Searching for activations that generalize over tasks

Nine previous positron emission tomography (PET) studies of human visual information processing were reanalyzed to determine the consistency of blood flow changes during a wide variety of active tasks relative to passive viewing of the same stimulus array. Consistent modulations were found in the early visual cortex, probably including area 17, and these modulations could reflect selective mechanisms. Blood flow decreases were found in some auditory and somatosensory areas, but did not appear to reflect a broad suppression of subcortical input. Outside the sensory cortex, consistent increases across experiments were found in the thalamus and cerebellum, but not in the cerebral cortex. Many cortical areas, however, did show consistent decreases.