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Published February 14, 2007 | Published + Supplemental Material
Journal Article Open

A Simple Connectivity Scheme for Sparse Coding in an Olfactory System

Abstract

Recent studies, using unbiased sampling of neuronal activity in vivo, indicate the existence of sparse codes in the brain. These codes are characterized by highly specific, associative (i.e., dependent on combinations of features) and often invariant neuronal responses. Sparse representations present many advantages for memory storage and are, thus, of wide interest in sensory physiology. Here, we study the statistics of connectivity in an olfactory network that contributes to the generation of such codes: Kenyon cells (KCs), the intrinsic neurons of the mushroom body (a structure involved in learning and memory in insects) receive inputs from a small population of broadly tuned principal neurons; from these inputs, KCs generate exquisitely selective responses and, thus, sparse representations. We find, surprisingly, that KCs are on average each connected to about 50% of their input population. Simple analysis indicates that such connectivity indeed maximizes the difference between input vectors to KCs and helps to explain their high specificity.

Additional Information

© 2007 Society for Neuroscience. Received Sept. 22, 2006; revised Jan. 9, 2007; accepted Jan. 10, 2007. This work was supported by the National Institute on Deafness and Other Communications Disorders, the National Science Foundation, the Gimbel Fund for Neuroscience (G.L.), and a Horowitz predoctoral fellowship from the Hebrew University (R.A.J.). We are grateful to Ofer Mazor, Vivek Jayaraman, Markus Meister, Glenn Turner, Ben Rubin, Mikko Vähäsöyrinki, Idan Segev, Gilad Jacobson, and three anonymous referees for discussions and/or critical comments, to Mike Walsh and Tim Heitzman for help with electronics, and to the Michigan Probes group for the gift of tetrodes.

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Supplemental Material - Supplementary_Information.pdf

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