EFFECTS OF EXTRA-COCHLEAR DIRECT CURRENT STIMULATION ON HEARING IN CONTROL AND TINNITUS SUBJECTS.

OBJECTIVE: To investigate the effects of extra-cochlear electrical stimulation on hearing in normal-hearing and tinnitus subjects. MATERIALS and METHODS: Group I - 49 tinnitus patients (n - 71 tinnitus ears). Group II (control) - 21 healthy subjects without tinnitus (n - 41 ears). Electrical stimulation was performed with the use of hydrotransmissive method. The active electrode was immersed inside external ear canal filled with 0.9% saline solution. The passive electrode was placed on the forehead. Direct current (train of squared pulses) was applied via the active electrode. Different pulse train frequencies were used: 0.25, 1, 2, 3, 4, 5, 6, 7, 8 kHz. The protocol was first done for positive, then negative current polarisation. For each frequency of stimulation and current polarity, the current level was slowly raised until the subjects report an auditory perception. RESULTS: Auditory perceptions were produced at lower levels for negative currents compared to positive currents. Larger levels of currents were required to produce auditory perception when the frequency of pulse train was increased. A sound perception was present for both positive and negative stimulation in group I -- in 41ears (57.75%), in group II -- in 36 ears (87.80%). In group I it was mainly present for stimulating frequencies 0.25-2kHz, in group II -- in the whole stimulating range (0.25-8kHz). In group I larger current intensities were needed to evoke sound perception. CONCLUSION: Positive and negative non-invasive electrical stimulation of the ear can produce an auditory perception indicating excitation of the auditory system. [ABSTRACT FROM AUTHOR]