The piriform cortex (PCx) receives direct input from the olfactory bulb (OB) and is the brain's main station for odor recognition and memory. The transformation of the odor code from OB to PCx is profound: mitral and tufted cells in olfactory glomeruli respond to individual odorant molecules, whereas pyramidal neurons (PNs) in the PCx responds to multiple, apparently random combinations of activated glomeruli. How these ‘discontinuous’ receptive fields are formed from OB inputs remains unknown. Counter to the prevailing view that olfactory PNs sum their inputs passively, we show for the first time that NMDA spikes within individual dendrites can both amplify OB inputs and impose combination selectivity upon them, while their ability to compartmentalize voltage signals allows different dendrites to represent different odorant combinations. Thus, the 2-layer integrative behavior of olfactory PN dendrites provides a parsimonious account for the nonlinear remapping of the odor code from bulb to cortex.

19The piriform cortex (PCx) receives direct input from the olfactory bulb (OB) and is the 20 brain's main station for odor recognition and memory. The transformation of the odor 21 code from OB to PCx is profound: mitral and tufted cells in olfactory glomeruli respond to 22 individual odorant molecules, whereas pyramidal neurons (PNs) in the PCx responds to 23 multiple, apparently random combinations of activated glomeruli. How these 24 "discontinuous" receptive fields are formed from OB inputs remains unknown. Counter to 25 the prevailing view that olfactory PNs sum their inputs passively, we show for the first 26 time that NMDA spikes within individual dendrites can both amplify OB inputs and impose 27 combination selectivity upon them, while their ability to compartmentalize voltage signals 28 allows different dendrites to represent different odorant combinations. Thus, the 2-layer 29 integrative behavior of olfactory PN dendrites provides a parsimonious account for the 30 nonlinear remapping of the odor code from bulb to cortex.

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