Reliability of UPO based control strategies in biological systems

TL;DR

This paper evaluates the reliability of UPO-based control strategies in biological systems, highlighting the challenges in accurately detecting UPOs amidst noise and nonstationarity, and questioning the link between control success and determinism.

Contribution

It introduces a hybrid UPO detection method combining multiple criteria, and critically assesses its effectiveness and limitations in noisy, real-world biological data.

Findings

UPO detection remains challenging in noisy, short data sets.

Accurate dynamical properties for control are rarely obtainable from noisy data.

Stringent criteria are necessary to reliably link control success with underlying determinism.

Abstract

Presence of recurrent and statistically significant unstable periodic orbits (UPOs) in time series obtained from biological systems are now routinely used as evidence for low dimensional chaos . Extracting accurate dynamical information from the detected UPO trajectories are vital for successful control strategies that either aim to stabilize the system near the fixed point or steer the system away from the periodic orbits. A hybrid UPO detection method from return maps that combines topological recurrence criterion, matrix fit algorithm and stringent criterion for fixed point location gives accurate and statistically significant UPOs even in the presence of significant noise. Geometry of the return map, frequency of UPOs visiting the same trajectory, length of the data set, strength of the noise and degree of nonstationarity affect the efficacy of the proposed method. Results suggest that establishing determinism from unambiguous UPO detection is often possible in short data sets with significant noise, but derived dynamical properties are rarely accurate and adequate for controlling the dynamics around these UPOs. A repeat chaos control experiment on epileptic hippocampal slices through more stringent control strategy and adaptive UPO tracking is reinterpreted in this context through simulation of similar control experiments on an analogous but stochastic computer model of epileptic brain slices. Reproduction of equivalent results suggests that far more stringent criteria are needed for linking apparent success of control in such experiments with possible determinism in the underlying dynamics.