Prospective memory (PM) is the cognitive ability to remember to execute an intended action at the appropriate time or in response to the appropriate cue in the future. While most memory research focuses on retrospective memory (remembering past events or facts), prospective memory underlies many of our daily activities: remembering to take medication, to attend a meeting, to pass a message to a friend, or to buy milk on the way home. Failures of prospective memory can have consequences ranging from minor inconvenience to life-threatening.
Types of Prospective Memory
Prospective memory tasks are classified into two major types. Event-based PM involves performing an action when a specific external cue occurs (e.g., give a message to a friend when you see them). Time-based PM involves performing an action at a specific time or after a specific time interval (e.g., take medication at 2 PM). Time-based PM is generally harder than event-based PM because it requires self-initiated monitoring of time passage rather than relying on environmental cues.
Theoretical Models
Two competing models dominate PM research. The preparatory attentional and memory processes (PAM) theory proposes that PM requires dedicating attentional resources to monitoring for the PM cue, which consumes resources and slows ongoing task performance. The multiprocess framework (McDaniel and Einstein) proposes that PM retrieval can sometimes occur spontaneously (automatically, without monitoring costs) when the PM cue is sufficiently distinctive or strongly associated with the intention, while more demanding PM tasks require strategic monitoring.
Prospective memory shows a complex relationship with aging. In laboratory tasks, older adults typically show PM impairments, particularly for time-based tasks. However, in naturalistic studies, older adults often outperform younger adults on PM tasks — the age-prospective memory paradox. This paradox likely reflects older adults' greater use of external aids (calendars, alarms, notes), more structured routines, and stronger motivation to fulfill their intentions. It highlights the gap between laboratory and real-world cognitive performance.
Neural Correlates
The rostral prefrontal cortex (Brodmann area 10) is particularly important for prospective memory. This region is activated during the maintenance of an intention and may support the "gateway hypothesis" — managing the balance between internally and externally directed attention needed to monitor for a PM cue while performing an ongoing task. Disruption of this region through lesions or TMS impairs PM performance.
Everyday Importance
Prospective memory failures are among the most common cognitive complaints in daily life and are particularly concerning for patient populations. Failures to take medication, attend appointments, or perform safety-critical procedures can have serious consequences. Strategies to support PM include external cues (alarms, notes, smartphone reminders), implementation intentions (forming specific "if-then" plans: "When I see the pharmacy, I will buy my medication"), and environmental modification (placing the item you need to remember near your keys).