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At least 631 records · Page 35Linked to original sources
PubMed1985

Changes in flash but not pattern evoked cortical potentials after subchronic application of a monoamine oxidase (MAO) type A inhibitor in man.

Changes in flash but not pattern evoked cortical potentials after subchronic application of the MAO type A inhibitor pirlindole in man are reported. Pirlindole affects the deamination of serotonin and noradrenaline in the central nervous system and has serotonin reuptake inhibiting properties. Flash and pattern evoked cortical potentials were recorded in 6 healthy men before and after a 7 day period of treatment with 3 X 75 mg/day of pirlindole. After drug treatment, an increase in P100 latency to flash stimuli was seen without a change in the latency to pattern stimuli. This indicates that different neuronal systems process flash and pattern stimuli.

Adult↗
PubMedDate not supplied

Visual evoked potentials in a patient with prosopagnosia.

Visual evoked potentials (VEPs) were recorded from a 53-year-old man with prosopagnosia during presentation of slides of known and unknown faces and under two control conditions. ANOVA comparisons with a normal male group showed no differences in P100 amplitude, P300 amplitude or P300 latency. There were no significant evoked potential differences between the patient and controls specifically related to the face conditions. There was, however, a significant delay in the latency of P100 from both hemispheres during all types of stimuli. This prolonged latency was asymmetrical, showing a right sided emphasis with the control conditions: pattern reversal and slides of geometric designs. This finding, of a dissociation in the interhemispheric delay, provides physiological evidence of stimulus-specific organisation at an early, sensory level. The fact that the P100 component showed a marked delay, yet P300 fell within normal limits for amplitude and latency, suggests that this patient's problem lies at a perceptual level.

Agnosia↗
PubMedDate not supplied

Effects of scopolamine on visual evoked potentials in aging and dementia.

The unusual combination of a normal pattern reversal VEP and a delayed flash VEP has been reported in patients with dementia of Alzheimer's type (DAT). Hyoscine hydrobromide has been reported to produce a similar VEP abnormality in young, healthy subjects. In the present study, we assessed the relative sensitivity of DAT patients and healthy young, middle-aged and elderly subjects to temporary cholinergic blockade. We report VEP latency values following 3 doses of scopolamine and after a peripheral anticholinergic agent. Flash P2 latency was not significantly slower in DAT patients than in the healthy elderly. Scopolamine increased P2 latency in the young controls but did not affect any other group. The pattern reversal P100 was normal in DAT, and a significant increase in latency occurred following scopolamine administration in both the control and patient groups.

Adult↗
PubMed1988

Separate brain potential characteristics in children with reading disability and attention deficit disorder: color and letter relevance effects.

This experiment was on event-related potential (ERP) indicants of the selective neural processing of black vs. white and letter vs. nonletter stimuli in boys (8-12 years of age) with and without a reading disability (RD) and/or attentional deficit disorder (ADD). Selective neural processing was measured by the increase or difference in ERP amplitude in response to stimuli that were relevant as compared to irrelevant to the color or letter attention task. The 52 children that participated in the study constituted four groups: 25 normal reading children (17 without ADD and 8 with ADD), and 27 RD children (11 without ADD and 16 with ADD). ERPs were recorded over the left and right occipital, central, and frontal regions. Selective neural processing due to stimulus relevance was reduced in boys with RD as compared to normal readers. This reduced selectivity was indicated by a predominantly symmetrical reduction in the magnitude of a positive difference potential over the central regions, between 300 and 360 msec, and then by a left greater than right hemisphere reduction in the magnitude of a positive difference potential over the occipital regions, at about 400 msec. Task relevance increased the within-subject and condition variability of this occipital positive component and this effect was greater for boys without than with RD, particularly over the left hemisphere. Selective neural processing due to stimulus relevance was greater in boys with ADD as compared to those without ADD. This was indicated by an increase in the magnitude of a positive difference potential between 320 and 400 msec over the central and frontal regions and a slow, late, negative difference potential between 600 and 800 msec over the central and occipital regions. These ADD effects tended to be greater over the right than left hemisphere. The unique polarity, scalp distribution, and time course of the effects of RD as compared to ADD on ERPs to relevant stimuli clearly indicated these two disorders, in part, involve different underlying brain deficits.

