Reorganization of somatosensory cortex subsequent to dorsal column injury: a study of the marmoset and the squirrel monkey

Abstract

The importance of accurate cortical representation and processing of hand use is clearly appreciated when one considers the behavioral deficits observed after the dorsal columns have been interrupted. Animals experience gross deficits in their ability to accurately guide the affected hand, and additionally, once the item is within its grasp, the animal may keep looking for it due to the loss of tactile sensation. We were able to conclude that somatosensory cortical areas including 3b, 3a, area 1 and possibly area 2 undergo considerable reorganization subsequent to dorsal column injury in the marmoset. We posited that one likely source of this reorganization is the sprouting of collateral axons of primary afferent fibers that remain intact after injury. Whether these postsynaptic nuclei are appropriate targets that go on to make connections with corresponding parts of the body representation in cortex plays a crucial role in determining if amplification of an appropriate signal will occur, or if misperception of the source of input takes place. Prior studies in rats indicate that application of chondroitinase ABC (chABC) to the dorsal column nuclei subsequent to dorsal column pathway damage leads to functional reactive sprouting. We sought to determine how somatosensory cortical organization is affected subsequent to dorsal column pathway damage and chABC application to the cuneate nucleus in squirrel monkeys. In the chABC-treated animals, these recordings showed that cortical territories once activated by deafferented peripheral inputs had become primarily responsive to the D1 afferents that remained intact after the lesion. It will be necessary to not only promote the eventual formation of new and functional synapses but also to provide the guidance necessary for these new circuits to confer behavioral benefits to those affected by SCI.