Speed sensitive excitation shapes the tuning of a collision-detecting neuron

Abstract

Event Abstract Back to Event Speed sensitive excitation shapes the tuning of a collision-detecting neuron Motion detection, an ubiquitous computation performed by visual systems, is used to guide a range of vital behaviors, including escape from threats. The Lobula Giant Movement Detector (LGMD), an identified locust neuron in a neural pathway important for escape responses, has been found to be sensitive to stimulus speed but only weakly directionally selective. Both speed sensitivity and direction selectivity together are hallmarks of motion detection, thus we are interested, in this system, in how speed sensitivity alone is generated. We investigated a mechanism that relies solely upon the activation time-course of peripheral receptors as a speed signal by recording intracellularly at several stages along the visual processing pathway. We found that photoreceptor responses carry information about the speed of a moving edge in the slope their of membrane potential deflections, and that these responses can be well mimicked by stationary luminance changes of varying rate at single facets. Immediately post-synaptic to photoreceptors, large monopolar cells (LMCs) appear to transform variation of response slope to variation in response magnitude and timing, consistent with a high pass filtering of photoreceptor responses. LGMD responses to the same stimuli showed similar modulation in both magnitude and timing, showing that the motion speed sensitivity of the LGMD at least partially arises from changes in activation speed of individual photoreceptors. Since the LGMD integrates input originating from a large number of facets on the compound eye (~7,500), we are building a model to extrapolate from the modulation observed in single facet inputs to the magnitude and timing of excitation received from the population of inputs during more complex visual stimuli. We further investigated if these single facet speed signals could help tune the neuron to certain classes of stimuli. Looming stimuli, generated by objects approaching on a collision-course with the animal, most robustly activate the LGMD. Since both angular speed and the rate of luminance change at single facets increase during such stimuli, the dependence of latency on luminance change rate could help tune the LGMD to looming stimuli by synchronizing the excitatory input into the cell. We tested this idea by presenting pseudo-looming stimuli that excited exactly 45 targeted facets (~9x45°) in a precise spatio-temporal pattern that was either consistent with a looming stimulus edge or temporally shuffled to redistribute the speeds experienced by individual facets. We find that the pseudo-looming stimuli evoked tightly clustered spike responses, resulting in high instantaneous firing rates. The shuffled stimuli, however, evoked lower peak firing rates but often evoked similar numbers of spikes. These results indicate that motion speed dependence imparted by the activation rate of photoreceptors plays a role in tuning the LGMD to looming stimuli. Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009. Presentation Type: Poster Presentation Topic: Poster Presentations Citation: (2009). Speed sensitive excitation shapes the tuning of a collision-detecting neuron. Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.159 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: 03 Feb 2009; Published Online: 03 Feb 2009. 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 Google Google Scholar PubMed 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.