The cognitive neuroscience of constructive memory: remembering the past and imagining the future

Abstract

Episodic memory is widely conceived as a fundamentally constructive, rather than reproductive, process that is prone to various kinds of errors and illusions. With a view towards examining the functions served by a constructive episodic memory system, we consider recent neuropsychological and neuroimaging studies indicating that some types of memory distortions reflect the operation of adaptive processes. An important function of a constructive episodic memory is to allow individuals to simulate or imagine future episodes, happenings and scenarios. Since the future is not an exact repetition of the past, simulation of future episodes requires a system that can draw on the past in a manner that flexibly extracts and recombines elements of previous experiences. Consistent with this constructive episodic simulation hypothesis, we consider cognitive, neuropsychological and neuroimaging evidence showing that there is considerable overlap in the psychological and neural processes involved in remembering the past and imagining the future.

Figure 1

Performance of patients with amnesia and Alzheimer's disease on the Deese–Roediger–McDermott (DRM) paradigm (Roediger & McDermott 1995). Participants study lists of words (e.g. tired, bed, awake, rest, dream, night, etc.) that are related to a non-presented lure word (e.g. sleep). A subsequent old–new recognition test contains studied words (e.g. tired, dream), new words that are unrelated to the study list items (e.g. butter) and new words that are related to the study list items (e.g. sleep). Both patient groups show significantly reduced recognition accuracy (i.e. hits—false alarms to new unrelated words) and also make fewer related false alarms (i.e. false alarms to new related words—false alarms to new unrelated words) relative to age-matched controls. Note that the ‘controls’ were the age-matched control group for the amnesic patients (data for controls and amnesics are obtained from Schacter et al. 1996c) and the ‘older adults’ were the age-matched control group for Alzheimer's patients (data for older adults and Alzheimer's patients are obtained from Budson et al. 2000). AD, Alzheimer's disease.

Figure 2

Neural regions engaged during both true and false recognition (adapted from Slotnick & Schacter 2004). A prototype recognition paradigm was employed; all stimuli presented during study were abstract, unfamiliar shapes. During recognition testing, participants made recognition judgements about old studied shapes, new prototypical shapes visually related to studied shapes and new shapes unrelated to studied shapes. A number of regions previously implicated in true recognition, including hippocampus, lateral parietal cortex, and dorsolateral and inferior prefrontal cortex, showed significant and comparable levels of activity during false recognition of new related shapes (i.e. prototypes) and true recognition of studied shapes compared with correct rejections of new unrelated shapes. The percentage of signal changed extracted from the left lateral parietal cortex is also shown. BA, Brodmann area; CR, correct rejection; FA, false alarm.

Figure 3

Common and distinct regions engaged by the construction and elaboration of past and future events (Addis et al. 2007). A conjunction analysis of activity during the construction of past and future events revealed a few regions exhibiting common activity, such as left hippocampus and right occipital gyrus (BA 19). Contrast analyses identified a number of regions exhibiting differentially more activity for future events, including the right frontal pole and hippocampus. The elaboration phase was marked by striking overlap between past and future events, including left hippocampus, left temporal pole, bilateral parietal lobule (BA 39) and retrosplenial cortex. Plots of per cent signal change during the past event, future event and control (semantic and imagery) tasks are also shown. BA, Brodmann area.

Figure 4

Sagittal slice (x=−4) illustrating the striking commonalities in the medial left prefrontal and parietal regions engaged when (a) remembering the past and (b) imagining the future (adapted from Addis et al. 2007). These marked similarities of activation were also evident in areas of the medial temporal lobe (bilateral parahippocampal gyrus) and lateral cortex (left temporal pole and left bilateral inferior parietal cortex). This extensive pattern of common activity was not present during the construction of past and future events (figure 4); it only emerged during the elaboration of these events (shown here, relative to elaboration phase of a semantic and an imagery control task).