Looking back, thinking ahead: A neuropsychological view on cognitive correlates of time, space and prospective memory

The aim of this thesis was to better understand the cognitive architecture underlying complex functions relevant for daily life. A special focus was placed on prospective memory (PM).
PM is defined as remembering to carry out intended actions at an appropriate moment in the future. This moment can either be coupled with a specific time (time-based, TBPM) or event (event-based or EBPM). It involves multiple cognitive operations, including the formation of an intention, remembering it over a delay period, and executing the intention.
We investigated how PM is affected in dementia and its prodromal stage mild cognitive impairment, conditions characterized by memory impairments. A meta-analysis showed that both patient groups show large EBPM and TBPM deficits. The findings of this meta-analysis stress the importance of regarding PM as a relevant aspect of cognitive dysfunctioning.
Next, we delineated what cognitive functions are involved in PM. We found dissociations between EBPM and TBPM in stroke patients, and differences in their cognitive correlates: TBPM was found to be more cognitively complex than EBPM. An explanation for these differences is that EBPM involves an external cue that should automatically evoke retrieval of the intention, whereas TBPM requires self-initiated retrieval which demands more effort.
Subsequently, we performed a confirmative analysis of ideas based on PM theories. Using Bayesian statistics, we tested several alternative hypotheses on the differential contribution of sequential processes, visuospatial processing and vigilance in TBPM versus EBPM. However, none of the hypotheses gained support over the null-hypothesis that none of these variables contributed to PM. Exploratory analyses did show involvement of several of these processes in PM, and dissociations between EBPM and TBPM, in congruence with the results of chapter three. More than providing firm answers, this study generated new questions about the cognitive architecture of PM. We therefore further investigated processes thought to be related to PM.
First, dissociations between spatial and temporal order memory were examined in stroke patients. By demonstrating that these two aspects of contextual memory can be differentially affected in stroke, we concluded that they are dissociable. Seven patients (18%) showed selective impairment in either remembering the spatial location of recently shown objects, or the order in which these were presented. Also, we found evidence for lateralization of temporal order memory to the left hemisphere.
Next, we investigated how different cognitive functions are related to time perception. Seven stroke patients (19%) showed time perception deficits, and dissociations were found between different task dimensions (estimation versus reproduction of time intervals). How people perceive the passage of time was shown to be correlated with (working) memory and information processing speed.
In the studies performed in the stroke population we focused on finding dissociations by contrasting performance on different cognitive tasks in patients with focal brain damage. Also, we studied a condition with more diffuse brain damage: multiple sclerosis (MS). We found that cognitive deficits in MS patients with severe disabilities are severe and widespread. Notably, speed of information processing largely determined performance in the other cognitive domains.