Retrograde amnesia in the chick: Resistance to the reminder effect

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Abstract

Retrograde amnesia (RA) for learned peck-suppression in chicks was produced by flurothyl (CF2CH2OCH2CF3). In Experiment 1 (N = 154), RA 24 hr after strong flurothyl treatment was demonstrated by a retention test that served also as a reminder of the suppression training; a second retention test 24 hr later showed no reminder-induced restoration of memory. In Experiments 2, 3, and 4 (N = 728), moderate flurothyl treatment was used and the reminder was delayed for 2 hr after the 24-hr retention test; a second retention test 24 hr later indicated a weak, variable reminder effect. This is interpreted as reflecting the cumulation of two sub-threshold engrams, the first resulting from partial consolidation of the original training and the second resulting from information input of the reminder treatment. By this interpretation, restoration of learned performance by a reminder occurs when the two cumulated sub-threshold engrams exceed the threshold for retrieval. The reminder effect supports the argument that RA treatments are often incomplete and leave a weak engram that confounds interpretation of RA experiments.

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    The author thanks Mary W. Garman, Richard O. Meinecke and Mayme Y. Bailey for excellent technical assistance.

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