McLean Hospital 115 Mill Street Belmont, MA 02478
Daniel G. Dillon, PhD, was trained in human neuroscience at Duke University, where he worked under Dr. Kevin LaBar and studied learning and memory. As a post-doctoral fellow with Dr. Diego Pizzagalli at Harvard University, he investigated brain systems implicated in anhedonia, which refers to the loss of pleasure and is a cardinal symptom of unipolar depression.
Currently, research in Dr. Dillon’s Motivated Learning and Memory Laboratory is centered on understanding how anhedonia affects memory formation, focusing on the hypothesis that in healthy adults, signals from brain reward systems boost the activation of memory networks, leading to robust memories for rewarding experiences. Because anhedonia has been linked to dysfunction in brain reward systems, the lab proposes that signals from reward to memory networks are diminished in depression and that memory for positive experiences suffers accordingly. The goal of this work is to provide a mechanistic explanation for memory deficits in depression.
The ability to rapidly learn and remember complex information is crucial to personal and professional success. However, the stress associated with this challenge can elicit depression in vulnerable people. This can trigger a vicious cycle. The negative effects of depression on learning, motivation, and memory increasingly destabilize day to day life. Because the brain mechanisms responsible for these problems are poorly understood, they are difficult to treat.
Dr. Dillon’s Motivated Learning and Memory Laboratory, founded in 2014 and part of the Center for Depression, Anxiety and Stress Research (CDASR), works to examine this problem using various techniques. These include computational models, functional magnetic resonance imaging (fMRI), and measurements of electrical activity on the scalp (electroencephalography, or EEG). The focus is working to understand how depression affects the brain systems that support motivation, learning, and memory. The long-term goal of Dr. Dillon’s work is to contribute valuable discoveries that will help prevent and treat depression.
Research conducted in the CDASR at McLean (and elsewhere) suggests that anhedonic depression reflects negative effects of stress on dopamine neurons. These neurons project from the midbrain to the striatum, hippocampus, and prefrontal cortex, and they play a key role in reinforcement learning and episodic memory.
Intriguingly, the failure to learn effective coping strategies is a defining feature of depression, which frequently involves troublesome memory deficits. Unfortunately, the neural basis of these problems is poorly understood. Dr. Dillon looks to fill this knowledge gap by testing a straightforward hypothesis: in addition to its role in anhedonia, dysfunction in dopamine circuitry impairs learning and memory in depression.
As a first test of this hypothesis, Dr. Dillon used fMRI to examine memory for rewarded and non-rewarded objects in healthy and depressed adults. He anticipated that unexpected rewards would lead to strong memories in healthy—but not depressed—individuals. Indeed, healthy participants showed better memory for rewarded vs. non-rewarded objects, but the depressed group did not. Furthermore, the rewards elicited stronger activation of the dopaminergic midbrain in healthy vs. depressed individuals. These results provide initial support for the proposal that dopamine dysfunction impairs episodic memory in depression.
Currently, Dr. Dillon is using computational models to more rigorously link dopamine dysfunction to episodic memory deficits and poor reinforcement learning in depression.
Dr. Dillon also aims to identify neural circuits that could be targeted for prevention and treatment of depression and other conditions. Because dopamine dysfunction is not confined to depression, he anticipates extending his efforts to other clinical conditions, potentially including substance abuse and bipolar disorder. Furthermore, his work should improve understanding of individual differences in learning and memory in healthy adults.
Dillon DG, Holmes AJ, Birk JL, Brooks N, Lyons-Ruth K, Pizzagalli DA. Childhood adversity is associated with left basal ganglia dysfunction during reward anticipation. Biological Psychiatry 2009;66:206-213.
Dillon DG, Dobbins IG, Pizzagalli DA. Weak reward source memory in depression reflects blunted activation of VTA/SN and parahippocampus. Social Cognitive and Affective Neuroscience 2014;9(10):1576-83.
Dillon DG, Pizzagalli DA. Evidence of successful modulation of brain activation and subjective experience during reappraisal of negative emotion in unmedicated depression. Psychiatry Research 2013;212:99-107.
Belmont campus - de Marneffe Building, Room 244