Impact of non-invasive brain stimulation on transcallosal modulation in mild traumatic brain injury: a multimodal pilot investigation

Background: We combined performance on working memory (WM) tasks with diffusion (dMRI) and functional (fMRI) magnetic resonance imaging in young adults who had suffered a concussion to better understand the inter-hemispheric effects of unilateral repetitive transcranial magnetic stimulation (rTMS). Methods: The article is presenting pilot data on 8 symptomatic patients with persistent post-concussion symptoms for over 6 months. They received 20 sessions of rTMS over the left dorsolateral prefrontal cortex. Fractional anisotropy and mean diffusivity of the corpus callosum (CC) and fMRI measurement of blood-oxygen-level dependent signal changes during WM tasks were carried out before and after rTMS stimulation. Results: After participants had completed the rTMS sessions, we observed three main results: (1) bilateralization of activation within the WM network; (2) shift from transcallosal inhibition to transcallosal activation of the right-sided WM network via the anterior callosal fibres; and (3) shift from transcallosal activation to transcallosal inhibition of the right-sided WM network via the posterior parts of the CC. More nuanced patterns of transcallosal mediation in the region of the right-sided WM network were observed via the medial part of the CC. Conclusion: Our preliminary results encourage trends of further research supporting the use of rTMS to restore inter-hemispheric balance within the bilateral WM network in young adults with a history of concussion.