Imaging of cerebral hemodynamic and light scattering responses to somatosensory electrical stimulation using a digital RGB color camera (Conference Presentation)

We investigated a rapid imaging method to monitor the spatial distribution of total hemoglobin concentration (CHbT), the tissue oxygen saturation (StO2), and the scattering power b in the expression of musp=a(lambda)^-b as the scattering parameters in cerebral cortex using a digital red-green-blue camera. In the method, Monte Carlo simulation (MCS) for light transport in brain tissue is used to specify a relation among the RGB-values and the concentration of oxygenated hemoglobin (CHbO), that of deoxygenated hemoglobin (CHbR), and the scattering power b. In the present study, we performed sequential recordings of RGB images of in vivo exposed brain of rats before, during, and after hindlimb electrical stimulation. The remarkable increases in CHbO, CHbT, and StO2 were induced by hindlimb electrical stimulation whereas significant decreases in the scattering power b and CHbR were observed after the onset of stimulation. It has been reported that cerebral blood flow (CBF) and blood oxygen level-dependent (BOLD) signal responses show better correlation with post-synaptic local field potentials than with spiking activity. Positive CBF and BOLD responses during stimulation are associated with an increase in neuronal activity and decrease in deoxyhemoglobin content. Therefore, the decrease in the scattering power b of somatosensory cortex after hindlimb electrical stimulation is indicative of slow post-synaptic potential change. The results in this study indicate potential of RGB camera-based imaging to evaluate both hemodynamics and synaptic activity in brain tissue.