A computational framework for temporal sharpening of stimulus input in the olfactory system

Abstract

Zak JD. A computational framework for temporal sharpening of stimulus input in the olfactory system. J Neurophysiol 115: 1749-1751, 2016. First published September 2, 2015; doi:10.1152/jn.00785.2015.-The olfactory bulb glomerulus is a dense amalgamation of many unique and interconnected cell types. The mechanisms by which these neurons transform incoming information from the sensory periphery have been extensively studied but often with conflicting findings. A recent study by Carey et al. (J Neurophysiol 113: 3112-3129, 2015) details the computational framework for parallel modes of temporal refinement of stimulus input to the olfactory system mediated by local neurons within individual glomeruli. mitral cells; modeling; olfactory bulb; sensory systems A KEY FEATURE OF THE OLFACTORY SYSTEM is its ability to extract stimulus information in a temporally phasic manner that is constrained by the respiratory cycle. This arrangement allows for independent sampling of the stimulus environment with each new sniff. Because of the sinusoidal nature of olfactory input, it is important that the activity of bulbar output neurons is tightly coupled with the respiration cycle to avoid crosscontamination between sampling events. Indeed, experimental evidence suggests that the activity of olfactory receptor neurons (ORNs) far outlasts the activity of downstream olfactory bulb output neurons (mitral cells, MCs; Carey and Wachowiak 2011). How the spike output of MCs is temporally refined with respect to sensory input remains largely unresolved, but it is postulated to result from both excitatory and inhibitory signaling from local neurons that also comprise the glomerular neuropil (Hayar et al. 2004;Murphy et al. 2005;Najac et al. 2015). The mechanisms by which small groups of neurons permutate input arising from naturalistic stimuli is an important component of stimulus feature extraction (Vizcay et al. 2015) and have broad applications to systems neuroscience.In a recent publication, Carey et al. (2015) explored a series of model olfactory bulb glomerulus circuit configurations with respect to sensory input and temporal refinement of MC spike output. A major goal of this study was to better understand the cellular elements and mechanisms that transform incoming sensory signals within the earliest stages of the olfactory system. The series of models implemented within this study were highly constrained by experimental measurements, and results were compared with experimentally observed in vivo MC spike responses in rats, resultant from naturalistic odor stimuli. The primary findings of these studies reveal that local, glomerulus-specific, GABAergic and glutamatergic neurons are independently capable of temporally sharpening MC spike output. Furthermore, within the model environment, a more precise match to experimentally observed data is achieved when inhibitory and excitatory neurons operate in parallel. These findings provide novel insight into information transfer in the olfactory system that may prove to have commonalities a...