Figure 2.

Instrumental learning in the spinal cord. (a) The apparatus used to study instrumental learning. Leg position is monitored using a contact electrode constructed from a 7 cm (length) × 0.7mm (diameter) stainless-steel rod that is taped to the foot. When the leg is extended, the contact electrode contacts an underlying salt solution and completes an electrical circuit that is monitored by a computer. Completion of the circuit generates an electrical stimulus that is applied to the tibialis anterior muscle. This stimulation elicits a flexion response, lifting the tip of the contact electrode out of the salt solution and breaking the electrical circuit. (b) A computer measures the number of responses (times the contact electrode touches the salt solution) and the amount of time in solution. Our measure of learning is derived using the following formula: Flexion duration_i= (60 − Time in solution_i)/(Flexion number_i + 1), where i is the current training bin. (c) Using a master-yoke paradigm, we are able to directly compare the effects of response-contingent (controllable, master) and noncontingent (uncontrollable, yoked) FES training on behavior. In this paradigm, subjects are trained with controllable or uncontrollable stimulation paradigms and then are tested under common conditions (all subjects are exposed to response-contingent stimulation). Learning is indicated by an increase in flexion duration over time. Master rats reacquire the task more rapidly. Prior training with uncontrollable shock (yoked) disrupts learning for up to 48 h. (d) Differences in flexion duration cannot be attributed to differences in the subject’s capacities to make the flexion response. Yoked rats exhibited the highest rate of responding, despite their inability to learn. Adapted from Grau et al³