Two distinct visual microcircuits required for figure-ground discrimination in flies
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1
Howard Hughes Medical Institute/University of California Los Angeles, United States
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2
King's College London, United Kingdom
Sensory systems can receive multiple information streams within a single modality. For example, a visual stimulus can contain information about depth, motion, color, texture, and more. Within a visual scene, small objects often appear against dynamic backgrounds, and the ability to distinguish these components and respond appropriately to both is essential to many behaviors. How does the visual system parse the scene into the relevant component parts, and what is the underlying neural circuitry that processes these information streams into a neural signal that can then be used to guide behavior?
We describe two distinct circuits in the visual system that are essential for the discrimination of moving figures against moving backgrounds: one for tracking the figure embedded within a moving background, and the other for tracking the background containing an embedded figure. We used the Gal4-UAS expression system to inactivate each of two neuronal circuits that contain cells in the third optic ganglion of the adult fly, the lobula plate. The first circuit comprises a small set of cells in the mushroom body and in the lobula plate, defined by the expression of the Odd-skipped protein in adults. The second circuit comprises the well-known Horizontal System (HS) of motion-detecting neurons. Flies with each of these circuits inactivated were screened to determine the effects of circuit inactivation on their ability to discriminate figures from moving backgrounds.
Using an arena in which we measured flies’ steering responses to visual stimuli displayed on an array of LEDs, we measured spatial and temporal variation of the flies’ responses to moving figures against moving backgrounds. We found that Odd-skipped inactivated flies show a strong response to the moving background, but no response to the moving figure. By contrast, inactivating the HS circuit left flies with robust figure responses, but strongly perturbed background responses when a figure was present. Both Odd-skipped and HS inactivated flies showed responses to moving figures on static backgrounds and to panoramic motion with no figure; only their ability to discriminate figures from moving backgrounds was disrupted.
Our data implicate these two small circuits in the fly brain specifically for figure-ground discrimination. The circuits form two distinct information streams for figure motion and wide-field background motion processing. Intriguingly, these circuits are anatomically distinct from each other, such that the HS circuit resides entirely within the lobula plate, and the Odd-skipped circuit contains cells in both visual and non-visual parts of the brain. Thus, the circuits appear to be both anatomically and functionally separated, matching the computational separation of figure, ground, and figure-ground processes in the fly brain.
Keywords:
circuit inactivation,
Drosophila,
figure-ground discrimination,
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 and student poster award)
Topic:
Sensory: Vision
Citation:
Fox
JL,
Kelley
RG,
Aptekar
JW,
Larsen
C and
Frye
MA
(2012). Two distinct visual microcircuits required for figure-ground discrimination in flies.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00208
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Received:
29 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Jessica L Fox, Howard Hughes Medical Institute/University of California Los Angeles, Los Angeles, CA, 90095, United States, jlf88@case.edu