Microstructural diffusivity (DTI) changes underlying visual short‐term memory deficits in Alzheimer's Disease detected by digital screening

Abstract

AbstractBackgroundDeficits in visual short‐term memory (STM), rather than episodic long‐term memory, have recently been found to be associated with Alzheimer’s Disease (AD). However, the brain microstructural underpinning of selective abilities within visual STM remains poorly described.Method52 AD and 60 age‐matched healthy controls were recruited from the Oxford Centre for Cognitive Disorders. We used a novel digital visual STM task – the “What was where?” task (Figure 1) and extracted four metrics: Identification Accuracy (percentage of correctly identified items), Target detection (probability of correctly identifying the target), Misbinding (erroneously localizing an item to the remembered location of another item in memory) and Guessing (random guessing), (Figure 1). We then applied TBSS (Tract‐Based Spatial Statistics) to investigate in which areas of the brain microstructural disruption of physiological diffusivity correlated with behavioural performance.ResultIn AD patients, a core area including Forceps Major, left Optic Radiation (OR) and left Middle Longitudinal Fasciculus (MLF) was commonly associated with performance across all four metrics (Figure 2). Misbinding also involved the left MLF (part III), left inferior Fronto‐Occipital Fasciculus (IFOF) and left Vertical Occipital Fasciculus (VOF). Target detection additionally was associated with Superior Longitudinal Fasciculus (SLF), and Identification Accuracy with left Superior Thalamic Radiation (STR) in AD and also right OR in controls.ConclusionThere is a common shared area of altered diffusivity in AD patients that underlies a global impairment in visual STM, while distinct types of memory errors were associated with disruption of additional contribution of selective white matter fibers.