Donna Kwan

Deficits in past remembering extend to future imagining in a case of developmental amnesia

Patient and neuroimaging studies report that the ability to remember past personal experiences and the ability to envision future personal experiences are interconnected. Loss of episodic memory is typically accompanied by loss of future imagining, and engaging in either activity recruits common brain areas. The relationship between episodic memory and future imagining is also suggested by their co-emergence in ontogenetic development. However, it is unknown whether a failure of one ability to emerge in early development precludes the development of the other ability. To investigate this possibility, we tested H.C., a young woman with amnesia of developmental origin associated with bilateral hippocampal loss, and demographically matched controls on an adapted version of the Autobiographical Interview using Galton-Crovitz cueing. In response to cue words, participants described both past personal events and imagined future personal events that occurred, or could occur, in near and distant time periods. Results indicated a parallel pattern of impairment for both past and future event generation in H.C., such that her narratives of both types of events were similarly deficient. These results indicate that mental time travel can be compromised in hippocampal amnesia, whether acquired in early or later life, possibly as a result of a deficit in reassembling and binding together details of stored information from earlier episodes.

Future decision-making without episodic mental time travel

Deficits in episodic memory are associated with deficits in the ability to imagine future experiences (i.e., mental time travel). We show that K.C., a person with episodic amnesia and an inability to imagine future experiences, nonetheless systematically discounts the value of future rewards, and his discounting is within the range of controls in terms of both rate and consistency. Because K.C. is neither able to imagine personal uses for the rewards nor provide a rationale for selecting larger future rewards over smaller current rewards, this study demonstrates a dissociation between imagining and making decisions involving the future. Thus, although those capable of mental time travel may use it in making decisions about future rewards, these results demonstrate that it is not required for such decisions.

Dissociations in future thinking following hippocampal damage: evidence from discounting and time perspective in episodic amnesia.

Recollecting past experiences and imagining future experiences activate a common set of brain regions that includes the hippocampus (Schacter, Addis, & Buckner, 2007), and both functions are impaired in people with compromised hippocampal function (Klein, Loftus, & Kihlstrom, 2002; Tulving, 1985). These findings indicate a role for the hippocampus that extends beyond declarative memory. However, a case study revealed that a person with extensive medial temporal lobe (MTL) damage and episodic amnesia was able to forgo smaller, immediate rewards for a larger future payoff to a degree similar to control participants (Kwan et al., 2012). This finding suggests that typical regard for the future does not depend on hippocampal integrity. To test this hypothesis, the current study examined the nature and limits of the role of the hippocampus in future thinking and decision making in amnesic individuals with hippocampal damage and associated impairments in episodic memory and future imagining. The amnesic individuals were administered a delay discounting task to assess valuation of future rewards, a probability discounting task to assess risk taking, and the Zimbardo Time Perspective Inventory to assess personal orientation toward the past, present, and future. Comparisons with demographically matched controls indicated that aspects of temporal thought and future-oriented decision making are preserved in individuals with hippocampal amnesia despite their inability to imagine themselves in detailed future events. Thus, even extensive MTL damage and the resulting episodic amnesia do not preclude prudent decision making, including consideration of future financial outcomes and personal identification with the past and future.

Memory as social glue: close interpersonal relationships in amnesic patients.

Memory may be crucial for establishing and/or maintaining social bonds. Using the National Social life, Health, and Aging Project questionnaire, we examined close interpersonal relationships in three amnesic people: K.C. and D.A. (who are adult-onset cases) and H.C. (who has developmental amnesia). All three patients were less involved than demographically matched controls with neighbors and religious and community groups. A higher-than-normal percentage of the adult-onset (K.C. and D.A.) cases’ close relationships were with family members, and they had made few new close friends in the decades since the onset of their amnesia. On the other hand, the patient with developmental amnesia (H.C.) had forged a couple of close relationships, including one with her fiancé. Social networks appear to be winnowed, but not obliterated, by amnesia. The obvious explanation for the patients’ reduced social functioning stems from their memory impairment, but we discuss other potentially important factors for future study.

An Allais Paradox Without Mental Time Travel

The capacity to anticipate future experiences of regret has been hypothesized to explain otherwise irrational aspects of human decision‐making, including the certainty effect (Kahneman and Tversky (1979) Econometrica 47:263–291) and the common ratio effect (Allais (1953) Econometrica 21:503–546). The anticipated regret hypothesis predicts that individuals incapable of episodically imagining their personal futures, as has been reported for people with extensive damage to medial temporal lobe structures and resulting deficits in episodic thought, should be immune to these effects. We report that K.C., who has extensive bilateral damage to his hippocampus and adjacent medial temporal lobe structures and nearly complete deficits in his ability to episodically imagine his personal future, nonetheless displays both the certainty and the common ratio effects. These results suggest that the episodic anticipation of future regret does not explain the general human tendency to display the certainty and common ratio effects.

No evidence of risk-taking or impulsive behaviour in a person with episodic amnesia: Implications for the role of the hippocampus in future-regarding decision-making

Does advantageous decision-making require one to explicitly remember the outcome of a series of past decisions or to imagine future personal consequences of ones choices? Findings that amnesic people with hippocampal damage cannot form a clear preference for advantageous decks over many learning trials on the Iowa Gambling Task (IGT) have been taken to suggest that complex decision-making on the IGT depends on declarative (episodic) memory and hippocampal integrity. Alternatively, impaired IGT performance in amnesic individuals could be secondary to risk-taking and/or impulsive behaviour resulting from impaired episodic future thinking (i.e. prospection) known to accompany amnesia. We tested this possibility in the amnesic individual K.C. using the IGT and the Toronto Gambling Task (TGT), a novel task that dissociates impulsivity from risk-taking without placing demands on declarative memory. K.C. did not develop a preference for advantageous over disadvantageous decks on the IGT and, instead, showed a slight preference for short-term gains and an inability to acquire a more adaptive appreciation of longer-term losses. He also did not display impulsive or risk-taking behaviour on the TGT, despite a profound inability to imagine personal future experiences. These findings suggest that impaired decision-making on the IGT in amnesia is unlikely to reflect a predilection to act in the moment or failure to take future consequences into account. Instead, some forms of future-regarding decision-making may be dissociable, with performance on tasks relying on declarative learning or on episodic-constructive processes more likely to be impaired.

Moral Judgment in Episodic Amnesia

To investigate the role of episodic thought about the past and future in moral judgment, we administered a well‐established moral judgment battery to individuals with hippocampal damage and deficits in episodic thought (insert Greene et al. 2001). Healthy controls select deontological answers in high‐conflict moral scenarios more frequently when they vividly imagine themselves in the scenarios than when they imagine scenarios abstractly, at some personal remove. If this bias is mediated by episodic thought, individuals with deficits in episodic thought should not exhibit this effect. We report that individuals with deficits in episodic memory and future thought make moral judgments and exhibit the biasing effect of vivid, personal imaginings on moral judgment. These results strongly suggest that the biasing effect of vivid personal imagining on moral judgment is not due to episodic thought about the past and future.