Amygdala and hippocampus volumetry and diffusivity in relation to dreaming

Abstract

Microstructural analyses by MRI brain scans and by DTI analysis of MR images were used to investigate the possible relationship between deep gray matter structures (amygdala and hippocampus) and dreaming in healthy subjects. Thirty-four subjects ranging in age 20s to 70s underwent to a MRI protocol for the assessment of volume and mean diffusivity (MD) in the amygdala and hippocampus and were asked to fill out a dream diary via audiotape recording upon morning awakening for two weeks. Multiple regression analyses evaluated the relationships between anatomical measures and quantitative and qualitative measures of the reported dreams. The main result points to a dissociation between some quantitative and qualitative aspects of dream reports. While the mean number of dreams recalled per day did not show any significant relationship with the neuroanatomical measures, significant associations with some qualitative features of the recalled dreams (emotional load, bizarreness, and vividness) and, to some extent, with the length of dream reports were observed. Particularly, a higher MD of the left amygdala, reflecting a decreased microstructural integrity, was associated with shorter dream reports and lower scores on emotional load. Bizarreness of dream reports was negatively correlated with the left amygdala volume and positively correlated with the right amygdala MD. Some specific, although weaker, relationships were also found between bizarreness and hippocampal measures. These findings indicate some direct relationships between volumetric and ultrastructural measures of the hippocampus-amygdala complex and specific qualitative features of dreaming.

Figure 1

Pie graphs of the relative percentages of variance (R2) explained by the anatomical measures (both volumes and mean diffusivity) of hippocampus and amygdala entering in the multiple regression equations, which considered each measure of dream recall as the dependent variable (TWC, EL, B, and VV). Each pie graph expresses the components of the total variance (100%) explained by the anatomical measures and residuals. TWC = total word count, EL = emotional load, B = bizarreness, VV = visual vividness, LH = left hippocampus, RH = right hippocampus, LA = left amygdala, RA = right amygdala. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Figure 2

Scatterplots of the partial correlations between the anatomical measures (both volumes and mean diffusivity) of hippocampus and amygdala significantly entering in the regression equation (ordinate) and the considered measures of dream recall (abscissa). TWC, total word count; EL, emotional load; B, bizarreness; VV, visual vividness; R, right; L, left; Vol, volume; MD, mean diffusivity. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]