Frequency tuning in the rat whisker barrel cortex revealed through RBC flux maps

The rodent whisker barrel cortex is ideal for studies related to sensory processing and neural plasticity in the brain. However, its small spatial dimensions challenge optical and other imaging technologies mapping cortical hemodynamics as functional resolution (the ability to spatially and selectively discriminate signals from microvascular compartments) limit measurement accuracy. To precisely map hemodynamic activity within the rat posteriomedial barrel subfield (PMBSF), we used functional Laser Doppler Imaging (fLDI) at high spatial resolution with optimized detection and analysis. In this configuration, we demonstrate prominent whisker deflection-induced fLDI hemodynamic responses from microvascular regions indicating the technique's specificity to smaller vessel compartments. Clusters of fLDI activation were confined within the PMBSF region during deflection of either single or all whiskers. Stereotaxic co-ordinate mapping was performed over all animals leading to an average maximum activity cluster at +5.3, -3.5 from the Bregma. The maximum activity cluster during all whisker stimulation combined with the principal activation cluster during deflection of the C1 whisker were used as a reference to characterize the fLDI maps within the PMBSF. fLDI activation area increased with the frequency of whisker deflection. In a quantitative analysis, we reveal the increase in the spatial extent of fLDI activation with stimulation frequency as spatially non-uniform with a bias towards the caudal region for low and rostral region for higher stimulation frequencies.