# The self-tuned sensitivity of circadian clocks

## TL;DR

This paper demonstrates that circadian clocks in organisms like extit{Synechococcus elongatus} can adaptively tune their sensitivity to environmental cues, enhancing entrainment during periods of frequent environmental change, akin to an adaptive Kalman filter.

## Contribution

It reveals a natural mechanism for circadian clocks to dynamically adjust sensitivity based on environmental mismatch, supported by experimental and theoretical analysis.

## Key findings

- Circadian clocks can increase sensitivity during environmental mismatch.
- Clock-metabolism coupling enables faster entrainment.
- Analogous behavior observed in yeast stress response pathways.

## Abstract

Living organisms need to be sensitive to a changing environment while also ignoring uninformative environmental fluctuations. Here, we show that the circadian clock in \textit{Synechococcus elongatus} can naturally tune its environmental sensitivity, through a clock-metabolism coupling quantified in recent experiments. The metabolic coupling can detect mismatch between clock predictions and the day-night light cycle, and temporarily raise the clock's sensitivity to light changes and thus entrain faster. We also analyze analogous behavior in recent experiments on switching between slow and fast osmotic stress response pathways in yeast. In both cases, cells can raise their sensitivity to new external information in epochs of frequent challenging stress, much like a Kalman filter with adaptive gain in signal processing. Our work suggests a new class of experiments that probe the history-dependence of environmental sensitivity in biophysical sensing mechanisms.