Arousal↗
PubMed1992

Visual evoked potentials related to behavioral asymmetries during foveal attention in the two extrapersonal hemispaces.

In a group of male and female subjects we studied the VEPs related to the solution of a lexical decision task presented in the Left and Right Hemispaces with respect to the Central position in order to explore the electrophysiological correlates of the performance asymmetries obtained when overt spatial attention is directed to the Left or Right Hemispace. When stimuli were presented in the Left Hemispace a significant asymmetry was observed between the two hemispheres of the negative activity around 280 msec in the occipital-parietal areas. Moreover a general increase in the Central and Frontal areas of both the hemispheres was observed. In this paper we discuss why these effects can be considered to be the cause of the costs on accuracy observed in the male subjects. The differences obtained with the female group are discussed in relation to the observed modification on the negative activity around 400 msec with stimuli in the Left Hemispace. These findings give some suggestions about the interaction of structural and attentional mechanisms in the brain during the solution of a lateralized cognitive task.

Adult↗
PubMed1981

EP components, visual processing stages, and the effect of a barbiturate.

In a 2 x 2 x 2 factorial experiment, ten subjects carried out a visual choice reaction task. In addition to RT measurement, evoked potentials (EPs) were recorded from the central (Cz) and occipital (Oz) derivations. Independent variables were drug treatment (barbiturate versus placebo), visual stimulus intensity and visual stimulus degradation. The reaction time data showed that visual intensity and degradation had additive effects, which indicates that these variables affect independent stages, i.e. stimulus preprocessing and stimulus encoding. The effect of barbiturate on RT was additive with intensity but appeared to interact with degradation. This suggests a selective effect of that drug on the encoding state. EP components also showed selective effects of intensity, degradation and drug treatment. It was suggested that these components may be related to stages in the reaction process.

Adult↗
PubMed1995

An event-related potential examination of attended and unattended stimuli in visual selection using bilateral stimulus presentation.

The experiment reported here examined an interference paradigm using a bilateral stimulus presentation in which stimuli were presented simultaneously in the left and right visual fields. The lateralization of the early visual components allowed an ERP examination of material presented in each field. Attention was directed to one field or the other on each trial by a 100% valid cue. Two letters were nominated as targets and the simultaneous presentation allowed presentation of material compatible, incompatible or neutral with reference to the target. A negative peak was observed at 230 ms post stimulus at occipital and temporal sites. There was a variation in this peak for unattended stimuli, with compatible and incompatible target letters being significantly different to non-target letters. Contrary to previous research, this finding suggests that material is not filtered out at an early stage as proposed by early selection. It was found that the response to unattended target material also varied according to the type of item presented at the attended location. These findings were discussed in relation to previous studies which found no difference in the processing of unattended target and non-target material, and also in relation to suggestions that automatic processing of unattended material occurs only when there is controlled processing occurring simultaneously.

Adult↗
PubMed1994

Effects of stimulus alternation, repetition and response requirements on event-related potentials to patterned visual stimuli.

Event-related potentials (ERPs) were recorded to square-pattern stimuli presented either to the upper or the lower half of the visual field. In the Same task the subjects had to respond to the fifth stimulus of a microsequence of stimuli that appeared on the same half field, whereas in the Different task the target stimulus was the alternation of stimulus location after a microsequence of four stimuli to the same half field. The pattern-specific CII component (a negative wave to lower half-field stimulation with 100 ms latency) appeared to be insensitive to task variables. N1 increased to the uncertain alternations of stimulus location. An N2 component with temporal maximum emerged to Nogo stimuli (to the fifth stimulus in the same location in the Different task and the alternation after four identical stimuli in the Same task). An anterior N2 was characteristic to the Nogo stimuli of the Different task. P3 latency was longer, and it had more anterior distribution to the Nogo stimuli.

Adolescent↗
PubMed1994

Season, gender, and P300.

