The Compound Action Potential in Subjects Receiving a Cochlear Implant

Abstract

Hypothesis The compound action potential (CAP) is a purely neural component of the cochlea’s response to sound, and may provide information about the existing neural substrate in cochlear implant (CI) subjects that can help account for variance in speech perception outcomes. Background Measurement of the ‘total response’ (TR), or sum of the magnitudes of spectral components in the ongoing responses to tone bursts across frequencies, has been shown to account for 40–50% of variance in speech perception outcomes. The ongoing response is composed of both hair cell and neural components. This correlation may be improved with the addition of the CAP. Methods Intraoperative round window electrocochleography (ECochG) was performed in adult and pediatric CI subjects (n=238). Stimuli were tones of different frequencies (250 Hz–4 kHz) at 90 dB nHL. The CAP was assessed in two ways, as an amplitude and with a scaling factor derived from a function fitted to the response. The results were correlated with CNC word scores at 6 months post-implantation (n=51). Results Only about half of the subjects had a measurable CAP at any frequency. The consonant-nucleus-consonant (CNC) word scores correlated weakly with both amplitude (r2=0.20, p < 0.001) and scaling factor (r2=0.25, p < 0.01). In contrast, the TR alone accounted for 43% of the variance, and addition of either CAP measurement in multiple regression did not account for additional variance. Conclusions The underlying pathology in CI patients causes the CAP to be often absent and highly variable when present. The TR is a better predictor of speech perception outcomes than the CAP.

Clinical role of electrocochleography in children with auditory neuropathy spectrum disorder

“…Only subjects with a TR greater than −6 dB (0.5 μV) were included in this analysis because in smaller responses the signal to noise ratio was too low for these neural features to be detected. In CI subjects a CAP is often visible as a pronounced negative deflection of the potential at the onset of the response (Figure 1A, portion in red), but across subjects the morphology is highly variable and difficult to quantify [33]. Similarly, the presence of an ANN is detectable by distortions in the ongoing portion of the response but its magnitude is difficult to quantify because it is mixed with the CM (Figure 1 A, in the blue box).…”

Reliability of Measures of N1 Peak Amplitude of the Compound Action Potential in Younger and Older Adults

“…Baseline-corrected amplitude measurements are computationally simpler than peak-to-peak amplitude measurements, requiring the identification of only a single peak in the waveform. For these reasons, baseline-corrected amplitude measurements have become increasingly common in ECochG studies (e.g., Harris et al, 2018;Parthasarathy, Datta, Torres, Hopkins, & Bartlett, 2014;Scott et al, 2016).…”

Electrocochleography in Cochlear Implant Users with Residual Acoustic Hearing: A Systematic Review

“…The prognostic value of intraoperative ECoG to predict postoperative speech outcomes was investigated in a series of studies from the same research group [ 21 , 22 , 38 , 49 ]. The ECoG total response (TR) metric—the sum of first and second harmonics of the Fast Fourier transform (FFT) analysis—was used in these studies.…”

“…TR accounted for 46% of variability in speech recognition for adults, while 15–36% of variability was accounted for by children. When CAP responses that reflect purely neural contributions were used as a metric, a weak correlation ( r = 0.44) was reported between the CAP amplitudes and postoperative CNC word score [ 49 ].…”