Organisms over the large evolutionary history have developed dedicated systems for sensation and volition, which consist of representations of these sensations and motor actions organized as maps at different levels in the central nervous system. These body maps are dynamic and malleable reflecting the complex ever-changing environment with which organisms interact. The dynamic or plastic nature of sensorimotor representations is studied by elucidating changes in body maps in the brain and the behavior of the animal after disruption of sensory pathways. For the present talk, I will discuss the changes in body maps in monkeys and rats after lesions of dorsal columns in the spinal cord.

In the first part, I will examine the effects of the lesions on the organization of the primary motor cortex in monkeys. Briefly, the results showed that overall organization of the motor cortex was not affected but there were significant changes in the nature of evoked movements of digit 1. I will also discuss data on the motor cortex topography in rats with dorsal funiculus lesions, which show extensive reorganization.

In the second part, I will explore the extent of the large-scale plasticity in the entire somatosensory system that has already been shown in the primary somatosensory cortex and thalamus after dorsal column lesions. I will specifically focus on the large-scale changes observed in higher somatosensory cortical regions and at the level of brainstem in monkeys.
For the third and final part, I will talk about mechanisms of large-scale plasticity observed in the primary somatosensory cortex of monkeys after dorsal column lesions. Specifically, I will show data that suggests the origin of expanded face inputs in the deprived hand region of the primary somatosensory cortex is due to growth of new connections at brainstem level and not at the cortical level.