Bar cells: Underlying neuro-physiological mechanisms
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1
Uppsala University, Department of Neuroscience, Sweden
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2
The University of Adelade, Discipline of Physiology, Australia
As an animal moves through the world, its own movement generates widefield optic flow across the visual field that it can use for several behavioral tasks, such as maintaining a straight trajectory or avoiding obstacles. Behavioral evidence shows that many animals can also disambiguate the motion of discrete objects that move independently of the remaining visual surround from such self-generated optic flow. In the insect optic ganglia, we find neurons specialized for detecting these two types of motion: Some respond optimally to widefield optic flow whereas others are specifically tuned to the relative motion of discrete figures (Olberg, 1981).
In the dragonfly lobula there are two types of neurons tuned to the relative motion of discrete figures: Small target motion detectors (STMDs) and bar cells (O'Carroll, 1993). Whereas STMDs are tuned to small figures (Nordström, 2012), the bar cell response increases with bar height, but there is no response to the type of widefield stimuli generated during ego-motion (O'Carroll et al., 2012). Bar cells thus respond specifically to the motion of elongated, discrete figures. We here investigate the neurophysiological mechanisms that underlie this tuning.
In the vertebrate visual cortex bar sensitivity is generated by aligning output from rows of neurons with small receptive fields (simple cells). Vertebrate simple cells share several physiological properties with elementary STMDs (ESTDMs), the input elements to STMDs (Wiederman et al., 2008). To investigate whether dragonfly bar cells generate their specific sensitivity to elongated features by spatially pooling the input from a row of elementary small target tuned motion detectors, we quantify responses to key parameters involved in ESTMD tuning (Wiederman et al., 2008). We show that whereas the velocity tuning and the high gain to sub-pixel targets suggest that bar cells share input mechanisms with STMDs, other responses point to a different type of input. For example, as opposed to STMDs, bar cell responses are often contrast polarity invariant, and they respond equally well to a bar and to a single edge moving across the visual field. The neurons also show a surprisingly strong spatial summation.
Early anatomical studies of the fly optic lobes showed that the column underlying each facet is represented by up to 100 unique interneurons, leading to the suggestion that visual input is processed in many parallel streams (e.g. Fischbach and Dittrich, 1989). In support of this notion, local motion is computed differently in the inputs to SMTDs (Wiederman et al., 2008) and to the neurons coding for widefield optic flow (Hassenstein and Reichardt, 1956). Our findings that bar cells generate their specific sensitivity to discrete, elongated figures by using different visual input from the STMDs provide further evidence for the notion of parallel visual input pathways.
References
Fischbach, K. & Dittrich, A. (1989) The optic lobe of Drosophila melanogaster. Part I: A Golgi analysis of wild-type structure. Cell Tissue Res, 258, 441-475.
Hassenstein, B. & Reichardt, W. (1956) Systemtheoretische Analyse der Zeit, Reihenfolgen und Vorzeichenauswertung Bei der Bewegungsperzeption des Rüsselkafers Chlorophanus. Z Naturforsch, 11, 513-524.
Nordström, K. (2012) Neural specializations for small target detection in insects. Curr Opin Neurobiol.
O'Carroll, D.C. (1993) Feature-detecting neurons in dragonflies. Nature, 362, 541-543.
O'Carroll, D.C., Bolzon, D.M. & Nordström, K. (2012) Bar cells: a novel class of insect feature detector In: Proc. 10th International Conference of Neuroethology.
Olberg, R.M. (1981) Object- and self-movement detectors in the ventral nerve cord of the dragonfly. J Comp Physiol A, 141, 327-334.
Wiederman, S.D., Shoemaker, P.A. & O'carroll, D.C. (2008) A model for the detection of moving targets in visual clutter inspired by insect physiology. PLoS ONE, 3, e2784.
Keywords:
dragonfly,
feature detection,
motion vision
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for Participant Symposium)
Topic:
Sensory: Vision
Citation:
Nordstrom
K,
Bolzon
D and
O'Carroll
D
(2012). Bar cells: Underlying neuro-physiological mechanisms.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00279
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Received:
30 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Karin Nordstrom, Uppsala University, Department of Neuroscience, Uppsala, 75124, Sweden, Karin.Nordstrom@neuro.uu.se