Electrophysiological correlates of objective memory impairments in community-dwelling older adults at risk of dementia

Background The electrophysiological correlates of Short-Term Memory Binding (STMB) have been previously investigated in older adults at risk of dementia (i.e., Mild Cognitive Impairment -MCI). Pietto et al. (2016) reported reduced early electrophysiological activity (100-250 ms) over fronto-central (FC) and parieto-occipital (PO) regions in MCI patients recruited from clinic. We investigated if such an electrophysiological pattern is also observed in a larger sample of community-dwelling older adults with MCI who had not sought medical advice. Methods A sample of 215 community-dwelling older adults were recruited into the study. They were assessed with a battery of cognitive tests including CERAD (Aguirre-Acevedo et al., 2016), the Addenbrooke?s Cognitive Examination (ACE-R), the STMB Task, clinical, and functional scales. The STMB task assesses the ability to detect changes between two consecutive visual arrays of coloured shapes. Changes consisted of shapes swapping colours (the binding condition). Time-locked EEG signals were collected while participants performed the STMB task. Monte Carlo tests and non-parametric bootstrapping running 1000 permutations revealed electrodes and time windows of relevance. Results A group of 108 participants met classical criteria for MCI (Petersen, 2004; Winblad et al., 2004). They showed impaired STMB abilities. ERP analyses revealed significant Group x Time Windows interactions (pHC) on right fronto-central (FC) regions (900-1200ms) during shape-colour encoding, and on left FC and PO regions (872-1200ms) during retrieval. Conclusion Altered spatio-temporal dynamics underpinning STMB deficits in MCI patients followed a pattern similar to that described by Pietto et al. (2016). Of note, we observed hyper-recruitment for late ERP linked to encoding and retrieval over anterior and posterior regions of the STMB network. Such hyper-recruitment may reflect compensatory changes in the early stages of MCI. These results confirm the usefulness of EEG-based cognitive biomarkers to screen community-dwelling older adults at risk of dementia. Aguirre-Acevedo et al. (2016). Int. Psychogeriatr, 28(3), 503-510. Pietto et al. (2016). Journal of Alzheimer?s Disease, 53(4), 1325-1340.