Severity of amnesia and the effectiveness of reactivation treatment: Evidence for a retrieval process

Abstract

Reactivation of memory following retrograde amnesia treatment may be based on additional learning (storage model) or on gaining access to previously unavailable information (retrieval model). If further learning at reactivation summates with the residual memory, then the effectiveness of reactivation treatment should be inversely related to the degree of amnesia. The present experiment addressed this issue. Severity of retrograde amnesia was manipulated in adult rats by varying the delay (.5, 5, or 10 min) between punishment training and amnestic treatment (hypothermia). Prior to testing 24 h later, one half of the subjects received reactivation treatment (recooling). Passive avoidance latencies from the nonrecooled subjects showed the typical temporal gradient of amnesia. Recooling significantly improved retention in the strong amnesia group (.5 min), marginally improved retention in the moderate amnesia group, and failed to improve retention in the weak amnesia group. Controls for systemic stress demonstrated that the reactivation effect was not a performance artifact. In addition, test scores from a trained-only group were shown to reliably exceed the reactivation scores, suggesting that the magnitude of reactivation was not constrained by either functional or arbitrary ceiling limits. These findings were interpreted as consistent with a recently proposed “contextual cues” model as well as other retrieval-oriented interpretations of amnesia.