Somatosensory cortical plasticity after toe-to-index transfer

We quantified and compared neuroimaging data and behavioral data (cortical plasticity and hand sensibility, respectively) from a patient who underwent toe-to-index transplantation. Magnetoencephalographic (MEG) recordings of somatosensory-evoked fields (SEFs) response to mechanical tactile stimulation of the index and little fingers of both hands were obtained in parallel with a hand sensibility test from the patient at multiple sessions (week 4, 12, and 24 after the operation). Cortical plasticity refers to SEFs' latency, dipole strength, and primary somatosensory representation, and the Euclidean distance between primary somatosensory representations of the index and the little fingers. Hand sensibility refers to a patient's conscious perception of tactile stimulation applied to the transplanted index finger and scored by Semmes-Weinstein monofilaments. SEFs recordings from six healthy participants at one session were used for comparative purposes. At week 4, although the patient had no conscious perception in the left transplanted index to tactile stimulation, SEFs were recorded in response to tactile stimulation. At weeks 12 and 24, the Euclidean distance between primary somatosensory representations of the transplanted index and little fingers increased, together with SEFs dipole strength, whereas SEFs latencies decreased. These occurred in parallel to improvement in hand sensibility. Primary somatosensory representations of the index and little fingers of the patient's intact right hand were similar to those of the healthy participants' right hand, indicating the consistency of MEG recording during the follow-up sessions. In conclusion, a combination of neuroimaging and behavioral data may be essential for better assessment of functional recovery after a toe-to-digit operation because the cortical recovery observed by MEG preceded that of hand sensibility observed clinically.