Compensatory Role of the Amygdala During Motor Timing and Selection in Parkinson's Disease

Alterations of amygdala function in Parkinson's Disease (PD) are associated with emotion-related clinical features such as impaired facial recognition, but the effects on motor performance in an emotionally-neutral task are unclear. We studied fMRI from healthy and PD subjects while they squeezed a rubber bulb to keep a bar within two parallel "tracks" that were scrolling downward. At discrete intervals, there were bifurcations of each track, and the subject had to follow either the inside or outside track requiring squeezing at 5% or 15% of maximum voluntary contraction. During the control condition (Control), subjects had to follow the inside and outside tracks alternately. In the timing (Timing) and selection (Selection) tasks, the time between bifurcations jittered randomly and the color of the bar determined which path to choose, respectively. We determined which Regions of Interest (ROIs) were activated at the time of bifurcations, by assessing both the connectivity between ROIs and the timing of activation. The caudate and putamen were activated in both (Selection-Control) and (Timing-Control) contrasts in all subjects, however only in PD subjects was the amygdala significantly activated. In addition, the amygdala was activated faster in both Selection and Timing tasks compared to the Control task in PD subjects. In PD subjects, the greatest connectivity was to/from the amygdala, while in healthy subjects the strongest connectivity was seen between the caudate and putamen. Our results suggest that PD subjects recruit the amygdala to maintain performance in motor timing and program selection even during emotionally-neutral tasks.