Preliminary results on correlation between neural response imaging and 'most comfortable levels' in cochlear implantation.

During cochlear implantation, precise placement of the cochlear electrodes against the cochlear nerve is one of the most important steps, necessary to enable the patient to be aware of the stimulus from the implanted device. Neural response imaging (NRI) is a new tool which measures the evoked compound action potential generated as a result of electrical stimulation of the cochlea by properly placed electrodes during surgery. The aim of this study was to examine the correlation between intra-operative NRI recordings and 'most comfortable levels' (M levels) measured during standard fitting with the SoundWave fitting software, in cochlear implantation patients. Seven adult subjects were included in the study. The average duration of profound bilateral deafness was seven years (range = 19 years) and the mean age at implantation was 24 years (range = 17-34 years). All subjects underwent implantation and reached the one-month fitting session; one patient reached the two-month fitting session. The intra-operative NRI threshold (tNRI) was observed to be much higher than the first fitting M levels. The tNRI was 203 per cent of the sequential M value and 246 per cent of the paired M value. All but one intra-operative tNRI values were greater than 150 clinical units (CU), and all first fitting M levels were on average below 100 CU. No obvious correlation was found between individual intra-operative tNRI and first fitting M levels. The M levels at one month were much higher than the first fitting M levels, with much more dispersion.