Abnormal functional brain asymmetry in depression: evidence of biologic commonality between major depression and dysthymia

Abstract

Prior studies have found abnormalities of functional brain asymmetry in patients having a major depressive disorder (MDD). This study aimed to replicate findings of reduced right hemisphere advantage for perceiving dichotic complex tones in depressed patients, and to determine whether patients having "pure" dysthymia show the same abnormality of perceptual asymmetry as MDD. It also examined gender differences in lateralization, and the extent to which abnormalities of perceptual asymmetry in depressed patients are dependent on gender. Unmedicated patients having either a MDD (n=96) or "pure" dysthymic disorder (n=42) and healthy controls (n=114) were tested on dichotic fused-words and complex-tone tests. Patient and control groups differed in right hemisphere advantage for complex tones, but not left hemisphere advantage for words. Reduced right hemisphere advantage for tones was equally present in MDD and dysthymia, but was more evident among depressed men than depressed women. Also, healthy men had greater hemispheric asymmetry than healthy women for both words and tones, whereas this gender difference was not seen for depressed patients. Dysthymia and MDD share a common abnormality of hemispheric asymmetry for dichotic listening.

Figure 1

Mean perceptual asymmetry scores and standard errors on the fused-words and complex tones tests for men and women having a depressive disorder and healthy controls. Perceptual asymmetry score= 100 (right−left)/(right +left), based on the number of correct responses for right and left ear presentations. Scores greater than zero indicate a left hemisphere (right ear) advantage; scores less than zero indicate a right hemisphere (left ear) advantage.

Figure 2

Mean perceptual asymmetry scores and standard errors on the fused-words and complex tones tests for men and women having a major depressive disorder (MDD) or dysthymic disorder. Perceptual asymmetry score= 100 (right−left)/(right +left), based on the number of correct responses for right and left ear presentations. Scores greater than zero indicate a left hemisphere (right ear) advantage; scores less than zero indicate a right hemisphere (left ear) advantage.