Mild Cognitive Impairment Exhibits Neural Deficits in Working Memory Capacity

Mild cognitive impairment (MCI) serves as a transitional stage between healthy aging and various types of dementia, including Alzheimer's disease (AD). Previous clinical studies have demonstrated poorer selective attention and working memory performance in MCI patients compared to healthy individuals. However, the neural substrates underlying these deficits in MCI remain poorly understood. In this study, we aimed to
investigate the neural deficits associated with storage capacity and selective filtering in visual working memory among Thai MCI patients and healthy individuals. We measured EEG activity while participants performed a variant of the delay match-to-sample task, which required remembering varying numbers of relevant color targets while ignoring varying numbers of irrelevant distractors or without distractors. Two event-
related potentials (ERPs), the posterior contralateral delay activity (CDA) and frontal biasing activity were used to track working memory capacity and selective filtering functions, respectively. The MCI group exhibited significantly poorer working memory performance compared to the healthy control group, irrespective of the number of targets and distractors. The CDA amplitude was significantly lower in the MCI group compared to the control group, particularly when working memory capacity was full (approximately 3-4 targets with no distractors). That said, there was no significant difference in frontal biasing activity between the healthy aging and MCI groups. Overall, these findings suggest that MCI exhibits neural deficits in the posterior parietal cortex, resulting in reduced working memory capacity without impacting the selective filtering function of the
frontal cortex.