Brain scans of people with binge eating disorder or bulimia show altered activity in areas associated with habit formation and suggest new treatment options for eating disorders. Habitual behavior is automatically triggered by external stimuli for example, you reach for your seat belt as soon as you get into the car.
Researchers have identified two areas in a part of the brain called the striatum that are active in lab rats when they perform habitual behaviors. Although the human brain is somewhat similar to the rat brain, neuroscientists were not sure what the analogous structures were in the human brain or whether such structures even existed.
Allan Wang, a neuroscientist at the Stanford University School of Medicine in California, and his colleagues investigated which areas of the rat’s cerebral cortex are connected to the striatum. Then, using high-resolution magnetic resonance imaging data from 178 participants in the Human Connectome Project, an initiative to map the human brain, they worked backward from the cortex to identify candidate regions of the human brain.
This led them to two structures:
- sensorimotor putamen
- associative caudate.
Because habitual behavior is likely to play a role in binge eating disorder and bulimia nervosa, the team then examined the brains of 34 women with either disorder to see if there was a change in activity in these two structures.
Functional magnetic resonance imaging revealed changes in these areas in people with eating disorders compared to those without. Imaging showed changes in gray matter structure and in particular in dopamine signaling in the sensorimotor putamen.
Changed connections
In people with binge eating disorder or bulimia, the connections between some parts of the cerebral cortex and the habit-reinforcing sensorimotor putamen were much stronger than in healthy controls: connectivity to the anterior cingulate cortex was reduced, but it was increased to the orbitofrontal cortex. and motor cortex.
“Connectivity with the sensory motor putamen was the main differentiator between the controls we looked at and the binge eating group,” says Wang.
“This study adds nicely to some growing evidence suggesting that brain circuits that include the putamen are likely involved in binge eating,” says psychiatrist Laura Berner of the Icahn School of Medicine at Mount Sinai in New York.
The degree to which the brain images differed was directly related to self-reported eating disorder severity.
Dopamine is a neurotransmitter released in response to reward, and researchers expected the brains of people with eating disorders to show the effects of repeated exposure to reward. The putamen appeared to have fewer dopamine receptors than healthy brains, and the researchers believe that the increased release of dopamine could desensitize dopamine receptors and reduce their number.
The researchers caution that they cannot say definitively that the sensorimotor putamen and associative caudate are the human equivalents of the habit-forming regions of the rat striatum, but the work opens new avenues for investigating habit formation.
It also suggests that new treatments for binge eating and bulimia should be explored. In the past, these conditions were resistant to treatment. Psychiatrist Joanna Steinglass of Columbia University Irving Medical Center in New York says binge eating is perhaps the most common eating disorder, but “is the least studied in terms of bio-behavioral mechanisms.”
Wang says this work could pave the way for treatments that target brain areas involved in such disorders, using techniques such as deep brain stimulation or transcranial magnetic stimulation. He speculates that future treatments for many psychiatric illnesses not just binge eating disorders and bulimia could directly target brain circuits.
Written by: Vaishali Verma
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Reference: https://www.nature.com/articles/d41586-023-00967-5
