Lifetime sparseness (SL), which is independent of detection threshold, was calculated as (1 – {[SNj rj/N]2/SNj [rj2/N])/(1 – 1/N), where rj was the response of the neuron to odorant

j (charge transfer) and N was the total number of odors (Willmore and Tolhurst, 2001). We are grateful to M. Scanziani for helpful comments and P. Abelkop for technical assistance. Supported by R01DC04682 (J.S.I.) and 5F31DC009366 (C.P.). “
“Sensory information is transmitted to the brain, EGFR inhibitor where it is processed to create an internal representation of the external world. In vision and touch, information central to perception is ordered in space in the external world, and this order is maintained from the peripheral Selleck SCR7 sense organs to the cortex. The quality of an odor, however, does not exhibit a discernible spatial order in the physical world, and this poses the question of how odors are represented in the brain. Olfactory perception is initiated by the recognition of odorant molecules by a large repertoire of receptors in the olfactory sensory epithelium (Buck and Axel, 1991). Individual olfactory neurons

express one of approximately 1,000 receptors, and each receptor interacts with multiple odorants (Chess et al., 1994 and Malnic et al., 1999). Neurons expressing a given receptor project with precision to two spatially invariant glomeruli in the olfactory bulb (Mombaerts et al., 1996). Thus, the randomly distributed population of neurons activated by an odorant in the olfactory epithelium is consolidated into a discrete stereotyped map of glomerular activity in the olfactory bulb (Bozza et al., 2004, Meister and Bonhoeffer, 2001, Rubin and Katz, click here 1999 and Uchida et al., 2000). This highly ordered map of spatially

invariant glomeruli must then be integrated and transformed in higher olfactory centers to encode the synthetic features of odors. Mitral and tufted cells each extend an apical dendrite into a single glomerulus and send axons to several telencephalic areas, including significant input to the piriform cortex. Anatomic tracing reveals that axons from individual glomeruli project diffusely to the piriform without apparent spatial order (Ghosh et al., 2011, Miyamichi et al., 2011 and Sosulski et al., 2011). Electrophysiological (Rennaker et al., 2007 and Poo and Isaacson, 2009) and optical imaging (Stettler and Axel, 2009) experiments reveal that individual odorants activate sparse subpopulations of neurons distributed across the piriform without spatial preference. These data are in accordance with a model in which piriform neurons receive convergent input from random collections of glomeruli (Davison and Ehlers, 2011 and Stettler and Axel, 2009).