THE CONTINUOUS PERFORMANCE-TEST, IDENTICAL PAIRS VERSION (CPT-IP) .3.BRAIN FUNCTIONING DURING PERFORMANCE OF NUMBERS AND SHAPES SUBTASKS

The numbers and shapes subtasks of the CPT-IP are difficulty-matched m easures of independent aspects of attentional skill that have been use d to differentiate the impairments of schizophrenics and major depress ives. Previous studies suggest that they tap into lateralized aspects of attentional performance. To investigate this hypothesis, seven subj ects free of psychiatric illness were presented with these CPT-IP subt asks during a SPECT procedure. Subtasks - 4-digit number strings and n onsense shapes - were administered on successive weeks, in counterbala nced order, simultaneous with administration of 10 mCi Tc-99m HMPAO. S canning took place after 10 min of test performance. Quantitative data were extracted from each scan via a semi-automated region of interest (ROI) analysis which defined eight cortical and four subcortical ROI on each of five transverse slices. Data for each ROI were normalized a nd compared between task conditions. Results indicate that the two tas ks produce different patterns of functioning within two general areas of the brain. First, during Numbers task performance, left-sided activ ity was increased on multiple transverse slices in an anterior subcort ical region that incorporated the anterior cingulate, frontal white ma tter, and much of the basal ganglia. Left-sided activity was also incr eased in a posterior subcortical region including the left side of the thalamus. Lateralization of function, defined as relative activity on the left and right sides, changed within these regions across tasks, but primarily as a result of the contribution of increased or decrease d activity on the left side alone. Second, relative perfusion to occip ital regions, bilaterally, was more extensive during the Shapes task. These results suggest that subtle alterations in stimulus parameters c an affect activation patterns in regions that are critically associate d with task performance. They also suggest that the Numbers task may p rovide more robust activation of anterior attention systems, that may better discriminate the functioning of these systems in normal and psy chopathological groups. (C) 1997 Elsevier Science Ireland Ltd.