Program#/Poster#: 665.11/KK29 Title: Bottom-up stimulus selection in the cholinergic isthmic nucleus in the Barn Owl Location: Hall A-C Presentation Time: Tuesday, Nov 18, 2008, 3:00 PM - 4:00 PM Authors: *A. ASADOLLAHI, E. KNUDSEN; Neurobio., Stanford Univ., Stanford, CA Abstract: Stimulus selection is a fundamental component of attention. Bottom-up sensory competition plays an important role in stimulus selection. We studied bottom-up stimulus competition in the midbrain cholinergic nucleus isthmi pars parvocellularis (Ipc) (nucleus parabigeminus in mammals), a nucleus that interconnects reciprocally and topographically with the optic tectum (superior colliculus in mammals), a structure known to contribute to spatial attention. We recorded extracellular single and multi-unit activity of Ipc neurons to explore sensory competition in anesthetized barn owls. We presented two stimuli simultaneously to assess spatial sensory competition in this structure, one stimulus inside the receptive field “target” and the other stimulus outside the receptive field “competitor”. We recorded neuronal responses to systematically varying the target’s or the competitor’s strength while maintaining the other constant. Our results reveal strong suppressive interactions in this nucleus: stronger stimulus suppresses responses to the weaker stimulus. These suppressive effects are long distance and hold in both auditory and visual domains. In contrast auditory and visual stimuli have facilitatory interactions when they appear simultaneously at the same location in space inside the receptive field. Disclosures: A. Asadollahi, None; E. Knudsen, None. Support: NIH 1R01-DC00155-25 [Authors]. [Abstract Title]. Program No. XXX.XX. 2008 Neuroscience Meeting Planner. Washington, DC: Society for Neuroscience, 2008. Online. 2008 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.

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