Supplementary Figure 5: Reduction in DKL does not occur spontaneously. | Nature Neuroscience

Supplementary Figure 5: Reduction in DKL does not occur spontaneously.

From: Patterns across multiple memories are identified over time

Supplementary Figure 5

(a) To determine whether mice might naturally gravitate towards improved matching to the distribution used in the first set of experiments (Fig. 1), we performed a set of control experiments. Mice were trained to locate a single platform for 9 days, located at the mean of the original distribution, then probed after a 1 d or 30 d delay. Example paths from a probe 1 d and 30 d later are shown. (b) The DKL between mouse search paths and the original distribution showed a trend towards an increase at the 30 d delay (Mann-Whitney U-test: 1 d n = 11, 30 d n = 12, ranksum = 118, P = 0.41). This was in the opposite direction to the first experiments (Fig. 1d), and indicates that the reduction in DKL depended on exposure to the original platform distribution and did not emerge spontaneously. (c) Mice exhibited decreased accuracy in their memory for the single platform location after a 30 d delay, as shown by the number of platform crossings during the probe (Mann-Whitney U-test: ranksum = 169.5, P = 0.02). (d) The decrease in accuracy did not reflect an increase in the spread of their search paths, as evidenced by the lack of difference in search path entropy (t-test: t21 = 1.68, P = 0.11). Likewise, animals trained on a distribution did not show an increase in entropy after a 30 d delay (t-test 1 d vs. 30 d: t90 = 1.35, P = 0.18). (e) To determine whether the observed decrease in accuracy of a single platform memory could account for a reduced DKL over time if extrapolated to a multiple-platform memory situation, we conducted a Monte Carlo simulation. Simulated probe search path distributions were constructed using kernel density estimation with the 9 platform locations from the first set of experiments (Supplementary Fig. 1a) used as the kernel centers. The kernels were circular Gaussians with standard deviations based on the search paths of the single platform mice (σ = 19 cm). The kernel locations were randomly shuffled in space to simulate memory error. The memory error was sampled from a normal distribution with mean 0 and different standard deviations. 100 samples were drawn for each level of standard deviation, and for each sample the DKL between the simulated path and the actual platform distribution was calculated. As the standard deviation in memory error increased, the DKL also increased. Therefore, an observed change in single platform memory accuracy would not account for a drop in DKL when applied to a multi-platform situation. Data shown is mean ± s.e.m. (*: P < 0.05)

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