Somatosensory evoked BOLD signals with ultra-high temporal resolution

While functional magnetic resonance imaging (fMRI) is very well established as a tool in neuroimaging and neurocognitive research, it is limited by a comparatively low temporal resolution (typically around one to two seconds). Here, we apply and improve a method, previously introduced by Nagy et al. (2023), which combines an event-related stimulation paradigm with subsequent data reordering. For this, we applied electrical median-nerve stimulation with temporal accuracy of the fMRI imaging slices. The application of the stimuli was timed to occur simultaneously with each slice once and the slices were reordered according to their delay to the stimulus, thus reconstructing the BOLD-signal following the stimulation. By reordering the slices, we can increase the temporal resolution to the time it takes to acquire one slice, i.e. 60 ms. In combination with multiband acquisition, the amount of necessary trials, and therefore measurement time, can be further reduced. We show that this method allows to precisely sample the hemodynamic response in the somatosensory system with high signal-to-noise ratio. Further analyses revealed different hemodynamic responses in primary and secondary somatosensory cortex. We propose that this method provides the basis for future research which could greatly improve the sensitivity of statistical analysis of fMRI data through increased flexibility regarding individualized and voxel-specific BOLD-responses.