Time-dependent effects of pyramidotomy in the operantly conditioned rats.

The effect of unilateral transection of bulbar pyramid on operantly conditioning in rats, have been shown to be in direct relationship with the time of its execution. Stable instrumental reflexes reappeared on average 3.9 days after the transection of the bulbar pyramid. However, preliminary transection of the pyramid led to the prolongation of stabilization of operant conditioning after an average of 16.5 days. These findings are considered to be in view of the mechanisms of switching of descending influences of corticospinal and cortico--rubrospinal systems.