Neural synchrony and white matter variations in the human brain--relation between evoked γ frequency and corpus callosum morphology.

Synchronous gamma oscillations frame a general principle of functional connectivity and communication in the cortex. Efficient communication and coordination across neural networks rely upon the temporal precision of neural signals, which depends on the structural properties of the fibre bundles serving neural signal transmission. Therefore a direct relation between the geometry of cortical connections and the formation of stimulus-driven synchronous neural activity can be assumed. The aim of the present study was to identify the neuroanatomical correspondents of individual gamma frequency variations. For that purpose we used voxel-based morphometry (VBM) to correlate the frequency of visually evoked gamma band responses (eGBR) with local inter-individual variations in white matter (WM) density across a group of 17 individuals. Analyses demonstrate an association of eGBR frequency and white matter density in the individual human brain. Individuals with a higher eGBR frequency demonstrate increased white matter in fibres of the corpus callosum, whereas participants with low-density callosal WM show lower eGBR frequencies. The observed positive correlation between callosal white matter measure and frequency of visually evoked GBR may indicate that additional or better-myelinated callosal pathways facilitate a more efficient inter-hemispheric information transfer, which is likely to benefit the integration and processing of information and consequently to facilitate more efficient synchronization of neural activity between the two hemispheres.