Abstract
Nervous systems need to detect stimulus changes based on their neuronal responses without using any additional information on the number, times, and types of stimulus changes. Here, two relatively simple, biologically realistic change point detection methods are compared with two common analysis methods. The four methods are applied to intra- and extracellularly recorded responses of a single cricket interneuron (AN2) to acoustic simulation. Solely based on these recorded responses, the methods should detect an unknown number of different types of sound intensity in- and decreases shortly after their occurrences. For this task, the methods rely on calculating an adjusting interspike interval (ISI). Both simple methods try to separate responses to intensity in- or decreases from activity during constant stimulation. The Pure-ISI method performs this task based on the distribution of the ISI, while the ISI-Ratio method uses the ratio of actual and previous ISI. These methods are compared to the frequently used Moving-Average method, which calculates mean and standard deviation of the instantaneous spike rate in a moving interval. Additionally, a classification method provides the upper limit of the change point detection performance that can be expected for the cricket interneuron responses. The classification learns the statistical properties of the actual and previous ISI during stimulus changes and constant stimulation from a training data set. The main results are: (1) The Moving-Average method requires a stable activity in a long interval to estimate the previous activity, which was not always given in our data set. (2) The Pure-ISI method can reliably detect stimulus intensity increases when the neuron bursts, but it fails to identify intensity decreases. (3) The ISI-Ratio method detects stimulus in- and decreases well, if the spike train is not too noisy. (4) The classification method shows good performance for the detection of stimulus in- and decreases. But due to the statistical learning, this method tends to confuse responses to constant stimulation with responses triggered by a stimulus change. Our results suggest that stimulus change detection does not require computationally costly mechanisms. Simple nervous systems like the cricket's could effectively apply ISI-Ratios to solve this fundamental task.
Highlights
Has anything relevant changed in the sensory environment? This question is so essential for all organisms that the major task of sensory systems is to reflect behaviorally relevant stimulus changes in their neuronal activity
Approaches that rely on spike patterns occurring after the stimulus change that would not be readily available to the nervous system, are called “offline.” In contrast, “online” algorithms identify a change point (CP) in the stimulus based on data that is updated in every time step of the experimental recording
All methods rely on the hypothesis that the distributions of “actual” interspike intervals (ISI) and its previous ISI are distinguishable under the three conditions
Summary
Has anything relevant changed in the sensory environment? This question is so essential for all organisms that the major task of sensory systems is to reflect behaviorally relevant stimulus changes in their neuronal activity. A common application is the identification of the response latency to stimulus onset/offset of a single stimulus (Oram and Perrett, 1992; Ratnam et al, 2003; Levakova et al, 2015). This requires a good estimation of the starting point of the neural response. Approaches that rely on spike patterns occurring after the stimulus change that would not be readily available to the nervous system, are called “offline.” In contrast, “online” algorithms identify a CP in the stimulus based on data that is updated in every time step of the experimental recording. Since offline algorithms use a larger amount of data for making a decision, they are usually more accurate and detect changes with shorter delay than online methods (Aminikhanghahi and Cook, 2017)
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