Hemispheric Asymmetry in TMS-Induced Effects on Spatial Attention: A Meta-Analysis

Respiratory phases modulate visuo-spatial attention: Evidence from line bisection and landmark tasks

This study explores the influence of respiratory phases on visuo-spatial attention during neuropsychological assessments with healthy adults. In Experiment 1, participants performed line bisection at peak inhalation vs. peak exhalation. Experiments 2 and 3 studied the landmark task, where participants determined which side of a pre-bisected line was shorter, again correlated with the respiratory phase. Experiment 1 revealed leftward bias during inhalation and rightward bias during exhalation. Experiments 2 and 3 confirmed these results in the landmark task. These findings suggest that respiration-related signals modulate the allocation of visuo-spatial attention.

Electrophysiological hemispheric asymmetries induced by parietal stimulation eliciting visual percepts

OBJECTIVE

We aimed to establish if the electrophysiological activity resulting from the direct stimulation of the intraparietal sulcus and eliciting visual percepts is hemispheric-specific.

METHODS

We tested nineteen participants. Each received 360 TMS pulses at phosphene threshold intensity over right and left IPS while recording EEG. After each pulse, participants had to report if they had seen a phosphene.

RESULTS

Parietal phosphene perception is associated with hemispheric-specific activations: phosphenes elicited by left TMS involve central and frontal electrodes at about 30 ms, and frontal, central and parieto-occipital electrodes from 120 to 250 ms; phosphenes elicited by right parietal TMS involve parietal and centro-parietal electrodes at about 60 ms, and frontal, central and parietal electrodes from 150 to 250 ms. Correlated Component Analysis shows that primary visual areas are not activated when phosphenes are produced by TMS over IPS.

CONCLUSIONS

Our results show that direct stimulation of IPS gives rise to sustained patterns of activity specific to the stimulated hemisphere. Moreover, elicited parietal phosphenes are associated with evoked activity specific to the stimulated hemisphere and located outside early visual processing areas.

SIGNIFICANCE

This study highlights hemispheric differences in the electrophysiological dynamics related to parietal phosphenes, and shows that the dorsal pathway can give rise to visual conscious percepts.

Exploring the Correlation Between Sleep Chronotype and the Volumes of Subcortical Structures and Hippocampal Subfields in Young Healthy Population

BACKGROUND/OBJECTIVES

Chronotypes significantly influence sleep quality, daily performance, and overall activity levels. Although there is growing evidence indicating that individuals with a late chronotype are more likely to experience cognitive decline, the specific neural mechanisms that contribute to this risk remain unclear. This study aims to explore the relationship between morning and evening preferences and the volumes of subcortical structures in a young, healthy population.

METHODS

A total of 123 participants (80 females), aged between 18 and 35 years, were recruited. They underwent MRI scans and completed several self-reported assessments, including the morningness-eveningness scale of the Chronotype Questionnaire (ChQ-ME), the amplitude scale of the Chronotype Questionnaire (ChQ-AM), the Epworth Sleepiness Scale (ESS), and the Pittsburgh Sleep Quality Index (PSQI). Participants were classified into early chronotype (EC) and late chronotype (LC) groups based on their ChQ-ME scores. High-resolution T1-weighted imaging was utilized to analyze the volumes of subcortical structures and hippocampal subfields.

RESULTS

The volumetric analysis indicated that the LC group showed significant reductions in the right Caudate (p = 0.03) and the left SR-SL-SM (p = 0.03) compared to the EC group. Additionally, a notable leftward hemispheric laterality of the Subiculum (p = 0.048) was observed in the EC group relative to the LC group. Furthermore, the ChQ-AM revealed significant positive (r = 0.23) and negative (r = -0.19) correlations with the volumes of the left thalamus and right amygdala, respectively. The PSQI demonstrated a significant negative correlation (r = -0.21) with the right SR-SL-SM, while the ESS indicated a significant positive correlation (r = 0.24) with the left SR-SL-SM. Multiple regression analysis indicated that variations in daytime sleepiness are linked to the change of the left SR-SL-SM volume.

CONCLUSIONS

Overall, the findings suggest that chronotype preferences are associated with the changes in the volumes of subcortical structures and hippocampal subfields and highlight the role of chronotypes in the neural mechanisms of these brain structures.

Visual Field Deficits in Albinism in Comparison to Idiopathic Infantile Nystagmus

Purpose

This is the first systematic comparison of visual field (VF) deficits in people with albinism (PwA) and idiopathic infantile nystagmus (PwIIN) using static perimetry. We also compare best-corrected visual acuity (BCVA) and optical coherence tomography measures of the fovea, parafovea, and circumpapillary retinal nerve fiber layer in PwA.

Methods

VF testing was performed on 62 PwA and 36 PwIIN using a Humphrey Field Analyzer (SITA FAST 24-2). Mean detection thresholds for each eye were calculated, along with quadrants and central measures. Retinal layers were manually segmented in the macular region.

Results

Mean detection thresholds were significantly lower than normative values for PwA (-3.10 ± 1.67 dB, P << 0.0001) and PwIIN (-1.70 ± 1.54 dB, P < 0.0001). Mean detection thresholds were significantly lower in PwA compared to PwIIN (P < 0.0001) and significantly worse for left compared to right eyes in PwA (P = 0.0002) but not in PwIIN (P = 0.37). In PwA, the superior nasal VF was significantly worse than other quadrants (P < 0.05). PwIIN appeared to show a mild relative arcuate scotoma. In PwA, central detection thresholds were correlated with foveal changes in the inner and outer retina. VF was strongly correlated to BCVA in both groups.

Conclusions

Clear peripheral and central VF deficits exist in PwA and PwIIN, and static VF results need to be interpreted with caution clinically. Since PwA exhibit considerably lower detection thresholds compared to PwIIN, VF defects are unlikely to be due to nystagmus in PwA. In addition to horizontal VF asymmetry, PwA exhibit both vertical and interocular asymmetries, which needs further exploration.

The myth of TMS-induced ipsilateral enhancement in visual detection paradigms: a Systematic review and Meta-Analysis of inhibitory parietal TMS studies in healthy participants

Spatial attention control involves specialized functions in both hemispheres of the brain, leading to hemispheric asymmetries. Neuropsychological models explain this lateralization mainly based on patient studies of hemineglect. Studies in healthy volunteers can mimic hemineglect using transcranial magnetic stimulation (TMS) by disrupting the left/right posterior parietal cortex (PPC) during visual detection tasks, enabling a comparison of hemispheric contributions to stimulus detection in the contra- versus ipsilateral hemifields. Kinsbourne's opponent processor model and Heilman's hemispatial model present contrasting hypotheses regarding the behavioral consequences of unilateral PPC disruption. A pivotal prediction in distinguishing between these models is the occurrence of ipsilateral enhancement. Our meta-analysis assessed inhibitory TMS effects on PPC during visual detection tasks across ten studies (1994-2022). PPC disruption caused contralateral impairment for bilateral stimuli, but no ipsilateral enhancement for unilateral or bilateral stimuli. These results are at odds with influential reports of ipsilateral enhancement after PPC disruption in healthy volunteers that have shaped the field of spatial attention research and should prompt a re-evaluation of current theoretical models of attention and their application to novel brain stimulation-based therapeutic interventions.