Sustained neural rhythms reveal endogenous oscillations supporting speech perception

Abstract

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.

A silent disco: Differential effects of beat-based and pattern-based temporal expectations on persistent entrainment of low-frequency neural oscillations

“…Finally, three recent studies have found evidence for persistent entrainment in the auditory domain, in response to isochronous sequences of tones (Pesnot Lerousseau et al, 2021;Wilsch, Mercier, Obleser, Schroeder, & Haegens, 2020) and isochronously presented speech (van Bree, Sohoglu, Davis, & Zoefel, 2021). However, in the first two cases, persistent entrainment was not specific to the frequency of the input (Wilsch et al, 2020), or only occurred in the gamma range, but not the delta range, which is of importance for temporal expectations (Pesnot Lerousseau et al, 2021).…”

Effects of Slow Oscillatory Transcranial Alternating Current Stimulation on Motor Cortical Excitability Assessed by Transcranial Magnetic Stimulation

“…However, unlike the well-documented immediate (online) effects of tES, there is less agreement regarding the magnitude and duration of post-stimulus (offline) effects (for review see, Veniero et al, 2015 ). These offline effects cannot be fully explained by a direct continuation of online entrainment (referred to as entrainment “echoes”), since these “echoes” only persist for a few oscillatory cycles following cessation of stimulation ( Marshall et al, 2006 ; Thut et al, 2011 ; Hanslmayr et al, 2014 ; van Bree et al, 2021 ). Therefore, longer-lasting offline effects (referred to as aftereffects) lasting up to 70 min are likely to reflect mechanisms other than entrainment per se (e.g., synaptic plasticity) ( Neuling et al, 2013 ; Veniero et al, 2015 ; Vossen et al, 2015 ; Kasten et al, 2016 ).…”

Neural synchronization is strongest to the spectral flux of slow music and depends on familiarity and beat salience

“…For visualizing the mean frequency response per musical feature, the coherence values at each stimulation tempo were normalized by dividing by the mean coherence across all other stimulation tempi per frequency bin (Fig. 2E-H) (van Bree et al, 2021). As strong coherence was found at the stimulation tempo and the first harmonic, the SRCoh values of each frequency vector were compared between musical features.…”