Lyons Lisa C, Rawashdeh Oliver, Katzoff Ayelet, Susswein Abraham J, Eskin Arnold
Department of Biology and Biochemistry, University of Houston, Houston, TX 77204-5001, USA.
Proc Natl Acad Sci U S A. 2005 Aug 30;102(35):12589-94. doi: 10.1073/pnas.0503847102. Epub 2005 Aug 22.
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.
理解记忆的调节以及记忆形成的潜在机制已成为神经科学研究中的关键问题。此前，我们发现，对于一种非联想式学习形式——敏化作用，昼夜节律时钟会调节加州海兔（Aplysia californica）中长时记忆而非短时记忆的形成。为了确定昼夜节律对记忆调节的范围，我们研究了一种联想式操作性学习范式，即学习食物不可食用（LFI）。与在主观夜间进行训练和测试的动物相比，当加州海兔在主观白天进行训练和测试时，对LFI的长时记忆显著更强。相比之下，无论在主观白天还是夜间进行训练，动物对LFI的短时记忆水平相似。LFI长时记忆的昼夜节律调节取决于训练时间，而非测试时间。为了拓宽我们对昼夜节律调节记忆的研究，我们将研究扩展到了夜行性物种——条纹海兔（Aplysia fasciata）。与白天训练时在加州海兔中观察到的显著记忆不同，条纹海兔在白天训练时对LFI没有长时记忆。然而，条纹海兔在夜间进行训练和测试时表现出显著的长时记忆。因此，昼夜节律时钟与动物的活动期同步调节记忆形成。我们对长时敏化作用和LFI的昼夜节律调节研究结果表明，记忆形成的昼夜节律调节可能是一种普遍现象，对许多类型的长时学习可能具有广泛的潜在影响。
