NEURAL MECHANISMS OF ABNORMAL SENSATIONS AFTER NERVE INJURY

Patients with injured nerves often report that tapping at the site of injury produces tingling sensations in the original territory of the nerve. Recordings from single nerve fibers in primates indicate that a sensitivity to mechanical stimuli develops after a nerve injury at regenerating nerve fibers; this sensitivity likely accounts for the sensations reported by patients. Vibratory stimuli were applied to regenerating fibers to determine their frequency-response properties. Fibers were grouped into three types, based on their responses: ( 1) fibers most sensitive to frequencies less than 5 Hz; (2) fibers most sensitive to middle frequencies (10-50 Hz); and (3) fibers most sensitive to frequencies greater than 100 Hz. These responses are similar to those of normal mechanoreceptors in the skin responsible for touch sensation. On the basis of these results, we propose a mechanism that explains the development of mechanosensitivity in injured nerve fibers.