Apathy is a common behavioral symptom in elderly people (with or without dementia) [1
] and constitutes the main cause of close relatives’ suffering [2
]. Apathy is linked to poor quality of life [3
] and lower instrumental activities in daily life [2
], and appears significantly associated with cognitive decline [1
]. Defined as diminished goal-directed behaviors (GDB) [4
], apathy is commonly divided into three dimensions: loss or decrease of initiative, loss or decrease of interest, and affective blunting [4
]. Lack of initiative corresponds to the incapacity to act or to begin routine and non-routine activities spontaneously (self-initiation) or in response to external stimuli, while lack of interest corresponds to the incapacity to feel or show an attraction for routine activities or new events [4
]. In fact, in most clinical situations these two apathy dimensions are probably closely related: loss of interest could contribute to loss of action initiation (e.g. if I am not interested in this book, I will not read it) and initiation difficulties could lead to loss of interest (e.g. if I have difficulties participating in some activities, I will give them up). As for the third dimension, emotional blunting, it corresponds to a decrease in positive and negative emotional reactions [4
]. However, its assessment is rather problematic, especially considering how difficult it is for close relatives to understand loss of ‘experienced’ emotion.
Few studies have tried to examine the relationships between the different facets of apathy in aging and specific psychological mechanisms, and the nature of apathy problems in elderly people is still misunderstood. Some studies in healthy elderly people or elderly patients with dementia [e.g. [6
]] showed that apathy was associated with poor performance on several executive tests, such as the Verbal Fluency test, the Trail Making Test-Part B and the Stroop Color Interference test. Moreover, Robert et al. [8
] found a significant link between apathy and performance on the dual-task procedure developed by Baddeley et al. [9
]. Finally, another study by Robert et al. [10
] highlighted an association between apathy in patients with mild cognitive impairment and episodic memory deficits in tasks that trigger effortful conscious processes (free recall on a selective reminding test).
However, most studies on apathy [e.g. [10
]] considered only the global apathy score and did not distinguish between the three apathy dimensions mentioned by Robert et al. [4
]. In addition, in these studies, the relationships between cognitive mechanisms and apathy were only exploratory and not based on specific hypotheses. Consequently, these studies do not really provide adequate information about the nature of apathy problems.
In the current study, we decided to explore the relationships between apathy dimensions (chiefly lack of initiative and interest) and prospective memory (PM), a process which plays a central role in action execution and is closely related to self-initiated behaviors [11
]. More specifically, given that apathy corresponds to an incapacity to translate an intention into action [11
], PM problems might constitute a key component of GDB reduction, especially lack of initiative, since PM allows one to remember acting [12
PM refers to remembering to perform an intended action at some point in the future [13
]; for example, ‘I have to go to work, prepare my talk for this afternoon and remember to pick the children up from school.’ It includes several cognitive processes divided into four steps: (1) the formation of an intention; (2) the maintenance of this intention in memory during the execution of another task; (3) the identification of the suitable situation or time to realize the intention; (4) the execution of the intention according to one's plans [14
]. In addition, it should be noted that individual differences in working memory significantly influence PM performance [e.g. [15
]]. Deficits affecting any one of the four steps proposed by Kliegel et al. [14
] may account for apathy (mainly lack of initiative) by hindering the capacity to translate an intention into action. More specifically, PM seems closely related to self-initiated behaviors [13
], insofar as PM allows one to connect together the complex sequences of GDB and to execute one's plans in the correct order and at the appropriate time [16
]. In this context, PM deficits, on the one hand, may play a role in the development of apathy (mainly lack of initiative) by affecting adaptation to the constraints of the time/environment, the ability to consider internal signals that act prospectively as triggers for the initiation of behavior, or the ability to switch between the ongoing task and the PM task [e.g. [11
]]. On the other hand, some aspects of apathy (e.g. lack of interest) may account for PM deficits by hindering the execution of delayed intentions.
However, although both PM impairments and apathy are common in aging, no study to our knowledge has examined the relationships between PM and specific dimensions of apathy. Thus, the aim of this study was to explore the relationships between the facets of apathy and PM in aging. We hypothesized that there would be a strong relationship between lack of initiative, lack of interest and PM, and suggested that this relationship could go in either direction: PM deficits may play a role in the development of some aspects of apathy (such as lack of initiative) over the medium or long term, and the presence of some aspects of apathy (such as lack of interest) may account for PM deficits. In addition, we investigated whether this strong relationship between PM and apathy would remain significant even after controlling for interindividual differences in variables supposed to be related both to PM and apathy (i.e. global cognitive functioning, working memory, processing speed and negative mood). Note that we considered a specific aspect of depression, namely negative mood, which does not overlap with the apathy dimensions. To test these hypotheses, we investigated the links between the three apathy dimensions (initiative, interest and emotion), as assessed with the Apathy Inventory (AI) [17
], and an event-based PM task. To assess PM, we used the task developed by Blanco-Campal et al. [18
], which consists in remembering to perform an action (such as pressing a particular key on a computer keyboard) when a particular cue event occurs, while also performing an ongoing task. The cognitive processes recruited in PM tasks, and the likelihood of success, are determined by the nature and demands of the ongoing task and the parameters of the PM cue [19
]. We chose the most demanding condition (non-specific–non-salient condition; see below), which requires a range of executive processes, including the maintenance of the intention in working memory during the ongoing task, the monitoring of the environment and thus the allocation of greater attentional resources to identify the cue that signals the initiation of the action, the switch from the ongoing task to the PM task once the intention has been recalled, and the interruption of the ongoing task when the intention is to be performed [18
]. We assume that PM situations of this kind (especially the initiation and execution of the intention, i.e. steps 3 and 4, which require executive functions) [21
] tap particularly well into a specific set of cognitive processes that are essential for GDB [11
], such as monitoring for the target cue, inhibition of work on the ongoing task [22
] and cognitive flexibility to switch to the PM task set [23
Finally, in agreement with Walters’ [24
] study, we chose to adopt a perspective that considers cognitive aging along a continuum. Indeed, Walters’ [24
] study – conducted on more than 10,000 participants with and without dementia – showed (by using taxometric analysis) that differences in performance on a variety of cognitive tasks (episodic and working memory, executive function, language) are quantitative (continuum) rather than qualitative (distinct entity) [24
]. Thus, in the present study, we performed analyses on one group of people presenting with more or fewer cognitive difficulties, without making group comparisons.