Robust neuronal oscillatory entrainment to speech displays individual variation in lateralisation

Nietzsche H L Lam,Annika Hultén,Peter Hagoort,Jan-Mathijs Schoffelen

doi:10.1080/23273798.2018.1437456

Abstract

ABSTRACTNeural oscillations may be instrumental for the tracking and segmentation of continuous speech. Earlier work has suggested that delta, theta and gamma oscillations entrain to the speech rhythm. We used magnetoencephalography and a large sample of 102 participants to investigate oscillatory entrainment to speech, and observed robust entrainment of delta and theta activity, and weak group-level gamma entrainment. We show that the peak frequency and the hemispheric lateralisation of the entrainment are subject to considerable individual variability. The first finding may support the involvement of intrinsic oscillations in entrainment, and the second finding suggests that there is no systematic default right-hemispheric bias for processing acoustic signals on a slow time scale. Although low frequency entrainment to speech is a robust phenomenon, the characteristics of entrainment vary across individuals, and this variation is important for understanding the underlying neural mechanisms of entrainment, as well as its functional significance.

Highlights

Human speech represents one of the most complex auditory signals that are perceived, containing information at multiple temporal scales that needs to be processed and integrated for adequate comprehension
A popular perspective on early auditory processing of speech is that neuronal oscillations play an important mechanistic role in the processing and prediction of temporally structured perceptual information
Frequency-specific phase synchronisation of cortical oscillatory activity to the envelope of the auditory input signal has been proposed to provide an initial temporal parsing mechanism of the relevant linguistic structures needed for speech processing

Summary

Introduction

Human speech represents one of the most complex auditory signals that are perceived, containing information at multiple temporal scales that needs to be processed and integrated for adequate comprehension. Focusing on the early stages of auditory processing, the input needs to be parsed into relevant temporal segments, which can be further processed by the brain system for language, and integrated into a meaningful linguistic context. This cascade of processing operations results in comprehension. Upon presentation of a periodic external signal, alignment of neural oscillatory activity to the signals’ rhythm allows for these periodic occurrences of high levels of neuronal excitability to align with certain periodic events in the signal This synchronisation of rhythms is referred to as entrainment, and facilitates optimal sampling in discrete time windows. In these studies entrainment of neural oscillations with rhythmic auditory or visual stimuli have been shown to shape perception (Busch, Dubois, & VanRullen, 2009; de Graaf et al, 2013; Lakatos et al, 2005; Lakatos, Chen, O’Connell, Mills, & Schroeder, 2007; Lakatos, Karmos, Mehta, Ulbert, & Schroeder, 2008; Romei, Gross, & Thut, 2010; Spaak, de Lange, & Jensen, 2014)

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