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First published online August 25, 2003

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A hydrodynamic topographic map in the midbrain of goldfish Carassius auratus

Dennis T. T. Plachta^1,2,*, Wolf Hanke¹ and Horst Bleckmann¹

¹ Institut für Zoologie, Universität Bonn, Poppelsdorfer Schloss, Bonn, Germany
² Department of Biology, University of Maryland, College Park, MO 20748, USA

View larger version (13K): [in a new window]   Fig. 1. Experimental setup. 1, experimental animal; 2, styrofoam supporting structure; 3, site of operation; 4, recording electrode(s); 5, sphere and supported rod moving the sphere either anterior to posterior (AP) or posterior to anterior (PA) along the side of the fish; 6, laser for the horizontal light sheet; 7, laser for the vertical light sheet; 8, camera for the horizontal light sheet; 9, underwater camera for the vertical light sheet; 10, water level.

View larger version (34K): [in a new window]   Fig. 3. (A-C) Examples of the responses of a TS1 unit (A), a highly directional TS2 unit (B), and a TS3 unit (C) to a sphere moving from anterior-to-posterior (left) or from posterior-to-anterior (right). Top traces in A-C show original recordings. In each case raster plots of the responses to 10 stimulus presentations are also shown. The two vertical lines in the bottom traces indicate the positions of the trigger contacts. The fish symbol indicates size, location and orientation of the fish relative to the path of the moving sphere between trigger contacts. Note that sphere movements were made manually and were normalized to a length scale so that the trigger contacts indicate the length of the path (23.8 cm). Mean sphere velocity was 10.7 cm s-1 in A, 9.8 cm s-1 in B and 9.9 cm s-1 in C. Arrows 1-4 in the top traces of C mark the time when the PIV images shown in D were taken. Vertical scale bars, 50 µV (A), 100 µV (B,C). (D) Velocity vector plots of vertical particle motions. The flags indicate direction and velocity of water motions. The width of each image is 58 mm, the size of each interrogation area (subimage that was subjected to the correlation procedure) is 5 mmx5 mm with an overlap of less than 50%. Scale bar, 10 mm s-1.

View larger version (61K): [in a new window]   Fig. 2. Verification of a recording site in the midbrain. (A) Cresyl Violet stained transverse hemisection through the midbrain of the goldfish (right), shown as a line drawing (left). The arrow in the enlarged part of the right hemisection (B) points to the location of an electrolytic lesion. OT, optic tectum; TS, torus semicircularis; VCg, granular layer of the valvula cerebelli; VCm, molecular layer of the valvula cerebelli. Scale bar, 1 mm.

View larger version (16K): [in a new window]   Fig. 5. (A) Examples of the data obtained from two units recorded simultaneously with electrode 2 (E2, red) and electrode 3 (E3, blue). Left, responses to sphere movements in the AP direction; right in the PA direction. Top traces show original recordings. The two vertical lines in the bottom traces indicate the position of sphere start and stop trigger points. Between the two trigger points the time axis was transformed to equal the distance axis (23.8 cm). Vertical scale bars, 100 µV. (B) The position of the multi-electrode device relative to the fish midbrain surface is indicated (below). Red, E2; blue, E3. Colored circles to the left of the fish show sphere positions at times labeled 1, 2, 3 and 4 in A. Arrows indicate direction of sphere motion.

View larger version (12K): [in a new window]   Fig. 4. Lateral extent of main response areas of 48 midbrain lateral line units, including all TS2 units (above the horizontal line) and 13 TS1 units (below the horizontal line). The main response area of a unit is the sum of the sphere positions that elicited the first well-defined bursts (see text) from that unit, pooled for both sphere-run directions. Black, green and violet colours indicate rostral, intermediate and caudal response areas, respectively. As indicated in the enlarged brain drawing using the same colour code, units were recorded in the anterio-lateral (black), medio-lateral (green) and posterior-lateral (violet) TS.

View larger version (22K): [in a new window]   Fig. 6. Histograms of peristimulus distance of the neural activity of 5 unit pairs recorded simultaneously from two electrodes spaced 250 µm apart. Each histogram is based on 10 trials. Left, responses to AP motion; right, responses to PA motion. Blue, responses of units recorded with the more anterior electrode; red, responses of units recorded with the more posterior electrode. Insets on the right indicate electrode positions for each recording set relative to the midbrain surface.

View larger version (16K): [in a new window]   Fig. 7. Depth distribution of units responsive only to the moving sphere (grey) or only to the vibrating sphere (black). The depths (relative to the surface of the optic tectum) were taken from readings of the microdrives that guided the electrodes. In two cases electrode depth was not determined, hence the figure contains only 46 instead of 48 motion-sensitive cells.