Temporal clustering analysis of cerebral blood flow activation maps measured by laser speckle contrast imaging

Temporal and spatial orchestration of neurovascular coupling in brain neuronal activity is crucial for comprehending the mechanism of functional cerebral metabolism and pathophysiology. Laser speckle contrast imaging (LSCI) through a thinned skull over the somatosensory cortex is utilized to map the spatiotemporal characteristics of local cerebral blood flow (CBF) in anesthetized rats during sciatic nerve stimulation. The time course of signals from all spatial loci among the massive dataset is hard to analyze, especially for the thousands of images, each of which composes millions of pixels. We introduce a temporal clustering analysis (TCA) method, which is proven as an efficient method to analyze functional magnetic resonance imaging (fMRI) data in the temporal domain. The timing and location of CBF activation shows that contralateral hindlimb sensory cortical microflow is activated to increase promptly in less than 1 s after the onset of 2-s electrical stimulation and is evolved in different discrete regions. This pattern is similar but slightly elaborated from the results obtained from laser Doppler flowmetry (LDF) and fMRI. We present this combination to investigate interacting brain regions, which might lead to a better understanding of the nature of brain parcellation and effective connectivity.