Fig. 7. Correlation analysis of fractional anisotropy values and several measures of freezing.

Linear regressions of fractional anisotropy values for the regions of interest shown in Fig. 2 were performed in relation to three assays of trace and delay fear conditioning performed 24 hours after the initial conditioning procedure: contextual freezing (to the training context), preCue freezing (in the novel context), and normalized freezing to cue presentation in the novel context ((Cue-preCue) / preCue). The r² value indicating the relative variability (%) for each regression accounted for by the regression function is noted in each panel. A moderately strong correlation was found for contextual freezing and fractional anisotropy in the lateral corpus callosum (r=0.603, r²=0.364, p=0.0004). The correlation was statistically significant according to a Z test (p<0.05, N=29, power: 0.95). The relationship of contextual freezing and fractional anisotropy in the medial corpus callosum was statistically significant (p=0.01, N=29, power: 0.728), but of low strength (r= 0.464, r²=0.215). Fractional anisotropy and normalized cue freezing in the medial corpus callosum was also statistically significant (r=0.489, r²=0.239, p=0.028, power: 0.78, N=29), and of low strength.