Event Abstract Back to Event Sparse coding of natural stimuli in the midbrain Maurice J. Chacron1* 1 McGill University, Department of Physiology, Canada Sparse neural codes (i.e. codes in which neurons respond selectively to few sensory stimuli) have been observed widely across animal taxa including the human hippocampus, monkey visual cortex, locust olfactory system, and songbird HVC. Theoretical studies suggest that the generation of sparse neural codes critically depends on non-linear mechanisms. Systems with easily characterized natural stimuli and anatomy are expected to yield significant insight into the nature of these non-linear mechanisms. Weakly electric fish provide an attractive model system for studying sparse coding due to their well-characterized anatomy and physiology. We recorded from neurons located within the midbrain Torus Semicircularis (TS, equivalent to the inferior Colliculus) using the patch clamp technique in vivo. We used transient natural communication stimuli called chirps that must be distinguished from a background stimulus. We found that some TS neurons fired either a single action potential (type A) or a burst of action potentials (type B) only in response to the chirp and not to the background. In contrast, afferent neurons have been shown to respond to both the background and the chirp. The TS neurons thus provide a neural correlate of segregating a transient signal from a background. Most surprisingly, some neurons were able to distinguish between background and chirp even when the two stimuli had similar temporal frequency content. We used a combination of mathematical modeling and in vivo manipulations of neural activity via pharmacology and current injection to reveal the mechanisms that make TS neurons selective for chirp stimuli. We found that, in type A neurons, the background caused a hyperpolarization in the membrane potential via shunting inhibition below the spiking threshold. The increased membrane conductance promoted spiking in response to coincident activity elicited by the chirp stimulus and activation of high-threshold potassium channels prevents further spiking in response to the chirp. In contrast, we found that the mechanism by which type B neurons selectively responded to chirps involved integration of input from both ON-type and OFF-type afferent neurons. These two neuron types are shown to be approximately out of phase in their linear responses to the background but approximately in phase in their nonlinear responses to the chirp. Simple integration of both of these inputs by TS neurons is therefore sufficient to explain why they only respond to the chirp. These results show a mechanism by which neurons can segregate streams of information and may have applications to other systems such as detecting transients occurring over a background in both the visual and auditory systems. Conference: Computational and Systems Neuroscience 2010, Salt Lake City, UT, United States, 25 Feb - 2 Mar, 2010. Presentation Type: Poster Presentation Topic: Poster session III Citation: Chacron MJ (2010). Sparse coding of natural stimuli in the midbrain. Front. Neurosci. Conference Abstract: Computational and Systems Neuroscience 2010. doi: 10.3389/conf.fnins.2010.03.00279 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 Mar 2010; Published Online: 05 Mar 2010. * Correspondence: Maurice J Chacron, McGill University, Department of Physiology, Montréal, Canada, maurice.chacron@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Maurice J Chacron Google Maurice J Chacron Google Scholar Maurice J Chacron PubMed Maurice J Chacron Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.