THE PERFORMANCE OF SCHIZOPHRENIC AND DEPRESSED SUBJECTS ON TESTS OF FLUENCY - SUPPORT FOR A COMPROMISE IN DORSOLATERAL PREFRONTAL FUNCTIONING

Fifty-seven subjects (21 schizophrenia, 13 depressed, and 23 normal) m atched for NART Verbal IQ were compared on two fluency tests (the Verb al Fluency Test and the Design Fluency Test) and on the modified Wisco nsin Card Sorting Test. Both the clinical groups performed significant ly below the normals on measures of production on the fluency tests, b ut not on measures of error. This finding is consistent with the notio n proposed by Crowe (1992) that both clinical groups feature compromis e in the dorsolateral prefrontal cortex (DLPFC) bilaterally but not of the orbital prefrontal area. The two clinical groups performed consis tently across the tests employed, with the single exception that the s chizophrenic subjects tended to produce more perseverative and nonpers everative errors than did the depressed subjects. A comparison of the performance of the subjects across the time-slices of the fluency test s revealed that the performance on the verbal fluency tests decreased from each time-slice to the next, while on the design fluency test the re was an initial drop in performance from the first to the second tim e-slice but a consistent performance from that time on. The finding su pports the notion of DLPFC compromise in schizophrenic subjects, and e xpands these observations to performance on both verbal and nonverbal tests of fluency.