Y-D Zhou | PubMed Health

PubMed2006

Modulation of somatosensory event-related potential components in a tactile-visual cross-modal task.

Human tactile discrimination studies have shown that visual stimuli enhance tactile performance. Other studies on event-related potentials showed that somatosensory N140 was enhanced when attention of human subjects was directed to tactile stimuli. Therefore, we hypothesized that N140 would be modulated when human subjects performed tactile cross-modal delay tasks. Scalp-event-related potentials were recorded from normal subjects performing either a tactile-tactile unimodal, or a tactile-visual cross-modal delayed matching-to-sample task. Identical tactile stimuli were used in both tasks. N140 component evoked by the tactile stimuli was enhanced in the cross-modal task. Enhancement of this component was also observed in control cross-modal tasks. The results suggest that tactile-visual cross-modal association affects tactile sensory-perceptual processes in humans.

Adult↗

PubMed2005

Sequential neural processes of tactile-visual crossmodal working memory.

Working memory is essential to learning and performing sensory-motor behaviors that in many situations require the integration of stimuli of one modality with stimuli of another. In the present study, we focused on the neural mechanisms underlying crossmodal working memory. We hypothesized that in performance of the tactile crossmodal working memory task, there would be sequentially discrete task-correlated neural activities representing the processes of crossmodal working memory. Scalp-recorded event-related potentials were collected from 15 electrodes in humans performing each of four tasks: tactile-tactile unimodal delayed matching-to-sample task, tactile-visual crossmodal delayed matching-to-sample task, tactile unimodal control spatial task, and tactile crossmodal control spatial task. Two positive event-related potential peaks were observed during the delay of the task. One peak (late positive component-1) was at about 330 ms after the onset of the tactile stimulus, and the other (late positive component-2) was at about 600 ms. Late positive component-1 was observed in all four tasks. There was no significant difference in late positive component-1 either between the unimodal tasks, or between the crossmodal tasks, but late positive component-1 was significantly larger in the crossmodal tasks than that in the unimodal tasks, and showed a specific pattern of larger activity over parietal areas than activity over frontal areas. Late positive component-2 was not observed in the unimodal matching task but was observed in all other three tasks over parietal areas. During the late delay (1000 ms-1500 ms), significant differences in negative potentials (late negative component) were found between the tasks. The present study shows sequential changes in event-related potentials during the retention period of working memory tasks. It indicates that in performance of a crossmodal working memory task, there are sequentially discrete neural processes that may represent neural activities related to different cognitive functions, such as crossmodal transfer of information, and the working memory of the stimulus.

Adult↗

PubMed2005

Patterned firing of parietal cells in a haptic working memory task.

Abstract Cells in the somatosensory cortex of the monkey are known to exhibit sustained elevations of firing frequency during the short-term mnemonic retention of tactile information in a haptic delay task. In this study, we examine the possibility that those firing elevations are accompanied by changes in firing pattern. Patterns are identified by the application of a pattern-searching algorithm to the interspike intervals of spike trains. By sequential use of sets of pattern templates with a range of temporal resolutions, we find patterned activity in the majority of the cells investigated. In general, the degree of patterning significantly increases during active memory. Surrogate analysis suggests that the observed patterns may not be simple linear stochastic functions of instantaneous or average firing frequency. Therefore, during the active retention of a memorandum, the activity of a 'memory cell' may be characterized not only by changes in frequency but also by changes in pattern.

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