Relationship between intracortical inhibition and motor behavior; implications for incomplete spinal cord injury

The sensorimotor cortices of the human brain contain intracortical inhibitory circuits that influence the neural output to muscles. Intracortical circuits of short and long-interval intracortical inhibition (SICI and LICI) can be probed using paired-pulse TMS paradigms while recording activity from the muscles. We recently identified changes in SICI and LICI within the motor cortex in individuals with incomplete cervical spinal cord injury. Decreases in the range of intensities eliciting SICI recruitment were observed without a difference in the depth of SICI. Active LICI was increased at higher conditioning intensities relative to controls. These changes may be linked to plastic and physiological changes of GABAergic cortical systems with SCI. Here we discuss the role of SICI and LICI in motor behavior and how the observed changes in these measures that follow SCI may explain motor impairments seen in this population.