INM-6 Seminar: Talk by Aditya Gilra

National Centre for Biological Sciences, Bangalore, India

Connectivity and roles of interneurons in an olfactory bulb microcircuit model

Stimulus encoding by primary sensory brain areas provides a data-rich context for understanding their circuit mechanisms. The vertebrate olfactory bulb is an input area having unusual two-layer dendro-dendritic connections whose roles in odor coding are unclear. To probe these roles, I will present a detailed compartmental model of the rat olfactory bulb, built with Prof Upinder Bhalla (NCBS), that synthesizes a wide range of experimental observations on bulbar physiology and response dynamics. Our model predicts sparse, long-range, asymmetrical and differential inhibition between bulbar principal neurons namely mitral cells, mediated by their lateral dendrites activating deep-layer inhibitory interneurons (granule cells). These connections are sufficient and possibly necessary to decorrelate the respiratory-phases of odor responses of sister mitral cells, as observed (Dhawale, et al. 2010). To replicate observed linear summation of odor responses (Gupta and Bhalla, in revision), we predict that superficial layer interneurons (periglomerular cells) linearize the mitral cell input-output transformation, unlike previous models of contrast enhancement.

While proposing these computational roles for the two most numerous classes of bulbar interneurons, I will also discuss their implications for odor coding, and compare and contrast the roles of inhibition in olfaction versus vision and audition. Further, I will present a preliminary simplified model to study what plasticity rules might give rise to our predicted inhibition between mitral cells.