Dysfunction of the magnocellular stream in Alzheimer's disease evaluated by pattern electroretinograms and visual evoked potentials

BackgroundVisuo-spatial disturbances could represent a clinical feature of early stage Alzheimer's disease (AD). The magnocellular (M) pathway has anatomo-physiological characteristic which make it more suitable for detecting form, motion and depth compared with parvocellular one (P).ObjectiveAim of our study was to evaluate specific visual subsystem involvement in a group of AD patients, recording isoluminant chromatic and luminance pattern electroretinograms and pattern visual evoked potentials.Material and methodsdata were obtained from 15 AD patients (9 females and 6 males, mean age ± 1SD: 77.6 ± 4.01 years) not yet undergoing any treatment, and from 10 age-matched healthy controls. Diagnosis of probable AD was clinically and neuroradiologically established. PERGs were recorded monocularly in response to equiluminant red-green (R-G), blue-yellow (B-Y) and luminance yellow-black (Y-Bk) horizontal square gratings of 0.3 c/deg and 90% contrast, reversed at 1 Hz. VEPs were recorded in response to full-field (14 deg) equiluminant chromatic R-G, B-Y and luminance Y-Bk sinusoidal gratings of 2 c/deg, presented in onset (300 ms)–offset (700 ms) mode, at the contrast levels of 90%.ResultsAll data were retrieved in terms of peak-amplitude and latency and assessed using the Student's t-test for paired data. Temporal differences of PERGs and VEPs, evoked by Y-Bk grating in AD patients compared with controls, suggest a specific impairment of the magnocellular stream.ConclusionsOur study support the hypothesis that the impairment of the PERGs and VEPs arising from the magnocellular streams of visual processing may indicate a primary dysfunction of the M-pathways in AD.