The assessment of visually guided reaching in prodromal Alzheimer’s disease

One of the first brain regions to show metabolic changes typical in Alzheimer’s Disease (AD) is the precuneus (Dubois et al., 2014; Gordon et al., 2018). Focal damage to this brain area is known to cause deficits in reaching to objects in peripheral vision (Cavanna & Trimble, 2006; Karnath & Perenin, 2005). This impairment may therefore be present in individuals with AD, and even those with signs of pre-clinical AD, but no prior study has addressed this question. The aim of this study was to investigate the frequency and severity of peripheral misreaching in patients with amnestic Mild Cognitive Impairment (MCI) and typical AD, by comparison with age-matched controls (HC). We assessed both visually-guided reaching to peripheral and central targets, using two different tasks: lateral reaching in the fronto-parallel plane and reaching in radial depth. Both tasks were conducted on first their dominant and non-dominant side. Preliminary analysis shows no clear group-level difference in reaching accuracy. However, even the HC group showed a relatively high level of peripheral misreaching, compared to what is more typically seen in younger individuals (McIntosh, Mulroue, Blangero, Pisella, & Rossetti, 2011; Rossetti, Pisella, & Vighetto, 2003). Moreover, a small proportion of AD patients do show clear deficits, suggesting that there may be a subgroup of MCI and AD patients that develop peripheral misreaching.