Early visual evoked potentials and mismatch negativity in Alzheimer's disease and mild cognitive impairment

Background: Cortical visual association areas are highly vulnerable to Alzheimer's disease (AD) microscopic pathology. Visual evoked potentials (VEPs) provide the tools to examine the functional integrity of these areas and may provide useful indicators of early disease progression. Objective: To assess the functional integrity of visual association area processing in AD and amnestic mild cognitive impairment (aMCI) using VEPs. Methods: We investigated the visual processing of healthy older adults (n = 26), AD (n = 20), and aMCI (n = 25) patients in a visual oddball paradigm designed to elicit the visual P1, N1, and visual mismatch negativity (vMMN). Results: AD patients showed a significant reduction of P1 and N1 VEP amplitudes and aMCI patients showed a reduction in N1 amplitude compared to healthy older adults. P1 amplitude in response to deviant stimuli and vMMN amplitude were found to be associated with the degree of cognitive impairment as measured by the Mini-Mental State Examination. Conclusions: Changes in VEPs in AD may be a consequence of the microscopic AD pathology typically found in the extrastriate cortex. Neural measures of visual processing may help to better characterize subgroups of aMCI patients likely to develop AD. Additionally, VEPs and vMMN may provide objective markers of cognitive decline.