Generating sparse and selective third-order responses in the olfactory system of the fly

Abstract

In the antennal lobe of Drosophila, information about odors is transferred from olfactory receptor neurons (ORNs) to projection neurons (PNs), which then send axons to neurons in the lateral horn of the protocerebrum (LHNs) and to Kenyon cells (KCs) in the mushroom body. The transformation from ORN to PN responses can be described by a normalization model similar to what has been used in modeling visually responsive neurons. We study the implications of this transformation for the generation of LHN and KC responses under the hypothesis that LHN responses are highly selective and therefore suitable for driving innate behaviors, whereas KCs provide a more general sparse representation of odors suitable for forming learned behavioral associations. Our results indicate that the transformation from ORN to PN firing rates in the antennal lobe equalizes the magnitudes of and decorrelates responses to different odors through feedforward nonlinearities and lateral suppression within the circuitry of the antennal lobe, and we study how these two components affect LHN and KC responses.antennal lobe | decorrelation | lateral horn | normalization | olfaction I n the olfactory system, as in other sensory systems, signals from primary receptors are processed and transformed before being relayed to higher brain areas. In Drosophila melanogaster, olfactory receptor neurons (ORNs) located in the antennae and maxillary palps synapse onto projection neurons (PNs) within the glomeruli of the antennal lobes (Fig. S1). ORNs expressing a given receptor converge on an anatomically invariant glomerulus. PNs innervate a single glomerulus and thus receive their primary input from ORNs expressing the same olfactory receptor (1), although crossglomerular interactions mediated by interneurons are also present (2-5). The PNs send their axons to two distinct regions of the fly brain, the lateral horn and the mushroom body. By constructing models of neurons in these regions, we study the effects of the transformations arising from circuitry within the antennal lobe on the capacity of neurons in the lateral horn and the mushroom body to represent and discriminate odors.Any functional interpretation of the transformation from ORN to PN responses depends on the nature of the processing being performed by the third-order neurons that receive PN input. The lateral horn and mushroom body appear to be involved in different forms of sensory processing. The lateral horn is believed to be important in generating innate behaviors (6), including those elicited by pheromones (7). PN projections to lateral horn neurons (LHNs) are spatially stereotyped (8, 9) and clustered (10), suggesting that circuits in this region may be "hardwired" for the detection of specific odors that elicit innate behavioral responses. The mushroom body is implicated in decision making (11) and in the formation of associative memories (12, 13). Both calcium imaging (14) and electrophysiology (15) indicate that the responses of Kenyon cell (KCs) in the mushroom body are sparse, with e...

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“…4f ). As argued above, the model structure of leading-suppressive cells is probably generated by slow feedforward inhibition (Luo et al, 2010). The role of excitation and inhibition in shaping temporal filters and in decorrelating responses between cells in a population has been appreciated previously (Schmuker and Schneider, 2007;Wiechert et al, 2010;George et al, 2011).…”

Plant odour stimuli reshape pheromonal representation in neurons of the antennal lobe macroglomerular complex of a male moth

“…Heptanal-induced inhibition of the MGC neurons through the LN network might thus synchronize MGC PNs and provide a more coincident input to upstream neurons in the mushroom bodies. There, the Kenyon cells are thought to need simultaneous input from several PNs, because they have been described as sparse coding cells in different insect species (Demmer and Kloppenburg, 2009;Ito et al, 2008;Jortner et al, 2007;Luo et al, 2010;Perez-Orive et al, 2002;Szyszka et al, 2005;Wang et al, 2004).…”

Synapsin is required to “boost” memory strength for highly salient events

“…In terms of physiology, both the level of activity and the combination of activated mushroom body Kenyon cells varies, albeit slightly, with odor concentration. It will be interesting to see whether and which parameter set of biologically plausible mushroom body models (Luo et al 2010, Nehrkorn et al 2015 can account for both the high memory scores found when using a high odor concentration in training and in testing (Fig. 3A,B; Mishra et al 2013, loc.…”