EFFECTS OF PSYCHOTROPIC-DRUGS ON DIGIT SUBSTITUTION - COMPARISON OF THE COMPUTERIZED SYMBOL-DIGIT SUBSTITUTION AND TRADITIONAL DIGIT-SYMBOLSUBSTITUTION TESTS

The digit-symbol substitution test (DSST), performed with paper and pe ncil or computerized, is widely used to reveal decrements in human att ention and cognition. We programmed sets of adjustable tasks (digit-sy mbol, digit-digit, symbol-digit, symbol-symbol) into a microcomputer a nd compared the symbol-digit substitution (SDST) and the digit copying test (DDCT) with the traditional DSST in two placebo-controlled doubl e-blind studies of psychotropic drugs with pre-trained young healthy s ubjects. Performances were measured before drug intake and several tim es after it; matched, different codes were used at consecutive tests. DSST and SDST substitutions remained at the baseline level after place bo, while the simple DDCT performance improved during the placebo sess ion. The prolonged (3 min) test was not exhaustive because interim cou nts at 90 s predicted the final performance well. In Trial I, 15 mg di azepam orally reduced DSST and SDST functions in a similar way, but it also impaired simple copying in the DDCT, though to a lesser extent. Ebastine, an H-1-antihistamine, proved inert alone and failed to incre ase the effects of diazepam on these variables. In Trial II, 7.5 mg zo piclone, 0.4 mg suriclone and 50 mg chlorpromazine, alone and in combi nations, impaired the DSST performance in the manner expected. The dru g effects were similar in the SDST, and somewhat less in the DDCT, whi le the substitution errors were subject related and not altered signif icantly by any treatment. The simple correlation matrices (Pearson, Sp earman), confirmed by analysis of covariance, showed that the results of DSST correlated fairly well with those of SDST after zopiclone, chl orpromazine and their combination, but not after suriclone or its comb ination with chlorpromazine. The DDCT results correlated with those of the substitution tests when analysing pooled baseline values, but not when analysing the performances after drug intake. Subjective visual analogue variables correlated poorly or not at all with objective perf ormances. Our results suggest that manual dexterity in these computeri zed tests might contribute significantly to the total impairment of pe rformance in response to different drugs. The DSST and SDST matched ea ch other fairly well in their sensitivity to drug effects, yet this si milarity may depend on the drug used.