Growth of new brainstem connections in adult monkeys with massive sensory loss

Somatotopic maps in the cortex and the thalamus of adult monkeys and humans reorganize in response to altered inputs. After toss of the sensory affere nts from the forelimb in monkeys because of transection of the dorsal colum ns of the spinal cord, therapeutic amputation of an arm or transection of t he dorsal roots of the peripheral nerves, the deprived portions of the hand and arm representations in primary somatosensory cortex (area 3b), become responsive to inputs from the face and any remaining afferents from the arm . Cortical and subcortical mechanisms that underlie this reorganization are uncertain and appear to be manifold. Here we show that the face afferents from the trigeminal nucleus of the brainstem sprout and grow into the cunea te nucleus in adult monkeys after lesions of the dorsal columns of the spin al cord or therapeutic amputation of an arm. This growth may underlie the l arge-scale expansion of the face representation into the hand region of som atosensory cortex that follows such deafferentations.