Reduced dorsal visual stream α2-adrenergic receptor availability is not associated with visuospatial impairment in...

Visuospatial deficits are a common and disabling feature of Parkinson's disease (PD) that are linked to dysfunctions of the dorsal visual stream (DVS) and the cholinergic system. However, a body of evidence also points to the possible role of noradrenergic dysfunction, but direct in vivo evidence has remained lacking until the recent development of molecular imaging techniques.

Thirty PD patients and thirty matched healthy controls underwent PET imaging using [¹¹C]yohimbine, a new radiotracer now available for human use, to quantify α2-AR availability. Visuospatial cognition was assessed using the MoCA visuospatial subscore, the Visual Object and Space Perception (VOSP) Number Location subtest, and the 15-Objects test.

Compared with controls, PD patients showed reduced performance on the VOSP Number Location and 15-Objects tests (both p < 0.05). Voxel-wise analyses revealed reduced [¹¹C]yohimbine binding in DVS regions, including the superior parietal lobule, posterior cingulate cortex, and supramarginal gyri (p_FWE <0.05), but no correlations were observed between α2-AR availability and visuospatial performances. Bayesian analyses provided moderate evidence for the absence of association (BF₀₁ > 3).

Despite reduced α2-AR availability within DVS regions, no significant association was observed with visuospatial performance. These findings do not support a simple direct association between DVS α2-AR availability and visuospatial impairment in this cohort of patients with PD.