Hemispheric differences in altered reactivity of brain oscillations at rest after posterior lesions

Jessica Gallina,Marco Zanon,Mattia Pietrelli,Caterina Bertini

doi:10.1007/s00429-021-02279-8

Abstract

A variety of evidence supports the dominance of the right hemisphere in perceptual and visuo-spatial processing. Although growing evidence shows a strong link between alpha oscillations and the functionality of the visual system, asymmetries in alpha oscillatory patterns still need to be investigated. Converging findings indicate that the typical alpha desynchronization occurring in the transition from the eyes-closed to the eyes-open resting state might represent an index of reactivity of the visual system. Thus, investigating hemispheric asymmetries in EEG reactivity at the opening of the eyes in brain-lesioned patients may shed light on the contribution of specific cortical sites and each hemisphere in regulating the oscillatory patterns reflecting the functionality of the visual system. To this aim, EEG signal was recorded during eyes-closed and eyes-open resting state in hemianopic patients with posterior left or right lesions, patients without hemianopia with anterior lesions and healthy controls. Hemianopics with both left and right posterior lesions showed a reduced alpha reactivity at the opening of the eyes, suggesting that posterior cortices have a pivotal role in the functionality of alpha oscillations. However, right-lesioned hemianopics showed a greater dysfunction, demonstrated by a reactivity reduction more distributed over the scalp, compared to left-lesioned hemianopics. Moreover, they also revealed impaired reactivity in the theta range. This favors the hypothesis of a specialized role of the right hemisphere in orchestrating oscillatory patterns, both coordinating widespread alpha oscillatory activity and organizing focal processing in the theta range, to support visual processing at the opening of the eyes.

Highlights

There is a longstanding agreement about the existence of hemispheric asymmetries in visuo-spatial abilities (Duecker and Sack 2015; Heilman and Van Den Abell 1980; Kinsbourne 1977)
The results showed that all groups presented a significant desynchronization of alpha power at the opening of the eyes, across all scalp regions
Decreased alpha power during the eyes-open condition compared to the eyes-closed condition was found in posterior, central and anterior sites, in both the left and the right hemispheres

Summary

Introduction

There is a longstanding agreement about the existence of hemispheric asymmetries in visuo-spatial abilities (Duecker and Sack 2015; Heilman and Van Den Abell 1980; Kinsbourne 1977). The individual alpha frequency of occipital oscillations represents a measure of temporal resolution of visual perception (Cecere et al 2015; Samaha and Postle 2015; Klimesch et al 2007; Valera et al 1981), whereas alpha power (Romei et al 2008a, b) and phase (Mathewson et al 2009, 2012; Bush et al 2009) reflect variations in cortical excitability and visual awareness. Recent perspectives have proposed an association between alpha power at rest and the tonic and distributed synchronous activity of the underlying neurons (Sadaghiani and Kleinschmidt 2016; Klimesh et al 2007), possibly indexing active suppression of neural predictions in the visual system (Sadaghiani and Kleinschmidt 2016) and, reflecting an active engagement of the neurons of the underlying neural population

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Conclusion