The effect of stimulation time on discrimination of odor mixtures in honey bees

FERNANDEZ P; LOCATELLI F; RENNEL N; DELEO G; SMITH B

San Diego, EEUU.

Congreso; XXXVII Annual Meeting of American Society for Neurosciences (SFN),; 2007

American Society for Neurosciences

Program#/Poster#: 612.19/MM2 Title: The effect of stimulation time on discrimination of odor mixtures in honey bees Location: San Diego Convention Center: Halls B-H Presentation Start/End Time: Tuesday, Nov 06, 2007, 10:00 AM -11:00 AM Authors: P. C. FERNANDEZ, F. F. LOCATELLI, G. DELEO, N. RENNELL, *B. H. SMITH; Schl Life Sci., Arizona State Univ., Tempe, AZ Electrophysiological and imaging recordings in the insect Antennal Lobe (AL) suggest that the neural representation of an odor evolves until it reaches a steady state around 1000 ms. Discriminability of patterns for pairs of odors typically increases with time through the steady state. However, it has not yet been demonstrated in an insect that behavioral discriminability increases across the same time period. In order to test this hypothesis, we used Proboscis Extension Response (PER) conditioning in honey bees Apis mellifera to examine generalization and discrimination of different ratios of binary odor mixtures (1-hexanol: 2-octanone). First, we conditioned bees to discriminate 9:1 or 1:9 ratios (odor delivery time: 4000 ms) and then tested with a range of ratios (9:1, 7:3, 5:5, 3:7, 1:9). This learning protocol produced steep decreases in response from the reinforced (+) through the non-reinforced (-) mixture. We used calcium imaging to measure neural activity patterns evoked by the range of test ratios at the level of projection neurons in the AL. The pattern of responses showed a gradient of activation that correlates to the generalization gradient observed in the behavioral assays. Then, we conditioned bees to discriminate ratios 9:1 (+) vs. 1:9 (-) using 4 different odor delivery times (200, 500, 1000 and 2000 ms) during both training and testing. Bees are able to discriminate odorants with 200 ms pulses. Stimulus duration affected discrimination because there was a significant interaction between training and test durations. When conditioned to stimulus durations above 500 ms, responses to all test stimulus durations, including 200 ms, were significantly longer than with conditioning to 500 ms or shorter durations. Discrimination was generally poorer when test stimulus durations exceed the training duration. These results indicate that some information about stimulus length (independent of identity) is stored in the memory. Finally, we analyzed the temporal evolution of glomerular activity patterns for the ratios 1:9 and 9:1. After stimulation, each ratio showed a differential trajectory, departing from a near origin and evolving through an odor specific region. Euclidean distances showed that odors start separating by 125 ms and reach maximal separation by 500 ms. Results are, overall, consistent with a model in which temporal information is used to detect and discriminate odors. However, the results are not consistent with a simple model in which more time means better discrimination. Disclosures:  P.C. Fernandez, None; F.F. Locatelli, None; G. Deleo, None; N. Rennell, None; B.H. Smith , None. Support: NIH-NIDCD Grant DC007997 [Authors]. [Abstract Title]. Program No. XXX.XX. 2007 Neuroscience Meeting Planner. San Diego, CA: Society for Neuroscience, 2007. Online.2007 Copyright by the Society for Neuroscience all rights reserved. Permission to republish any abstract or part of any abstract in any form must be obtained in writing by SfN office prior to publication.