Light therapy in patients with seasonal affective disorder has been reported to enhance visual P300 amplitude. This findings raises the possibility that variations in P300 occur naturally in nonpatients as a function of seasonal variation in sunlight. In the present investigation, P300 was studied in a sample of psychiatrically screened normal subjects who were tested at different times of the year. P300 was larger in women than men and varied in relation to season. This pattern is relevant to studies in which subjects are tested under varying sunlight conditions, such as different seasons. In addition, variations in P300 in normal subjects may be relevant to an understanding of the effectiveness of light therapy for patients with seasonal affective disorder.

Adult↗
PubMed1995

Event-related potentials as indices of display-monitoring performance.

We evaluated event-related potentials (ERP) as indices of performance in three visual display-monitoring tasks: (a) signal detection, (b) running memory and (c) computation. Using factor analysis, we developed a global measure of performance (PFI) for each task. Task-relevant and irrelevant-probe stimuli elicited ERPs, which included components P1, N1, P2, P300, slow waves, and fronto-central negativities. In tasks (a) and (b), P300 amplitude in the task-relevant ERPs increased when the task was engaged, and was greater for accurate-than for inaccurate-response trials. In tasks (a) and (c), the irrelevant-probe ERPs also differed among task and performance conditions. To relate ERP measures to PF1, we developed linear regression models distinguished by three factors: general versus individual-subject, stimulus relevance, and signal-to-noise ratio (SNR). Model accuracy and reliability were highest for individual-subject, relevant-stimulus and high-SNR models, where average R2 values for the three tasks were 0.44, 0.46, and 0.38, respectively. We discuss implications of the models for performance monitoring and implications of the ERP effects for human information processing.

Adult↗
PubMed1982

Independent systems of orientation columns in upper and lower layers of monkey visual cortex.

Using a multi-microelectrode, in 5 animals, orientation tuning was measured simultaneously in 30 closely spaced parallel penetrations perpendicular to the surface of the striate cortex. Actual penetration angles were determined by three-dimensional track reconstruction. Above and below layer IVc, two columnar systems were found whose orientation angles were independent.

Animals↗
PubMed1989

Iso- and cross-oriented columns in cat striate cortex: a study with simultaneous single- and multi-unit recordings.

The constancy of orientation tuning in vertical columns of the visual cortex of the cat was examined with conventional and newly developed multi-electrode methods. Preferred orientation was measured with single- and multi-unit recordings in 68 penetrations approximately perpendicular to the cortical layers and with inter-recording steps of only 40-70 microns. The tuning curves obtained revealed three types of penetration sequences: no-shift penetrations (37%), one-shift penetrations (41%) and double-shift penetrations (22%). Particular attention was paid to the orientation tuning at the transition zones below layer IV. The use of the multi-unit recording technique enabled the measurement of cross-oriented activity within a single electrode position mostly around the border between layers IV and V. Altering the type of anaesthesia (ventilation with room air or nitrous oxide-oxygen) produced only a quantitative change in the percentage of the encountered penetration types. The results suggest that upper and lower layers follow different principles of functional organization. As a consequence different types of columns, especially iso- and cross-oriented ones, are produced in a systematic way.

Animals↗
PubMed1983

Pattern reversal visual evoked potentials in awake rats.

A method for recording pattern reversal evoked potentials (PREPs) from awake restrained rats has been developed. The procedure of Onofrj et al. [26] was modified to eliminate the need for anesthetic, thereby avoiding possible interactions of the anesthetic with other manipulations of interest. Rats were restrained in a harness and placed in front of a pattern generating TV screen displaying a black and white alternating square wave grating. Using various stimulation and recording parameters, normative data are presented from 141 adult male Long-Evans hooded and 11 adult male Sprague-Dawley albino rats. Reliable waveforms were recorded with five identifiable peaks. The labels and mean latencies of these peaks in hooded rats were: N1, 47.3 msec; P1, 65.7 msec; N2, 83.3 msec; P2, 94.4 msec; and N3, 129.8 msec. Spatial acuity functions generated with PREPs gave acuity estimates which corresponded closely to values determined behaviorally for hooded and albino rats [4,11].

Animals↗
PubMed2005

Higher-order activity beyond the word level: cortical dynamics of simple transitive sentence comprehension.

