The biochemistry of dysfunctional emotions: proton MR spectroscopic findings in major depressive disorder

Key neural systems involved in the processing and communication of emotions are impaired in patients with major depressive disorder (MDD). Emotional and behavioral symptoms are thought to be caused by damage or dysfunction in specific areas of the brain that are responsible for directing attention, motivating behavior, and learning the significance of environmental stimuli. Functional brain studies with positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) give support for functional abnormalities in MDD that are predominantly located in areas known to play an important role in the communication and processing of emotions. Disturbances in emotional processing as they are observed in MDD, if any, have very subtle morphometrical brain correlates. With proton magnetic resonance spectroscopy (H-1 MRS), brain metabolites can be measured noninvasively in vivo, thus furthering the understanding of the effects of changes in neurotransmitters within the brain. The current literature on H-1 MRS studies in MDD is small with a large diversity of MRS methods applied, brain regions studied, and metabolite changes found. Nevertheless, there is strong evidence that changes in neurometabolite concentrations in MDD occur within brain regions, which are involved in the processing and communication of emotions that can be monitored by H-1 MRS. This review summarizes the literature about biochemical changes quantified via H-1 MRS in MDD patients in brain regions that play an important role for the communication and processing of emotions.