Neural bases of unconscious orienting of attention in hemianopic patients: Hemispheric differences

Sánchez-López, Javier; Savazzi, Silvia; Pedersini, Caterina A.; Cardobi, Nicolò; Marzi, Carlo Alberto

doi:10.1016/j.cortex.2020.02.015

Cited by 5 publications

(3 citation statements)

References 75 publications

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“…Importantly, hemianopic patients with posterior lesions did not show altered patterns of functional connectivity in the beta range at rest, both intra- and inter-hemispheres. Altered oscillatory activity in the beta band has been reported in stroke patients in task-related oscillatory activity (Guggisberg et al 2015 ) and also in hemianopics, mostly associated to impaired stimulus processing in visual and attentional tasks (Allaman et al 2021 ; Sanchez-Lopez et al 2020 ). However, the present findings suggest that, when looking at oscillatory patterns at rest, a damage to the posterior brain areas impair the functional connectivity patterns selectively in the range of alpha.…”

Section: Discussionmentioning

confidence: 99%

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

et al. 2022

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Emerging evidence suggests a role of the posterior cortices in regulating alpha oscillatory activity and organizing low-level processing in non-alpha frequency bands. Therefore, posterior brain lesions, which damage the neural circuits of the visual system, might affect functional connectivity patterns of brain rhythms. To test this hypothesis, eyes-closed resting state EEG signal was acquired from patients with hemianopia with left and right posterior lesions, patients without hemianopia with more anterior lesions and healthy controls. Left-lesioned hemianopics showed reduced intrahemispheric connectivity in the range of upper alpha only in the lesioned hemisphere, whereas right-lesioned hemianopics exhibited reduced intrahemispheric alpha connectivity in both hemispheres. In terms of network topology, these impairments were characterized by reduced local functional segregation, with no associated change in global functional integration. This suggests a crucial role of posterior cortices in promoting functional connectivity in the range of alpha. Right-lesioned hemianopics revealed also additional impairments in the theta range, with increased connectivity in this frequency band, characterized by both increased local segregated activity and decreased global integration. This indicates that lesions to right posterior cortices lead to stronger impairments in alpha connectivity and induce additional alterations in local and global low-level processing, suggesting a specialization of the right hemisphere in generating alpha oscillations and in coordinating complex interplays with lower frequency bands. Importantly, hemianopic patient’s visual performance in the blind field was linked to alpha functional connectivity, corroborating the notion that alpha oscillatory patterns represent a biomarker of the integrity and the functioning of the underlying visual system.

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Section: Discussionmentioning

confidence: 99%

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

et al. 2022

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“…For example, Chokron et al (2016) have outlined how the exact nature of the visual deficit in hemianopic patients is influenced by the lesion side, with performance in different tasks impaired according to the lesion being located in the right or left occipital cortex. In an EEG study, Sanchez-Lopez et al (2020) reported that showing a stimulus after either a valid or invalid cue elicited a differential time-frequency activity depending on the hemifield of presentation.…”

Section: Introductionmentioning

confidence: 99%

“…In an EEG study, Sanchez‐Lopez et al. (2020) reported that showing a stimulus after either a valid or invalid cue elicited a differential time‐frequency activity depending on the hemifield of presentation.…”

Section: Introductionmentioning

confidence: 99%

Mapping the routes of perception: Hemispheric asymmetries in signal propagation dynamics

Bonfanti,

Mazzi,

Savazzi

2024

Psychophysiology

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The visual system has long been considered equivalent across hemispheres. However, an increasing amount of data shows that functional differences may exist in this regard. We therefore tried to characterize the emergence of visual perception and the spatiotemporal dynamics resulting from the stimulation of visual cortices in order to detect possible interhemispheric asymmetries. Eighteen participants were tested. Each of them received 360 transcranial magnetic stimulation (TMS) pulses at phosphene threshold intensity over left and right early visual areas while electroencephalography was being recorded. After each single pulse, participants had to report the presence or absence of a phosphene. Local mean field power analysis of TMS‐evoked potentials showed an effect of both site (left vs. right TMS) of stimulation and hemisphere (ipsilateral vs. contralateral to the TMS): while right TMS determined early stronger activations, left TMS determined later stronger activity in contralateral electrodes. The interhemispheric signal propagation index revealed differences in how TMS‐evoked activity spreads: left TMS‐induced activity diffused contralaterally more than right stimulation. With regard to phosphenes perception, distinct electrophysiological patterns were found to reflect similar perceptual experiences: left TMS‐evoked phosphenes are associated with early occipito‐parietal and frontal activity followed by late central activity; right TMS‐evoked phosphenes determine only late, fronto‐central, and parietal activations. Our results show that left and right occipital TMS elicits differential electrophysiological patterns in the brain, both per se and as a function of phosphene perception. These distinct activation patterns may suggest a different role of the two hemispheres in processing visual information and giving rise to perception.

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What cortical areas are responsible for blindsight in hemianopic patients?

Sánchez-López

Cardobi

Pedersini

et al. 2020

Cortex

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Neural bases of unconscious orienting of attention in hemianopic patients: Hemispheric differences

Cited by 5 publications

References 75 publications

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

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

Mapping the routes of perception: Hemispheric asymmetries in signal propagation dynamics

What cortical areas are responsible for blindsight in hemianopic patients?

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