Datensatz

Zusammenfassung

Despite extensive efforts to identify corpus callosum (CC) mediated interhemispheric (i-) functional connectivity (FC), several reports have demonstrated nearly intact i-FC in post-callosotomy brains. To relate the controversial studies to dynamic functional changes in the brain, it is plausible to investigate how correlations change in i-FC mediated by callosal projection neurons. Here, we developed a bilateral line-scanning functional magnetic resonance imaging (fMRI) method to detect laminar-specific blood-oxygen-level-dependent (BOLD) fMRI signals from symmetric forepaw somatosensory cortex (FP-S1) regions with spatial and temporal resolution (100 μm, 100 ms) in rodent brains. We investigated laminar-specific correlation features under both evoked and resting-state (rs-) conditions in anesthetized rats (55 trials of 4 rats). In evoked fMRI, we sorted all trials into two groups based on BOLD signals detected in left CC ipsilateral to stimulation. Interestingly, Group 1 showed negative correlations between superficial layers of right FP-S1 and all layers of left FP-S1 (Fig. C), possibly highlighting the transcallosal postsynaptic inhibitory effect in a delayed time scale negatively coupled to the BOLD signal detected in the draining veins of activated right FP-S1. In contrast, Group 2 only showed positive correlations between infragranular layers of right FP-S1 and all layers of left FP-S1, implying direct neuronal activation coupled BOLD signals across bilateral FP-S1. We also sorted all trials into two clusters based on rs-CC fMRI signals detected at a high frequency band (0.08-0.1 Hz) completely distinguishing from an ultra-slow fluctuation (0.01-0.02 Hz). Notably, Cluster 1 showed positive correlations between Layer 2-6 of right and left FP-S1, but weak or zero correlations of Cluster 2 were observed (Fig. E), possibly indicating brain state-dependent i-FC changes. This work provides a unique laminar-specific i-fMRI mapping scheme to investigate evoked and rs-FC, distinguishing transcallosal-mediated neuronal interactions across two hemispheres.