An examination of time- and event-based prospective memory in individuals with Parkinson's disease using a novel paradigm

Abstract

Abstract Prospective memory (PM) refers to the ability to execute delayed future intentions, and is inherent to many everyday tasks, such as remembering to take medication. Consequently, PM difficulties can have a profound impact on an individual’s quality of life and independence. There is now considerable literature showing that PM is disrupted in many clinical conditions, including Parkinson’s disease (PD). PD is a neurodegenerative condition characterized by a loss of dopaminergic cells in the substantia nigra and basal ganglia, which can result in impairment to both motor and cognitive functions. Whilst a number of studies have demonstrated an association between PD and PM impairment, further research is necessary to better understand the nature and specificity of PM difficulties in this clinical group. In particular, it is currently unclear whether event-based PM (EBPM) and time-based PM (TBPM) are equivalently impaired. Whereas in the former type of task, an individual is required to perform a specified action at the occurrence of a particular external event, in the latter, they are required to perform the intended action after a predetermined period of time has passed, or at a specific time in the future. Thus, TBPM tasks are generally thought to place greater demands on internal self-initiated processes than EBPM tasks, because they require the individual to use their own internal resources to monitor time and perform the intended action when required. One issue that further complicates this literature is that by providing participants with a device for monitoring time, traditional TBPM paradigms may inadvertently provide event-based cues. In the present study, we therefore assessed PM function in a sample of 21 individuals with PD and 21 demographically matched controls using a novel task that examined TBPM in the presence and absence of event-based cues. The task also permitted assessment of EBPM. The results showed that individuals with PD did not differ from the control participants in terms of their performance on the novel PM measure. Across both groups however, TBPM performance was affected by the presence versus absence of the event-based cue. Specifically, PM accuracy was higher in the presence of the event-based cue. These results highlight the importance of examining TBPM in the absence of event-based cues (such as time-monitoring devices), as the presence of such cues appears to facilitate performance. The absence of any PM impairment among individuals with PD suggests that our measure may have lacked sensitivity to detect the group effects observed in other studies. This finding highlights, however, that individuals with PD can demonstrate intact functioning on PM tasks that are not overly challenging. These results are explored in the context of existing models and literature relating to PM and PD, and modifications to the measure are suggested to enhance its sensitivity to PM difficulties.