Neural theta oscillations support semantic memory retrieval

Martin Marko,Igor Riečanský,Barbora Cimrová

doi:10.1038/s41598-019-53813-y

Abstract

Lexical–semantic retrieval emerges through the interactions of distributed prefrontal and perisylvian brain networks. Growing evidence suggests that synchronous theta band neural oscillations might play a role in this process, yet, their functional significance remains elusive. Here, we used transcranial alternating current stimulation to induce exogenous theta oscillations at 6 Hz (θ-tACS) over left prefrontal and posterior perisylvian cortex with a 180° (anti-phase) and 0° (in-phase) relative phase difference while participants performed automatic and controlled retrieval tasks. We demonstrate that θ-tACS significantly modulated the retrieval performance and its effects were both task- and phase-specific: the in-phase tACS impaired controlled retrieval, whereas the anti-phase tACS improved controlled but impaired automatic retrieval. These findings indicate that theta band oscillatory brain activity supports binding of semantically related representations via a phase-dependent modulation of semantic activation or maintenance.

Highlights

Lexical–semantic retrieval emerges through the interactions of distributed prefrontal and perisylvian brain networks
Changes in the theta-band synchronization have been repeatedly observed during lexical–semantic retrieval, indicating that theta could mediate the activation, propagation, and coupling of lexical– semantic representations distributed over the cortex[18,19,20], which has been attributed to semantic representation system
Using linear mixed-effect models (LMEM), the response time (RT) were modeled as a function of transcranial alternating current stimulation (tACS), while controlling for associative chain test33 (ACT) block and random subject intercepts

Summary

Introduction

Lexical–semantic retrieval emerges through the interactions of distributed prefrontal and perisylvian brain networks. We demonstrate that θ-tACS significantly modulated the retrieval performance and its effects were both task- and phase-specific: the in-phase tACS impaired controlled retrieval, whereas the anti-phase tACS improved controlled but impaired automatic retrieval These findings indicate that theta band oscillatory brain activity supports binding of semantically related representations via a phase-dependent modulation of semantic activation or maintenance. It has become increasingly evident that synchronous neural oscillations in specific frequency bands are coupled with distinct cognitive functions[13,14] Their causal role has been supported by studies using non-invasive brain stimulation[15], indicating that neural oscillations are not an epiphenomenon of neural activity but an integral neurobiological mechanism by which the brain implements cognitive functions. These findings indicate that theta synchronization may be generally associated with an involvement of domain-general executive control or controlled semantic processing rather than lexical-semantic representation

Methods

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Discussion

Conclusion