Functional Changes in Sensorimotor Regions of the Brain Following Spinal Injury

Neurorobotics has been successfully used as novel output pathway for patients with severe nerve damage including spinal injury. However, a spinal injury is also a brain injury and it is difficult to assess the mechanisms that allow the injured brain to control an external device such as a cursor on a computer screen. We have therefore been using a rat model of spinal cord injury to assess functional changes in the sensorimotor regions of the brain to spinal cord injury. Arrays of microelectrodes were chronically implanted into the sensorimotor region of the brain and used to monitor neuronal activity before and after spinal cord hemisection. Neurons were recorded while the animal performed a spontaneous reaching task. Population functions were generated to identify forepaw contact and the ability to accurately identify contact on a single trial basis was used as a measure of the ability of the neural circuits to code for sensorimotor motor output. Our data suggest that while there was a significant decrease in the response of these neurons to passive stimulation of their receptive fields after spinal lesion and microstimulation was no longer able to generate coordinated muscle contraction, the population function was able to predict paw contact during spontaneous reaching. Furthermore, the latency of the peak of the response for single trial contact was significantly earlier post-hemisection compared to pre-hemisection. These results are discussed in terms of how they relate to strategies used by the animal to compensate for the loss of passive sensory stimulation