Blood flow increases linearly in rat somatosensory cortex with increased whisker movement frequency

It has long been known that the level of neuronal activity is correlated to the level of localized blood flow. Despite the importance of functional hyperemia in the brain, the relationship between blood flow and electrical activity has not been clearly demonstrated parametrically in a single region of cerebral cortex. We investigated both the magnitude and temporal characteristics of the blood flow response in somatosensory cortex while varying the frequencies of whisker movement. The full whisker pad on one side of the rat's face was repeatedly moved for 13 s at frequencies of 1.5, 2, 3, 4, 6, 8, and 10.5 Hz, and the resulting changes in blood flow were quantified using Laser-Doppler flowmetry (LDF). The magnitude of the blood flow response increased linearly with increasing frequency while the temporal parameters of time to half maximal value and time to return halfway to baseline after stimulus termination did not vary. Baseline blood flow levels were elevated by breathing rats on a 5% CO2 mixture. No significant alteration in the LDF plateau response to whisker movement was observed compared to normal air, suggesting sustained vasodilation reserve capacity remained after CO2-induced vasodilation. These data demonstrate linear blood flow responses to presumptive linear increases in neuronal activity with sufficient vascular reserve capacity to overcome moderate CO2-induced dilation, and support the use of blood flow changes in neuroimaging studies. They provide a framework to study the neurobiological signal transduction mechanisms coupling neuronal electrical activity with regional alterations in blood flow.