Different correlates of memory decline in Alzheimer’s diseases and Frontotemporal dementia: evidence from a novel digital biomarker

Abstract Background Oculomotor behaviours (i.e., eye tracking - ET) linked to cognitive performance can differentiate between the trajectories of neurodegeneration that lead to the Alzheimer?s disease Syndrome (ADS) or Fronto-temporal Dementia (FTD). We recently reported that a novel digital biomarker that combines ET and Short-Term Memory Binding (STMB) accurately predicted among MCI patients who would develop ADS or non-AD dementias (Parra et al., 2022). A sub-group of the latter group developed FTD. We investigated the correlates of these different neurodegenerative pathways. Methods The study involved 32 MCI patients of whom 24 developed ADS and 8 FTD in a three-year longitudinal study. We also recruited 42 controls (HC). Saccade Amplitude and Fixation Duration were measured at baseline while participants performed the STMB Task. This task assesses the ability to detect changes between two consecutive arrays of bicoloured objects. Changes affect either colours (control condition) or colour combinations (binding condition). Results Saccade Amplitudes and Fixation Durations were affected in both MCI-ADS and MCI-FTD patients. However, patterns of impairment significantly differed between these risk conditions. Mean Saccade Amplitude followed the pattern MCI-FTD > MCI-ADS > HC (p MCI-FTD > MCI-AD (p