Role of the hippocampus in remembering the past and imagining the future

Abstract

It has been proposed that a core network of brain regions, including the hippocampus, supports both past remembering and future imagining. We investigated the importance of the hippocampus for these functions. Five patients with bilateral hippocampal damage and one patient with large medial temporal lobe lesions were tested for their ability to recount autobiographical episodes from the remote past, the recent past, and to imagine plausible episodes in the near future. The patients with hippocampal damage had intact remote autobiographical memory, modestly impaired recent memory, and an intact ability to imagine the future. The patient with large medial temporal lobe lesions had intact remote memory, markedly impaired recent memory, and also had an intact ability to imagine the future. The findings suggest that the capacity for imagining the future, like the capacity for remembering the remote past, is independent of the hippocampus.episodic memory | semantic memory | medial temporal lobe | remote memory | amnesia B ilateral damage to medial temporal lobe structures impairs the formation of new memories and also impairs recall of facts, events, and autobiographical experiences that were acquired during the years before the damage occurred (1, 2). This finding suggests that common mechanisms may underlie the ability to form new memories and the ability to recollect recent memories. There has also been interest in the possible link between remembering past experiences and imagining plausible episodes in the future (3). It was noted, for example, that the memory-impaired patient KC was impaired at generating autobiographical details about his past and also could not imagine future autobiographical episodes (4, 5). A link between past remembering and future imagining has received additional support from other patient studies. Thus, the densely amnesic patient DB had difficulty imagining future episodes (6). Similarly, four of five memory-impaired patients with lesions involving the hippocampus were reported to have difficulty constructing future autobiographical scenarios (7). Moreover, elderly individuals who provided fewer specific details about the recent past also provided fewer specific details about the future (8). Last, patients with mild Alzheimer's disease were impaired at providing autobiographical details about both past and future events (9).Consistent with these observations, neuroimaging studies have described substantial overlap between the brain regions activated when volunteers retrieve past memories and when they imagine future experiences (e.g., refs. 10-14). Schacter et al. (14) suggested that a core network of brain regions supports past remembering and future imagining. The key components of this network are proposed to be the medial prefrontal cortex, posterior regions in medial and lateral parietal cortex, lateral temporal cortex, and the medial temporal lobe including hippocampus (14,15).Within this network, the importance of the hippocampus and related medial temporal lobe structures for f...

A role for the hippocampus in encoding simulations of future events

“…Our results have important implications for the debate on whether hippocampal damage disrupts the ability to imagine the future (9)(10)(11)(12)(13)(14)(15)17). It is possible that with a damaged hippocampus, the ability to construct detailed scenarios may remain intact, whereas encoding of these representations is disrupted.…”

“…It is possible that with a damaged hippocampus, the ability to construct detailed scenarios may remain intact, whereas encoding of these representations is disrupted. This appears to be the case both for the children with hippocampal damage who were less accurate in later recalling their imagined events (14) and for the patients with hippocampal damage whose imagined events were described as repetitive, as if they could not recall the portions of the event that they had already constructed (15). Depending on the nature and location of damage-whether it is confined to the anterior/posterior regions identified here, whether it affects the entire hippocampus, and whether it is confined to the hippocampus or also affects other neighboring regions-differential impairments may be seen in tasks that require the generation of imagined episodic details, the encoding of imagined events, or both.…”

“…Recently, however, an adult developmental amnesic patient (13), a group of developmental amnesic school-aged children (14), and a group of patients with bilateral hippocampal damage but spared remote episodic memory (15), were all shown to be unimpaired at imagining detailed future events, implying that a fully intact hippocampus may not be required for episodic simulation. The role of the hippocampus in imagining the future, which has emerged recently as a critical issue in the cognitive neuroscience of memory, future thinking, and imagination (5,6,16), is therefore currently controversial (15,17).…”

The anterior medial temporal lobes: Their role in food intake and body weight regulation

“…Information related to recent eating is encoded in memory and influences future food intake (e.g., [54,55,58]). The hippocampus encodes information relative not only to past events but also to future ones [153]. The amygdala is involved in representing future positive events [146].…”

Autonoetic consciousness: Reconsidering the role of episodic memory in future-oriented self-projection

“…Second, the coherence and complexity of reported memory content-often employed as an index of episodicity (e.g., Anderson, 2012;Hurley, Maguire, & Vargha-Khadem, 2011;Race et al, 2011;Squire et al, 2010; for a discussion and critique see Arnold et al, 2011)-has neither rational nor empirical justification. While relearned personal histories (e.g., "So, what is episodic memory?")…”