# Perfect spike detection via time reversal

## TL;DR

This paper introduces a novel method for perfect retrospective spike detection in neuronal simulations, improving accuracy by propagating thresholds with time-inverted dynamics, applicable to linear neuron models.

## Contribution

It develops and benchmarks a new geometric method for exact spike detection that surpasses traditional approximate methods in accuracy and efficiency.

## Key findings

- The method guarantees perfect spike detection within linear neuron models.
- It is faster than root-finding based perfect detection methods.
- Missed spikes are extremely rare with existing approximate methods.

## Abstract

Spiking neuronal networks are usually simulated with three main simulation schemes: the classical time-driven and event-driven schemes, and the more recent hybrid scheme. All three schemes evolve the state of a neuron through a series of checkpoints: equally spaced in the first scheme and determined neuron-wise by spike events in the latter two. The time-driven and the hybrid scheme determine whether the membrane potential of a neuron crosses a threshold at the end of of the time interval between consecutive checkpoints. Threshold crossing can, however, occur within the interval even if this test is negative. Spikes can therefore be missed. The present work derives, implements, and benchmarks a method for perfect retrospective spike detection. This method can be applied to neuron models with affine or linear subthreshold dynamics. The idea behind the method is to propagate the threshold with a time-inverted dynamics, testing whether the threshold crosses the neuron state to be evolved, rather than vice versa. Algebraically this translates into a set of inequalities necessary and sufficient for threshold crossing. This test is slower than the imperfect one, but faster than an alternative perfect tests based on bisection or root-finding methods. Comparison confirms earlier results that the imperfect test rarely misses spikes (less than a fraction $1/10^8$ of missed spikes) in biologically relevant settings. This study offers an alternative geometric point of view on neuronal dynamics.