Behavioral impulsivity in Parkinson’s disease may be linked to limbic-motor connections

CHICAGO — Behavioral impulsivity in Parkinson’s disease may be linked to several factors, including connections between the limbic system and motor function, per a presenter at the American Neurological Association annual meeting.

“You can study impulsivity in different ways,” Daniel O. Claassen, MD, MS, professor of neurology at Vanderbilt University Medical Center, said during his presentation. “You can talk about cognitive impulsivity and motor impulsivity. The main way we’ve started doing this is investigating motor inhibition.”

Claassen highlighted two cognitive neuroscience tasks developed for measuring dopamine’s impact on behaviors related to motor inhibition: the stop-signal task and the Simon conflict task.

The stop-signal task is designed as a speeded choice reaction to a “go” stimulus, in this case an arrow pointing either to the left or to the right; inhibition is logged given the speed of response to press the image following the appearance of the arrow target, and also logged with a “stop” stimulus, such as when the arrow changes color and the speed at which the motor response is stifled when pressing the image is not required.

Contrary to logic, patients with impulse-control disorder (ICD) performed better on the stop-signal task compared with those who displayed better impulse control, Claassen said. In addition, patients with PD perform slower on this task, and those with ICD perform faster.

The Simon conflict task involves spatial reactions in which one is presented a choice to respond to a circle on one’s left or right side; participants are told to fashion their responses according to the task-relevant attribute rather than the location of the stimulus. Inhibition in this case depends on one’s ability to suppress impulses to respond to stimuli on the same side as shown.

According to Claassen, those with PD are less proficient at suppressing incorrect responses with the Simon task. In addition, he said, there tend to be more errors with faster reaction times and fewer errors with slower reactions, and the introduction of amphetamines in treatment always speeds up reaction times.

With current data, there appears to be evidence that dopamine can regulate impulse control in PD, but whether it is compensatory or present in non-PD states is unknown. Claassen said research may indicate dopamine is likely governed through limbic-motor integration.

Hypotheses regarding limbic system control over cognitive function and how it relates to movement disorders could extend to the field of sports psychology, Claassen noted, where signs of anxiety or nervousness may denote a decrease in athletic performance related to limbic-motor dysregulation.

“We’re designing future experiments that assess motor function and sensory motor integration and thinking about ways to manipulate these to test the hypothesis,” Claassen said.