REGIONAL CEREBRAL BLOOD-FLOW DURING THE WISCONSIN CARD SORTING TEST IN NORMAL SUBJECTS STUDIED BY XE-133 DYNAMIC SPECT - COMPARISON OF ABSOLUTE VALUES, PERCENT DISTRIBUTION VALUES, AND COVARIANCE ANALYSIS

We studied regional cerebral blood flow (rCBF) by xenon-133 dynamic si ngle photon emission computed tomography (SPECT) in 17 normal voluntee rs who were performing the Wisconsin Card Sorting Test (WCST), a task that is particularly sensitive to disturbance of the prefrontal cortex , and a simple matching-to-sample task (BAR) as a sensorimotor control . Three methods for statistical analysis of regional ''subtraction'' d ata were used: absolute rCBF values, percent distribution values, and means adjusted for global CBF changes (covariance analysis). The absol ute values had high variance, due to the combination of interindividua l differences in global flow and intra-individual variation, and showe d no statistically significant regional changes. This variation was gr eatly reduced by percent values and covariance analysis, which had qui te similar outcomes. With both methods, significant increases of rCBF during the WCST as compared with the BAR were seen-in the right anteri or dorsolateral prefrontal and left occipital cortices, and reduction of rCBF in the left pararolandic region. Moreover, significant correla tions with performance were found in the medial regions of the frontal lobes, with opposite trends for the right and left hemisphere. The po sterior dorsolateral prefrontal region showed a negative correlation w ith sensory-motor frequency, an index related to the task's difficulty . These results are consistent with previous findings using other rCBF techniques and confirm the statistical advantage of normalization and covariance methods, which yield practically identical results, at lea st in this analysis based on regions of interest.