Complete reorganization of the motor cortex of adult rats following long‐term spinal cord injuries

Abstract

Understanding brain reorganization following long-term spinal cord injuries is important for optimizing recoveries based on residual function as well as developing brain-controlled assistive devices. Although it has been shown that the motor cortex undergoes partial reorganization within a few weeks after peripheral and spinal cord injuries, it is not known if the motor cortex of rats is capable of large-scale reorganization after longer recovery periods. Here we determined the organization of the rat (Rattus norvegicus) motor cortex at 5 or more months after chronic lesions of the spinal cord at cervical levels using intracortical microstimulation. The results show that, in the rats with the lesions, stimulation of neurons in the de-efferented forelimb motor cortex no longer evokes movements of the forelimb. Instead, movements of the body parts in the adjacent representations, namely the whiskers and neck were evoked. In addition, at many sites, movements of the ipsilateral forelimb were observed at threshold currents. The extent of representations of the eye, jaw and tongue movements was unaltered by the lesion. Thus, large-scale reorganization of the motor cortex leads to complete filling-in of the de-efferented cortex by neighboring representations following long-term partial spinal cord injuries at cervical levels in adult rats.

Large-scale reorganization of the somatosensory cortex following spinal cord injuries is due to brainstem plasticity

“…The maximal extent of the lesion and boundaries of the white matter and grey matter were measured and plotted on a graph paper for each section. The corresponding boundaries were joined to visualize the extent of the lesion in a coronal view of the spinal cord 50 .…”

Ipsilateral cortical inputs to the rostral and caudal motor areas in rats

“…Briefly, parylene‐coated tungsten microelectrodes (1 MΩ at 1 kHz; MicroProbe, Gaithersburg, MD) were inserted perpendicular to the cortical surface to a depth of about 1500 μm from the surface using a hydraulic microdrive (Kopf Instruments, Tujunga, CA). The stimulation parameters were 60‐ms trains of 0.2‐ms monophasic cathodal pulses (DC) at 150 Hz (Kambi et al, ; Mohammed and Jain, ; Tandon et al, , ). Initially, a 50‐μA current was used to determine whether any movement was evoked.…”

Cortical Reorganization of Sensorimotor Systems and the Role of Intracortical Circuits After Spinal Cord Injury

“…1). These disrupted cortical motor maps persist in a long term in rats after cervical spinal cord injury, with an enduring expansion of whisker and neck representations and an emergence of ipsilateral forelimb movements when measured between 5 and 15 months post injury [68] (Fig. 1).…”

“…Therefore, for meaningful functional recovery after injury to occur, mechanisms of cortical plasticity will be required for the cortex to relearn previous motor patterns using an altered motor pathway. Humans, primates, and rodents all show changes in cortical motor maps after spinal cord injury [57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72]. In humans with spinal cord injury, there is increased activity in existing and novel areas within motor, somatosensory, and parietal cortex, as well as in the thalamus, basal ganglia, and cerebellum during movement execution, in comparison to controls [73][74][75][76][77].…”