Neuronal mechanisms of conitioned placing reactions in cats.

Neuronal correlates of conditioned placing reaction of cat’s forepaw were studied. The conditioned reaction evoking by tactile stimulation of the paw’s ventral side had the same motor pattern, consisting mainly in successive flexion and extension of elbow joint, as the placing reaction evoked by paw’s dorsal side stimulation in naive animals. The activity of single neurons from the m. biceps representation area in pericruciate motor cortex and VL thalamic nucleus was recorded. As a result of learning the excitatory response of cortical neurons to paw’s ventral side stimulation in 20-50 ms post-stimulus interval was 2-2.5 times more than the response to the same stimulation in naive cats. This short-latency increase of response was not accompanied by modifications of sensory inflow to the motor cortex or movement related afferentation changes arriving from VL nucleus. There were no marked differences in excitability of cortical neurons of naive and trained animals as well. The results suggest a functional plasticity of the neuronal net in the motor cortex, consisting of a change in the efficiency of connections between neurons receiving sensory determined afferent excitation and the functional groups of neurons controlling the contraction of different muscles.