1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

273 Poster Central Olfaction and Chemical EcologyPATTERN RECOGNITION FOR OPTICAL MICROBEADARRAYS WITH A NEUROMORPHIC MODEL OF THEOLFACTORY BULBRaman B. 1 , Kotseroglou T. 2 , Lebl M. 2 , Clark L. 2 , Gutierrez-Osuna R. 11 Computer Science, Texas A&M University, College Station, TX;2 Illumina, Inc., San Diego, CAWe present a biologically-inspired approach for sensor-basedmachine olfaction that combines a prototype chemical detection systembased on microbead array technology with a computational model ofsignal processing in the olfactory bulb. The sensor array containshundreds of microbeads coated with solvatochromic dyes adsorbed in,or covalently attached on, the matrix of various microspheres. Whenexposed to odors, each bead sensor responds with intensity changes,spectral shifts and time-dependent variations associated with thefluorescent sensors. The microbead array responses are subsequentlyprocessed using a computational model that captures two key functionsin the early olfactory pathway: chemotopic convergence of receptorneurons onto glomeruli, and center on-off surround lateral interactionsmediated by granule cells. The first circuit, based on Kohonen selforganizingmaps, is used to perform dimensionality reduction,transforming the high-dimensional microbead array response into anorganized spatial pattern (i.e., an odor image). The second circuit,based on Grossberg´s additive model, is used to enhance the contrast ofthese spatial patterns, improving the separability of odors. The model isvalidated on an experimental dataset containing the response of a largearray of microbead sensors to five different analytes. Our resultsindicate that the model is able to improve the separability between odorpatterns compared to that available at the receptor or glomerular levels.274 Poster Central Olfaction and Chemical EcologyMICROELECTRODE ARRAY ANALYSIS OF ODORANT-EVOKED SPATIAL ACTIVITY PATTERNS IN PIRIFORMCORTEXRennaker R. 1 , Ruyle A. 1 , Chen C.F. 2 , Wilson D.A. 2 1 Aerospace andMechanical Engineering, University of Oklahoma, Norman, OK;2 Zoology, University of Oklahoma, Norman, OKMost sensory cortices incorporate a spatial dimension in the encodingof stimulus identity, resulting for example, in retinotopic, somatotopicand tonotopic patterns of cortical evoked activity. While a form ofodotopic patterning exists in the olfactory bulb, the evidence for spatialencoding of odorant identity in the piriform cortex is less clear (cf. Zouet al., 2005 and Illig & Haberly, 2003). Here, we used simultaneous unitrecordings across large regions of anterior piriform cortex (aPCX) tofurther examine cortical spatial odorant coding. Simultaneousrecordings of single- and multi-unit activity across large regions ofaPCX were performed using fixed microelectrode arrays of 6-8electrodes nominally spaced at 250-500µ apart, and/or extraction ofmultiple single-units recorded from a single microelectrode in urethaneanesthetizedrats. Spontaneous activity, phase locking to respiration,and odorant-evoked activity were analyzed. Odorants included avariety of monomolecular esters, and more complex lemon andpeppermint. Analyses of both small (units near a single electrode) andlarge scale (1-2 mm) spatial patterns were performed. Initial resultssuggest" (1) An individual odorant can activate widely spaced neuronsthroughout the aPCX, and conversely nearby neurons may not respondto the same odorants. (2) Highly volatile (more intense) odorantsactivate larger regions of aPCX, perhaps through caudal expansion.Additional analyses of both spatial and temporal patterning on smalland large scales will be presented. Funded by a grant from NIDCD.275 Poster Central Olfaction and Chemical EcologyOLFACTORY EXPERIENCE DE-CORRELATES ENCODINGOF MIXTURES FROM COMPONENTS IN RAT PIRIFORMCORTEXKadohisa M. 1 , Wilson D.A. 1 1 Zoology, University of Oklahoma,Norman, OKOlfactory system encoding of odors has been hypothesized to besimilar to visual object encoding. Perceptual odor objects arehypothesized to be synthesized by central circuits through experience.We tested whether experience with an odor mixture would enhance thedistinctiveness of cortical coding of the mixture compared to itscomponents. Rats were trained in a Go, No-Go odor discrimination taskwhere the S+ was a mixture of acetic acid, limonene and eugenol. S-odorants were the individual components or clean air. After reachingbehavioral performance criterion, rats were urethane-anesthetized andsingle-unit recordings made from anterior piriform cortex. Odor naïverats served as controls. Responses to the mixture and components, aswell as the novel odor isoamyl acetate were analyzed. The proportion ofodor responsive cells, odor response magnitude, and correlationanalyses of population odor responses were determined. The resultssuggest that odor experience reduces average aPCX odor-evokedresponse magnitude to all odorants tested, similar to results reported forthe olfactory bulb (Buonviso & Chaput, 2000). Importantly, odorexperience produced a significant de-correlation between corticalresponses to the mixture and its individual components. Responsecorrelations within pairs of the components were either unchanged orenhanced. These results suggest that cortical encoding of the mixturebecomes more distinct from its components through experience,perhaps contributing to reported experiential effects on mixtureperception and impaired ability to identify components within mixtures.Supported by NIDCD.276 Poster Central Olfaction and Chemical EcologyELECTROPHYSIOLOGICAL, BEHAVIORAL ANDCOMPUTATIONAL INVESTIGATION OF THE FUNCTIONALROLE OF SYNAPTIC ADAPTATION IN OLFACTORYCORTEXLinster C. 1 , Kadohisa M. 2 , Wilson D.A. 2 1 Cornell University, Ithaca,NY; 2 Zoology, University of Oklahoma, Norman, OKSegmentation of target odorants from background odorants is afundamental computational requirement for the olfactory system.Recent data from our lab (DAW) have shown that odor specificadaptation in piriform neurons, mediated at least partially by synapticadaptation between the olfactory bulb outputs and piriform cortexpyramidal cells, may provide an ideal mechanism for odor-backgroundsegmentation. This rapid synaptic adaptation acts as a high-pass filter toenhance cortical responsivity to changing stimuli, while reducingresponsivity to static, potentially background stimuli. Interestingly, theadaptation observed at the level of pyramidal cell is very odor specific,while that observed at the synaptic level is specific only to certain odorfeatures.Using previously developed computational models of theolfactory system (CL), we here show how synaptic plasticity andassociative memory function within piriform cortex interacts withsynaptic adaptation at the olfactory bulb input to create odor specificadaptation, and in turn contribute to background segmentation. In thecomputational model, we also test how known physiological effects ofacetylcholine in piriform cortex contribute to the cholinergicmodulation of this odor specific adaptation. Supported by NSF grant#0338981 to CL and DAW69