Time and category information in pattern-based codes

TL;DR

This paper investigates how neural spike patterns encode sensory information, analyzing the roles of pattern timing and categories, and how they interact and relate to stimulus features using information theory.

Contribution

It introduces a formal information-theoretic framework to quantify the roles and interactions of pattern timing and categories in neural coding, addressing their correlation with stimulus features.

Findings

Pattern timing and categories can carry redundant or synergistic information.

The framework clarifies conditions where timing and categories independently encode stimulus features.

Neural responses can represent both what and when features through different pattern aspects.

Abstract

Sensory stimuli are usually composed of different features (the what) appearing at irregular times (the when). Neural responses often use spike patterns to represent sensory information. The what is hypothesized to be encoded in the identity of the elicited patterns (the pattern categories), and the when, in the time positions of patterns (the pattern timing). However, this standard view is oversimplified. In the real world, the what and the when might not be separable concepts, for instance, if they are correlated in the stimulus. In addition, neuronal dynamics can condition the pattern timing to be correlated with the pattern categories. Hence, timing and categories of patterns may not constitute independent channels of information. In this paper, we assess the role of spike patterns in the neural code, irrespective of the nature of the patterns. We first define information-theoretical quantities that allow us to quantify the information encoded by different aspects of the neural response. We also introduce the notion of synergy/redundancy between time positions and categories of patterns. We subsequently establish the relation between the what and the when in the stimulus with the timing and the categories of patterns. To that aim, we quantify the mutual information between different aspects of the stimulus and different aspects of the response. This formal framework allows us to determine the precise conditions under which the standard view holds, as well as the departures from this simple case. Finally, we study the capability of different response aspects to represent the what and the when in the neural response.