Intracortical connections are altered after long-standing deprivation of dorsal column inputs in the hand region of area 3b in squirrel monkeys

摘要

A complete unilateral lesion of the dorsal column somatosensory pathway in the upper cervical spinal cord deactivates neurons in the hand region in contralateral somatosensory cortex (areas 3b and 1). Over weeks to months of recovery, parts of the hand region become reactivated by touch on the hand or face. In order to determine if changes in cortical connections potentially contribute to this reactivation, we injected tracers into electrophysiologically identified locations in cortex of area 3b representing the reactivated hand and normally activated face in adult squirrel monkeys. Our results indicated that most of the expected connections of area 3b remained for partially reactivated area 3b, including the majority of intrinsic connections within area 3b; feedback connections from area 1, secondary somatosensory cortex (S2), parietal ventral area (PV) and other cortical areas; and thalamic inputs from the ventroposterior lateral nucleus (VPL). In addition, tracer injections in the reactivated hand region of area 3b labeled more neurons in the face and shoulder regions of area 3b than in normal monkeys, and injections in the face region of area 3b labeled more neurons in the hand region. Unexpectedly, the intrinsic connections within area 3b hand cortex were more widespread after incomplete dorsal column lesions (DCLs) than after a complete DCL. Although these additional connections were limited, these changes in connections may contribute to the reactivation process after injuries.