Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Reaction times and event-related potentials in correct and incorrect trials were studied in a bimanual choice reaction task. In a focused attention (FA) condition, the stimulus modality was constant (visual or auditory); in a divided attention (DA) condition, the modality was varied at random from trial to trial. Stimulus- and response-triggered averages were computed from the midline EEG leads. In error trials, the ERP amplitude was reduced in the P300 range (300-500 msec) and enhanced in the slow wave range (500-700 msec) compared to correct reaction trials. Difference plots between the ERPs (incorrect minus correct reaction trials) revealed a large fronto-central negativity ("NE") and a parieto-occipital "slow wave." These components appeared larger in the response-triggered averages. We believe that they reflect two different stages of error processing. After auditory stimuli the NE peaked much later for DA than for FA, which supports the idea of an asymmetrical allocation of processing resources to the disadvantage of the auditory modality in our DA condition.
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PMID:Effects of crossmodal divided attention on late ERP components. II. Error processing in choice reaction tasks. 171 80

Visual evoked responses were recorded in response to a series of consonants and non-linguistic signs randomly presented. We compared, with a sample of 16 young volunteers, P300 and N400 latency and amplitude in order to detect possible asymmetries. Results in amplitude showed a significant asymmetry within right hemisphere, both in P300 and N400 components. Latency results failed to present any significant difference during the discrimination of consonants, while non-linguistic signs discrimination reflect an asymmetrical tendency in P300 component.
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PMID:[Hemispheric differences in visual evoked potentials during the discrimination of consonants and signs]. 180 37

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.
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PMID:Visual evoked potentials in a patient with prosopagnosia. 244 41

The nature of readiness-potentials (RPs) that may be associated with fully endogenous, 'freely' voluntary acts was investigated. Restriction on when to act were eliminated and instructions fostered 'spontaneity.' The 'self-initiated' RPs exhibited in these conditions were categorizable into two (possibly three) types, all of which could be exhibited by the same subject. Type I had an early onset at about -1050 +/- 175 msec and a long ramp-like form, resembling self-paced RPs. In type II the main negative shift began at about -575 +/- 150 msec, and at about -240 +/- 50 msec in type III. Type II partially resembled the similarly timed NS' component in self-paced RPs. For acts produced at known, preset times, in which freedom of choice was eliminated but planning to act was required, RPs resembled self-initiated type I RPs and self-paced RPs. All RPs were maximal at the vertex, especially type II even though it was also bilaterally asymmetrical. These distributions suggest that cortical areas other than area 4 and 6 contribute importantly, especially to type II. All RPs, whether in self-initiated or pre-planned acts, appear related specifically to preparation for a motor action. When task-related skin stimuli replaced self-initiated movements, under similar conditions of attentiveness (and expectancy), there were either no or relatively small event-preceding-slow potential shifts. All post-stimulus P300 waves were very large. Two volitional processes are postulated: process I is associated with development of pre-planning or preparation to act in the near future (seconds), whether voluntary choice is present (type I RPs) or absent (pre-set RPs); process II, with an onset at roughly 0.5 sec before the act, is associated more uniquely with voluntary choice and with the more specific as well as endogenous urge or intention to act; it can be present in the comparative absence of or in sequence and overlapping with process I.
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PMID:Readiness-potentials preceding unrestricted 'spontaneous' vs. pre-planned voluntary acts. 617 59

Cognitive event-related potentials, such as P300, are sensitive to manipulations of psychological variables and may provide evidence to support theories of brain mechanisms involved in cognition. However, the relationship between event-related potentials and the active neural structures is not yet understood. Electrical stimulation of the index and little fingers of the left hand in the context of a somatosensory target discrimination task, performed by healthy human subjects, elicited the middle-latency component of somatosensory evoked potentials, N60, the long-latency component, N140, and the P300 component. Identification of the generators for both the earlier components and P300, using equivalent electrical dipole modeling, was performed. Individual spatiotemporal seven-dipole models were developed in order to suggest locations of the sources generating each subject's scalp-recorded wave forms. Three dipoles with fairly weak moments, located in the primary and secondary sensory areas, explained the middle- and long-latency somatosensory evoked potential components, and the remaining four dipoles (4-7), with stronger dipole moments, were active during P300. There was a clear temporal separation of dipole activity between the somatosensory evoked potential components and the P300 component. Dipoles 4 and 5 were found quite symmetrically in the parahippocampal areas of the two hemispheres, while dipoles 6 and 7 were slightly asymmetrical. Dipole 7 was found in the left hippocampal area. Dipole 6 appeared in the right insular cortex. The locations of the four dipoles implicated in the generation of the somatosensory P300 were compared with the locations of four dipoles accounting for the auditory evoked P300 described in our previous paper [Tarkka et al. (1995) Electroenceph. clin. Neurophysiol. 96, 538-545]. No substantial difference in source locations of the P300 was found between auditory and somatosensory modality other than an asymmetrical activity in the somatosensory modality contralateral to the stimulated hand.
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PMID:Generators for human P300 elicited by somatosensory stimuli using multiple dipole source analysis. 892 41

