Electrophysiological correlates of visual short-term memory binding deficits in community-dwelling seniors at risk of dementia.

BACKGROUND

Visual Short-Term Memory Binding (VSTMB) is a preclinical marker of Alzheimer's disease (AD). Reduced early event-related potentials (ERPs) (100-250 ms) over fronto-central (FC) and parieto-occipital (PO) regions have been reported in patients with Mild Cognitive Impairment (MCI) seen in the clinic. We investigated such ERPs in a larger sample of community-dwelling older adults who had not sought medical advice.

METHODS

Participants (n = 215) were assessed with a neuropsychological battery and the VSTMB Task. The latter assessed the ability to detect changes between two consecutive arrays of shapes or colored shapes (the Binding condition). Time-locked EEG signals were collected during the task.

RESULTS

Those who met the MCI criteria (n = 108) showed binding impairment. ERP analyses revealed significant Group x Time Windows interactions. Early ERP showed reduced neural recruitment (MCI < healthy controls (HC)) over the right FC regions, left PO, and right centro-parietal (CP) regions during Binding encoding, and over PO regions bilaterally and left FC during retrieval. Late ERP showed increased neural recruitment (MCI > HC) on left FC and PO regions during retrieval.

CONCLUSIONS

Hyper-recruitment may reflect functional reorganization aimed at behavioral compensation in the early stages of MCI. The role of such amplitude shifts as pointers of transition points in the AD continuum needs further investigation.