Using Multimodal Optical Brain Imaging to Investigate Resting-State Functional Connectivity in Frontal Cortex

Multimodal optical brain imaging consists of near infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS). NIRS probes blood oxygenation level in cortex, while DCS measures cerebral blood flow. Blood oxygenation level and cerebral blood flow are two different classes of hemodynamic variables, each reflecting different aspect on the neural activity in the brain. In the present study, the multimodal optical imaging was used to investigate resting-state functional connectivity (RSFC) in the frontal cortex. 10 normal adults participated in the experiment in which 8 minutes of spontaneous activity of brain was separately recorded by NIRS and DCS. The measured area included left inferior frontal cortex (IFC) and left dorsolateral prefrontal cortex (DLPFC). Low frequency component of blood oxygenation signal (i.e., oxygenated hemoglobin, deoxygenated hemoglobin and total hemoglobin) was used to reveal oxygenation-based RSFC, while the cerebral blood flow signal in the same frequency range was used to identify cerebral blood flow-based RSFC. Both blood oxygenation-based and cerebral blood flow-based RSFC showed that the intra-regional connectivity within DLPFC was stronger than the inter-regional connectivity between DLPFC and IFC, implying that DLPFC and IFC, each belongs to a distinct functional area, though they are anatomically adjacent. Quantitative comparison between RSFC revealed by the two classes of hemodynamic variables showed the oxygenation-based RSFC was stronger than the cerebral blood flow-based RSFC, indicating the blood oxygenation in a functional area was more synchronized in time than the cerebral blood in resting-state.