Hitting the right pitch: Cortical tracking of fundamental frequency changes across speech rates in auditory and sensorimotor regions
Neuronal entrainment to speech properties is essential for language processing, particularly through oscillatory tracking of slower rhythms corresponding to the syllabic rate. However, it remains less explored whether brain rhythms also synchronize with higher-frequency speech components, particularly the fundamental frequency (F0) or pitch. We used magnetoencephalography (MEG) to investigate cortical tracking of F0 while participants listened to sentences produced at natural normal and fast rates, but also to time-compressed speech. We examined how pitch changes accompanying natural increases in speech rate modulate brain-to-speech coupling and compared this with artificially accelerated speech, where F0 is unchanged. We also explored whether this coupling is confined to the auditory cortex or involves a broader cortical network. We computed whole-brain cortico-acoustic coupling between the MEG source time-series and the speech signal, alongside spectral power modulations in frequency bands centered on the mean F0 of the speech material. We found significant brain-to-F0 coupling in the right auditory, inferior parietal, insular, and pre- and postcentral regions across all speech rate conditions. Importantly, the peak neuro-acoustic coupling frequency adjusted to reflect the F0 increase due to natural rate acceleration. Interestingly, we found significant brain-speech coupling around F0 not only in the primary auditory cortex but also in a postcentral somatosensory region likely corresponding to the ventral larynx area. These findings provide new insights into frequency-specific cortical tracking of F0 during the perception of naturally-produced speech at varying rates and suggest the involvement of an auditory-somato-motor network that may facilitate the recognition of articulatory features during speech perception.