Endogenous Delta/Theta Sound-Brain Phase Entrainment Accelerates the Buildup of Auditory Streaming

• Published in: Current biology 2015-12, Vol.25 (24), p.3196-3201
• Main Authors: Riecke, Lars, Sack, Alexander T., Schroeder, Charles E.
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Auditory Cortex - physiology; Auditory Perception - physiology; Delta Rhythm; Female; Healthy Volunteers; Humans; Male; Noise; Theta Rhythm; Young Adult
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2015.10.045

In many natural listening situations, meaningful sounds (e.g., speech) fluctuate in slow rhythms among other sounds. When a slow rhythmic auditory stream is selectively attended, endogenous delta (1‒4 Hz) oscillations in auditory cortex may shift their timing so that higher-excitability neuronal phases become aligned with salient events in that stream [1, 2]. As a consequence of this stream-brain phase entrainment [3], these events are processed and perceived more readily than temporally non-overlapping events [4–11], essentially enhancing the neural segregation between the attended stream and temporally noncoherent streams [12]. Stream-brain phase entrainment is robust to acoustic interference [13–20] provided that target stream-evoked rhythmic activity can be segregated from noncoherent activity evoked by other sounds [21], a process that usually builds up over time [22–27]. However, it has remained unclear whether stream-brain phase entrainment functionally contributes to this buildup of rhythmic streams or whether it is merely an epiphenomenon of it. Here, we addressed this issue directly by experimentally manipulating endogenous stream-brain phase entrainment in human auditory cortex with non-invasive transcranial alternating current stimulation (TACS) [28–30]. We assessed the consequences of these manipulations on the perceptual buildup of the target stream (the time required to recognize its presence in a noisy background), using behavioral measures in 20 healthy listeners performing a naturalistic listening task. Experimentally induced cyclic 4-Hz variations in stream-brain phase entrainment reliably caused a cyclic 4-Hz pattern in perceptual buildup time. Our findings demonstrate that strong endogenous delta/theta stream-brain phase entrainment accelerates the perceptual emergence of task-relevant rhythmic streams in noisy environments. •4-Hz transcranial alternating current stimulation modulates auditory streaming•Delta/theta stream-brain phase entrainment accelerates the buildup of streaming•Endogenous stream-brain phase entrainment is a cause, not result, of streaming Riecke et al. studied how humans can identify a rhythmic sound sequence in background noise. Using brain stimulation, they found that synchronization of ongoing brain rhythms with a sound sequence accelerates the detection of this sequence. This implies that the brain can employ its ongoing rhythms as critical instruments in scene analysis.