Entrainment of Perceptually Relevant Brain Oscillations by Non-Invasive Rhythmic Stimulation of the Human Brain

Gregor Thut,Joachim Gross,Philippe G Schyns

doi:10.3389/fpsyg.2011.00170

Abstract

The notion of driving brain oscillations by directly stimulating neuronal elements with rhythmic stimulation protocols has become increasingly popular in research on brain rhythms. Induction of brain oscillations in a controlled and functionally meaningful way would likely prove highly beneficial for the study of brain oscillations, and their therapeutic control. We here review conventional and new non-invasive brain stimulation protocols as to their suitability for controlled intervention into human brain oscillations. We focus on one such type of intervention, the direct entrainment of brain oscillations by a periodic external drive. We review highlights of the literature on entraining brain rhythms linked to perception and attention, and point out controversies. Behaviourally, such entrainment seems to alter specific aspects of perception depending on the frequency of stimulation, informing models on the functional role of oscillatory activity. This indicates that human brain oscillations and function may be promoted in a controlled way by focal entrainment, with great potential for probing into brain oscillations and their causal role.

Highlights

Physiological rhythms are ubiquitous in living organisms (e.g., Glass, 2001)
We highlight challenges in the quest for entrainment. In light of these challenges, we argue that providing converging evidence for entrainment on both the level of EEG-signals and behavioral measures will likely prove essential to disambiguate entrainment from other forms of interactions between rhythmic brain stimulation and brain rhythms
In the light of these controversies, we argue that complementary probes into entrainment, e.g., via behavioral measures, can provide important information

Summary

Introduction

Physiological rhythms are ubiquitous in living organisms (e.g., Glass, 2001). In the brain, oscillations are supported by distinct neuronal elements across different spatial scales (e.g., Buzsáki and Draguhn, 2004). These controversial results can be reconciled by a model in which transient EEG/MEG-responses to external stimuli and self-sustained (ongoing) EEG/MEG oscillations are tightly linked (Basar, 1980; David et al, 2006; Zaehle et al, 2010a) According to this view, the neural elements under study have specific oscillatory properties which determine both the (early parts of the) EEG/MEG-response to, e.g., a single pulse stimulus (e.g., Van Der Werf and Paus, 2006; Rosanova et al, 2009), and the frequencies of oscillations that can be entrained per area (e.g., Herrmann, 2001). The design of this study did not allow to resolve to what extent expectations and internal control drove these effects, or alternatively whether direct sensory entrainment of visual brain rhythms may have played a pivotal role

Limitations

Conclusion