Dynamical Functional Reorganization In Somatosensory And Motor Cortex After The Contralateral Seventh Cervical Nerve Root Transfer To The Injured Nerve Of A Forelimb

The operation of the contralateral healthy cervical seventh(C7) nerve root transfer for treatment of nerve root avulsion of brachial plexus, initially created by Gu, has been widely accepted. Clinically, at the early after anastomosis, the patients could move their injured hands only simultaneously with the healthy hand movement. As time passed, some of the patients started to move and get feeling from their injured hands. The functional change in the cortex during the period is unknown. Here we report the process of functional reorganization and the corresponding brain mechanisms following the operation of contralateral C7 nerve root transfer in adult Sprague-Dowley rats. Three aspects were observed. Firstly, we quantitatively tested objective assessment of peripheral nerve regeneration by grasping test. Secondly, the representation of the injured forepaw was observed using electrically stimulating the motor cortex of two hemispheres. Thirdly, the representation of the injured forepaw and the healthy forepaw in the somatosensory cortex was studied using electrical stimuli on the forepaw.1. The time course of functional recovery of the injured forepaw was clearly demonstrated by the grasping test.2. There was no cortical area control the injured forepaw until the 5^th month after the operation, however, then, the ipsilateral cortex or both sides of motor cortex emerged to control the injured forepaw 5-7 months after the operation. Surprisingly, the injured forepaw was onlycontrolled by the contralateral motor cortex 8-16 months after the operation. A dynamic trans-hemispherical functional reorganization corresponding to the injured forepaw was observed after operation. Ablation of the ipsilateral motor cortex did not influence this contralateral reconstructed representation indicating that the inter-hemispherical callosal pathway does not involve the trans-hemisphere reorganization.Two related mechanisms of the trans-hemispherical functional reorganization were hypothesized.3. Sensory function of the injured forepaw gradually recovered after the operation. The sensory representation of the injured forepaw was observed in the ipsilateral somatosensory cortex. The overlapped representation of both the injured forepaw and the healthy forepaw was exhibited 5-9 months after the operation. However, the separate representation of the injured forepaw was found in the ipsilateral somatosensory cortex 10-16 months after the operation. No trans-hemispherical functional reorganization in somatosensory cortex was observed after operation.In our experiments, it is found that unilateral motor cortex controlled bilateral forepaws. The control of the injured forepaw shifted from the ipsilateral cortex to bilateral cortex, and finally got to the contralateral cortex. A dynamic reorganization occurred. Under the experimental condition, we found that there is the overlapped representation of bilateral forepaws in the ipsilateral somatosensory cortex, and then separated. However, we did not find that the trans-hemispherical reorganization. This work provided the first data of the brain mechanisms underlying the treatment of nerve root avulsion of brachial plexus with the contralateral seventh cervical nerve root, which found the theoretical bases of the clinical treatment.