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Retrieval and Reconsolidation: Toward a Neurobiology of Remembering

Susan J. Sara

"(...) remembering is an activity similar to perceiving, in the sense that it involves the apprehension and comprehension of contemporary stimuli in the light of past experience. 
(Tulving and Thomson 1973; Craik 1983)

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Retrieval must somehow involve initial activation of relevant intrinsic networks, selection of relevant extrinsic stimuli, and integration of these different sources of information into a meaningful trace. From subjective experience we know that memory retrieval takes time—it may be a matter of milliseconds, but can extend to minutes or more. Retrieval can occur spontaneously, but it can be the fruit of great effort as well. The role of subtle, but significant, environmental stimuli in triggering these processes is intuitively obvious, and has been investigated systematically in animals and humans. Nevertheless, virtually nothing is known about the physiological processes underlying the act of remembering. The initial process must involve some orientation of attention to a particular stimulus or ensemble of stimuli. How those particular stimuli are recognized as “meaningful” or how they can activate the specific distributed network presumed to be the neuronal substrate of the memory still remains unknown.
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Preliminary results confirm that memory storage, memory retrieval, and its reconsolidation share some common processes (Mansuy et al. 1998). We have argued that activation of brainstem neuromodulatory systems, through a conditioned arousal response to the context, will play an essential role in both retrieval and reconsolidation. Release of neuromodulators, particularly NA, will facilitate attention and sensory processing of incoming information during retrieval. The effects of NA and other modulators in triggering intracellular processes upon which stable long-term memory is dependent would promote reconsolidation of the newly reorganized memory. Thus, a high level of attention and arousal at the time of retrieval will play a capital role in reinforcing the memory, since neuromodulatory systems are activated during these behavioral states."