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Assessing Causal Relationships of Oscillatory Neural Activity Mediating Speech

Periodic Reporting for period 1 - ACRONAM-Speech (Assessing Causal Relationships of Oscillatory Neural Activity Mediating Speech)

Reporting period: 2018-01-01 to 2019-12-31

Our environment is dominated by regular structure, particularly in the auditory domain (speech, music, dance). Previous research has shown that rhythmic neural activity, also called neural oscillations, adjusts to this input rhythm, creating stimulus-brain alignment, or neural entrainment. Although neural entrainment has been associated with improved speech comprehension, it remained unclear whether it is indeed causally relevant for speech perception; i.e. if changes in neural entrainment cause changes in speech perception. This question was addressed in the current project. We manipulated entrainment using a brain stimulation technique shown to influence neural oscillations (transcranial alternating current stimulation, or tACS), and measured consequences for both neural activity and perception in human participants. We found that stimulus-brain alignment indeed causally modulates speech processing. This research therefore reveals potential novel treatment of clinical conditions such as hearing impairment.
In a first study, we found that our manipulation of neural entrainment leads to changes in neural responses to speech, as measured with brain imaging methods (functional magnetic resonance imaging, or fMRI). In several follow-up studies, we found that a similar stimulation protocol leads to changes in speech perception, as measured by asking participants to report words they were presented with acoustically. We also published several articles providing recommendations for the field on how to optimise parameters of transcranial current stimulation, and analyses of the acquired data. Results were disseminated in the form of articles in internationally renowned journals, conference presentation, and to the general public (e.g. social media).
Our results are remarkable as they open up new possibilities for the treatment of populations who struggle at present, such as hearing-impaired listeners. Previous research has demonstrated altered neural entrainment in these populations; our findings suggest that these changes might be treated with electrical stimulation. As all our studies were conducted in healthy participants, a replication in (e.g. hearing-impaired) patients is the logical next step, leading to exciting new directions in a recent field of research.