Frequency variation of a pattern-flash visual stimulus during PET differentially activates brain from striate through frontal cortex.

We evaluate regional cerebral blood flow (rCBF) in 19 healthy elderly subjects, mean age 64 +/- 11 (SD, years), during a passive visual stimulus in which pattern-flash frequency was parametrically manipulated. Using goggles with a grid of red lights imbedded into each lens, we performed five positron emission tomography (PET) H2(15)O water scans on each subject at alternating (left to right eye) flash frequencies of 0, 1, 4, 7, and 14 Hz. We found a biphasic rising and falling rCBF response in the striate cortex (7 Hz peak) and left anterior cingulate (4 Hz peak), 1 Hz activation in left middle temporal gyrus (V5), monotonically increasing rCBF in posterior areas (lateral and inferior visual association areas, Brodmann 18 and 19), and monotonically decreasing rCBF in anterior areas (frontal, cingulate, and superior temporal) predominantly in right hemisphere. We suggest the striate rCBF changes at all frequencies primarily reflect lateral geniculate input, the middle temporal activation at 1 Hz reflects perception of apparent motion, and the posterior extrastriate rCBF monotonic increase represents a neural response to increasing luminance intensity and form and color complexity that occur as pattern-flash frequency increases. The anterior monotonic rCBF decrease may represent active cross-modal functional suppression of brain areas irrelevant for processing the passive visual stimulus. Pattern-flash rCBF responses were highly reproducible (no series effect), more so in posterior than in anterior brain regions. The reproducibility and systematically changing rCBF responses to this passive stimulus suggest that it could be successfully used as a disease probe to evaluate neural function and drug effects in cognitively impaired patients.