Colloquium Series 2017-2018

Aimee Nelson
McMaster University

Changes in the organization of the motor cortex that follow incomplete spinal cord injury

Movement training for improving upper limb control is an essential component of rehabilitation for individuals with spinal cord injury (SCI). Understanding the cortical representation of arm muscles in SCI is fundamental to designing more effective movement training regimes.  In uninjured individuals, the primary motor cortex (M1) contains overlapping muscle representations, an organization that reflects muscle synergies. This organizational feature has yet to be studied in SCI yet is considered a key element that defines the coordinated action of multiple muscles during human movement. Using Transcranial magnetic stimulation (TMS), we investigated the bilateral representation and overlapping distribution of muscles of the upper limb in chronic cervical SCI and aged-matched controls (n=9, each group). Muscles studied included the abductor pollicus brevis (APB), flexor carpi radialis (FCR) and biceps brachii (BB) and the cortical territory (cm²), overlapping territory (cm²) of the target muscles, and center of gravity were computed. Results indicate a reduction in the cortical territory dedicated to all three muscles in SCI (i.e. reduced complete overlap) compared to uninjured controls.  Further, SCI had greater cortical territory dedicated to a single or dual muscle representation. These data indicate that overlapping organization is preserved in the motor cortex of SCI, however, the overlapping representation does not extend to all three muscles. The implication from these data is that movement training emphasizing synergies that incorporate all three muscles (APB, FCR, BB) may promote greater representational overlap (similar to uninjured controls) and provide functional gains in motor control.