PET measured evoked cerebral blood flow responses in an awake monkey

We have developed a method to measure task-related regional cerebral blood flow (BF) responses in an awake, trained monkey using positron emission tomography (PET) and H₂¹⁵O. We trained an animal with operant conditioning using only positive reinforcement to climb unassisted into a modified primate chair that was then positioned in the PET scanner. A special headholder and acrylic skull cap permitted precise placement and accurate repositioning. We measured BF qualitatively with bolus injection of H₂¹⁵O and a 40-s scan. Each session included scans at rest interposed with scans during vibration of a forepaw. Regional responses were identified us-ing subtraction image analysis. After global normalization, a resting image was subtracted on a pixel-by-pixel basis from a comparable image collected during vibration. The region of peak response occurred in contralateral sensorimotor cortex with a mean magnitude of 11.6% (±3.2%) of the global mean value for 10 separate experiments, significantly greater than the mean qualitative BF change (0.4 ± 3.6%; p < 0.00001) in the same region for seven rest-rest pairs. This newly developed technique forms the basis for a wide variety of experiments.