Activity of cortical and caudatal neurons accompanying instrumental prolongation of the extension phase of reaching in rats.

Activity of 38 cortical and 59 caudatal neurons was examined in 11 rats trained to push, with one forepaw, a hinged vertical partition accessible through a narrow horizontal tube. The rats had to overcome blockade of the operandum lasting from 0 to 130 ms. Periresponse histograms (+/- 512 ms around the onset of a series of reaching movements) showed that reach-related phasic and series-related tonic excitation prevailed in motor cortex and caudate nucleus, respectively, while inhibitory activity changes did not differ between the two structures. Perireach histograms (+/- 196 ms around onset of successful or unsuccessful displacements of locked or free operandum) showed that excitation of cortical neurons was related to amplitude and duration of the extension but no significant activity peaks corresponded to the sudden release of the movement blockage. Similar, but less expressed, changes were found in caudate neurons. It is concluded that the rats learned to prolong the extension phase of reaching but that the movement continued to be preprogrammed and independent of proprioceptive or other sensory feedback.