Imaging of synaptically‐evoked blood volume and blood oxygenation optical changes in rat somatosensory cortex

Abstract

The objective of these studies was to determine the extent to which optical imaging can dissociate changes due to either blood volume or blood oxygenation during synaptic activation of the cortex. Towards that aim, a closed cranial‐window rat preparation was used that allowed for optical imaging of somatosensory cortex during stimulation of a sciatic nerve. High‐magnification imaging using 550 nm light showed that optical changes were restricted to the dilating pial arterioles (thus representing blood volume changes), whereas the changes occurring under 660 nm light were restricted to the venous compartments (thus representing changes in blood oxygenation). A simple linear model revealed that blood volume optical changes acquired with 550 nm light were tightly correlated to the diameters of the pial arterioles (p < 0.001). Low‐magnification imaging showed that blood volume changes were closely localized to cortical regions undergoing increased neuronal activity. In contrast, blood oxygenation changes were maximal in the larger veins at sites distant to the areas of increased neuronal activity. In conclusion, these data demonstrate that optical imaging can dissociate changes due to either blood volume or blood oxygenation by selecting the appropriate optical wavelength. Further, optical images of blood volume provide a more accurate localization of neuronal activity than do those of blood oxygenation.