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The summating potentials (SP) to free-field 1-, 2-, 4-, and 8-kHz, 90-dB HL tone bursts were recorded by means of transtympanic electrocochleography in 45 patients divided into three groups: those with Meniere's disease, those whose diagnosis was uncertain, and control subjects. The similarities across frequencies between the human SP (promontory) and the experimental SP (DIF component from basal turn) suggest that the SP recorded in electrocochleography originates mostly from the base of the cochlea; negative values were observed at low frequencies (1 to 2 kHz), positive values at high frequencies (8 kHz). Patients with Meniere's disease showed significantly larger SP values than control subjects. The effect of orally administered glycerol on the SP and action potential amplitudes was evaluated by means of automated recordings repeated every 5 minutes. Summating potential values were remarkably constant in the control group. A decrease in SP absolute amplitude was observed in most patients with Meniere's disease and some subjects with uncertain diagnoses, specifically at low frequencies. These changes were frequently associated with action potential amplitude and auditory threshold improvements at low frequencies. It is assumed that the glycerol-induced SP changes at low frequencies are related to modifications in the low frequency mechanical response of the basilar membrane at the basal turn.

Electrical stimulation of the ear in humans was performed with an extracochlear electrode on the round window. With positive currents, suppression of tinnitus could be induced. With negative currents, auditory sensations were evoked. Since electrical stimulation with DC currents may be hazardous in the long term, it cannot yet be proposed for the suppression of tinnitus. However, electrically evoked hearing sensations with AC currents seem to be of definite interest for some totally deaf patients.

The biocompatibility of the bioactive glass-ceramic Ceravital was investigated experimentally both in vivo and in vitro. In the former, ceramic discs were interposed in 30 rat middle ears for periods ranging from 6 weeks to 12 months. In the latter, Ceravital otological prosthesis were placed in human fibroblast culture. Reactions to the biomaterial were assessed by means of scanning electron microscopy (SEM) with chemical analysis facilities (EDAX, WDAX) and light microscopy. The interface reactions were similar in both in vivo and in vitro studies and confirmed the findings of other authors regarding the implants' biocompatibility and bioactivity. The technique of ion etching, however, enabled clear demonstration of this bioactivity on the implant surface, exposed merely to the middle-ear secretions, thus questioning the necessity of placing bone pâté on the implant head at surgery, in order to encourage bioactive bonding with the overlying drum. A clinical trial of Ceravital in 128 patients with an average follow-up period of 2 years is reported. Forty per cent of these patients underwent a type II tympanoplasty, 60 per cent a type III. Though relatively short-term, the results to date have been encouraging: 88 per cent of the implants have been well-tolerated; 70 per cent of the cases have yielded a satisfactory hearing result; and only 3 per cent of the implanted prostheses have been extruded.