State-dependent representations of mixtures by the olfactory bulb

Abstract

AbstractSensory systems are often tasked to analyse complex signals from the environment, separating relevant from irrelevant parts. This process of decomposing signals is challenging when a mixture of signals does not equal the sum of its parts, leading to an unpredictable corruption of signal patterns. In olfaction, nonlinear summation is prevalent at various stages of sensory processing. Here, we investigate how the olfactory system deals with binary mixtures of odours under different brain states, using two-photon imaging of olfactory bulb (OB) output neurons. Unlike previous studies using anaesthetised animals, we found that mixture summation is more linear in awake, head-fixed mice performing an odour detection task. Furthermore, evoked responses were substantially more dampened and variable in the awake mice. Despite this, decoding analyses indicated that the data from behaving mice was able to encode mixture responses well, though the time course of decoding accuracy did not correlate with the linearity of summation. Finally, a comparison with naïve mice indicated that mixture summation was equally linear, although the ability to interpret mixture responses in terms of component responses is degraded in disengaged mice. Altogether, our results demonstrate that the mixture representation in the primary olfactory area is state-dependent, but the analytical perception may not strictly correlate with linearity in summation.