Effect of Circadian Phase on Memory Acquisition and Recall: Operant Conditioning vs. Classical Conditioning

Madeleine V Garren,Terry L Page,Stephen B Sexauer,Troy Zars

doi:10.1371/journal.pone.0058693

Madeleine V Garren, Terry L Page + Show 2 more

Open Access

https://doi.org/10.1371/journal.pone.0058693

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Journal: PloS one	Publication Date: Mar 22, 2013
Citations: 22	License type: CC BY 4.0

Affiliation: Vanderbilt University

Abstract

There have been several studies on the role of circadian clocks in the regulation of associative learning and memory processes in both vertebrate and invertebrate species. The results have been quite variable and at present it is unclear to what extent the variability observed reflects species differences or differences in methodology. Previous results have shown that following differential classical conditioning in the cockroach, Rhyparobia maderae, in an olfactory discrimination task, formation of the short-term and long-term memory is under strict circadian control. In contrast, there appeared to be no circadian regulation of the ability to recall established memories. In the present study, we show that following operant conditioning of the same species in a very similar olfactory discrimination task, there is no impact of the circadian system on either short-term or long-term memory formation. On the other hand, ability to recall established memories is strongly tied to the circadian phase of training. On the basis of these data and those previously reported for phylogenetically diverse species, it is suggested that there may be fundamental differences in the way the circadian system regulates learning and memory in classical and operant conditioning.

Highlights

In the past decade, several studies have indicated that circadian clocks may have varied effects on learning and memory
The ability to form a memory may be independent of circadian phase, but phase may function as a contextual cue such that recall and performance are better at 24-hour intervals following learning as demonstrated in hamsters [1] and rats [2,3,4]
In the present study we show that R. maderae can be trained via an operant conditioning protocol that utilizes the same sensory cues that were used for classical conditioning

Summary

Introduction

Several studies have indicated that circadian clocks may have varied effects on learning and memory. One of the problems with sorting out the various results to come to clear understanding of underlying principles of the circadian system’s role in associative memory formation is that the experiments have used various species, various conditioning paradigms, and various stimuli for reinforcement. It is unclear whether differences in results reflect fundamental differences in the role of the circadian system in learning and memory or, alternatively, reflect a ‘‘hodge-podge’’ of species and methodological differences that obscures any underlying general principles

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