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

Abstract

AbstractBackgroundOculomotor 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.MethodsThe 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).ResultsSaccade 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 <0.0001) with such responses being significantly more pronounced during retrieval than encoding, particularly in the MCI‐FTD group. Mean Fixation Duration followed the pattern HC > MCI‐FTD > MCI‐AD (p <0.0001) which was similar across memory processes.ConclusionWhile memory deficits in MCI‐AD appear to be driven by encoding impairments, as suggested by both ET metrics, deficits in MCI‐FTD appear to be largely accounted for by impairments in retrieval. The fact that such a distinct pattern was more pronounced for Saccade Amplitudes points toward an early involvement of the frontal lobes. Identifying different correlates of memory impairment in MCI patients at risk of these common neurodegenerative diseases would be challenging for pure cognitive assessments. This highlights the role that the novel digital biomarker can play in refining theories of memory decline and in phenotyping dementia risk profiles.Parra, M. A., Juan Granada, J., & Fernández, G. (2022). Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring. https://doi.org/10.1002/dad2.12386. eCollection 2022.