Rhythmic Modulation of Entrained Auditory Oscillations by Visual Inputs

Temporal structure is ubiquitous in sensory signals, and the brain has been shown to robustly represent information about temporal structure in the phase of low frequency neural oscillations. In a related construct, the integration of information across the different senses has been proposed to be at least partly due to the phase resetting of these low frequency oscillations. As a consequence, oscillations represent a potential contributor to the encoding of complex multisensory signals with informative temporal structures. Here we investigated these interactions using electroencephalography (EEG). We entrained low frequency (3 Hz) delta oscillations using a repetitive auditory stimulus-broadband amplitude modulated noise. Following entrainment, we presented auditory and audiovisual stimuli at variable delays. We examined whether the power of oscillations at the entrained frequency was dependent on the delay (and thus, potentially, phase) at which subsequent stimulation was delivered, and whether this relationship was different for subsequent multisensory (i.e., audiovisual) stimuli when compared with auditory stimuli alone. Our findings demonstrate that, when the subsequent stimuli are solely auditory, the power of oscillations at the entrained frequency is rhythmically modulated by when the stimulus was delivered. For audiovisual stimuli, however, no such dependency is present, yielding consistent power modulations. These effects indicate that reciprocal oscillatory mechanisms may be involved in the continuous encoding of complex temporally structured multisensory inputs such as speech.