Figure 1.
Training and testing protocol.
Mice with no prior experience with the water maze were given two training trials in different arms of the water maze with the submerged platform in the same relative alignment to the magnetic field (A & B). In this example, the mouse is being trained to orient to magnetic south. For testing the following morning, the submerged platform was removed (C). The mice were released individually from a central release device (Figure S1) and had free access to all four arms of the maze. Magnetic field alignment was changed between trials, and data pooled across testing groups, so an equal number of mice were tested in each of the four magnetic field alignments, i.e., magnetic North (mN) at geographic North, East, South or West; each mouse tested only once. Orientation direction was calculated by the tracking software as the vector sum of the times spent in the four arms during the 60 sec testing trial (D).
Figure 2.
C57BL/6 mice rapidly learn the magnetic direction of a submerged platform in the plus water maze (data in Table S2).
Directional responses from mice given two training trails in the late afternoon (Figure 1A & B), and then tested the following morning (Figure 1C). A) The distribution of topographic bearings, i.e., deviations from the north arm of the maze (topN), was indistinguishable from random (p > 0.10, Rayleigh test). B) The same was true of the distribution of magnetic bearings, i.e., deviations from the alignment of magnetic north in testing (magN). C) In contrast, the distribution of bearings relative to the trained magnetic direction (black triangle) was non-randomly distributed, and the 95% confidence interval for the mean vector bearing contained the trained direction. Each data point is the directional response of a single mouse tested in one of the four magnetic field alignments (see Methods & Methods). Arrow in the center of (C) is the mean vector for distributions of bearings that are non-randomly distributed. The length of the arrow is proportional to the mean vector length (r), a measure of the clustering of bearings ranging from 0 to 1; radius of the circle corresponds to r = 1. Dashed lines show the 95% confidence interval for the mean vector bearing [52]. ‘n.s.’- not significant (p > 0.10; Rayleigh Test).
Figure 3.
Replication of learned response (data in Table S3).
A) The distribution of topographic bearings was indistinguishable from random (p > 0.10, Rayleigh test). B) The distributions of magnetic bearings from north- and south-trained mice were significantly different (p < 0.02, U2=0.253 Watson U2 test). Due to the unequal sample sizes (Table S3), however, these responses did not cancel out and the overall distribution of magnetic bearings was non-randomly distributed. C) The distribution of bearings relative to the trained magnetic direction (black triangle) was non-randomly distributed, and the 95% confidence interval for the mean vector bearing contained the trained direction.