In the present study, we introduce an electroencephalography (EEG)-based, real-time, cortical rhythmic activity monitoring system which can monitor spatiotemporal changes of cortical rhythmic activity on a subject's cortical surface, not on the subject's scalp surface, with a high temporal resolution. In the monitoring system, a frequency domain inverse operator is preliminarily constructed, considering the subject's anatomical information and sensor configurations, and then the spectral current power at each cortical vertex is calculated for the Fourier transforms of successive sections of continuous data, when a particular frequency band is given. A preliminary offline simulation study using four sets of artifact-free, eye-closed, resting EEG data acquired from two dementia patients and two normal subjects demonstrates that spatiotemporal changes of cortical rhythmic activity can be monitored at the cortical level with a maximal delay time of about 200 ms, when 18 channel EEG data are analyzed under a Pentium4 3.4 GHz environment. The first pilot system is applied to two human experiments-(1) cortical alpha rhythm changes induced by opening and closing eyes and (2) cortical mu rhythm changes originated from the arm movements-and demonstrated the feasibility of the developed system.
Objective: We investigated cognitive inhibition in nonclinical individuals with schizotypal traits using eventrelated potentials. Methods: College students with psychometrically defined schizotypal traits (n = 16) and normal controls (n = 15) participated. The computerized Stroop task with three types of stimuli, i.e., congruent, incongruent, and neutral words, was used to measure cognitive inhibition. Results: The schizotypaltrait group committed significantly more errors in response to incongruent words than did the control group. The control group showed frontal negativity (FN) of significantly greater amplitude in response to incongruent than to congruent and neutral stimuli, whereas the schizotypal-trait group showed no significant difference in FN amplitude between incongruent and congruent/neutral stimuli at 300 -400 ms poststimulus. A source localization analysis conducted in different waveforms for incongruent minus congruent conditions at 300 -400 ms poststimulus showed reduced activation in the left cingulate cortex and in the middle/medial prefrontal cortex in the schizotypal-trait group compared with the control group. The two groups did not differ in the sustained potential amplitudes observed at 550 -650 ms after stimulus-onset at parietal sites. Conclusions: These results suggest that individuals with schizotypal traits have difficulties in conflict detection and cognitive inhibition, possibly mediated by the cingulate cortex and prefrontal cortex.
BackgroundWe investigated the electrophysiological correlates of object-repetition effects using an object categorization task, standardized low-resolution electromagnetic tomography (sLORETA), and individual magnetic resonance imaging. Sixteen healthy adults participated, and a total of 396 line drawings of living and non-living objects were used as stimuli. Of these stimuli, 274 were presented only once, and 122 were repeated after one to five intervening pictures. Participants were asked to categorize the objects as living or non-living things by pressing one of two buttons.ResultsThe old/new effect (i.e., a faster response time and more positive potentials in response to repeated stimuli than to stimuli initially presented) was observed at 350-550 ms post-stimulus. The distributions of cortical sources for the old and new stimuli were very similar at 250-650 ms after stimulus-onset. Activation in the right middle occipital gyrus/cuneus, right fusiform gyrus, left superior temporal gyrus, and right inferior frontal gyrus was significantly reduced in response to old compared with new stimuli at 250-350, 350-450, 450-550, and 550-650 ms after stimulus-onset, respectively. Priming in response time was correlated with the electrophysiological priming at left parietal area and repetition suppression at left superior temporal gyrus in 450-550 ms.ConclusionsThese results suggest processing of repeated objects is facilitated by sharpening perceptual representation and by efficient detection or attentional control of repeated objects.
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