Dynamics and function of neuronal oscillatory entrainment in the auditory system
While we have convincing evidence that attention to auditory stimuli modulates neuronal responses even at or before the level of primary auditory cortex (A1), the underlying physiological mechanisms were, until recently, unknown. Our earlier studies have demonstrated that perpetually ongoing, rhythmic excitability fluctuations of neuronal ensembles can actually track the timing of stimuli within rhythmic stimulus sequences or streams, by synchronizing to the rhythm of the streams. The mechanism enabling this dynamic tracking is termed oscillatory entrainment. After a short introduction to neuronal oscillations, I will present results of our recent studies showing that topographically organized neuronal oscillations entrained across all A1 neuronal ensembles in the non-human primate act as a spectrotemporal filter mechanism of selective attention. This two dimensional filter is organized in cortical space and time to match the properties of attended rhythmic stimuli. As a consequence, it amplifies attended and suppresses unattended frequency content at specific time points, which at the same time stabilizes the sensory representation of attended stimuli. Several recent studies from our lab and others indicate that the same mechanism aids in the segregation and perception of attended speech.