Sustained neural rhythms reveal endogenous oscillations supporting speech perception

• Published in: PLoS biology 2021-02, Vol.19 (2), p.e3001142-e3001142
• Main Authors: van Bree, Sander, Sohoglu, Ediz, Davis, Matthew H, Zoefel, Benedikt
• Format: Article
• Language: English
• Subjects: Adult; Biological Clocks; Biology and Life Sciences; Black line; Brain - physiology; Cognitive science; Electrical stimuli; Electroencephalography; Engineering and Technology; Entrainment; Female; Genetic aspects; Humans; Magnetoencephalography; Male; Medicine and Health Sciences; Middle Aged; Neural oscillations; Neural stimulation; Neuroscience; Noise; Oscillations; Perception; Phase coherence; Physical Sciences; Physiological aspects; Research and Analysis Methods; Rhythm; Rhythms; Social Sciences; Speech; Speech perception; Speech Perception - physiology; Standard error; Stimulation; Transcranial Direct Current Stimulation
• ISSN: 1545-7885; 1544-9173; 1545-7885
• DOI: 10.1371/journal.pbio.3001142

Rhythmic sensory or electrical stimulation will produce rhythmic brain responses. These rhythmic responses are often interpreted as endogenous neural oscillations aligned (or "entrained") to the stimulus rhythm. However, stimulus-aligned brain responses can also be explained as a sequence of evoked responses, which only appear regular due to the rhythmicity of the stimulus, without necessarily involving underlying neural oscillations. To distinguish evoked responses from true oscillatory activity, we tested whether rhythmic stimulation produces oscillatory responses which continue after the end of the stimulus. Such sustained effects provide evidence for true involvement of neural oscillations. In Experiment 1, we found that rhythmic intelligible, but not unintelligible speech produces oscillatory responses in magnetoencephalography (MEG) which outlast the stimulus at parietal sensors. In Experiment 2, we found that transcranial alternating current stimulation (tACS) leads to rhythmic fluctuations in speech perception outcomes after the end of electrical stimulation. We further report that the phase relation between electroencephalography (EEG) responses and rhythmic intelligible speech can predict the tACS phase that leads to most accurate speech perception. Together, we provide fundamental results for several lines of research-including neural entrainment and tACS-and reveal endogenous neural oscillations as a key underlying principle for speech perception.