Collaborative Research: Brain Mechanisms of Rhythm Perception: The Impact of the Motor System on Auditory Perception

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The perception of rhythmic patterns of events in time is central to our ability to find meaning in the sounds of language and music: the basis for much of human culture and communication. We do not passively receive temporal patterns, but actively engage with them by using a repeating 'pulse' or 'beat' to form an essential scaffold for our perception of time. This ability might be most obvious when expressed through dance, or simply tapping a foot to music, but it has deeper importance for how we comprehend sound even in the absence of movement. The scaffold provided by the beat cycle enables listeners to predict upcoming events, allowing more efficient encoding and learning of sensory patterns. How does this important perceptual mechanism work? New evidence suggests that perceiving patterns in sound doesn't depend only on the auditory system, but also involves activation of the motor system, even when the listener is not moving. This proposal tests the provocative and potentially transformative idea that motor planning activity is not only to help us move, but is also necessary for perception of patterns in the sounds we hear. This research has many potential societal benefits in both education and medicine. An understanding of the auditory-motor interactions underlying rhythm perception could explain a growing number of findings suggesting an important link between beat perception and language, including the development of reading in children, the perception of speech in noise, and attention, and may help drive improved educational interventions. The results could also provide a brain-based explanation for the growing use of rhythmic music in the treatment of movement disorders such as Parkinson's disease and possibly guide development of enhanced therapies and diagnostic tests. This proposal addresses a critical, and difficult, open question within auditory cognitive neuroscience: Does motor activity play a causal role in beat perception and if so, what is that role? Establishing this would be a transformative breakthrough in our understanding of the perception of time. While there is strong existing evidence that motor regions are active during beat perception, the dynamic functioning and interaction among parts of the cortical network supporting beat perception is not fully understood. In particular, a causal role of motor activity on auditory processing has not yet been demonstrated directly. This program of research directly examines whether motor planning regions influence processing in auditory cortex and whether a dynamic network is activated during beat perception. To achieve these objectives the investigators use two interlocking approaches: 1) Advanced quantitative methods of cortical source-resolved electroencephalographic (EEG) brain dynamics during beat perception tasks to identify regions in the brain whose activity patterns mirrors the endogenously perceived beat and to examine the directional flow of influence between these beat perception areas and other auditory processing areas; 2) Non-invasive transcranial magnetic stimulation (TMS) to transiently suppress and/or facilitate activity in beat perception areas.