AUDITORY BRAIN-STEM AND CORTICAL RESPONSES FOLLOWING EXTENSIVE TRANSCRANIAL MAGNETIC STIMULATION

The long term effects of transcranial electromagnetic stimulation (TEM S) on auditory brainstem and cortical evoked responses and on neuroana tomical structures in the auditory tract were investigated over a 12 m onth period in rabbits exposed to 1000 stimuli at 100% maximum stimula tion level (2.0 tesla instrument output) with a clinical magnetic coil positioned over the cranium. (1) The tone and click audiograms of the pre and post TEMS-exposed plugged ears were normal and did not differ significantly, suggesting that the protected cochlea is unaffected by TEMS. (2) The mean absolute and interwave latencies of auditory brain stem evoked responses (ABR) and the peak amplitudes of the vertex posi tive waves P-1, P-3, and P-4 in the exposed rabbits were within normal limits, and comparable those of the normal, pre-exposed animals. Wave P-5 in the exposed animals was more variable and significantly differ ent from the normal data in mean latency and amplitude. (3) The mean l atencies and amplitudes of the post exposed cortical (late) auditory e voked responses (CAER) were not significantly different from the non-e xposed ears. Light microscopic examination of sections of the cochlear nucleus and inferior colliculus, possible sources of waves P2 and P5, respectively, of the ABR, showed no EMS-related changes in cellular o rganization or histological damage. In conclusion, no deleterious effe cts of TEMS were observed on the protected ear or the peripheral and c entral auditory system of rabbits after extensive exposure to long ter m, high intensity, low frequency time-varying magnetic field stimulati on with a clinical instrument.