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

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.

Right Hemisphere Dominance for Unconscious Emotionally Salient Stimuli

“…From this perspective, interconnected attentional networks [105,106], regulating attentional allocation in visual space, might participate in these defensive mechanisms, promoting effective scanning and visual analysis of the environment. Thus, the well-known dominance of the right hemisphere in visuo-spatial performance [107][108][109][110][111][112], and attentional allocation [105,106,[113][114][115], might have favored connections and reciprocal signaling between the emotional subcortical circuit and the attentional networks within the same hemisphere, therefore strengthening the right-lateralized prevalence in rapid and unconscious detection of threat.…”

Alterations in resting-state functional connectivity after brain posterior lesions reflect the functionality of the visual system in hemianopic patients

“…As a consequence, in light of the importance of posterior cortices in generating, distributing and coordinating oscillatory patterns (Hindriks et al 2015 ; Thut et al 2011 ; Bollimunta et al 2008 ; Romei, et al 2008a , b ), it is of great interest to study the effects of lesions to these cortices on oscillations also at the network level. Indeed, as previously mentioned, evidence on hemianopic patients has shown that lesions to posterior cortices alter oscillatory activity at rest and that these alterations might represent a biomarker of the functionality of the visual system (Pietrelli et al 2019 ; Gallina et al 2021 ). However, it is still unknown whether lesions to posterior cortices might also induce specific post-lesional alterations of functional connectivity patterns in different frequency bands during resting state.…”

“…More precisely, posterior brain lesions in hemianopic patients have been shown to selectively reduce the alpha peak and power during rest, while the same was not observed after lesions to anterior regions (Pietrelli et al 2019 ), suggesting a role of posterior cortices in generating and distributing alpha oscillatory activity at rest. Moreover, evidence has shown that lesions to posterior cortices (and not lesions to anterior cortices) alter also the typical alpha power reduction observed in the transition from the eyes-closed resting state to the opening of the eyes (i.e., alpha reactivity; Gallina, et al 2021 ). Interestingly, when alpha reactivity was more severely impaired after right posterior lesions, a concurrent disruption in reactivity in the theta range at the opening of the eyes was also observed (Gallina et al 2021 ).…”

“…Moreover, evidence has shown that lesions to posterior cortices (and not lesions to anterior cortices) alter also the typical alpha power reduction observed in the transition from the eyes-closed resting state to the opening of the eyes (i.e., alpha reactivity; Gallina, et al 2021 ). Interestingly, when alpha reactivity was more severely impaired after right posterior lesions, a concurrent disruption in reactivity in the theta range at the opening of the eyes was also observed (Gallina et al 2021 ). This converging evidence suggests a role of posterior cortices in orchestrating these oscillatory patterns at rest, both coordinating widespread alpha oscillatory activity and organizing focal processing in the theta range and that lesions to these cortices and impairing the visual system might selectively disrupt this oscillatory activity.…”

Asymmetry of brain structure and function: 40 years after Sperry’s Nobel Prize

“…Other functions such as visual imagery are dominant in the left hemisphere for orthographic images and in the right for exogenous stimuli (Liu et al 2021;this issue). Some other functions do not even have an exact name or definition, such as the right hemispheric orchestration of oscillatory patterns to support visual processing (Gallina et al 2021;this issue). Hence, a significant amount of work is still required to polish the functional fabric of the human mind as we understand it before we can assess their functional and structural lateralisation comprehensively and with satisfying accuracy.…”