Iterative Metaplasticity Across Timescales: How Circadian, Ultradian, and Infradian Rhythms Modulate Memory Mechanisms

Work in recent years has provided strong evidence for the modulation of memory function and neuroplasticity mechanisms across circadian (daily), ultradian (shorter-than-daily), and infradian (longer-than-daily) timescales. Despite rapid progress, however, the field has yet to adopt a general framework to describe the overarching role of biological rhythms in memory. To this end, Iyer and colleagues introduced the term iterative metaplasticity, which they define as the “gating of receptivity to subsequent signals that repeats on a cyclic timebase.” The central concept is that the cyclic regulation of molecules involved in neuroplasticity may produce cycles in neuroplastic capacity—that is, the ability of neural cells to undergo activity-dependent change. Although Iyer and colleagues focus on the circadian timescale, we think their framework may be useful for understanding how biological rhythms influence memory more broadly. In this review, we provide examples and terminology to explain how the idea of iterative metaplasticity can be readily applied across circadian, ultradian, and infradian timescales. We suggest that iterative metaplasticity may not only support the temporal niching of neuroplasticity processes but also serve an essential role in the maintenance of memory function.

Infradian rhythms of daily shoot increment in Salix viminalis (salicaceae) clones

The structure of seasonal dynamics of daily growth of shoots of basket willow (Salix viminalis) is described and analyzed. Object: model inbred-clone population of S. viminalis. Material: developing shoots on annual saplings from cuttings. Methods: comparative morphological, chronobiological, numerical analysis of time series. The formation of dimorphic root systems of one-year saplings from cuttings is described. It is established that the seasonal dynamics of daily increment of shoots is determined by the interaction of linear and nonlinear components. Linear components are approximated by regression equations, and nonlinear components are approximated by harmonic oscillation equations. The rhythmicity of seasonal dynamics of shoot growth is described. Four groups of biorhythms were identified: annual with a period of about 96 days, subannual with a period of 4064 days, and infradian with a period of 1924 days and infradian with a period of 1016 days. The alternation of peaks and dips in the seasonal dynamics of shoot increment is determined by infradian biorhythms with a period of 19...24 days. Infradian biorhythms with different periods are synchronized with each other. The probable reason is the existence of a pulse synchronizer of biorhythms. Interclonal differences in the seasonal dynamics of the daily growth of shoots were not revealed. The probable cause of intraclonal differences is the ontogenetic heterogeneity of vegetative buds, from which annual shoots have developed. To verify this hypothesis, we plan to observe the development of seedlings grown from cuttings harvested from different parts of the uterine shoots. The results obtained are recommended to be taken into account when planning agroforestry measures for crop of S. viminalis.

Neurotransmitters and nitric oxide are released in various brain areas according to ultradian and infradian rhythms

The push-pull superfusion technique was used to investigate release of endogenous neurotransmitters and nitric oxide in various brain regions. The transmitters catecholamines, histamine, GABA, glutamate, as well and nitric oxide are released according to ultradian rhythms which generate fluctuations of vegetative functions such as blood pressure and arousal. More frequent infradian oscillations of neurotransmitter and nitric oxide release fates are implicated in mutual interneural control.

Neurotransmitters and nitric oxide are released in various brain areas according to ultradian and infradian rhythms

The push-pull superfusion technique was used to investigate release of endogenous neurotransmitters and nitric oxide in various brain regions. The transmitters catecholamines, histamine, GABA, glutamate, as well and nitric oxide are released according to ultradian rhythms which generate fluctuations of vegetative functions such as blood pressure and arousal. More frequent infradian oscillations of neurotransmitter and nitric oxide release fates are implicated in mutual interneural control.

RhythmicAlly: Your R and Shiny–Based Open-Source Ally for the Analysis of Biological Rhythms

Research on circadian rhythms often requires researchers to estimate period, robustness/power, and phase of the rhythm. These are important to estimate, owing to the fact that they act as readouts of different features of the underlying clock. The commonly used tools, to this end, suffer from being very expensive, having very limited interactivity, being very cumbersome to use, or a combination of these. As a step toward remedying the inaccessibility to users who may not be able to afford them and to ease the analysis of biological time-series data, we have written RhythmicAlly, an open-source program using R and Shiny that has the following advantages: (1) it is free, (2) it allows subjective marking of phases on actograms, (3) it provides high interactivity with graphs, (4) it allows visualization and storing of data for a batch of individuals simultaneously, and (5) it does what other free programs do but with fewer mouse clicks, thereby being more efficient and user-friendly. Moreover, our program can be used for a wide range of ultradian, circadian, and infradian rhythms from a variety of organisms, some examples of which are described here. The first version of RhythmicAlly is available on Github, and we aim to maintain the program with subsequent versions having updated methods of visualizing and analyzing time-series data.