Somatosensory evoked fields in comatose survivors after severe traumatic brain injury

Objective: To evaluate the cortical function quantitatively in patients in the chronic phase of severe traumatic brain injury. Methods: Thirteen patients with severe traumatic brain injury due to traffi c accident followed by persistent consciousness disturbance and disability were studied. Somatosensory evoked magnetic fields (SEFs) for unilateral me dian nerve stimulation were measured using a whole-head magnetoencephalogra phy system. The latency and electrical current dipole (ECD) moment for the N20m, P30m, N45m and P60m components were calculated and compared with thos e of 14 age-matched healthy adults. Results: The peak latency of N20m was longer (P < 0.05) and those of P30m a nd N45m were shorter (P < 0.01) in the patients than in normal adults. The ECD moment of N20m and P30m was smaller and that of N45m and P60m was large r in the patients than in normal adults (P < 0.01). Conclusions: These results can be explained by the hypothesis that diffuse brain injury induces decreased and delayed input of the somatosensory affer ent and compensational amplification of the response in the primary somatos ensory cortex. Middle-latency SEFs may be applicable as a cortical function al measure for patients with severe traumatic brain injury. (C) 2001 Elsevi er Science Ireland Ltd. All rights reserved.