Electrophysiological and behavioral effects of transcortical polarizing current: comparison with the behaviorally...

Passage of polarizing current through the cerebral cortex, with the anode at the surface (Anp), produces neurophysiological changes which may be related to those which occur during learning. This relationship was evaluated at the visual cortex of unanesthetized, Sprague-Dawley rats, under a number of experimental conditions, with chronic light flash (LF)-evoked electrocortical response recording and LF-shock avoidance. During experimental treatments electrophysiologically studied animals received either 30 paired presentations of Anp and LF or parametrically equal, unpaired presentations; behaviorally studied animals received either these treatments or 30 presentations of LF alone. Each LF presentation contained 15 LF at the rate of one/sec. Anp presentations consisted of a 15-sec rise of current from 0 to 9 muA/sq.mm, 15 sec of steady 9 muA/sq.mm, and a 15-sec period of current decrease from 9 back to 0 muA/sq.mm. Each presentation was separated from the next by a randomized interval of 45-120 sec. Paired Anp and LF produced large waves (50 muV or greater) in the late negative phase of the evoked response. These waves appeared towards the end of pairings, were evident in recordings made 48 h after pairings and again diminished, but rapidly reappeared when pairings were reintroduced. Anpp and LF pairings also produced a 55% decrease in the number of trials needed to reach criterion on the LF-shock avoidance task as compared to the performance of the group treated with LF alone. Unpaired Anp and LF had no discernable electrophysiological or behavioral effects.