Slow electrophysiological effects, which fluctuate throughout the course of a sentence, independent of transient responses to individual words, have been reported. However, this type of activity has scarcely been studied, and with only limited use of electrophysiological information, so that the brain areas in which these variations originate have not been clearly identified. To improve this state of affairs, a principal component analysis and a modern source analysis algorithm (LORETA) were applied to the slow activity underlying transitive sentence reading. Four components explained 97.3% of the variance. Of key interest was a slow variation that occurred throughout the entire sentence but peaked with the appearance of the verb. The main solution for this component was localized in prefrontal and temporal regions presumably involved in semantic sentence processing. This constitutes empirical evidence for cortical activity--related to semantic processes thought to be involved in thematic role assignment--developing throughout the sentence but presenting a conspicuous maximum with the appearance of the verb. This finding also highlights the central role of verb information in the understanding of transitive sentences.

Adult↗
PubMed2006

Masked and unmasked electrophysiological repetition effects of famous faces.

We investigated immediate repetition effects of sequentially presented famous face pairs. The first face (F1) was presented masked or unmasked and preceded the second face (F2) with different SOAs (84 ms vs. 500 ms). Participants judged F2 with regard to either semantic category (actor vs. singer; indirect task) or perceptual match with F1 (same vs. different; direct task). Repetition shortened RT for unmasked but not for masked F1 conditions. In event-related brain potentials (ERPs), unmasked repetition effects were influenced by task and SOA and consisted a modulation of an occipitotemporal N170, an inferior temporal N250r (200-300 ms), a central-parietal N400 (300-500 ms), and a parietal P600 (500-800 ms). An early occipital negativity (onset approximately 100 ms) was present at the 84-ms SOA but diminished in the 500-ms SOA condition, probably reflecting a fast decaying iconic memory trace. Masked repetition effects in the indirect task were limited to a significant early (100-150 ms) prefrontal/lateral frontal and central-parietal modulation, and a strong trend for a reduced N170 amplitude. This suggests that masked repetition modulated early visual processing but did not influence processes beyond approximately 200 ms that reflect the access to facial representations and semantic information for people.

Adolescent↗
PubMed2004

Face repetition effects in direct and indirect tasks: an event-related brain potentials study.

We investigated immediate repetition effects on event-related potentials (ERPs) during direct and indirect tasks for sequentially presented face pairs. The first face (F1) was presented masked or unmasked, and at different stimulus onset asynchronies (SOAs, 67 vs. 1000 ms) preceding the second face (F2). Experiment I (indirect task) required a semantic classification of F2, with F1 identity being irrelevant. Experiment II (direct task) used the same stimulus sequence but required a physical identity matching of F1 and F2. Whereas no masked repetition effects in behaviour or ERPs were seen, such effects were clearly shown for unmasked F1 faces. For short SOAs, an early-onset ( approximately 100 ms) occipital repetition effect, an inferior temporal N250r (200-300 ms) and a central-parietal N400 modulation (300-500 ms) were seen in both tasks, whereas a parietal P600 effect (500-800 ms) was only present in the indirect task. For long SOAs, the early occipital effect disappeared, suggesting that it reflects a fast decaying iconic memory trace. Clear task differences were seen for N250r, N400, and P600 modulations: P600 was larger for the indirect task, and may be a correlate of semantic analysis required by this task. By contrast, N250r and N400 were larger for the direct task, suggesting that these components are sensitive to task relevance and/or attentional focus to F1, and thus do not reflect purely automatic facilitation in processing. This suggests an influence of strategic processing on the activation of both perceptual representations of faces and semantic representations of people.

Adolescent↗
PubMed2005

Suppression of early evoked gamma band response in male alcoholics during a visual oddball task.

We investigated the early evoked gamma frequency band activity in alcoholics (n=122) and normal controls (n=72) during a visual oddball task. A time-frequency representation method was applied to EEG data in order to obtain phase-locked gamma band activity (29-45 Hz) and was analyzed within a 0-150 ms time window range. Significant reduction of the gamma band response in the frontal region during target stimulus processing was observed in alcoholic compared to control subjects. In contrast, significantly higher gamma band response for the non-target stimulus was observed in alcoholics compared to controls. It is suggested that the reduction in early evoked frontal gamma band response to targets may be associated with frontal lobe dysfunction commonly observed in alcoholics. This perhaps can be characterized by a deficient top-down processing mechanism.

Adult↗