Statistical comparisons of the background spike-activity and magnitude of spike-responses between two sets of data were made using non-parametric tests. Using Mann-Whitney U test, for each cell, comparisons were made between successive control runs, control vs. PTV cooled runs, control vs. PTV rewarmed runs and PTV cooled vs. PTV rewarmed runs (Siegel, 1956). For comparisons of activities of groups of cells, we used Wilcoxon pair-matched signed-rank (referred to as Wilcoxon test; Siegel, 1956). In all comparisons a P value of the difference between two sets of data was ≤0.05 at the two-tailed criterion was considered to be significant. The ±values in the text are the standard deviations. In the Figures, bars indicate the standard error of the mean (SEM).