JEB desktop wallpaper calendar 2016

Journal of Experimental Biology partnership with Dryad

  1. Fig. 1.

    The machine. (A) A cross section of the machine. The rat is haltered (see in more detail in B) on top of an air-cushioned (ain, air inlet) polystyrene spherical shell of 50 cm diameter and mass about 400 g. The haltering consists of a soft leather harness fastened by a hook and loop ribbon to three aluminum plates with axial joints. The haltering allows the animal to lift and lower its body, to rotate it about the yaw axis (the body orientation is measured by the angular incremental encoder, aie) and to tilt it somewhat. The animal rests with its full weight on top of the sphere. Any rotation of the sphere about the yaw axis is prevented by two wheels (w), which are supported by horizontal axes with tip bearings and which touch the sphere on its equator under 90°. The air cup is tilted by about 7° and lets the sphere swim against the wheels (w). The sphere can easily be rotated around any horizontal axis. Any rotation of the sphere is monitored by two motion detectors (HDNS2000, Agilent), which `look' on two 7 mm × 7 mm squares under 90° on the equator of the sphere. On the sphere surface a fine statistical pattern of black points is sputtered with an air brush. The signals from the motion detectors are fed to an incremental counter board implemented into the PC that controls the VR image generation. The image of the VE is projected from a DMD beamer (b) via two plane mirrors (p) from vertically below onto an angular amplification mirror (aam) (black lines indicate the limits of the illuminating light bundle). The aam is a polished rotational symmetric aluminum surface with a vertical rotation axis, which widens the elevation of the incoming light bundle by a constant factor of 39 over its whole surface (red light bundle). From the aam the light is projected onto a toroidal screen made of 24 segments of white elastic cotton. The torus acts as a horopter. The rat sees any object on the screen under the same angle as it is projected from the aam (blue light bundle). The screen covers the visual field of the rat from 20° below until 60° above the horizon and 360° of azimuth (green light bundle).

  2. Fig. 2.

    Photographs of the machine. (A) The machine in working configuration, screen lowered. w, one of two wheels preventing the sphere from rotation about the vertical axis. (In the lower left corner the small sister of the 50 cm sphere can be seen, designed for insect work.) (B) Machine with screen lifted. b, DDV 1800 (Liesegang) beamer; c, two small video `finger' cameras to control the rat's behaviour within the screen; md, motion detector. In the background the air support tube and the crank handle to lift and lower the screen are visible. The photo is a portrait of the late Sigmund Exner, 1846–1926 (physiologist at Vienna). (C) The optics in more detail. aam, angular amplification mirror; p, two plane mirrors. The beamer and its shielded output is seen on top. (D) The haltering of the rat. aie, angular incremental encoder. The light gray leather harness attached to aluminum sheets with axial joints is seen. The thin brass tube ending at the rat's mouth is always rotated with the haltering and delivers sugar water drops via a PC-controlled valve. For details, see text.

  3. Fig. 3.

    Results of Experiment 1 in a real environment. (A) Only the area under the white cylinder was baited. Shown are the percentages of visits under each cylinder (shading of bar represents the colour of the cylinders in the experiments). Animals learned the task in four sessions, with three runs per day and per session. Animals practically stopped visiting unbaited cylinders (one-way RM-ANOVA, F3,11=8.34, P<0.0001; post-hoc Bonferroni multiple comparison test, *P<0.01; N=6). (B) Time needed by animals to find the target area below the white cylinder was reduced over sessions (P<0.001). (C) Reversal-learning task. The black cylinder was baited. Animals learned to visit the black cylinder and practically stopped visiting the white cylinder (one-way ANOVA, F3,11=6.67, P<0.001; post-hoc Bonferroni multiple comparison test, *P<0.01, N=6). (D) Time needed by animals to visit the black cylinder was reduced over the course of the trials (P=0.002). The lines over the bars depict the significance between bars/data sets and which data set was found significant compared with which other data set in the experiments.

  4. Fig. 4.

    Experiment 2 in a virtual environment (distance between cylinders, 2 m). Entering the area under a virtual cylinder was rewarded by a sugar water drop. The cylinders had a radius of 25 cm, were 80 cm high, 2 m apart, suspended 20 cm above ground, and textured with black and white stripes. After a reward the animals had to cross an outer circle of r0=0.5 m before they could get another reward under the same cylinder. (A) The numbers of rewards (hits) per 10 min run increased over the course of 10 days (means± s.e.m., N=12 animals; one-way RM-ANOVA, F9,11=40.7, P<0.0001; post-hoc Bonferroni multiple comparison test, NS, non significant, **P<0.01; ***P<0.001; N=12). (B) The number of hits per 2 m distance increased over time (ANOVA, F9,11=22.1, P<0.0001; post-hoc test, NS, non significant; **P<0.01; ***P<0.001). The maximum number of hits achievable per 2 m was 1, animals reached a mean value of 0.76±0.024 (± s.e.m.). (C) The average trace length per 10 min increased over 10 days, i.e. the average speed of the animals. (D) The inter-individual variation of the trace length, averaged over all 10 days, versus the animal number.

  5. Fig. 5.

    Sample trajectories of day 1 (blue) and day 10 (red) for rat 9 in Experiment 2. (A) Map of virtual environment with cylinders drawn to scale. Hit cylinders are encircled by light grey discs. Starting points appear towards the top of the figure. (B) Detail of day 1 trajectory, as boxed in A. Dots mark every 30th trace sample (every 1.4 s). (C) Detail of day 10 trajectory, as boxed in A. (D) Rat average position relative to closest cylinder on day 1. (E) Histogram of body orientations on day 1 as measured using the angular incremental encoder. (F) Rat average position relative to closest cylinder on day 10. Note the much more peaked distribution, indicating that the rat spent more time in the vicinity of the cylinder than on day 1. (G) Histogram of body orientation on day 10. Note the pronounced orientation to S on day 10 compared to E, superimposed on a broadly distributed general orientation to SE. For details, see text.

  6. Fig. 7.

    Sample trajectories of day 1 (blue) and day 5 (red) for rat 9 in Experiment 3. (A) Map of virtual environment with cylinders drawn to scale. Hit cylinders are encircled by light grey discs. Starting points appear towards the top of the figure. (B) Detail of day 1 trajectory, as boxed in A. Dots mark every 30th trace sample (every 1.4 s). (C) Detail of day 5 trajectory, as boxed in A. (D) Rat average position relative to closest cylinder on day 1. (E) Histogram of body orientations on day 1 as measured using the angular incremental encoder. (F) Rat average position relative to closest cylinder on day 5. (G) Histogram of body orientation on day 5. Note the dominant orientation to ESE on day 5 compared to the orientation peak to S in day 1. For details, see text.

  7. Fig. 6.

    Experiment 3 was performed in an identical environment as Experiment 2 except the distance between columns was increased to 10 m and r0 to 2 m. (A) The numbers of rewards (hits) per 10 min run increased over the course of 5 days (ANOVA, F4,11=7.3, P<0.0001; post-hoc test, NS, non significant; *P<0.05; **P<0.01; ***P<0.001; N=12). (B) The numbers of hits per 10 m distance run increased over time (ANOVA, F4,11=5.37, P<0.002; post-hoc test, NS, non significant, *P<0.05; **P<0.01). The maximum achievable number of hits per 10 m was 1, animals reached 0.644. (C) The average trace length per 10 min increased a bit over 5 days, the animals were trained in Experiment 1. (D) The inter-individual variation of the trace length, averaged over all 5 days, versus the animal number.