April 8, 2019Neurology
Anhedonia is a diverse array of deficits in hedonic function, including reduced motivation or ability to experience pleasure. While earlier definitions of anhedonia emphasized the inability to experience pleasure, anhedonia is used by researchers to refer to reduced motivation, reduced anticipatory pleasure (wanting), reduced consummatory pleasure (liking), and deficits in reinforcement learning. In the DSM-V, anhedonia is a component of depressive disorders, substance related disorders, psychotic disorders, and personality disorders, where it is defined by either a reduced ability to experience pleasure, or a diminished interest in engaging in pleasurable activities.
Anhedonia is a risk factor for, and a symptom of, certain mental disorders and is predictive of illness severity, resistance to treatment, and suicide risk. While researchers have sought to understand the brain mechanisms that contribute to anhedonia, investigations on this condition have more commonly focused on adults rather than children. Importantly, previous studies often did not separate anhedonia from other related psychopathologies, such as low mood, anxiety, or attention-deficit/hyperactivity disorder.
According to an article published in the journal JAMA Psychiatry (15 March 2019), changes have been identified in brain connectivity and brain activity during rest and reward anticipation in children with anhedonia. The study, supported by the Emotion and Development Branch, part of NIMH's Division of Intramural Research Programs. sheds light on brain function associated with anhedonia and helps differentiate anhedonia from other related aspects of psychopathology.
For the study, fMRI data collected from more than 2,800 children (9-10 years old) were examined as part of the Adolescent Brain Cognitive Development (ABCD) Study. Some of the children included in the sample were identified as having anhedonia, low mood, anxiety, or attention-deficit/hyperactivity disorder (ADHD). fMRI data were collected while the children were at rest and while they completed tasks assessing reward anticipation and working memory. Analysis of brain connectivity at rest showed significant differences in children with anhedonia compared to children without anhedonia. Many of these differences were related to the connectivity between the arousal-related cingulo-opercular network and the reward-related ventral striatum area. These findings suggest that children with anhedonia have altered integration of reward and arousal compared to children without anhedonia.
When the authors examined brain activity during the tasks, they found that children with anhedonia showed hypoactivation of brain regions involved in integrating reward and arousal during the reward anticipation task, but not the working memory task. This hypoactivation was not seen in children with low mood, anxiety, or ADHD. In fact, children with ADHD showed the opposite pattern: abnormalities in brain activation during the working memory task, but the not the reward anticipation task. According to the authors, the study results suggest that children with anhedonia have differences in the way their brain integrates reward and arousal and in the way their brain activates when anticipating rewards. The authors added that anhedonia-specific alterations were found, such that youth with anhedonia, but not youth with low mood, anxiety, or ADHD, showed differences in the way they integrated reward and arousal and also showed diminished activity in reward-anticipation contexts.