Zeitschrift für Depression und Angst
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Hedonic Tone: A Bridge between the Psychobiology of Depression and its Comorbidities

Sternat T, Lodzinski A and Katzman MA

Treatment of Major Depressive Disorder (MDD), in many cases, offers less than optimal results, resulting in loss of function and remaining impairment. This is partially explained by the high prevalence of comorbid psychiatric illnesses that share common features, likely resulting in less than adequate treatment outcomes among patients receiving traditional psychiatric treatment. The term anhedonia does not sufficiently capture the complex and multifaceted reward-associated deficits seen in neuropsychiatric disorders. Deficits in reward-related processes can lead to behaviors that may appear to be the loss of interest or pleasure, and may preclude an individual from engaging in goal-oriented action. Investigators have identified a lifelong poor hedonic responsiveness, manifested as altered sensitivity to reinforcement, in patients with Attention Deficit Hyperactivity Disorder (ADHD), and suggest it as a common endophenotype for depression and the inattentive symptoms of ADHD. Research into the neurobiology of anhedonia has focused on the centers in the brain related to reward and motivation, and has identified the dopaminergic and associated circuits as playing a key role. Studies have shown that lesions in reward and motivation circuits result in anhedonia, and that decreased activation in the medial frontal cortex is believed to underlie abnormal positive affect processing in patients. In this paper, we propose that a specific phenotype of depression, which is more likely to be described as “treatment resistant” is associated with high risk of comorbidity with dysthymia, ADHD, and substance abuse, specifically cocaine abuse. We believe these patients experience a chronically lower hedonic tone that results in chronic anhedonia (as opposed to acute state anhedonia noted in a major depressive episode) related to unique pathophysiology and requiring treatment of the dopaminergic deficiency that characterizes its unique collection of comorbidities.