Dose effects of triazolam and scopolamine on metamemory

Abstract

The present study compared the acute dose effects of the benzodiazepine triazolam and the anticholinergic scopolamine on metamemory (knowledge and awareness of one's own memory) in a two-phase paradigm designed to assess effects on both monitoring and control components of metamemory in both semantic (general knowledge) and episodic memory (cued-recall) tasks. Placebo and 2 doses each of triazolam (0.125, 0.25 mg/70 kg, oral) and scopolamine (0.25, 0.50 mg/70 kg, subcutaneous) were administered to 80 healthy volunteers (16 per group) in a double-blind, double-dummy, independent groups design. Both triazolam and scopolamine impaired episodic memory (quantity and accuracy) but not semantic memory. Results suggested that both drugs impaired monitoring as reflected in absolute accuracy measures (impaired calibration in the direction of overconfidence) and control sensitivity (the relationship between confidence and behavior). Overall, the results did not provide evidence for differences between triazolam and scopolamine in memory or metamemory. In addition to the clinical relevance of the observed effects, this study adds to the accumulating body of cognitive psychopharmacological research illustrating the usefulness of drug-induced amnesia as a vehicle to explore memory and metamemory.

Figure 1

Triazolam (left panel) and scopolamine (right panel) time-course functions for performance on the circular lights task (mean number of correct responses during a 60-sec trial). X axis: time in min after capsule administration; arrow indicates time of subcutaneous injection; 0 indicates predrug. Brackets show 1 S.E.M.; for clarity of presentation, either the top or lower bracket is omitted. A filled symbol indicates an active drug that is significantly different (p ≤ 0.05) from the corresponding placebo value at the same timepoint.

Figure 2

Mean peak participant ratings of strength of drug effect as a function of drug condition. Brackets show 1 S.E.M. An asterisk (*) indicates an active drug value that is significantly different from placebo. A dagger (†) indicates a scopolamine value that is significantly different from the value of the corresponding triazolam dose.

Figure 3

Mean quantity and accuracy on the cued-recall task as a function of drug condition and phase (forced vs. free report). Brackets show 1 S.E.M. For both quantity and accuracy, all active doses were significantly different from placebo, with no significant differences between corresponding doses of triazolam and scopolamine; free report was significantly different from forced report.

Figure 4

Calibration curves of mean actual proportion correct on the cued-recall task for items receiving each confidence-rating category as a function of drug condition and item type (deceptive vs. control). Main diagonal represents perfect absolute accuracy.

Figure 5

Mean quantity and accuracy on the general knowledge task as a function of drug condition and phase (forced vs. free report). Brackets show 1 S.E.M. For both quantity and accuracy, free report was significantly different from forced report, and there were no differences among drug conditions.