Endogenous auditory and motor brain rhythms predictindividual speech tracking

Slow, endogenous brain rhythms in auditory cortex are hypothesized to track acoustic amplitude modulations during speech comprehension. Temporal predictions from the motor system are thought to enhance this tracking. However, direct evidence for the involvement of endogenous auditory and motor brain rhythms is lacking. Combining magnetoencephalographic recordings with behavioral data, we here show that endogenous peak frequencies of individuals resting-state theta rhythm in superior temporal gyrus predict speech tracking during comprehension. Importantly, endogenous rates of speech motor areas predicted auditory-cortical speech tracking only in individuals with high auditory-motor synchronization profiles. Higher rates in the supplementary motor area, and lower rates in inferior frontal gyrus, predicted stronger tracking. These findings align with participants behavioral data and provide compelling support for oscillatory accounts of auditory-motor interactions during speech perception. Interestingly, working memory capacity predicted speech comprehension performance particularly in individuals with low auditory-motor synchronization profiles. The findings highlight two partially independent speech processing routes across individuals: an auditory-motor route, related to enhanced comprehension performance, and an auditory working-memory route.