Being less affected by loss is predictive of apathy in people with Huntington’s disease (HD), a new study has found.
The study, “Insensitivity to Loss Predicts Apathy in Huntington’s Disease,” was published in the journal Movement Disorders.
Apathy — the feeling of indifference, where a person just doesn’t care — is common in some neurological conditions; it affects up to 80% of people with HD and can have a serious detrimental impact on quality of life. Apathy is considered a core feature of HD. It progresses with disease course, occurs before motor onset, and carriers of HD genes are significantly more likely than non-carriers to exhibit apathetic behaviors.
Despite this, it’s not clear what aspects of behavior are tied to apathy in HD. In this new study, researchers set out to identify specific apathy-related behaviors in this patient population, with the hope of finding specific areas for future studies and eventual interventions.
To do this, the team recruited 51 HD patients and 26 control participants, all of whom were subjected to a battery of psychological tests. Among these tests, apathy was measured using the Apathy Evaluation Scale (AES) and the Problem Behaviors Assessment for HD (PBA). The researchers then looked for associations between these apathy scores and other psychological assessments using statistical models.
Among the factors analyzed, sensitivity to loss was significantly linked with apathy. For this assessment, participants were asked to play a computer-based racing game that pitted them against a computer opponent that would always beat them (although the participants were not aware of that). The participants had the option of quitting the game at any time; a longer time to quitting in this assessment was indicative of less responsiveness toward negative outcomes. This was significantly associated with apathy among HD patients; participants with higher apathy scores tended to play the “game” for a longer period of time.
In another assessment, participants had to pump up a balloon, and were offered rewards for getting the balloon as big as possible, but got nothing if the balloon popped. The participants completed this assessment several times. HD patients with higher apathy scores were significantly less accurate (i.e. pumping the balloon much less than possible) over time if they experienced a loss (popping), but apathetic HD participants were comparatively more accurate if they got rewards. In contrast, control subjects demonstrated significant improvements in accuracy after both losses and rewards; again, this data is suggestive of dysregulated response to loss.
The researchers speculated that this differential sensitivity to loss and reward might be directly caused by alterations in the brains of HD patients, as brains process loss and reward through different mechanisms, but more research will be needed to evaluate this idea.
Other assessed factors, including irritability, impulsivity, perseverative behaviors, and memory loss, were not significantly associated with apathy in the models. Executive dysfunction trended toward an association with apathy; however, this did not reach statistical significance, which, the researchers speculated, may be due to the relatively small sample size included in this study. Executive dysfunction is an umbrella term for a range of cognitive, emotional and behavioral difficulties, including planning and organization, flexible thinking, motivation, and social behavior.
“[W]e have shown that apathy in HD is associated with a deficit in response to losses, whereas altered response to reward or altered reward-effort valuation is not necessary to develop apathetic behavior,” the researchers concluded.
They added that these results facilitate “the development of translational tasks of apathy for animal models, task-based functional imaging work to delineate the neurobiology, and paves the way for behavioral interventions to treat apathy in HD.”