Richard P. Bunge memorial lecture. Nerve injury and repair--a challenge to the plastic brain.

Repair and reconstruction of major nerve trunks in the upper extremity is a very challenging surgical problem. Today, there is no surgical repair technique that can assure recovery of tactile discrimination in the hand of an adult patient following nerve repair. In contrast, young individuals usually attain a complete recovery of functional sensibility. The outcome from nerve repair depends mainly on central nervous system factors including functional cortical reorganizational processes caused by misdirection in axonal outgrowth. Deafferentation due to local anesthetic block, amputation or nerve transection in the upper extremity leads to very rapid cortical synaptic remodeling, resulting in a distorted cortical hand representation as well as in enlarged and overlapping cortical receptive fields. Sensory relearning programs are aimed at refinement of these receptive fields to normalize the distorted hand map and improve processing at a high-order cortical level in the context of the 'new language spoken by the hand'. As peripheral nerve repair techniques cannot be further refined, there is a need for new and improved strategies for sensory relearning following nerve repair. We propose the utilization of multimodal capacity of the brain, using another sense (hearing) to substitute for lost hand sensation and to provide an alternate sensory input from the hand early after transection. The purpose was to modulate cortical reorganizations due to deafferentation to preserve cortical hand representation. Preliminary results from a prospective clinical randomized study indicate that the use of a Sensor Glove System, which stereophonically transposes the friction sound elicited by active touch, results in improved recovery of tactile discrimination in the nerve-injured hand. Future strategies for treatment of nerve injuries should promote cellular methods to minimize post-traumatic nerve cell death and to improve axonal outgrowth rate and orientation, but high on the agenda are new strategies for refined sensory relearning following nerve repair.