Identification of differently timed motor components of conditioned blink responses

Electromyographic recordings were made from the orbicularis oculi muscles o f cats in order to identify differently timed motor components of condition ed eye blink responses (CRs), Conditioning was established rapidly by pairi ng electrical stimulation of the hypothalamus (HS) with a click conditioned stimulus (CS) and a glabella tap unconditioned stimulus (US). Analysis of the EMG responses disclosed five different motor components of the CR that could be distinguished and characterized according to their latencies of oc currence. Four were associated with an increase in EMG activity elicited by the CS (16-48 ms, alpha(1); 48-80 ms, alpha(2); 80 to 120 ms, beta; greate r than or equal to 120 ms, gamma), and one was associated with a decrease i n activity (16 to 60 ms, alpha(i)). Analysis of the amplitudes of the diffe rent components of the CR during the course of conditioning and extinction disclosed that short latency, alpha(1) components of the CRs were acquired and extinguished in a manner equivalent to longer latency components of the CRs, The observations supported the hypothesis that short and long latency components of blink responses represented comparable rather than substanti ally different forms of Pavlovian conditioning. The alpha(2) response was p resent before conditioning began, and increased with other components after conditioning. The alpha(i) response component was also observed prior to c onditioning, and represents a previously undetected, inhibitory consequence of presenting weak (70 dB) acoustic stimuli. It could play a role in condi tioned inhibition, latent inhibition and blocking as well as suppression of the conditioned motor response during extinction. (C) 1999 Elsevier Scienc e B.V. All rights reserved.