Simultaneous Extratympanic Electrocochleography and Auditory Brainstem Responses Revisited

Abstract

The purpose of this study was to revisit the two-channel, simultaneous click-evoked extratympanic electrocochleography and auditory brainstem response (ECoG/ABR) recording technique for clinical use in normal hearing participants. Recording the compound action potential (AP) of the ECoG simultaneously with ABR may be useful when Wave I of the ABR is small or diminished in patients with sensorineural or retrocochlear disorder and minimizes overall test time. In contrast to some previous studies that used the extratympanic electrode both as non-inverting electrode for the ECoG and inverting electrode for ABR, this study maintained separate recording channel montages unique to conventional click-evoked ECoG and ABR recordings. That is, the ABR was recorded using a vertical channel (Cz to ipsilateral earlobe), while the ECoG with custom extratympanic electrode was recorded using a horizontal channel (tympanic membrane to contralateral earlobe). The extratympanic electrode is easy to fabricate in-house, or can be purchased commercially. Maintaining the conventional ABR montage permits continued use of traditional normative data. Broadband clicks at a fixed level of 85 dB nHL were presented with alternating polarity at stimulus rates of 9.3, 11.3, and 15.3/s. Different stimulation rates were explored to identify the most efficient rate without sacrificing time or waveform morphology. Results revealed larger ECoG AP than ABR Wave I, as expected, and no significant difference across stimulation rate and no interaction effect. Extratympanic electrode placement takes little additional clinic time and may improve the neurodiagnostic utility of the ABR.

Keywords: auditory brainstem response; electrocochleography; electrode; extratympanic; simultaneous.

Figure 1.

Extratympanic electrocochleography and auditory brainstem response (ECoG/ABR) recordings from one participant. From top left to top right and bottom right are the averaged responses for 9.3, 11.3, and 15.3/s, respectively. The set up implemented in this study resulted in positive-going ABR components and negative-going ECoG components.

Figure 2.

Amplitude comparison (n=10) between and auditory brainstem response (ABR) Wave I and extratympanic electrocochleography (ECoG) action potential (AP) for each of the three stimulation rates.

Figure 3.

Summating potential/action potential ratio (n=10) comparison across the three stimulation rates.