In previous studies, low amplitudes and asymmetrical topography with right-sided peaks of the P300-evoked response have been repeatedly described in schizophrenic patients. A total of 18 patients with cycloid psychosis fulfilling the criteria of Perris and Brockington and 18 controls were investigated with a standard auditory odd-ball paradigm and multichannel-evoked potential recordings. Patients had normal P300 topographies and latencies but significantly higher amplitudes than controls. Higher than normal P300 amplitudes have not been described in any other psychiatric disorder until now, and indicate an enhanced level of arousal. Future studies are expected to shed light on the question of whether high P300 amplitudes are transitory sequelae of the acute psychotic episode or a trait of cycloid psychosis.
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PMID:Specific P300 features in patients with cycloid psychosis. 902 Oct 2

The general reduction of P300 amplitude in response to auditory oddball stimuli is one of the most consistently replicated biological observations in schizophrenic patients. Several groups have reported a P300 asymmetry in schizophrenic patients, others have not been able to replicate this finding. In order to clarify this issue, we examined the effect of stimulus discriminability on P300 amplitude distribution in schizophrenic patients and in age-matched normal control subjects, using two different auditory oddball paradigms. The detection of the target tone was either simple or difficult, due to manipulation of pitch disparity. The P300 amplitude was comparatively smaller in the schizophrenic patient group compared to the healthy controls and in the difficult task compared to the simple. The schizophrenic patients showed a specific P300 amplitude reduction over left temporal electrode sites when the simple paradigm was used. The difficult paradigm did not elicit asymmetrical P300 amplitudes in schizophrenic patients.
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PMID:Left lateralized P300 amplitude deficit in schizophrenic patients depends on pitch disparity. 904 86

In previous studies, low amplitudes and asymmetrical topography with right-sided peaks of the P300-evoked response have been repeatedly described in schizophrenic patients. A sample consisting of 18 patients with cycloid psychosis fulfilling the criteria of Perris and Brockington and 18 controls was investigated with a standard auditory odd-ball paradigm and multichannel evoked potential recordings. Patients had normal P300 topographies and latencies but significantly higher amplitudes than the controls. Higher than normal P300 amplitudes have not been described in any other psychiatric disorder until now, and indicate an enhanced level of arousal. Future studies are expected to shed light on the question of whether high P300 amplitudes are transitory sequelae of the acute psychotic episode or a trait of cycloid psychosis.
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PMID:Specific P300 features in patients with cycloid psychosis. 905 Nov 64

Pathologically asymmetrical P300 fields with right lateralized peaks were described in core schizophrenia as an expression of left-temporal functional deficits, while higher than normal amplitudes were found in cycloid psychosis. This latter finding appeared to be specific for cycloid psychosis and was explained by a generalized cerebral hyperarousal. Based on some psychopathological analogies with cycloid psychosis, and on the comparable pharmacological treatment of the acute episodes, a group of 19 manic patients was investigated immediately after remission and clinical stabilization of an episode. Patients with psychotic features were excluded to avoid overlaps with cycloid psychosis. Patients showed normal P300 amplitudes and no pathological asymmetries of the field, but more posterior positive areas compared to age- and sex-matched controls. This indicates that the neurophysiological changes underlying mania are different from both core schizophrenia and cycloid psychosis. Based on previous three-dimensional source location studies, this finding indicates that disinhibition due to reduced frontal lobe activity, and not hyperarousal, is the basic functional mechanism of manic disorders.
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PMID:Distinct neurophysiological mechanisms for manic and cycloid psychoses: evidence from a P300 study on manic patients. 987 88

Previous studies of the auditory P300 event-related potential (ERP) have reported smaller amplitudes in chronic schizophrenics but similar consistencies have not been observed with visual P300s. This study examined P300s in symptomatically stable, medicated, chronic schizophrenics (n = 14) and normal controls (n = 14) performing a visual continuous performance task utilizing degraded stimuli to burden encoding processes. Performance analysis found slower response times, fewer target detections and more false alarms in patients than in controls. Analysis of ERPs showed P300 amplitudes of schizophrenics to be significantly smaller than those of controls and, unlike controls, schizophrenics failed to exhibit significant target vs. non-target P300 amplitude differences. Discriminant analysis indicated target and non-target midline (Fz, Cz, Pz) P300 amplitudes together correctly classified all patients and controls. Exploratory topographic analysis indicated that P300 amplitudes were not asymmetrical in patients, as has been observed with auditory P300s, and, unlike the performance measures, the P300s did not correlate with the patient's positive or negative symptom ratings. The implications of these findings are described in relation to attentional disturbances and trait versus state issues in schizophrenics.
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PMID:Event-related potentials in schizophrenic patients during a degraded stimulus version of the visual continuous performance task. 1009 72


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