SYSTEMATICS OF THE EVOKED SOMATOSENSORY CORTICAL POTENTIAL: A PSYCHOPHYSICAL‐ELECTROPHYSIOLOGICAL COMPARISON *

Throughout the history of physiological psychology there has been existent a frustrated enthusiasm for direct comparisons between psychophysical responses and electrophysiological measures from the same verbally responsive human subjects. Unfortunately, experimental surgery, unrelated to pathological conditions, as it should have, remained an unacceptable course of action, and little could be made of the diffused and minute electrical signals which certainly existed below the myographic and resting encephalographic noise. It was the work of G. B. Dawson5 which opened up a whole new spectrum of possibilities of experimental inquiries. Professor Dawson devised techniques for recording signals from the major peripheral nerves by percutaneous recording as well as suggesting the techniques of statistical averaging which are used by all of the participants in this conference. Our earlier workg8l took advantage of the ability to measure peripheral nerve action potentials in the intact human arm and studied the temporal and spatial coding correlates of estimates of sensory magnitude. The success of these earlier studies led us to the present investigations which are directed at the coding of sensory intensity and space as they are reflected in the somatosensory evoked cortical potential. Since Dawson's original work, considerable attention has been directed towards the improvement of techniques and the associated instrumentation. The membership of this conference includes some of the contributors to this aspect of this work, and the reader is specifically directed to the work of W. A. Clark, Jr.,Io B. S. Rosner" and Professor Rosenblith's Laboratory9 at MIT. Recent reviews by Davis and Ferris? and Rosenbliths are useful guides to the instrumentation complexities. As stated, the present studies were carried out to determine which measures of the evoked cortical responses could be correlated with behavioral measures, and therefore, were representative codes of psychological phenomena. Because of certain features of the recorded potentials it was also possible to tentatively associate certain portions of the averaged waveform with specific anatomic structures, Section A of our experiments and results section presents a description of the waveform which, along with the results of Section E, the effects of sleep on the evoked potential, contribute to this association. Section B presents the results of