Approche empirique pour déterminer les générateurs neurophysiologiques sous-jacents des potentiels évoqués auditifs engendrés par des sons de parole (Speech ABR)

Auditory evoked potentials to speech (Speech auditory brainstem response Speech ABR]) are a non-invasive way to investigate neurophysiological activity, at the level of the brainstem. The Speech ABR precise neurophyiological generators remain poorly defined. However, latencies and low-pass spectrum both suggest that these generators might lie in the upper brainstem (roughly between the cochlear nucleus and the inferior colliculus). Having considered the particular functional pattern of cells along the auditory pathway, specific stimuli have been synthesized to make out the acoustic sensitivity of Speech ABR components. Accordingly, hypotheses have been made on the probable neurophysiological generators, most likely to have elicited both Speech ABR components: onset response and frequency following response. Speech ABR have been recorded to pure tones, harmonic complex tones, /ba/ and /pa/ syllables, and their analogues (calculated as a sum of five weighted sine waves at the formant frequencies and amplitudes, and modulated by the syllables temporal envelopes). In addition, the Auditory Image Model (Patterson et al., 1995 17]), simulating the neural activity at the auditory periphery, i.e. inferior colliculus input, suggests that both analogues and syllables elicit the same amount of energy, in contrast to the recorded FFR. This contradiction means that the neurophysiological signal processing leading to FFR is made beyond auditory periphery. Indeed, FFR synchronisation on F0 seems to be the result of an overall processing of the whole stimulus spectrum. This behaviour reminds the functional characteristics of disc-shape cells in the inferior colliculus, as described in a previous study of physiological periodicity coding (Periodicity analysis network, Voutsas et al., 2005 42]).