A fronto-parietal network for rapid visual information processing: a PET study of sustained attention and working memory.

The rapid visual information processing (RVIP) task, a test of sustained attention which also requires working memory for its successful execution, has been used in a number of human psychopharmacological studies. Single digits are presented in quick succession (100 or 200 digits/min) on a computer screen, and target sequences of numbers must be detected with a button press. Although previous neuroimaging studies have implicated the frontal and parietal cortices in performance of simple sustained attention tasks, the neuroanatomical substrates of RVIP performance are not yet known. This information would prove invaluable in the interpretation of drug effects on this task, possibly delineating a neuronal network for neurotransmitter action. Therefore, this study investigated the functional anatomy of the RVIP task using positron emission tomography (PET) derived measures of regional cerebral blood flow (rCBF) in eight healthy volunteers. Subjects were required to perform variants of the RVIP task which manipulated both the level of working memory load and the speed of stimulus presentation. Compared with a rest condition (eyes closed), the RVIP task increased rCBF bilaterally in the inferior frontal gyri, parietal cortex and fusiform gyrus, and also in the right frontal superior gyrus rostrally. In comparison with a simple sustained attention control condition, the aforementioned right frontal activations were no longer apparent. We suggest that these data are consistent with the existence of a right fronto-parietal network for sustained, and possibly selective, attention, and a left fronto-parietal network for the phonological loop component of working memory.