Optical measures of changes in cerebral vascular tone during voluntary breath holding and a Sternberg memory task

The human cerebral vasculature responds to changes in blood pressure and demands for oxygenation viacerebral autoregulation. Changes in cerebrovascular tone (vasoconstriction and vasodilation) also medi-ate the changes in blood flow measured by the BOLD fMRI signal. This cerebrovascular reactivity is knownto vary with age. In two experiments, we demonstrate that cerebral pulse parameters measured usingoptical imaging can quantify changes in cerebral vascular tone, both globally and locally. In experiment1, 51 older adults (age range = 55–87) performed a voluntary breath-holding task while cerebral pulseamplitude measures were taken. We found significant pulse amplitude variations across breath-holdingperiods, indicating vasodilation during, and vasoconstriction after breath holding. The breath-holdingindex (BHI), a measure of cerebrovascular reactivity (CVR) was derived and found to correlate with age.BHI was also correlated with performance in the Modified Mini-Mental Status Examination, even aftercontrolling for age and education. In experiment 2, the same participants performed a Sternberg task,and changes in regional pulse amplitude between high (set-size 6) and low (set-size 2) task loads werecompared. Only task-related areas in the fronto-parietal network (FPN) showed significant reduction inpulse amplitude, indicating vasodilation. Non-task-related areas such as the somatosensory and audi-tory cortices did not show such reductions. Taken together, these experiments suggest that optical pulseparameters can index changes in brain vascular tone both globally and locally, using both physiologicaland cognitive load manipulations.