Motor-symptom laterality could affect feedback-based associative learning in Parkinson disease (PD), with left-onset medication-naïve patients being selectively impaired, according to a recent study. In addition, dysfunction in the right dorsal rostral putamen may underlie the observed deficit in associative learning in patients with left-sided onset. Researchers recruited 63 early-stage medication-naïve PD patients (29 left-onset medication-naïve patients, 34 right-onset medication-naïve patients) and 38 matched normal controls. Subjects completed an acquired equivalence task (including acquisition, retention, and generalization) and resting-state functional magnetic resonance imaging scans. They found:

• Left-onset patients made significantly more errors in acquisition (feedback-based associative learning) than right-onset patients and normal controls, whereas right-onset patients performed as well as normal controls.
• There was no significant difference among these 3 groups in the accuracy of either retention or generalization phase.
• The 3 groups did not show significant differences in response time.
• In the left-onset group, there was an inverse relationship between acquisition errors and regional homogeneity in the right dorsal rostral putamen.