Pathway-dependent brain stimulation responses indicate motion processing integrity after stroke

Homonymous hemianopia (HH), a common visual impairment resulting from occipital lobe lesions, affects a significant number of stroke survivors. Intensive perceptual training can foster recovery, possibly by enhancing surviving visual pathways. This study employed cortico-cortical paired associative stimulation (ccPAS) to induce associative plasticity within the residual and bidirectional primary visual cortex (V1)-middle temporal area (MT) pathways in stroke patients. We used ccPAS, which is thought to tap into Hebbian-like spike-timing dependent plasticity, over a motion processing pathway in stroke patients to transiently improve visual motion discrimination in their blind field. Sixteen stroke patients participated in this double-blind, crossover study comparing the effects of bidirectional ccPAS (V1-to-MT or MT-to-V1) on motion discrimination and EEG-Granger Causality. Additionally, we explored potential multimodal sources of inter-individual variability. Results showed that MT-to-V1 ccPAS enhanced motion direction discrimination, but the expected electrophysiological increase in top-down MT-to-V1 inputs was observed only in patients who showed improvement in motion discrimination. Good responders to MT-V1 ccPAS also demonstrated improved functional coupling between the cortical motion pathway and other relevant areas in the visual network, as well as more preserved ipsilesional V1-MT structural integrity. These findings indicate that targeted ccPAS can effectively engage functionally relevant residual visual pathways in stroke-affected brains, potentially offering new avenues for patient stratification and visual recovery strategies.