Topographic recordings of auditory evoked potentials to speech: subcortical and cortical responses.

Topographies of speech auditory brainstem response (speech ABR), a fine electrophysiological marker of speech encoding, have never been described. Yet, they could provide useful information to assess speech ABR generators and better characterize populations of interest (e.g., musicians, dyslexics). We present here a novel methodology of topographic speech ABR recording, using a 32-channel low sampling rate (5 kHz) EEG system. Quality of speech ABRs obtained with this conventional multichannel EEG system were compared to that of signals simultaneously recorded with a high sampling rate (13.3 kHz) EEG system. Correlations between speech ABRs recorded with the two systems revealed highly similar signals, without any significant difference between their signal-to-noise ratios (SNRs). Moreover, an advanced denoising method for multichannel data (denoising source separation) significantly improved SNR and allowed topography of speech ABR to be recovered.