A person may recognize what they intended to do yet fail to carry it out at the right moment. A study of methamphetamine dependence found this distinction in prospective memory: the ability to remember and execute a future intention.
Iudicello and colleagues compared 39 methamphetamine-dependent individuals with 26 demographically similar comparison participants using the Memory for Intentions Screening Test. Some instructions required acting at a specified time; others required acting when an event occurred. The investigators also examined recognition, error types and other cognitive abilities.
This was a human observational comparison. Methamphetamine was not experimentally administered, and the study did not test an acute concentration–impairment relationship.
The methamphetamine group performed significantly worse on overall prospective memory, with difficulties on both time-based and event-based tasks. The predicted disproportionate disadvantage on time-based tasks was not demonstrated. Recognition performance was comparable between groups, although ceiling effects limited that comparison.
Task-substitution errors were more common in the methamphetamine group. These include performing an incorrect action when a cue is encountered. Loss-of-time errors were also more common, with most of those errors involving action earlier than instructed. The pattern suggests difficulty coordinating an intention, its cue and its timing, rather than a uniform inability to retain information.
Participants were asked to telephone the examiner the next day and report their sleep duration. The groups did not differ significantly in successful completion. Failure was common in both groups, potentially limiting sensitivity. Thus, the laboratory difference should not be presented as proof of a group difference on every everyday activity.
Self-reported drug histories, comorbid conditions and the observational design constrain causal interpretation. Suggested brain mechanisms were not directly established by imaging in this experiment.
A missed appointment or mistimed action can have several explanations. This paper offers a framework for assessing future-intention memory; it cannot determine why one person failed to act. Compare the separate issue of holding and ordering information in working memory.