Grant: Discovery Grants Program - Individual

In our everyday lives, we interact with rhythmic auditory stimuli like speech and music almost constantly. Brain activity is also rhythmic, and brain rhythms synchronize with the rhythms of sounds. The fidelity of brain-environment synchrony predicts important aspects of the ability to understand the world of sound, and brain-environment synchrony is an important player in the formation of neural networks. Neural network formation is often identified based on the coupling of a low-frequency brain rhythm and higher-frequency amplitude fluctuations. However, in cases when the stimulus itself is rhythmic, it is impossible to disentangle whether fluctuations in high-frequency amplitude are driven by the stimulus and unrelated to synchronized low-frequency activity activity, or driven by functional coupling to the auditory system, reflecting establishment of a neural-network configuration that underlies successful listening. One important hypothesis regarding brain-environment synchrony's role in successful listening is that rhythmic brain activity is generated by oscillators. Predicting the circumstances under which brain-environment synchrony will be successful, and understanding how to improve brain-environment synchrony when it fails (as it does with advancing age), hinge on firmly establishing that any intervention is targeting a theoretical oscillator. However, when the stimulus itself is rhythmic, it is technically challenging or impossible to disentangle this possibility from an alternative hypothesis that observed brain activity is driven by the stimulus. The current research proposal will overcome these challenges by using transcranial alternating current stimulation (tACS) to interfere with brain-environment synchrony and neural-network formation during effortful listening and temporal prediction. TACS will be combined with computational modeling, electroencephalography (EEG), and behavior to measure, model, and investigate the related concepts of preferred rate, resonance, and entrainment regions in the human auditory system and how they change with advancing age. The aims of this research program are to understand auditory brain-environment synchrony, how it is accomplished, how it changes with age, and under what situations it will be successful. Findings from these studies will advance theory in the burgeoning field of neural oscillations and neural entrainment, and inform intervention development, as tACS has been proposed as a technique that could be used to improve brain-environment synchrony. Listening difficulties lead older adults to socially withdraw, which is in turn a strong predictor of dementia onset. As the proportion of Canada's population above age 65 continues to increase, understanding auditory brain-environment synchrony, and its age-related changes and their consequences for continued listening success, is of the utmost importance.