Correlation of functional and resting state connectivity of cerebral oxy-, deoxy-, and total hemoglobin concentration changes measured by near-infrared spectrophotometry

The aim is to study cerebral vascular functional connectivity during motor tasks and resting state using multichannel frequency-domain near-infrared spectrophotometry. Maps of 5.7 × 10.8 cm size displaying changes in cerebral oxyhemoglobin (O(2)Hb), deoxyhemoglobin (HHb), and total hemoglobin (tHb) concentrations were measured in the motor cortex in 12 subjects (mean age of 28.8±12.7 yrs) during resting state and during two palm squeezing tasks with different timing. For each condition, phase plane plots, cross correlation functions, and connectivity indices were generated for O(2)Hb, HHb, and tHb. The amplitude of the concentration changes in O(2)Hb and HHb depends on the age of the subject. We found large regions of connectivity, which were similar for resting state and task conditions. This means the spatial relationships during resting state, when changes in O(2)Hb, HHb, and tHb corresponded to spontaneous oscillations, were correlated to the spatial patterns during the activation tasks, when changes in O(2)Hb, HHb, and tHb concentration were related to the alternation of stimulation and rest. Thus, the vascular functional connectivity was also present during resting state. The findings suggest that the vascular response to functional activation may be a nonlinear synchronization phenomenon and that resting state processes are more important than previously expected.