Deficits in short-term memory, known as working memory, may underlie the compulsive “binge eating” observed in some Parkinson’s patients undergoing dopamine replacement therapy, a new study suggests.
The research “Reward sensitivity in Parkinson’s patients with binge eating” was published in the journal Parkinsonism and Related Disorders.
Parkinson’s patients using dopamine replacement therapy are at risk of developing impulse control disorders such as binge eating — consuming large portions of food, often quickly, without being able to stop and to the point of feeling uncomfortably full.
These disorders are reported to occur in 3.5% to 42.8% of patients, and likely reflect the interaction of dopaminergic treatments (dopamine agonists and/or dopamine replacement therapy) with the patient’s susceptibility and the underlying neurobiology of Parkinson’s.
Researchers at Scuola Internazionale Superiore di Studi Avanzati, in Trieste, Italy, investigated possible causes for this compulsive behavior in these patients.
They found that difficulties with “working memory,” a brain function that allows people to keep past information about an action — like eating until satisfied — in mind while carrying out that action, and in alterations to so-called reward sensitivity mechanisms are the causes underlying this behavior.
“Binge eating may affect different Parkinson’s patients as a side effect of dopaminergic drugs which they need to take,” Damiano Terenzi, the study’s first author, and Marilena Aiello, a research coordinator, said in a press release.
“In literature, impulse control disorders, such as hypersexuality or gambling, have often been described in Parkinson’s disease and associated to an alteration of working memory and of reward sensitivity. On binge eating, it has never been investigated,” they said.
Reward sensitivity is mediated by two factors: “liking,” a factor that measures the pleasure associated with a specific action, in this case eating; and “wanting,” the drive or desire to repeat the action linked to a pleasure sensation.
Researchers recruited Parkinson’s patients with and without binge eating disorders, and healthy people to serve as controls. All were assigned a number of tasks related to food liking and wanting.
Participants began the study by responding to prompts that distinguished their degree of liking and wanting different foods.
The visual stimuli used were high-quality colored photographs depicting items related to foods and those depicting unrelated items. The team selected sweet and salty foods, among those more frequently consumed by an independent sample of Parkinson’s patients. Sweet and salty foods were matched according to their frequency of consumption and tastiness.
Researchers then measured patients’ affective reactions towards foods (liking), and their motivation for food rewards (wanting).
Results showed that Parkinson’s patients who were binge eaters displayed an altered liking for sweet foods but not an increased wanting.
When measuring liking through patients’ attitudes and reactions — but not conscious reflection — binge eaters showed a negative attitude toward sweet food compared to controls, which the researchers said was “is in line with studies reporting a less positive attitude for palatable foods in individuals with eating alterations.” Importantly, this difference seemed to emerge only when implicit measures were used, while no differences emerged in self-report ratings of liking and wanting.
As with unsuccessful dieters, sweet foods are seen to pose a particular challenge for binge-eating Parkinson’s patients. As researchers noted, patients with impulse control disorders “frequently report preoccupations, the inability to control the urges or impulses … that arise to act on these urges.”
Patients with binge eating did not exhibit an increased “wanting” of food, a result that seems to contradict previous studies. This result was possible because the tasks used to measure “liking” and “wanting” failed to capture changes in food incentive salience, and that binge eating in Parkinson’s patients “is preferably associated with altered liking for rewards or … with affective abnormalities.” The team found an association between binge eating and depression in this patient population.
Most importantly, researchers also found that a potential deficit in working memory — a cognitive function — may underlie binge eating in Parkinson’s patients, making them unable to stop eating uncontrollably.
According to researchers, “this study gives precise indications about the mechanisms that are altered in binge eating in Parkinson patients. It is a first and important step to understanding its origins.”
“Other surveys must be conducted to confirm and explore this evidence regarding a behaviour which not only heavily affects the quality of life of patients but also exposes them to serious long-term consequences for their health, such as weight gain and related diseases,” the researchers concluded.
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