Tackling endogenous theta oscillations in primary auditory cortex
Poster D63 in Poster Session D with Social Hour, Friday, October 7, 5:30 - 7:15 pm EDT, Millennium Hall
Antje Strauß1, Cecile Pacoret2; 1University of Konstanz, 2University of Geneva
Accumulating evidence shows that auditory cortex is tracking rhythmic fluctuations of the speech signal, often framed as entrainment. The underlying mechanism, resonance or entrainment, and its functional significance, however, are still unclear. Following Notbohm et al. (2016), who have investigated individual alpha peaks in the visual cortex, we created ~19 sec long, amplitude modulated sweeps accelerating from 3 to 8 Hz, hence, spanning across the commonly reported range of theta oscillations. While recording EEG, 20 participants listened to 60 repetitions of the sweep at two different levels of loudness (at 52dB SPL and 12dB below; 120 trials in total). This pure listening task was interrupted twice by a short behavioral auditory discrimination task. Additionally, we recorded 3 minutes of resting state EEG in silence and 3 minutes in white noise. In total, the experiment lasted for about 60 minutes. We quantified the normalized Shannon Entropy (Notbohm et al., 2016) and the phase-locking value (PLV; Duecker et al., 2021) between the envelope of the sweep and the EEG signal. Interestingly, we found a u-shaped function of Entropy in the theta range over auditory areas compared to an occipital control region, but not compared to rest. The PLV, however, exhibited a linear decrease with increasing frequency compared to rest and occipital regions. Both findings are contrary to the notion of resonance and entrainment that would predict amplified responses at certain preferred frequencies. In sum, our preliminary data suggest that there is no oscillatory behavior in the theta range in auditory cortex.
Topic Areas: Perception: Auditory, Speech Perception