617 Modulation of brain potentials by hierarchical processing: A high-density ERP study

234

Abstracts

/International

Journal

respond to a target one, stated at the beginning of the task (probability = 0.201, by pressing a button, A varied mapping version (see Schneider, Shiffrin, 1977) of the oddball paradigm was developed: with a corpus of twelve geometric figures, at each recording block, a new one was designated as a target and the eleven others as the standard. Experimental design consisted in 16 samples during 4 hours on morning, with a non-constant routine (rest periods duration was randomised). Individual time series for the P300 component (latency and amplitude) in Pz site and detection performance (reaction time and error percentage) for 10 subjects were analysed with the Cosinor method. Signitlcant oscillations with periods between 60 and 120 minutes were found in both electrophysiological and behavioral components.

616 EVENT-RELATED POTENTIALS AND CATHECHOLAMINE METABOLITES IN NORMAL SUBJECTS

Y. Okajima*, D. Kuwakado, H. Isono, A. Iwanami, K. Kamijima Department of Psychiatry, Showa University School of Medicine, l-5-8 Hatanodai Shinagawaku Tokyo, 142 Japan Fifteen right-handed healthy volunteers (10 males and 5 females), who gave informed consent, serv@ as the study population (mean age, 26.8 years). Event-related potentials were recorded during two auditory tasks (an oddball task and a distraction task similar to that of Grillon et al.). In the oddball task, 85% of the stimuli were tones of 1 KHz, and the other 15% tones of 2 KHz (target stimuli). In the distraction task, 70% of the stimuli were tones of 1 KHz: 15% tones of 2 KHZ (target stimuli), and the other 15% white noise (novel stimuli). Subjects were instructed to press a button as quickly as possible for the infrequent high-pitch tones. The scalp EEG was recorded with Ag-AgCl disc electrodes from Fz, Cz, and Pz referred to linked earlobes. Bandpass was set to O.lS-60Hz. EEGs were sampled every 2.5 ms from 40 ms before to 600 ms after the stimulus onset. In the oddball task, P3 amplitude at Cz and Pz for target stimuli correlated negatively with plasma HVA level. In the distraction task, P3 amplitude at Pz for novel stimuli correlated negatively with plasma HVA level.

617 MODULATION OF BRAIN POTENTIALS BY HIERARCHICAL PROCESSING: A HIGH-DENSITY ERP STUDY Shihui Han*, Silu Fan, Lin Chen, Yan Zhuo Beijing Lab of Cognitive Science, University of Science and Technology of China, 19A Yuquan Road, P.O. Box 3908, Beijing 100039, People’s Republic of China The present study investigated how attention to global or local levels of hierarchical patterns modulates brain potentials by

of Psychophysiology300

(1998)

95-271

recording high-density event-related brain potentials (ERPs) evoked by hierarchical stimuli. 120-channel recordings of ERPs were obtained from subjects while they detected targets at global or local levels of hierarchical stimuli displayed in the left or the right visual field. We found that, relative to global stimuli, local stimuli elicited enhanced posterior Pl and N2. The N2 enhancement was stronger at the left than at the right hemisphere regardless of stimulus positions. The amplitudes of the frontal P2 to local stimuli were higher at the contralatera1 sides but lower at the ipsilateral sides than those to global stimuli. The interference effect was observed on the anterior N2 amplitudes and latencies. The computation of 3-dimensional current distributions showed similar distributions of current density foci over the posterior cortex in association with global and local processing within a time window of 80-230 ms after sensory stimulation. A contralateral frontal activity was observed for both global and local processing between 300-400 ms. However, an additional ipsilateral frontal focus between 230-350 ms was found specially for local processing. The results corroborate the findings of previous ERP studies and suggest that the frontal lobe is engaged in the cortical network for hierarchical analysis and may be particularly important for the selective processing of local parts of a global structure.

618 TO INHIBIT PAIN IS TO ACTIVELY SHIFT CONSCIOUS AWARENESS: SOMATOSENSORY EVENT-RB LATED POTENTIAL EVIDENCE DURING HYPNOTIC ANALGESIA J. Horton’,**, D. McClain-Furman&i’, I. M&szaros3, H.J. Crawford “Virginia Polytechnic Institute and State University, Blacksburg, VA., USA 2Clinch Valley College of the University of Virginia, Wise, USA 3Kossuth Lajos University, Debrecen, Hungary The successful inhibition of pain during hypnotic analgesia (HA), so that there is little or no conscious awareness of pain, requires an ability to actively control inhibitory processing of incoming stimuli. Reduced pain and distress during HA is positively correlated with hypnotic susceptibility level. Past work (e.g., Crawford and Gruzelier, 1992; Crawford et al., 1998; Kropotov et al., 1997) supports the proposal that (1) HA is an active process that requires inhibitory effort where the anterior frontal cortex participates in a topographically specific inhibitory feedback circuit that cooperates in the allocation of thalamocortical activities, and (2) highly hypnotizable persons can better suppress pain because of their more effective frontal attentional system. For noxious electrical stimuli presented to the left hand, we found highs exhibited somatosensory event-related potential (SERP) latencies that were faster than lows regardless of condition, as well as significantly