Since the publication of Tulving's (Reference Tulving1983b) treatise on episodic memory, psychologists and cognitive neuroscientists have amassed an impressive amount of data elucidating the cognitive and neural mechanisms that give rise to and support first-person accounts of the experienced past (for reviews, see Dickerson & Eichenbaum Reference Dickerson and Eichenbaum2010; Szpunar & McDermott Reference Szpunar, McDermott and Byrne2008b; Tulving Reference Tulving2002a). Nonetheless, relatively little is known about why healthy human adults possess this capacity. Mahr & Csibra (M&C) propose that the defining component of episodic memory – the capacity to mentally re-experience the self in subjective time or autonoetic consciousness – may have evolved to support the negotiation of epistemic authority in social communication. According to this account, episodic memory enables people to ascribe confidence in their reporting of the personal past when interacting with others.
Although episodic memory undoubtedly serves to fine-tune the nature and quality of human interactions, we suggest that social communication represents but one instance wherein this capacity bestows an advantage for its owner. The crux of our argument is that many non-social circumstances also require an accurate and confident recounting of specific past experiences as a means for supporting adaptive behavior. As one example, consider the behavior of an individual who decides to walk home along the longer of two paths on the basis of a recent negative experience along the shorter path. In this case, the debate (deciding between the longer, safer route vs. the more convenient, but riskier route) takes place within the individual's mind, and mentally re-experiencing a pertinent past episode may help justify the most appropriate course of action. Because it is difficult to ascertain the circumstances of our evolutionary history under which recollections first emerged to guide behavior, a comprehensive functional account of episodic memory should be able to explain why salient past experiences tend to guide behavior in both social and non-social domains. In formulating his theory of episodic memory, Tulving (Reference Tulving1985, pp. 9–10) seemingly envisioned such an account, stating that “the adaptive value of episodic memory and autonoetic consciousness lies in the heightened subjective certainty with which organisms endowed with such memory and consciousness believe, and are willing to act upon, information retrieved from memory … lead[ing] to more decisive action in the present and more effective planning for the future.”
Beyond providing a sense of added certainty in guiding behavior, episodic memory may also play a pivotal role in conceptualizing the self's existence across time. Current events often cue spontaneous retrieval of past events, and these recursive remindings (Hintzman Reference Hintzman2004) help bridge the recollected past with the anticipated future. Profoundly amnesic patients with episodic memory deficits that preclude recollection of much or all of the personal past and simulation of the personal future provide a window into the nature of this relation. Indeed, a striking deficit for patients with a dysfunctional episodic memory is that they are often “lost in time.” For example, about 40 years after a medial-temporal lobe resection to alleviate chronic seizures, patient HM mistakenly believed that he had memory problems for only about one year (Corkin Reference Corkin2013). Similarly, following a motorcycle accident that resulted in diffuse brain damage, patient KC was unable to answer the simple question “how old are you?” even though he knew the date of his birth, because he did not know the current year in which he lived (Rosenbaum et al. Reference Rosenbaum, Kohler, Schacter, Moscovitch, Westmacott, Black, Gao and Tulving2005).
Of course, the aforementioned observations of amnesic patients are selective and are not intended to imply that amnesic patients lack a self-concept or the ability to think about time. Indeed, semantic knowledge may be sufficient to support cognitions about the self (Klein & Gangi Reference Klein and Gangi2010). Moreover, M&C highlight that K.C. showed delayed discounting (Kwan et al. Reference Kwan, Craver, Green, Myerson, Boyer and Rosenbaum2012), suggesting that episodic memory is not necessary for some future-oriented aspects of cognition. Although people may be able imagine the future in a manner that does not involve episodic memory (Szpunar et al. Reference Szpunar, Spreng and Schacter2014), this should not eliminate the possibility that episodic memory is necessary for future thinking that requires extending the self in time. We believe that two pieces of evidence support our argument. First, given that nonhuman animals such as pigeons and rats can discount future outcomes (Vanderveldt et al. Reference Vanderveldt, Oliveira and Green2016), it is unlikely that episodic memory is necessary for judgments of intertemporal choice. Second, whereas healthy human adults use event simulations to curb their tendency to discount future outcomes (Benoit et al. Reference Benoit, Gilbert and Burgess2011; Peters & Büchel Reference Peters and Büchel2010), amnesic patients do not (Palombo et al. Reference Palombo, Keane and Verfaellie2015). For instance, even though Kwan et al. (Reference Kwan, Craver, Green, Myerson, Gao, Black and Rosenbaum2015) found that some amnesic patients could use personally relevant future scenarios to support farsighted decisions, their amnesic patients experienced great difficulty generating relevant future scenarios and were aided by either personal calendars or relatives. Hence, in the absence of external support, an impaired episodic memory system is associated with an impoverished perspective of the self across time.
Finally, whereas we and M&C have focused primarily on the adaptive value of the autonoetic component of episodic memory, that is, mentally re-experiencing the self in subjective time, Tulving (Reference Tulving, Stuss and Knight2002b) further mused about the capacity to be aware of the subjective time in which the self exists. The distinction is subtle but may be important for understanding the evolution of episodic memory and of the human race as a whole. In theorizing about its functions, Tulving noted that the awareness of subjective time is integral to the ability of humans to establish a continued culture by which the world is altered to suit their needs, rather than adapting to the world. If humans did not possess the capacity to project their minds into the future, they would have no reason to alter their behavior, based on relevant past experiences or otherwise, to suit the future that is yet to exist (Tulving & Szpunar Reference Tulving, Szpunar, Levine and Craik2012; see also Klein Reference Klein2013c).
