Auditory evoked cortical magnetic field (M100-M200) measurements in tinnitus and normal groups.

Recently, Hoke et al. (1989) and Pantev et al. (1989) demonstrated that the auditory evoked cortical magnetic field (AECMF) M100 component was larger, and M200 was smaller and occurred later in subjects with unilateral tinnitus compared with normal subjects. These group amplitude differences resulted in an M200/M100 amplitude ratio that was smaller for the subjects with tinnitus. The purposes of the present investigation were to: 1) extend the observations of Hoke et al. (1989), and, 2) determine whether contralateral AECMF differences existed following stimulation of the non-tinnitus and tinnitus ears of patients with tinnitus. Neuromagnetic AECMF recordings were recorded from 25 young normal hearing and 14 patients with unilateral tinnitus and hearing loss. The results failed to support the findings of Hoke et al. (1989). Specifically, there is no evidence suggesting that the M100 amplitude is larger, the M200 latency later, or, the M200/M100 amplitude ratios smaller, when the two samples are compared. Additionally, there were no differences in the amplitudes or latencies of M100 or M200 when results from stimulation of the tinnitus and non-tinnitus ears of tinnitus subjects were compared.