P212 Delayed feedback and the precision of a neural oscillator in weakly electric fish
Parisa Nazemi*1,2, John Lewis1,2
¹ Department of Biology, University of Ottawa, Ottawa, Canada ² Brain and Mind Research Institute, University of Ottawa, Ottawa, Canada
*Email: pnaze017@uottawa.ca
Introduction
Precision and reliability of neural oscillations are critical for many brain functions. Among all known biological oscillators, the electric organ discharge (EOD) in wave-type electric fish is the most precise, with sub-microsecond variations in cycle periods and a coefficient of variation of CV ~ 10⁻⁴[1]. The timing of the EOD is set by a medullary pacemaker network comprising 150 neurons with weak electrical coupling. How this pacemaker network achieves such high precision is not clear. One hypothesis is that pacemaker activity is regularized by electrical feedback from the EOD itself. Methods To investigate this, we use a computational model of a pacemaker neuron [2] with a delayed auto-feedback current stimulus. The stimulus waveform was chosen to mimic the electric field effects of the EOD. We also use a simple pulse stimulus for comparison. Results Our results show that feedback either increases or decreases the CV of the period, depending on the phase of delay:some delays led to low CV (regular oscillations) and others resulted in high CV (variable oscillations), corresponded to distinct regions of the phase response curve (PRC), witha clear relationship between CV and PRC slope (Fig. 1). Specifically, phases associated with the lowest CV (φ_L) and highest CV (φ_H) are near the points where the PRC crosses 1 with positive and negative slopes, respectively.We also tested other neural models [3, 4] with different PRCs and found that, as long as the PRC was type II, the results were similar. Discussion
These findings provide insights into how time-delayed feedback influence the regularity and sensitivity of neural oscillations. The positive slope of the PRC suggests greater stability and promotes regularity for repeated fixed-delay stimulation. This mechanism could explain how the pacemaker network in weakly electric fish maintains exceptional regularity. More broadly, our findings suggest that feedback-driven stabilization may be a general principle for ensuring precise timing in biological oscillators.
Figure 1. Figure 1. Relationship between the coefficient of variation (CV) of periods with the phase response curve (PRC). A: normalized CV of periods. B: PRC. φ_L and φ_H mark the intersections of the PRC with the baseline at 1, where the slopes are positive and negative, respectively. Acknowledgements Supported by an NSERC Discovery Grant to Dr. John Lewis References
