Conditioned activity of cortical motor neurons.

In awake rabbits, which received auditory stimuli paired with electric shock to a forelimb, the activity of 229 units were recorded. In 118 units conditioned responses were observed. In 68 units they were excitatory and in 50 units, inhibitory in accordance with the excitatory or inhibitory effect of the reinforcing stimulus. When the conditioned response appeared, 25 percent of the units showed a change of the response to reinforcement. In the majority of units conditioned responses could be extinguished and differentiation elaborated. Inhibitory conditioned unit activity is considered as one of the forms of internal inhibition.