Mammalian time memory
Subtitle: temporal modulation of learning and performance
By: by Sean Wendell Cain.
Published: 2006
Language: eng
Number of pages: 220
ISBN-13: 9780494160398
Description: In golden hamsters, the expression of a conditioned place preference (CPP) is regulated in a circadian pattern such that the preference is exhibited strongly at the circadian time of prior training but not at other circadian times. We found that the same "time-stamp" phenomenon was expressed following context conditioning with an aversive stimulus (conditioned place avoidance, CPA). The results suggest that in hamsters, the emotional valence associated with the place where arousing stimulation (rewarding and aversive) is encountered is highest at the circadian time of occurrence. We further found that this rhythmic CPA performance is evident in hamsters made arrhythmic by lesioning the suprachiasmatic nucleus. Though the time-stamp in CPA performance is not dependent on the SCN, it is not independent of the effects of SCN timing in the intact animal. That is, the time stamp in CPA performance is maintained for a longer period of time when the time of training matches the SCN-determined peak in arousal. Further, a 24-hour CPA time stamp cannot be obtained in hamsters that are homozygous for the circadian clock mutation, tau. However, a 24-hour time-stamp is rescued following lesions of the SCN in these clock mutant hamsters. We present evidence that dopamine signaling may be an important neural substrate for the rhythm in CPA performance. Hamsters chronically treated with haloperidol do not display the rhythm in CPA performance, though CPA itself is intact. Finally, we demonstrate that CPP and amphetamine sensitization in the rat display a similar time-stamp, in that optimal performance is found when training and testing times match. The time of training appears to be a context feature that is registered during conditioning even though time itself is not an explicit discriminative cue in these experiments. Rodents therefore seem to be predisposed to anticipate the recurrence of arousing events at circa-24 hour intervals.
Notes: Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 4148.

Thesis (Ph.D.)--University of Toronto, 2006.

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