Some considerations of different modes of action of nootropic drugs.

Four possible types of nootropic drugs are classified theoretically according to their possible effects on cognitive functions. Among the factors usually varied in psychopharmacological designs, the significance of the time of application of the drug is stressed. Considering the relations between the time of application of nootropic drugs within standardized experimental plans and their effects on cognitive processes, ideal time of application-response curves for each of these types of nootropic compounds are proposed. These curves may represent experimental tools in investigating the mode of action of nootropic drugs. Finally, some experimental results are presented which are relevant to this approach. Overall, however, the rationale of these theoretical considerations remains largely unproven because of the lack of studies to date designed to evaluate the mechanisms of drug action by varying the time of application of a nootropic compound.