Interhemispheric communication during demanding cognitive tasks shows pronounced interindividual variation. Differences in interhemispheric transfer time are constituted by the relative composition of slow and fast fibers. The speed of axonal conduction depends on the diameter of the axon and its myelination. To understand the possible genetic impact of myelin genes on performance in the Banich-Belger Task, a widely used paradigm to assess interhemispheric integration, 453 healthy adults were genotyped for 18 single nucleotide polymorphisms (SNPs) in six myelin-related candidate genes. We replicated the typical pattern of results in the Banich-Belger Task, supporting the idea that performance on cognitively demanding tasks is enhanced when cognitive processing is distributed across the two hemispheres. Moreover, allelic variations in the proteolipid protein 1 gene PLP1 and the contactin 1 gene CNTN1 correlated with the extent to which individual performance is enhanced by interhemispheric integration. Variation in myelin genes possibly affects the microstructure of the corpus callosum by altering oligodendrocyte structure. Therefore, these results provide a foundation for understanding how genetics plays a role in modulating the efficacy of transcallosal transmission.