Prospective memory (PM) tasks are common in everyday life and have been implicated in optimal daily functioning. However, less is known about the parameters of PM tasks that most influence functional decline, as well as the domains of everyday functioning most sensitive to PM impairment. The present study sought to examine these questions in individuals with traumatic brain injury (TBI).

Participants included 30 adults with chronic moderate-to-severe TBI who were at least one year removed from their injury (median [IQR] = 8.1 years [10.8]). Participants completed the Memory for Intentions Test (MIST), which is a 30-minute task that assesses time- and event-based PM with varying cue-intention delay length (2 versus 15 min) in the context of an ongoing task. Total scores were generated for each delay length and cue type. Additionally, participants completed a comprehensive neuropsychological battery, including assessments of processing speed, executive functions, attention, working memory, verbal fluency, and episodic learning and memory. Participants also completed questionnaires of self-reported cognitive and everyday functioning, including the Functional Behavior Profile (FBP), Prospective and Retrospective Memory Questionnaire (PRMQ) and a modified Lawton & Brody Instrumental Activities of Daily Living (IADL) Scale, which separately assessed 11 domains of everyday functioning.

Pearson’s r correlations revealed that total number of domains showing decline on the modified Lawton & Brody IADL scale was strongly correlated with MIST 15-min delay (MIST-15; r=-0.503, p=0.005), such that worse PM performance on long delay items was associated with more domains of IADL decline; this relationship was also reflected in the MIST Total Score (r=-0.389; p=0.033). No other MIST index was associated with IADL decline (ps>0.10). MIST-15 did not significantly correlate with any other measure of self-reported functioning (PRMQ, FBP; all ps>0.10), but was associated with specific declines in buying groceries (p=0.009), performing home repairs (p=0.021), shopping (p=0.033), and doing laundry (p=0.035). Relationships at a trend level included declines in housekeeping (p=0.05), managing finances (p=0.097), cooking (p=0.092), and taking medication (p=0.066). To determine specificity of the relationship between MIST-15 and everyday functioning, a linear regression was conducted using covariates that were significantly correlated with total number of domains of IADL decline (i.e., Selective Reminding Test total learning trials, CVLT-II Long Delay Free Recall, Symbol Digit Modalities Test total). This regression was statistically significant [F(4,24)=4.263; p=0.10; R2=0.415), and MIST-15 remained an independent predictor (p=0.047; R2 change=0.107).

Results suggest that the ability to remember to carry out intended actions after longer delay periods may be uniquely related to severity of declines in everyday functioning. Longer PM delays place higher demands on both memory and executive processes, as the encoded intention must survive a longer decay wherein monitoring for the appropriate cue is extended, and likely better mimic PM tasks in daily life (e.g., remembering to pick up milk after the workday). In light of these findings, clinicians may seek to include brief trials of long delay PM tasks as part of a comprehensive battery to screen for functional decline.