Hypothermia-induced amnesia for newly acquired and old reactivated memories: Commonalities and distinctions

Abstract

A series of six experiments compared the characteristics of hypothermia-induced amnesia for newly acquired and old reactivated memories. Old memory, when reactivated by cue exposure, was disrupted by mild or deep hypothermia treatment, while new memory was impaired only by deep cooling. Mild hypothermia had no disruptive influence on either new or old memories. Old, but not new, learning showed recovery from amnesia in a ' test-retest procedure. The onset of amnesia was more rapid for an old reactivated memory than for a newly acquired memory. The susceptibility of memory to disruption decreased over time following original learning or cue reactivation, although this decrease was, if anything, more rapid following the cuing procedure. Recovery from amnesia could be induced by a recooling reminder treatment and was similar for both new and old memories. It was suggested that activity of, or access to, memory rather than age per se determines susceptibility to disruption. The process of memory reactivation appears somewhat more sensitive, rapid, and brief than the process(es) of memory formation. However, that the underlying old memory remains stable over time was supported by the strong retention when specific implicit or explicit reactivation cues were available. The temporal organization has long been held as an important dimension in the study of the diseases of memory. Since the late 19th century, when Ribot (1883) formulated his "law of regression," old memories have been viewed as more stable and less susceptible to disruption than recently acquired learning. However, since this rule was based on anecdotal and observational reports of human amnesia and senility, it is not surprising that the clinical literature suggests little agreement on the validity of Ribot's

Behavioral impairments caused by injections of the protein synthesis inhibitor anisomycin after contextual retrieval reverse with time

“…At a theoretical level, the present results are consistent with the idea that postretrieval deficits reflect the animal's inability to retrieve a stored contextual memory (10)(11)(12)(13)(14)(15)19). The challenge for retrieval theories is to determine what mechanism would allow the original memory to be preserved while temporarily preventing the animal from having access to it.…”

“…Although there were different accounts of these effects, much of the early theorizing described the behavioral deficits as reflecting impairments in memory retrieval (10)(11)(12)(13)(14)(15). This focus on retrieval mechanisms resulted in part from the demonstrations that postretrieval performance impairments could be reversed through reminder treatments (14) or through the simple passage of time (9,15). These findings suggest that postretrieval manipulations alter performance without eliminating the original memory.…”

“…Some of the first studies of postretrieval impairments demonstrated that manipulations such as electroconvulsive shock (8) or hypothermia (9) after stimulus reexposure resulted in deficits in performance during subsequent tests. Although there were different accounts of these effects, much of the early theorizing described the behavioral deficits as reflecting impairments in memory retrieval (10)(11)(12)(13)(14)(15). This focus on retrieval mechanisms resulted in part from the demonstrations that postretrieval performance impairments could be reversed through reminder treatments (14) or through the simple passage of time (9,15).…”

Retrieval failure versus memory loss in experimental amnesia: Definitions and processes

“…Presumably, the stimulus "reactivates" the target memory into a state of active neural transmission Przybyslawski and Sara 1997;Nader et al 2000a). The experimental amnesia induced following reactivation of an old, previously consolidated memory is retrograde in much the same fashion as is amnesia induced very soon following training (see Mactutus et al 1982).…”

“…Presumably, the stimulus "reactivates" the target memory into a state of active neural transmission Przybyslawski and Sara 1997;Nader et al 2000a). The experimental amnesia induced following reactivation of an old, previously consolidated memory is retrograde in much the same fashion as is amnesia induced very soon following training (see Mactutus et al 1982).Reminder effects refer to the observation that, long after amnesia has been induced, presentation of a so-called reminder stimulus prior to testing can result in restoration of behavior indicative of the original learning Quartermain et al 1972). Typically, the stimulus that serves as the most effective reminder stimulus is the reinforcer from initial training (see Miller and Springer 1972).…”