Cutting a nerve of the hand alters the organization of digit maps in primary somatosensory cortex.

In non-human primates, forelimb nerve transection and repair alters the otherwise orderly and highly conserved organization of the digit maps in primary somatosensory cortex (S1). These same changes are presumed to occur in humans and to have meaningful implications for patient recovery. Here, using functional magnetic resonance imaging, we map digit responses in 21 patients with surgically repaired hand nerves and 30 controls. In S1 contralateral to the repaired hand, digit map arrangement is systematically altered and response amplitudes are elevated. At the individual level, map organization is more variable and less typical of controls, a pattern that, unexpectedly, is also evident in S1 of the uninjured hand. Our results show that hand nerve repair alters S1 organization in humans, consistent with animal models. These changes probably reflect disordered peripheral inputs following unguided nerve regeneration. The cortical circuitry itself may remain largely stable. The functional relevance of these changes remains uncertain. We find no credible links between altered S1 maps and functional impairments.