Surgical interference with pathways mediating responses conditioned to cortical stimulation.

Cats trained to avoid a foot shock (US) when electrical stimulation (CS) was applied to homotopic areas on either the right or left marginal gyrus were subjected to various degrees of surgical isolation of the stimulated areas. For ten cats a U-shaped incision on one hemisphere isolated the stimulated area from most of the intracortical connections, and the contralateral area was undercut to eliminate direct corticifugal conduction. Postoperative tests showed a highly significant superiority in conditioned reflex (CR) level for stimulation of U-cut cortex. Cats with cortex undercut had to be retrained before a stable level of CR could be reestablished. Four other animals underwent bilateral undercutting of varying extents so that the reorganization could be more carefully evaluated. Trigeminal neurotomies and other controls were utilized. It is concluded that the electrically applied CS normally is elaborated principally via corticifugal fibers and if these fibers are cut, additional training is necessary before the intracortically conducted CS can become effective.