EEG correlates of reinforced behavioral inhibition

Abstract

The search for neural substrates of behavior has often focused upon electroencephalographic changes recorded during task performance or inhibition of performance. With regard to the latter, investigators concerned with EEG correlates of Pavlovian internal inhibition have reported a predominance of cortical synchrony, i.e., slower waves, spindles, or both. Such a relationship between internal inhibition and synchrony has been reported in several situations, e.g., extinction (Kogan, 1960), satiation (Rowland & Goldstone, 1963), habituation (Hernandez-Peon, 1960), classical differential discrimination (Gluck & Rowland, 1959). These findings support the belief that cortical synchrony reflects the action of neural mechanisms governing behavioral inhibition.All of the above situations engender inactivity and relaxation, suggesting that cortical synchrony may be a reflection of lowered arousal level rather than of brain mechanisms underlying behavioral inhibition itself. The present study was undertaken to investigate this possibility. An instrumental vigilance paradigm was used in order to maintain a relatively high degree of arousal while seeking electrocortical correlates of behavioral inhibition. MethodThree adult cats, bearing chronically implanted, stainless steel skull electrodes, were maintained at 85% of ad lib weight and trained to inhibit licking in a vigilance situation. The apparatus consisted of a dimly illuminated 18 in. cubic chamber with a Lucite foodcup mounted on a 4 x 5 in. black panel affixed to the rear wall. Foodcup licks were detected by a Grasonstadler drinkometer, and recorded by a Davis Scientific Instruments Co. cumulative recorder. lliumination of a row of 10 6 W lamps, mounted 8 in. above the cup, Psychon. Sci., 1968, Vol. 10 (I) served as a discriminative stimulus. The training chamber was enclosed within an audiometry room (Industrial Acoustics) and a white masking noise was present throughout each session.The cats were trained to lick the foodcup for 0.3 cc of milk when the row of lamps was illuminated (8+). Inhibitory training was initiated following initial training on a schedule of continuous reinforcement. The first lick following 8+ onset was rewarded and terminated S+. Following the ensuing burst of consummatory licking, S-began. This condition consisted of the continued absence of 8+, and varied randomly within a session from 15-25 sec (mean of 20 sec). Each lick during S-reset the S-timer, thus delaying the next scheduled onset of 8+. As training progressed, 8+ duration was decreased to a maximum of 0.8 sec; licks having a longer latency were not rewarded, as they occurred during the Speriod. A daily session consisted of 50 8+ presentations.Electrocortical activity (ECoG) was recorded via a cable attached to the S's skull pedestal; it was 80 suspended as not to interfere with movements. ECoGs were recorded on a Grass IIID electroencephalograph with a band pass of I-75Hz. Recordings were made irregularly during initial phases of the experiment and routinely when stable inhibition...