Striatal dopamine denervation and sensory integration for balance in middle-aged and older adults

The dopaminergic system of the basal ganglia has been implicated in the integration of sensory information important for balance based on studies in patients with Parkinsonʹs disease. Striatal dopaminergic activity decreases with normal aging. Objective To investigate the relationship between regional striatal dopaminergic denervation and sensory information integration important for balance in middle-aged and older adults. Methods Community-dwelling subjects (N = 35; age 41–83) with no clinical diagnoses of conditions affecting balance underwent dynamic posturography testing (Sensory Organization Test/SOT) and C-11-beta-CFT dopamine transporter positron emission tomography. Results Reduced ventral striatal dopamine was significantly correlated with increased anterior–posterior sway in three SOT conditions. Specifically, during quiet standing (SOT Conditions #1, 2) and when repeatedly to sway-referenced visual environments (SOT Condition #3, Trial #3), pre-synaptic dopaminergic denervation in the anteroventral striatum explained over 20–25% of the variability in sway magnitude above and beyond that explained by age (p ≤ 0.01). Striatal dopaminergic denervation did not impact balance in sway-referenced floor conditions. Conclusions The SOT Condition #3 findings suggest that, in normal aging, the central ability to inhibit balance destabilizing vision-related postural control processes depends at least partially on striatal dopaminergic pathways. In contrast, striatal dopaminergic denervation does not appear to impair the ability to disengage destabilizing proprioceptive inputs and to trigger the vestibular control system during challenging sensory perturbations (SOT Conditions #4–6). Finally, quiet standing results (SOT Conditions #1, 2) justify the need to further investigate the impact of striatal dopaminergic denervation on the ability to tune muscle tone in healthy adults.