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.