Blood flow augmentation (mean, 29%) ex- ceededthesmallincreasesinoxygenutilization(mean,5%) to such an extent that a highly significant decrease in the extracted fraction of available oxygen was observed (mean,
-19%). Stimulus duration (onset 0, 1, or 5 min prior to isotopeadministration)hadnosignificanteffectonresponse magnitudeforanyvariable.Dynamicregulationofregional CBF byneuronalactivityperse,eitherbyalterationsinthe chemicalmicroenvironmentdirectlyconsequentonneuronal activity or by a neuronal-microvascular network, is an inference from these data that corresponds well with a considerablebodyofrelatedresearch.