Contribution of muscle spindle circuits to learning as suggested by training under flaxedil

Abstract

Fifteen naive cats, while completely paralyzed with Flaxedil, were subjected to a classical conditioning procedure in which tone (CS) was paired with shock to the hindpaw (US). Before each paralytic training session, five test trials with the CS alone were given and the cat was observed for conditioned responses. Six other cats were similarly trained and tested, except that they were paralyzed after completion of each training session. 1. 1. None of the fifteen cats trained while paralyzed showed conditioned motor responses to CS test trials after 500 to 1000 CS-US trials extended over 10 to 20 sessions. In contrast, the six cats trained normally with subsequent paralysis showed conditioned motor responses to the CS test trials after an average of 150 CS-US trials. 2. 2. The development of conditioned changes in cortical activity and pupillary diameter during training under paralysis indicated that the CNS was receptive to the conditioning procedure. 3. 3. Cats with prior training under Flaxedil developed conditioned motor responses during the first ten trials of the initial unparalyzed training session. In contrast, naive cats generally showed no conditioned motor responses until the third training session. 4. 4. The failure of conditioned motor responses to develop during paralytic training and the facilitation of the responses during subsequent normal training are discussed with emphasis upon the possible role of muscle spindles. It is suggested that conditioned responses of gamma motoneurons are established during paralytic training, but proprioceptive feedback is blocked. During subsequent training without paralysis, the added effect of afferent feedback mediated by conditioned and unconditioned responses of the gamma motoneurons may result in an accelerated appearance of the overt conditioned response.