Functional reorganization of the forepaw cortical representation immediately after thoracic spinal cord hemisection in rats

• Spinal hemisection increases cortical responses to stimuli above the lesion level.
• Spinal cord hemisection rapidly decreases cortical spontaneous activity.
• Incomplete spinal cord injury can rapidly affect the system above the lesion level.

Spinal cord injury may produce long-term reorganization of cortical circuits. Little is known, however, about the early neurophysiological changes occurring immediately after injury. On the one hand, complete thoracic spinal cord transection of the spinal cord immediately decreases the level of cortical spontaneous activity and increases the cortical responses to stimuli delivered to the forepaw, above the level of the lesion. On the other hand, a thoracic spinal cord hemisection produces an immediate cortical hyperexcitability in response to preserved spinothalamic inputs from stimuli delivered to the hindpaw, below the level of the lesion. Here we show that a thoracic spinal cord hemisection also produces a bilateral increase of the responses evoked in the forepaw cortex by forepaw stimuli, associated with a bilateral decrease of cortical spontaneous activity. Importantly, the increased cortical forepaw responses are immediate in the cortex contralateral to the hemisection (significant within 30 min after injury), but they are progressive in the cortex ipsilateral to the hemisection (reaching significance only 2.5 h after injury). Conversely, the decreased cortical spontaneous activity is progressive both ipsilaterally and contralaterally to the hemisection (again reaching significance only 2.5 h after injury). In synthesis, the present work reports a functional reorganization of the forepaw cortical representation immediately after thoracic spinal cord hemisection, which is likely important to fully understand the mechanisms underlying long-term cortical reorganization after incomplete spinal cord injuries.