Reduced activation of posterior cingulate cortex during imagery in subjects with high degrees of alexithymia: a functional magnetic resonance imaging study.

BACKGROUND: Although the brain areas involved in imagery have been reported, the neural bases of individual differences in imagery remain to be elucidated. People with high degrees of alexithymia (HDA) are known to have constricted imaginal capacities. The purpose of this study was to investigate neural correlates of imagery disturbance in subjects with HDA.
METHODS: A functional magnetic resonance imaging (fMRI) study was undertaken in 10 subjects with HDA and 10 subjects with low degrees of alexithymia (LDA), who were selected according to their scores on the 20-item Toronto Alexithymia Scale (TAS-20). The two groups' regional cerebral activation was compared during various imagery conditions. In those conditions, the subjects imaged a past happy (PH) event, a past sad (PS) event, a past neutral (PN) event, a future happy (FH) event, a future sad (FS) event, and a future neutral (FN) event. The activation levels during these conditions were compared with those during a rest condition (REST).
RESULTS: The t tests showed that the mean subjective ratings of both the vividness of the imagery and the intensity of emotion during the imagery were higher in the subjects with LDA than in those with HDA for the PS and FS imagery conditions. On the other hand, relative to the LDA group, the HDA group showed significantly less activation in the posterior cingulate cortex (PCC) during the PH and FH imagery conditions compared with REST and during the FH imagery condition compared with the FN imagery condition.
CONCLUSION: The present results suggest an association between an HDA and reduced activation of the PCC during happy imagery. Given the function of this brain region, these results might be related to a dysfunction of episodic memory retrieval during happy imagery in subjects with HDA.