Asymmetric transcallosal conduction delay leads to finer bimanual coordination

• Published in: Brain stimulation Vol. 14; no. 2; pp. 379 - 388
• Main Authors: Bortoletto, Marta, Bonzano, Laura, Zazio, Agnese, Ferrari, Clarissa, Pedullà, Ludovico, Gasparotti, Roberto, Miniussi, Carlo, Bove, Marco
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.03.2021; Elsevier
• Subjects: DTI; Effective connectivity; Information transfer; Interhemispheric inhibition; TMS-EEG; DTI; Interhemispheric inhibition; TMS-EEG; Information transfer; Effective connectivity
• ISSN: 1935-861X; 1876-4754; 1876-4754
• DOI: 10.1016/j.brs.2021.02.002

It has been theorized that hemispheric dominance and more segregated information processing have evolved to overcome long conduction delays through the corpus callosum (transcallosal conduction delay - TCD) but that this may still impact behavioral performance, mostly in tasks requiring high timing accuracy. Nevertheless, a thorough understanding of the temporal features of interhemispheric communication is lacking. Here, we aimed to assess the relationship between TCD and behavioral performance with a noninvasive directional cortical measure of TCD obtained from transcranial magnetic stimulation (TMS)-evoked potentials (TEPs) in the motor system. Twenty-one healthy right-handed subjects were tested. TEPs were recorded during an ipsilateral silent period (iSP) paradigm and integrated with diffusion tensor imaging (DTI) and an in-phase bimanual thumb-opposition task. Linear mixed models were applied to test relationships between measures. We found TEP indexes of transcallosal communication at ∼15 ms both after primary motor cortex stimulation (M1-P15) and after dorsal premotor cortex stimulation (dPMC-P15). Both M1-and dPMC-P15 were predicted by mean diffusivity in the callosal body. Moreover, M1-P15 was positively related to iSP. Importantly, M1-P15 latency was linked to bimanual coordination with direction-dependent effects, so that asymmetric TCD was the best predictor of bimanual coordination. Our findings support the idea that transcallosal timing in signal transmission is essential for interhemispheric communication and can impact the final behavioral outcome. However, they challenge the view that a short conduction delay is always beneficial. Rather, they suggest that the effect of the conduction delay may depend on the direction of information flow. •Early components of TMS-evoked potentials (TEPs) reflect transcallosal communication.•TEPs from M1 are linked to ipsilateral silent period and corpus callosum diffusivity.•TEPs from dorsal premotor cortex are linked to corpus callosum diffusivity.•Delay in M1-M1 transcallosal communication is linked to inphase bimanual coordination.•Short delay in M1-M1 transfer is beneficial or detrimental based on flow direction.