Classical conditioning of the human flexion reflex

Abstract

The eyeblink conditioning paradigm is a well established model for studying learning processes in humans and animals. In this study a flexion reflex conditioning paradigm was established using the standard delay paradigm. The flexion reflex was elicited in 10 young, healthy subjects by a train of electrical pulses (100 ms, 100 Hz, 0.65 ms) applied to the medial plantar nerve (unconditioned stimulus, US). A tone (1000 Hz, 550 ms) was presented via headphones as the conditioning stimulus and which coterminated with the US. Responses were recorded from the anterior tibial muscles. Subjects were conditioned within one session of 120 trials of paired stimuli. This was established statistically via the continuous change in characteristic parameters of the responses throughout the experiment. Although the process of limb muscle conditioning takes longer than eyeblink conditioning, this type of flexion-reflex conditioning may possibly serve as a further model for the study of plastic changes within the nervous system. Moreover, the considerable versatility of limb movements offers the advantage of greater possibilities for testing the conditioning result.