Plasticity in Pacemaker Period: a Dynamic Memory
In experimental studies of the wake-sleep cycle of higher vertebrates under constant conditions, it is common to find that the average free-running period of an animal’s rhythm, under a given set of conditions, varies to a small extent from one test of many cycles to the next. Recordings of the performance of a single animal over many months often show gradual trends toward shortening or lengthening of period; and it is not uncommon to observe sudden stepwise changes in period, sometimes caused by a known perturbation of the animal, occasionally due to unknown causes (“apparently spontaneous”). Such differences demonstrate, by definition, that the period of the circadian pacemaker is not uniquely determined by concurrent environmental conditions; in some way or another, the animal’s history can affect its circadian performance.
KeywordsBasic Period House Finch Unimodal State Discriminator Activity Nocturnal Rodent
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