The time course for visual extinction after a 'virtual' lesion of right posterior parietal cortex

A meta-analysis of functional neuroimaging tasks associated with pseudoneglect

Major evidence for a right-hemisphere dominance of the brain in spatial and/or attentional tasks comes from lesion studies in patients with spatial neglect. However, the neuroanatomy of the different forms of neglect remains a matter of debate, and it remains unclear how dysfunctions in neglect relate to intact processes. In the healthy brain, perceptual pseudoneglect has been considered to be a phenomenon complementary to specific subtypes of neglect as observed in paradigms such as the line bisection task. Therefore, the current study investigated the intact functional anatomy of perceptual pseudoneglect using a meta-analysis to compensate for some of the limitations of individual imaging studies. We collated the data from 24 articles that tested 952 participants with a range of paradigms (landmark task, line bisection, grating-scales task, and number line task) obtaining 337 foci. Using Activation Likelihood Estimation (ALE) we identified a right-hemisphere biased network of cortical areas, including superior and intraparietal regions, the intraoccipital sulcus together with other occipital regions, as well as inferior frontal areas that were associated with perceptual pseudoneglect in partial agreement with lesion studies in patients with neglect. Our study is the first meta-analysis on the mechanisms underlying perceptual judgments which have been shown to give rise to perceptual pseudoneglect.

Enhanced mind-matter interactions following rTMS induced frontal lobe inhibition

A major barrier to acceptance of psi is that effects are small and hard to replicate. To address this issue, we developed a novel neurobiological model to study this controversial phenomenon based upon the concept that the brain may act as a psi-inhibitory filter. Our previous research in individuals with frontal lobe damage suggests that this filter includes the left medial middle frontal region. We report our findings in healthy participants with rTMS induced reversible brain lesions. In support of our a priori hypothesis, we found a significant psi effect following rTMS inhibition of the left medial middle frontal lobe. This significant effect was found using a post hoc weighting procedure aligned with our overarching hypothesis. This suggests that the brain may inhibit psi and that individuals with neurological or reversible rTMS induced frontal lesions may comprise an enriched sample for detection and replication of this controversial phenomenon. Our findings are potentially transformative for the way we view interactions between the brain and seemingly random events.

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.

The behavioral and neural effects of parietal theta burst stimulation on the grasp network are stronger during a grasping task than at rest

Repetitive transcranial magnetic stimulation (TMS) is widely used in neuroscience and clinical settings to modulate human cortical activity. The effects of TMS on neural activity depend on the excitability of specific neural populations at the time of stimulation. Accordingly, the brain state at the time of stimulation may influence the persistent effects of repetitive TMS on distal brain activity and associated behaviors. We applied intermittent theta burst stimulation (iTBS) to a region in the posterior parietal cortex (PPC) associated with grasp control to evaluate the interaction between stimulation and brain state. Across two experiments, we demonstrate the immediate responses of motor cortex activity and motor performance to state-dependent parietal stimulation. We randomly assigned 72 healthy adult participants to one of three TMS intervention groups, followed by electrophysiological measures with TMS and behavioral measures. Participants in the first group received iTBS to PPC while performing a grasping task concurrently. Participants in the second group received iTBS to PPC while in a task-free, resting state. A third group of participants received iTBS to a parietal region outside the cortical grasping network while performing a grasping task concurrently. We compared changes in motor cortical excitability and motor performance in the three stimulation groups within an hour of each intervention. We found that parietal stimulation during a behavioral manipulation that activates the cortical grasping network increased downstream motor cortical excitability and improved motor performance relative to stimulation during rest. We conclude that constraining the brain state with a behavioral task during brain stimulation has the potential to optimize plasticity induction in cortical circuit mechanisms that mediate movement processes.

Evidence for a common mechanism of spatial attention and visual awareness: Towards construct validity of pseudoneglect

Present knowledge of attention and awareness centres on deficits in patients with right brain damage who show severe forms of inattention to the left, called spatial neglect. Yet the functions that are lost in neglect are poorly understood. In healthy people, they might produce “pseudoneglect”—subtle biases to the left found in various tests that could complement the leftward deficits in neglect. But pseudoneglect measures are poorly correlated. Thus, it is unclear whether they reflect anything but distinct surface features of the tests. To probe for a common mechanism, here we asked whether visual noise, known to increase leftward biases in the grating-scales task, has comparable effects on other measures of pseudoneglect. We measured biases using three perceptual tasks that require judgments about size (landmark task), luminance (greyscales task) and spatial frequency (grating-scales task), as well as two visual search tasks that permitted serial and parallel search or parallel search alone. In each task, we randomly selected pixels of the stimuli and set them to random luminance values, much like a poor TV signal. We found that participants biased their perceptual judgments more to the left with increasing levels of noise, regardless of task. Also, noise amplified the difference between long and short lines in the landmark task. In contrast, biases during visual searches were not influenced by noise. Our data provide crucial evidence that different measures of perceptual pseudoneglect, but not exploratory pseudoneglect, share a common mechanism. It can be speculated that this common mechanism feeds into specific, right-dominant processes of global awareness involved in the integration of visual information across the two hemispheres.

The Influence of Alertness on the Spatial Deployment of Visual Attention is Mediated by the Excitability of the Posterior Parietal Cortices

With a reduced level of alertness, healthy individuals typically show a rightward shift when deploying visual attention in space. The impact of alertness on the neural networks governing visuospatial attention is, however, poorly understood. By using a transcranial magnetic stimulation twin-coil approach, the present study aimed at investigating the effects of an alertness manipulation on the excitability of the left and the right posterior parietal cortices (PPCs), crucial nodes of the visuospatial attentional network. Participants’ visuospatial attentional deployment was assessed with a free visual exploration task and concurrent eye tracking. Their alertness level was manipulated through the time of the day, that is, by testing chronotypically defined evening types both during their circadian on- and off-peak times. The results revealed an increased excitability of the left compared with the right PPC during low alertness. On the horizontal dimension, these results were accompanied by a significant rightward shift in the center and a bilateral narrowing in the periphery of the visual exploration field, as well as a central upward shift on the vertical dimension. The findings show that the manipulation of non-spatial attentional aspects (i.e., alertness) can affect visuospatial attentional deployment and modulate the excitability of areas subtending spatial attentional control.