An early event-related cortical potential.

Psvcnor-nYsIoLoav Copyright © 1978 by The Society for Psychophysiological Research. Inc. Vol. 15. No. 4 Printed in u.s.,(_ An Early Event-Related Cortical Potential DOUGLAS S. GooDIN, KENNETH C. SQUIRES, BEVERLEY H. HENDERSON, AND ARNOLD STARR Department of Neurology, University of California, Irvine ABSTRACT A waveform subtraction procedure, in which evoked potentials to rare tones (p=.15) in an Ignore condition were subtracted from the analogous waveforms in an ‘Attend condition, revealed the existence of a previously unreported positive potential with a latency of approximately 165 msec (P165) which is related to cognitive stimulus processing. The potential was absent for frequent background tones. An analysis of latency and scalp distribution data showed that P165 could be differentiated from the stimulus-evoked P200 potential, and experiments in which muscle tension was varied did not change the form of P165, supporting a neurogenic origin. Most likely P165 is an early manifestation of decision processes related to the later N200 and P300 potentials. DESCRIPTORS: Decision-related cortical potentials, P300 wave, Information processing. Several late components which are sensitive to psychological variables have been identiﬁed in the auditory evoked potential waveform (for example, see Squires, Squires, & Hillyard, 1975). Of these event-related potentials, as distinguished from the obligatory stimulus-related potentials, the P300 component (Sutton, Braren, Zubin, & John, 1965) has been the most thoroughly studied. However, because the latency of P300 often exceeds the time required to make a behavioral response (Ritter, Simson, & Vaughan, 1972), and thus appears to reﬂect cognitive activity subsequent to the primary processes of stimulus identiﬁcation, stimulus classiﬁcation and response selection, there has re- cently been an increased interest in earlier latency potentials. These earlier potentials, such as N200 (Courchesne, Hillyard, & Galambos, 1975; Ford, Roth, Dirks, & Kopell, 1973; Picton, Hillyard, Krausz, & Galambos, 1974; Ritter et al., 1972; Simson, Vaughan, & Ritter, 1976, 1977; Squires, N. et al., 1975; Squires, Donchin, Heming, & McCarthy, 1977), may logically reflect the primary These data were separately analyzed in a previous study of the N200 and P300 potentials, which is reported elsewhere. We thank Drs. Ritter, Hillyard, Woods, and N. Squires for comments on previous versions of this manuscript. This research was supported by Grant PHS NSl1876. Address requests for reprints to: Dr. K. C. Squires. Depart~ ment of Neurology, University of California, Irvine, 101 City Drive South, Orange, California 92668. stimulus processing sequence, as Simson et al. (1977) have proposed. In this study we report the existence of an additional early potential which is dependent on psychological variables, and hence may be related to the event-related potentials pre- viously described. Method Forty-seven normal subjects (25 female, 22 male) ranging in age from 6 to 76 yrs were tested. Four of the subjects were familiar with the experimental design. Subjects were considered “normal” if they were fully employed or attending school. The mental status of the older, retired subjects was assessed using the “Mini- Mental Stateq test (Folstein, Folstein, & McHugh, 1975) and all who were included in the study scored 29 or 30 out of the 30 possible points. In addition to the 47 subjects tested, 2 other individuals were eliminated from the experiment due to low test scores and 1 was eliminated because of a psychiatric problem. Four hundred pre-recorded binaural tone bursts (50 msec, 60 dB SL) were presented through earphones at 3 rate of 1/ 1.5 sec in each run. Eighty-ﬁve percent of W tones had a frequency of 1000 Hz and ﬁfteen percent had a frequency of 2000 Hz. The stimulus sequence was fallq dom with the constraint that no two rare tones appeared In succession. After familiarizing the subject with the tone bursts. the stimulus sequence was presented twice with an interven- ing 5-10 min rest period. In one condition the subject W35 instructed to ignore the tones and to read a magalmf (“Ignore” condition). In a second condition (“Attend condition) the subject was instructed to keep a mema‘ 360 0048-5772/78/0700-0360$0.60/0 © 1978 The Society for Psychophysiological Research, Inc.