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 non-human 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 and 21 able-bodied controls using two fMRI experiments. Experiment 1 employed a lip movement task, while Experiment 2 investigated the full architecture of S1 face reorganisation 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 favour 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. These findings suggest that cortical face-to-hand remapping is not apparent in human cervical SCI patients. Beyond providing insight into the limitations of cortical reorganisation in humans, this highlights the need to reassess rehabilitation strategies based on the assumption of large-scale face-to-hand reorganisation after an SCI.