Autonomic versus cortical arousal in schizophrenics and non-psychotics

Abstract

ONE of the more provocative experimental studies in the recent literature on schizophrenia was the report by VENABLES~ in this journal that the two-flash fusion threshold (TFT) and tonic palmar skin potential (SP), psychophysical and psychophysiological indicants, respectively, of arousal, were correlated strongly but with opposite sign in schizophrenic and normal subjects. In two samples of non-paranoid schizophrenics, the TFT and the concurrent level of palmar SP were correlated -0.79 and -0.72 in contrast to correlations of $0.45 and $0.61 (all highly significant) found in two normal groups. Because low TFTs are associated with high levels of cortical arousal (vi& infra), the expected correlation with SP is negative and Venables provides a somewhat complicated rationale to account for the inversion of this relationship in his normal subjects. The TFT is an estimate of the shortest interval between two brief flashes of light which still allows the subject to perceive a double rather than a single flash. LINDSLEY~J and his students had demonstrated in the cat and monkey that two flashes separated by 100 msec, easily resolved by human subjects, yield two distinct evoked responses in the visual cortex while a 50 msec separation, seen as a single flash by humans, produces only a single cortical evoked response. Following brief electrical stimulation of the ascending reticular arousal system, however, this same 50 msec interflash interval evoked two distinct responses in the visual projection area, suggesting that reticular activation had increased the temporal resolving power of the cortex and, presumably, that a similar effect in a human subject might allow him to perceive the 50 msec pair as a double flash. Using averaging techniques to abstract the evoked response from the EEG, VAUGHAN and COSTAR have confirmed that, for human subjects, as the interflash interval is increased the evoked response to the second flash appears at the same interval at which some pairs begin to be seen as double. KOPELL, NOBLE and SILVERMANS found that the TFT is raised by a barbiturate and lowered by a stimulant, and ROSEN reports a correlation of -0.63 between the TFT and a forced-choice * This study formed a part of a doctoral dissertation submitted by the junior author to the Graduate Faculty of the University of Minnesota. It was supported in part by a grant to the senior author from the Graduate Medical Research Fund of the University. The authors are indebted to the Department of Psychiatry of the Minneapolis VA Hospital and especially to Dr. HAROLD GILBERSTADT and Dr. GAIL LUMRY for their generous support and cooperation.