Circadian modulation of complex learning in diurnal and nocturnal Aplysia

Lisa C. Lyons, Oliver Rawashdeh, Ayelet Katzoff, Abraham J. Susswein, Arnold Eskin

Research output: Contribution to journalArticlepeer-review

68 Scopus citations


Understanding modulation of memory, as well as the mechanisms underlying memory formation, has become a key issue in neuroscience research. Previously, we found that the formation of long-term, but not short-term, memory for a nonassociative form of learning, sensitization, was modulated by the circadian clock in the diurnal Aplysia californica. To define the scope of circadian modulation of memory, we examined an associative operant learning paradigm, learning that food is inedible (LFI). Significantly greater long-term memory of LFI occurred when A. californica were trained and tested during the subjective day, compared with animals trained and tested in the subjective night. In contrast, animals displayed similar levels of short-term memory for LFI when trained in either the subjective day or night. Circadian modulation of long-term memory for LFI was dependent on the time of training, rather than the time of testing. To broaden our investigation of circadian modulation of memory, we extended our studies to a nocturnal species, Aplysia fasciata. Contrary to the significant memory observed during the day with the diurnal A. californica, A. fasciata showed no long-term memory for LFI when trained during the day. However, A. fasciata demonstrated significant long-term memory when trained and tested during the night. Thus, the circadian clock modulates memory formation in phase with the animals' activity period. The results from our studies of circadian modulation of long-term sensitization and LFI suggest that circadian modulation of memory formation may be a general phenomenon with potentially widespread implications for many types of long-term learning.

Original languageEnglish
Pages (from-to)12589-12594
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number35
StatePublished - 30 Aug 2005


FundersFunder number
National Institute of Neurological Disorders and StrokeR01NS050589


    • Biological rhythms
    • Circadian clock
    • Long-term memory


    Dive into the research topics of 'Circadian modulation of complex learning in diurnal and nocturnal Aplysia'. Together they form a unique fingerprint.

    Cite this