Lateral asymmetry of the scalp distribution of somatosensory evoked potential amplitude

Attenuation of beta and gamma oscillations in schizophrenia spectrum patients following hand posture perturbation

Several electroencephalographic (EEG) studies in schizophrenia report that the patients have reduced evoked gamma activity following visual and auditory stimulation. Somatosensory gamma activity has not previously been examined. It has been suggested that a dysfunction basic to schizophrenia spectrum traits would involve proprioceptive information processing and this has recently been supported by the finding of diminished latency of early proprioceptive evoked potentials in a sample of chronic schizophrenia patients. The proprioceptive stimulus used previously, and presently, consisted of an abrupt increase of weight on a hand-held load. Eighteen first-time admitted schizophrenia spectrum patients and 18 healthy matched comparison subjects were included. Proprioceptive evoked potentials were recorded as 64-channels EEG for 120 trials in two runs differing in sequence. Contra-lateral evoked beta (latency 90 ms, frequency 21 Hz) and gamma (latency 70 ms, frequency 32 Hz) oscillations were attenuated in the patient group. The healthy comparison subjects had increased gamma amplitude in the left hemisphere in the regular sequence, a phenomenon not seen in the patients. The deviant findings were unexpectedly more circumscribed in the schizophrenia than in the schizotypal personality disorder (SPD) patients. Future studies should include several concurrent psychophysiological measures.

Hemispheric asymmetries in cognitive modeling: connectionist modeling of unilateral visual neglect

Neglect is an acquired cognitive disorder characterized by a lack of processing of one side of a stimulus or representational space. There are hemispheric asymmetries in its cause and in its effects, but implemented computational models of neglect have tended not to incorporate this fact. The authors report a series of neural network simulations of the line-bisection task. They test the hypothesis that simple, neuroanatomically realistic principles of connectivity in the nervous system can produce emergent behaviors that capture a wide range of quantitative and qualitative data observed in neglect patients presenting with general visuospatial neglect. They demonstrate that exploring low-level architectural principles in implemented computational models is both a productive avenue of research and offers the most parsimonious explanations of behaviors observed in patients.

Emotional processing deficits in individuals with unilateral brain damage

This article presents a review of the neural mechanisms underlying emotional processing deficits (EPDs) in individuals with unilateral brain damage. First, key theoretical issues pertaining to the neuropsychology of emotion are presented. These include parameters of emotional processing, the componential approach, emotional domains, and hypotheses regarding hemispheric specialization for emotion. Second, the literature on hemispheric asymmetries for emotion is reviewed in terms of processing mode (perception and expression) and communication channel (facial, prosodic-intonational, and lexical-verbal). Studies involving normal adults and individuals with right- or left-sided brain damage are reviewed. Third, recent findings identifying the role of the right hemisphere in emotional processing are described. The article is concluded by aligning these new data with findings from the general literature, providing added support for the right-hemisphere emotion hypothesis.

Lateralized spatial processes and their lexical implications

Numerous lateralized tasks have been identified as involving spatial processing, but the extent to which they use the same spatial process is largely unknown. The present research investigated relationships among significant asymmetries from seven visuo-spatial and two verbal tasks, combining samples from previous factor analytic experiments with those from three new studies (combined N=789). All of the spatial intercorrelations were negligible (r<0.20), unlike previous outcomes finding robust correlations within certain clusters of verbal asymmetries. However, lateral differences involving spatial quantitative processing on the one hand and figure-ground separation on the other, showed significant but independent correlations with one from visual lexical processing (word recognition). The results support three major conclusions. First, there are at least several and possibly many lateralized spatial processes. Second, hemispheric processes follow a modular architecture in preference to a diffuse or parallel distributed architecture. Finally, the dissociated correlations are consistent with a visual lexical processing model having both occipital and parietal components, potentially reconciling a current controversy over the cerebral localization of language.

Event-related potentials to airway occlusion in young and old subjects

Event-related potentials (ERPs) were recorded to both inspiratory and expiratory airway occlusion in young (21-28 years) and old (55-67 years) subjects under both attend and ignore conditions. Early and late components of the ERP (N1, P2, N2, P3) were observed to both types of occlusions in both conditions. Variations in these components were consistent in both direction and degree with those observed in oddball tasks employing exteroceptive stimuli. ERPs for breathing may serve to clarify sensory attributes of respiratory stimuli in humans and to identify central processing abnormalities in patient populations.

Functional interhemispheric asymmetries at birth as demonstrated by somatosensory evoked potentials

Functional cerebral hemispheric asymmetries detectable at birth have been suggested by a number of neuroanatomic, neuroradiologic, and clinical neurophysiologic modalities. The aim of this study was to determine whether functional interhemispheric asymmetries can be identified using electrophysiologic measures. As part of a prospective study, somatosensory evoked potentials following median nerve stimulation were recorded in nine healthy full-term newborns on day 2 or 3 of life, and somatosensory evoked potentials were repeated at 2 and 6 months of age. These children were subsequently examined at 1 and 3 years of age by a pediatric neurologist and all had normal examinations. Handedness was determined at 3 years by questioning the parent and by clinical observation. Three of nine were left-handers. All three left-handers had clearly identifiable neonatal N19 parietal potentials over the right hemisphere. Following right median nerve stimulation, contralateral parietal potentials were absent on two of the three and questionable in the third. Asymmetries were not clearly present in right-handers although only one showed an increased maturation of the right hemisphere relative to the left. At 2 months of age, interhemispheric differences were no longer clearly evident. This data suggests that preferential hemispheric asymmetries are masked by 2 months of age. This differential rate of development demonstrated by neonatal somatosensory evoked potentials may be an early indicator of ultimate handedness.