Abstracts

Rationale: Visuospatial functions are generally thought to be lateralized to the right hemisphere, whereas the left-hemispheric motor area is suggested to play a central role in responding with the right finger during a task. We aimed to visualize neural communications during a visuospatial-motor task to determine if visuospatial functions are predominantly processed in the right hemisphere and to assess the timing and white matter pathways of neural information flows from the right to the left hemisphere.

Methods: Eight right-handed patients (ages 8-20 years) with drug-resistant epilepsy underwent a visuospatial task during intracranial EEG recording. Patients were instructed to swiftly tap “Yes” if an incoming symbol matched the previous one, and “No” if it did not. We determined when and where the high-gamma amplitude (70-110 Hz) was augmented or attenuated. We defined functional connectivity modulations as simultaneous, significant, and sustained high-gamma modulations between cortical regions directly interconnected by white matter streamlines in tractography. Transfer entropy-based effective connectivity analysis determined neural information flows, indicating the directionality of neural communications through white matter pathways. Mixed model analysis assessed if local high-gamma amplitudes in given trials were associated with response accuracy or response times.

Results: On average, the response time was 985 ms, the total number of trials was 184, and the accurate response rate was 87.99%. Within 150 ms after stimulus onset (Fig. 1), high-gamma augmentation involved the bilateral occipital regions, accompanied by inter- and intra-hemispheric functional connectivity enhancement as well as bidirectional neural information flows between the low- and high-order visual cortices. Subsequently, functional connectivity enhancement became right-hemispheric dominant, and bidirectional neural information flows extensively occurred across the association cortices and precentral gyrus within the right hemisphere (Fig. 1-2). Early high-gamma augmentation in the right middle frontal region was associated with an increased chance of successful responses while prolonging the response time in given trials. Around 100 ms before response onset, inter-hemispheric functional connectivity enhancement and bidirectional neural information flows were noted between the right and left precentral gyri through the corpus callosum (Fig. 2).

Conclusions: The study provides novel evidence of intra-hemispheric, bidirectional neural communications predominantly occurring within the right hemisphere during the assessment of visuospatial stimuli. Engagement of the right middle frontal gyrus may reflect a cautious visuospatial assessment, increasing the chance of accurate responses. Information necessary for task responses with the right finger may be transferred between the right and left motor cortices through the corpus callosum 100 ms prior to the response.

Funding: Funding: KAKENHI JP23KJ2197 (to R.U.), NIH R01 NS064033 (to E.A.).