CHARACTERIZATION OF CEREBRAL BLOOD OXYGENATION AND FLOW CHANGES DURING PROLONGED BRAIN ACTIVATION

The behavior of cerebral blood flow and oxygenation during prolonged b rain activation was studied using magnetic resonance imaging (MRI) sen sitized to flow and oxygenation changes, as well as positron emission tomography sensitized to flow. Neuronal habituation effects and hemody namic changes were evaluated across tasks and cortical regions. Nine t ypes of activation stimuli or tasks, including motor activation, vibro tactile stimulation, and several types of visual stimulation, were use d. Both flow and oxygenation were evaluated in separate time course se ries as well as simultaneously using two different MRI methods. In mos t cases, the activation-induced increase in flow and oxygenation remai ned elevated for the entire stimulation duration. These results sugges t that both flow rate and oxygenation consumption rate remain constant during the entire time that primary cortical neurons are activated by a task or a stimulus. (C) 1997 Wiley-Liss, Inc.