Prospective memory is the ability to remember doing something at a specific point in time in the future (i.e., time-based prospective memory) or when a specific event occurs (i.e., event-based prospective memory) [
1]. Whether brain regions involved in time-based and event-based prospective memory overlap or differ is hardly understood, particularly when it comes to ageing. Most neuroimaging studies in older adults tested event-based prospective memory using fMRI but not time-based prospective memory [
2‐
6]. One study that did assess both types of prospective memory reported that network activity was similar as both tasks activated frontal and parietal brain regions, the insula, and the thalamus [
4]. The time-based task in that study, however, was very similar to an event-based task since a clock was always in plain view so the participants did not need to remember the time-based intention by themselves. Instead, they were reminded by an external cue (i.e., the clock) which was constantly visible. Therefore, it could be that brain activity was similar in both tasks just because the task setup was very similar. It would be important to test whether older adults activate other brain regions when they need to remember time-based intentions by themselves [
1,
7,
8]. This would help determine whether ageing affects time-based and event-based prospective memory differently in the brain.
Remembering prospective intentions is important for maintaining health and independence in older adults (e.g., remembering to meet a doctor or to take medication at a specific time) [
9,
10]. Finding ways to improve or facilitate prospective memory may therefore promote healthy ageing. Motivation influences how well people encode and retrieve memories [
11]. Enhancing motivation, for example by providing incentives, may thus be a way to improve prospective memory. Whether and how incentives influence prospective memory in older adults is not fully understood. There is evidence to suggest that event-based prospective memory can be improved when incentives include a prosocial component (i.e., a donation) [
12]. This might be particularly motivating for older adults since they are usually more empathic and thus, more prosocial [
13]. In addition, there is evidence to suggest that goals and interests change across adulthood [
14], with avoiding losses becoming more important for older adults than achieving gains [
15]. This is supported by an event-based prospective memory study, in which older adults performed better when they tried to avoid financial losses rather than to achieve financial gains [
12]. It would be important to complement insights gained from event-based prospective memory with what happens to time-based prospective memory when losing an incentive was to be avoided. Prospective memory failures in daily life are often followed by financial losses (e.g., forgetting to pay a bill on time or forgetting to return a rented item on time may lead to financial extra charges). A better understanding of the consequences that follow prospective memory failure would therefore help to discern the mechanisms involved in motivational processes of prospective memory. In addition, we know nothing about incentive-related processing in the brain when prospective memory tasks are used. In other cognitive domains, such as decision making, the monetary incentive delay task has often been used to investigate incentive-related processing in the brain [
16‐
18]. It has been found that younger adults activate a fronto-striatal-thalamic network during anticipation of an incentive, regardless of whether they try to achieve gains or to avoid losses [
19]. Older adults, in contrast, activate the lateral prefrontal cortex in addition to midbrain areas and the insula [
18]. It would be important to test whether these differences in older adults’ activity patterns are specific to the monetary incentive delay task or whether they can be generalised to prospective memory tasks.
The aims of the current study are, therefore, threefold. First, we investigate the functional neuroanatomy of prospective memory with a particular emphasis on the question whether brain regions involved in time-based and event-based prospective memory overlap or differ. We expect them to differ when using a time-based prospective memory paradigm in which participants actively align their intentions with time. Second, we test whether event-based or time-based prospective memory can be modulated when participants have to avoid losing an incentive. We hypothesize that this will improve prospective memory. Third, we investigate the neuroanatomical correlates of incentive-related processing during prospective memory tasks. We expect increased prefrontal and midbrain activity when participants avoid losing an incentive and that the strength of activity increase will be associated with prospective memory task performance.