehensive assessment, and should precede analysis over time. Examples of spatial analysis have shown that different ERP field configurations follow the presentation of noun and verb meaning of homophone words; that the ERP effects to subjective contours resemble those to attention in time course and topography; that the 'cognitive' P300 component reflects the specific stimulus location; and that subliminal information influences the configuration of late ERP fields.

Attention↗
PubMed1981

Sleep deprivation: effect on sleep stages and EEG power density in man.

Sleep was analysed in 8 young adults subjects during two baseline nights and two recovery nights following 40.5 h sleep deprivation. Sleep stages were scored from the polygraph records according to conventional criteria. In addition, the EEG records of the entire nights were subjected to spectral analysis to compute the frequency distribution of the power density in the 0.25-25 Hz range for 0.5 Hz or 1.0 Hz bins. In the first recovery night, the power density in the delta band was significantly higher than baseline for total sleep time as well as for sleep stages 2, 3 and 4, 4 and REM. These changes were not restricted to the delta band, but extended to higher frequency bands. Minor, but significant, effects of sleep deprivation were seen in the power density distribution of the second recovery night. In the baseline nights, a progressive reduction of power density in the delta/theta range was present for successive non-REM-REM sleep cycles for total sleep time and stages 2, 3 and 4, and 4. The results show that effects of sleep deprivation as well as trends within the sleep periods are readily apparent from spectral analysis, but are inadequately reflected by conventional sleep scoring. When the power density values were integrated over the entire frequency range (0.75-25 Hz) for each non-REM-REM sleep cycle, an exponential decline from cycle 1 to cycle 3 was suggested. The present findings support the hypothesis that the EEG power density in the low frequency range is an indicator of a progressively declining process during sleep whose initial value is determined by the duration of prior waking.

Adult↗