Preserved aspects of cortical foot control in paraplegia.

While several recent imaging studies confirm that motor foot areas can still be activated in complete and chronic paraplegia, it remains unclear whether their functionality is also maintained or declines after years of "non-use". Force control is one of the most important and best investigated functions within the motor cortex. It has been repeatedly reported that the motor cortex is more active when higher forces have to be applied. We thus addressed the question of preserved cortical functions by comparing motor force control patterns in the event-related potentials of 10 motor complete paraplegic subjects and 10 controls after attempted (paraplegic patients)/executed (healthy controls) ballistic foot movements with three different force levels. In addition to the peak amplitudes reflecting force levels, peak latencies were also investigated to elucidate timing as another functional aspect of motor control. No significant group difference was found for the peak latencies, indicating that the timing of motor cortical activation is preserved. Concerning amplitudes, we found preserved cortical modulation of higher forces but distorted low force modulation, especially early after injury. These findings thus suggest that important aspects of cortical control over paralyzed limbs are maintained despite years of "non-use".