Word Class and Context Affect Alpha-Band Oscillatory Dynamics in an Older Population

Monika S Mellem,Marcel C M Bastiaansen,Andrei V Medvedev,Lea K Pilgrim,Rhonda B Friedman

doi:10.3389/fpsyg.2012.00097

Abstract

Differences in the oscillatory EEG dynamics of reading open class (OC) and closed class (CC) words have previously been found (Bastiaansen et al., 2005) and are thought to reflect differences in lexical-semantic content between these word classes. In particular, the theta-band (4–7 Hz) seems to play a prominent role in lexical-semantic retrieval. We tested whether this theta effect is robust in an older population of subjects. Additionally, we examined how the context of a word can modulate the oscillatory dynamics underlying retrieval for the two different classes of words. Older participants (mean age 55) read words presented in either syntactically correct sentences or in a scrambled order (“scrambled sentence”) while their EEG was recorded. We performed time–frequency analysis to examine how power varied based on the context or class of the word. We observed larger power decreases in the alpha (8–12 Hz) band between 200–700 ms for the OC compared to CC words, but this was true only for the scrambled sentence context. We did not observe differences in theta power between these conditions. Context exerted an effect on the alpha and low beta (13–18 Hz) bands between 0 and 700 ms. These results suggest that the previously observed word class effects on theta power changes in a younger participant sample do not seem to be a robust effect in this older population. Though this is an indirect comparison between studies, it may suggest the existence of aging effects on word retrieval dynamics for different populations. Additionally, the interaction between word class and context suggests that word retrieval mechanisms interact with sentence-level comprehension mechanisms in the alpha-band.

Highlights

Understanding the myriad of operations underlying language comprehension in the brain is an ongoing challenge in the field
We did not find any significant effects in the evoked responses for either the open class (OC)–closed class (CC) comparison (Figure 2A) or the sentence–scrambled sentence (S–SS) comparison (Figure 2B)
This effect resulted from a greater power decrease for OC words than for CC words

Summary

Introduction

Understanding the myriad of operations underlying language comprehension in the brain is an ongoing challenge in the field. Neuronal networks supporting these operations must dynamically assemble locally and flexibly communicate across long distances. Oscillatory synchronization is thought to reflect the transient formation of functional brain networks (Varela et al, 2001; Fries, 2005), and this synchronization can be measured through EEG or MEG spectral analysis. Power analysis is thought to reflect the recruitment of local neuronal networks while coherence analysis reflects dynamic linking between brain areas involved in a global network. The study of oscillatory dynamics is a promising method to complement current ERP analysis and examine functional networks for language processing

Methods

Results

Discussion

Conclusion