Cochlear activity in silent cue-target intervals shows a theta-rhythmic pattern and is correlated to attentional alpha modulations

Abstract

There is still a controversial debate regarding, where in the processing hierarchy of the central nervous system (CNS) selective attention takes effect. The auditory system can influence cochlear processes via direct and mediated (by the inferior colliculus) projections from the auditory cortex to the superior olivary complex (SOC). Studies illustrating attentional modulations of cochlear responses have so far been limited to sound evoked responses. The aim of the present study was to investigate intermodal (audiovisual) selective attention in humans simultaneously at the cortical and cochlear level during a stimulus-free cue-target period. We found that cochlear activity in the silent cue-target periods was modulated by a theta-rhythmic pattern (~4 Hz). While this pattern was present independently of attentional focus, cochlear theta activity was clearly enhanced when attending to the upcoming auditory input. On a cortical level classical posterior alpha and beta power enhancements were found during auditory selective attention. Interestingly, participants with a stronger attentional modulation of cochlear theta activity show to lesser extent the classical posterior alpha effect. These results hint at a putative theta-rhythmic sampling of auditory input at the cochlear level. Furthermore, our results point to an interindividual variability to what extent efferent pathways are engaged in an attentional context and linked to neural processes outside of the auditory system.

Neural speech tracking shifts from the syllabic to the modulation rate of speech as intelligibility decreases

“…Furthermore, this subcortical activity can even be modulated by attention ( 19, 20, 23 ). Interestingly, top-down attentional modulations of auditory activity can already be detected at the hair cells in the inner ear measured as otoacoustic activity (faint sounds emitted by the outer hair cells; see 24 ). Other studies have shown that even subcortical nuclei on the auditory pathway are behaviorally relevant for speech recognition (medial geniculate bodies; 25 ).…”