Since the publication of Tulving's (Reference Tulving1983b) treatise on episodic memory, psychologists and cognitive neuroscientists have amassed an impressive amount of data elucidating the cognitive and neural mechanisms that give rise to and support first-person accounts of the experienced past (for reviews, see Dickerson & Eichenbaum Reference Dickerson and Eichenbaum2010; Szpunar & McDermott Reference Szpunar, McDermott and Byrne2008b; Tulving Reference Tulving2002a). Nonetheless, relatively little is known about why healthy human adults possess this capacity. Mahr & Csibra (M&C) propose that the defining component of episodic memory – the capacity to mentally re-experience the self in subjective time or autonoetic consciousness – may have evolved to support the negotiation of epistemic authority in social communication. According to this account, episodic memory enables people to ascribe confidence in their reporting of the personal past when interacting with others.
Although episodic memory undoubtedly serves to fine-tune the nature and quality of human interactions, we suggest that social communication represents but one instance wherein this capacity bestows an advantage for its owner. The crux of our argument is that many non-social circumstances also require an accurate and confident recounting of specific past experiences as a means for supporting adaptive behavior. As one example, consider the behavior of an individual who decides to walk home along the longer of two paths on the basis of a recent negative experience along the shorter path. In this case, the debate (deciding between the longer, safer route vs. the more convenient, but riskier route) takes place within the individual's mind, and mentally re-experiencing a pertinent past episode may help justify the most appropriate course of action. Because it is difficult to ascertain the circumstances of our evolutionary history under which recollections first emerged to guide behavior, a comprehensive functional account of episodic memory should be able to explain why salient past experiences tend to guide behavior in both social and non-social domains. In formulating his theory of episodic memory, Tulving (Reference Tulving1985, pp. 9–10) seemingly envisioned such an account, stating that “the adaptive value of episodic memory and autonoetic consciousness lies in the heightened subjective certainty with which organisms endowed with such memory and consciousness believe, and are willing to act upon, information retrieved from memory … lead[ing] to more decisive action in the present and more effective planning for the future.”
Beyond providing a sense of added certainty in guiding behavior, episodic memory may also play a pivotal role in conceptualizing the self's existence across time. Current events often cue spontaneous retrieval of past events, and these recursive remindings (Hintzman Reference Hintzman2004) help bridge the recollected past with the anticipated future. Profoundly amnesic patients with episodic memory deficits that preclude recollection of much or all of the personal past and simulation of the personal future provide a window into the nature of this relation. Indeed, a striking deficit for patients with a dysfunctional episodic memory is that they are often “lost in time.” For example, about 40 years after a medial-temporal lobe resection to alleviate chronic seizures, patient HM mistakenly believed that he had memory problems for only about one year (Corkin Reference Corkin2013). Similarly, following a motorcycle accident that resulted in diffuse brain damage, patient KC was unable to answer the simple question “how old are you?” even though he knew the date of his birth, because he did not know the current year in which he lived (Rosenbaum et al. Reference Rosenbaum, Kohler, Schacter, Moscovitch, Westmacott, Black, Gao and Tulving2005).
Of course, the aforementioned observations of amnesic patients are selective and are not intended to imply that amnesic patients lack a self-concept or the ability to think about time. Indeed, semantic knowledge may be sufficient to support cognitions about the self (Klein & Gangi Reference Klein and Gangi2010). Moreover, M&C highlight that K.C. showed delayed discounting (Kwan et al. Reference Kwan, Craver, Green, Myerson, Boyer and Rosenbaum2012), suggesting that episodic memory is not necessary for some future-oriented aspects of cognition. Although people may be able imagine the future in a manner that does not involve episodic memory (Szpunar et al. Reference Szpunar, Spreng and Schacter2014), this should not eliminate the possibility that episodic memory is necessary for future thinking that requires extending the self in time. We believe that two pieces of evidence support our argument. First, given that nonhuman animals such as pigeons and rats can discount future outcomes (Vanderveldt et al. Reference Vanderveldt, Oliveira and Green2016), it is unlikely that episodic memory is necessary for judgments of intertemporal choice. Second, whereas healthy human adults use event simulations to curb their tendency to discount future outcomes (Benoit et al. Reference Benoit, Gilbert and Burgess2011; Peters & Büchel Reference Peters and Büchel2010), amnesic patients do not (Palombo et al. Reference Palombo, Keane and Verfaellie2015). For instance, even though Kwan et al. (Reference Kwan, Craver, Green, Myerson, Gao, Black and Rosenbaum2015) found that some amnesic patients could use personally relevant future scenarios to support farsighted decisions, their amnesic patients experienced great difficulty generating relevant future scenarios and were aided by either personal calendars or relatives. Hence, in the absence of external support, an impaired episodic memory system is associated with an impoverished perspective of the self across time.
Finally, whereas we and M&C have focused primarily on the adaptive value of the autonoetic component of episodic memory, that is, mentally re-experiencing the self in subjective time, Tulving (Reference Tulving, Stuss and Knight2002b) further mused about the capacity to be aware of the subjective time in which the self exists. The distinction is subtle but may be important for understanding the evolution of episodic memory and of the human race as a whole. In theorizing about its functions, Tulving noted that the awareness of subjective time is integral to the ability of humans to establish a continued culture by which the world is altered to suit their needs, rather than adapting to the world. If humans did not possess the capacity to project their minds into the future, they would have no reason to alter their behavior, based on relevant past experiences or otherwise, to suit the future that is yet to exist (Tulving & Szpunar Reference Tulving, Szpunar, Levine and Craik2012; see also Klein Reference Klein2013c).