Revisiting Face-to-Hand Area Remapping in the Human Primary Somatosensory Cortex after a Cervical Spinal Cord Injury

Abstract

Spinal cord injury (SCI) leads to profound disruptions in sensorimotor processing. Seminal research in nonhuman primates suggests this sensory deprivation causes functional remapping in the primary somatosensory cortex (S1), where somatotopic representations of deprived body parts, such as the hand in cervical SCI, become responsive to touch on intact body parts, such as the face. However, evidence for such remapping in humans remains inconclusive. We investigated face-to-hand remapping in 16 chronic cervical SCI patients (15 male, 1 female) and 21 able-bodied controls (19 male, 2 female) using two fMRI experiments. Experiment 1 employed a lip movement task, while Experiment 2 investigated the full architecture of S1 face reorganization through vibrotactile stimulation of the forehead, lips, and chin. We assessed (1) the level of face activity in the anatomical S1 hand area, (2) cortical shifts in peak face activity, (3) face-part separability in the S1 hand area, and (4) correlations with clinical characteristics that may drive face-to-hand area remapping. Our results revealed no significant evidence in favor of face-to-hand area remapping in tetraplegic patients across markers of face-to-hand remapping during either lip movement or vibrotactile stimulation of face parts. Furthermore, our markers of remapping did not correlate with clinical characteristics. Together, these findings indicate that cortical face-to-hand remapping could not be demonstrated in our cohort of chronic cervical SCI patients, highlighting the need to revisit assumptions of large-scale face-to-hand reorganization after SCI.