The Evolution of Episodic Memory: The HIPPOCAMPUS Rises Is this the beginning of the story weve looking for: How might Hippocampus have become the locus of Experience of, for, and by the SELF? Here (below) we have liberally excerpted verbatim from the FULL TEXT of these recent article (see the link below)which we encourage members to read if full. Of course, we love it. Why? Because it agrees with what we ve thinking. And more. It provides a trail of bread crumbs that we can follow here in future posts to confirm this strange idea of ours. ncbi.nlm.nih.gov/pmc/articles/PMC3690604/ FULL TEXT In humans, episodic memory has been defined as the capacity to recall specific experiences, as if one were to “mentally time travel” to reexperience individual events Although a prominent view holds that episodic memory is unique to humans accumulating evidence indicates that birds and rodents can demonstrate a memory capacity that satisfies behavioral criteria for episodic memory Does this evidence imply that episodic memory capacity is fundamentally conserved across avian and mammalian species? Or does it suggest “episodic-like” memory capacity evolved separately in a few species and thus is the result of convergent evolution? We go beyond previous efforts by integrating the behavioral evidence across species with a comparative analysis of the neurobiology and neural mechanisms underlying episodic memory capacity. We also discuss the potential functions of episodic memory in an evolutionary context, as well as species-specific divergences. Episodic memory is the remarkable capacity to remember specific personal experiences. Although it was originally thought that this capacity was particular to humans, the ample evidence reviewed here indicates that core properties of episodic memory are present across mammals, as well as in birds. Because the concept of episodic memory was first studied in cognitive psychology, one approach is to define it in terms of the subjective experience associated with episodic recall. Specifically, Tulving proposed that episodic recall involves the ability to “mentally time travel” to reexperience specific events, a capacity that requires a sense of self, subjective time, and autonoetic awareness (conscious awareness that the experience occurred in the past). Although this definition may capture the phenomenological aspects associated with episodic memory in humans, it relies entirely on verbal reports of subjective mental experiences. Because this definition of episodic memory precludes its investigation in animals, the hypothesis that this capacity is unique to humans lacks falsifiability. The absence of objective measures for episodic memory is also not conducive to rigorous scientific investigation in human studies. A more productive approach to defining episodic memory is to identify fundamental features that can be measured experimentally This cross-species approach to episodic memory research is made possible by the use of operational definitions that can be applied across species The most common approach to investigate episodic memory capacity across species is to determine whether animals can remember events within the context in which they occurred (e.g., memory for what-where-when, what-where, or what-when). The events-in-context approach capitalizes on the fact that, in the episodic memory system, information about specific events is tied to the spatial, temporal, and other situational contexts in which they occurred Episodic memory in mammals depends on the hippocampus, the parahippocampal region, and the prefrontal cortex. However, until recently, it was unclear how this network of structures could give rise to episodic memory. In fact, considerable progress has been made in recent years toward understanding the specific contribution of each structure, as well as the nature of their functional relationships. Before reaching the hippocampus, information about the “what,” “where,” or “when” of individual events is not yet integrated into a single representation and thus does not satisfy the structure criterion for episodic memory. Episodic memory requires the integration of the representation of a single event with its distinctive contextual information, and it is this process that critically depends on the hippocampus Here, we describe a model, derived primarily from rodent and primates studies, summarizing the neural mechanisms thought to support the encoding and expression of episodic memories in mammals Importantly, we described a comparable neural circuit in birds, which includes homologous (hippocampus, and to some degree, parahippocampal region) and analogous (dorsal ventricular ridge association areas, nidopallium caudolaterale “prefrontal” area) structures. Finally, we submit that this fundamental circuit underlies episodic memory capacity across species but that species-specific divergences have also evolved around this central architecture. Because the hippocampus is essential for spatial memory across species, ranging from humans to teleost fish, it is likely that its role was limited to the processing of “where” information when it first emerged We propose that episodic memory capacity emerged at a later time, when the hippocampus began supporting the integration of information about events in context (e.g., “what”, “where,” and/or “when” information). Accumulating evidence suggests that the hippocampus also plays a critical role in forming what-when associations, including memory for the order in which specific events occurred. For instance, in sequence memory paradigms, rats with hippocampal damage were shown to have normal memory for the individual items presented (what) but consistently failed to remember the temporal relationships among events [what-when. Functional neuroimaging studies have shown that the hippocampus is strongly engaged during performance of similar tasks in humans as well Furthermore, recent electrophysiological evidence suggests that a fundamental role of the hippocampus is to provide an internal representation of elapsed time, which could support the formation of what-when memories In fact, recent studies have shown that individual hippocampal neurons exhibit robust timing signals during stimulus-free intervals [“time cells”. and during the presentation of sequences of events . In addition, the pattern of activity in hippocampal ensembles has been shown to gradually change over time, a form of population coding that could serve as a timing signal . The above lesion and electrophysiological studies provide converging evidence that this capacity primarily depends on subregion CA1 of the hippocampus. The change to supporting episodic memory likely occurred when the hippocampus began receiving highly processed event and contextual information from higher association areas. In light of the cross-species behavioral and neurobiological similarities reviewed here, it is tempting to conclude that episodic memory capacity emerged before mammals and reptiles diverged
Posted on: Thu, 09 Oct 2014 05:01:12 +0000
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