Low n1 visual responses in patients diagnosed with early-onset alzheimer's disease with CSF support

Time until diagnosis in patients with early-onset Alzheimer's disease(EOAD) is longer than late-onset cases. It is needed to have an objective diagnostic tool that is less affected by demographic characteristics such as education and culture. The aim of this study is to investigate differences of N1 event-related potential(ERP) recorded during passive monitoring paradigm between EOAD and healthy controls(HC) and the utility of N1 component as a diagnostic tool of EOAD. The data of 17 individuals with EOAD, whose diagnoses are supported by CSF biomarkers, and 17 HCs matched for age, education, and gender were analyzed. The ERPs of the participants, whose neuropsychological evaluations were made, were recorded with passive monitoring paradigm. 10cd/m2 of light was used and the mean amplitudes of the N1 components(130-200 msec) recorded from the midline in the frontal, central, parietal, and occipital were compared across the groups. The N1 components were divided into two subcomponents: anterior(frontocentral) and posterior(parietooccipital). Correlation analyzes were performed between N1 subcomponents and CSF biomarker values and cognitive composite Z-scores. ROC analysis was performed to determine the sensitivity and specificity of the mean N1 amplitude values. Group*Location interaction effect was found in the analyses [F (3.96) = 5.040, p =.018]. In posthoc analyses, both the N1 mean amplitudes from the frontal areas(p= .001) and the central areas(p = .003) of the EOADs were lower than the counterparts in the HCs. On the contrary, no significant difference was observed in the parietal and occipital areas across the groups (p = .128, p = .894, respectively). In addition, main group effect was found [F (1,32) = 5.614, p = .024]. In posthoc analyses, N1 mean amplitudes of EOADs were lower than HCs (p = .024). A high level of correlation was found between CSF Aß(1-42) values and posterior N1 mean amplitudes(p = .011). Also, the frontocentral mean N1 amplitudes could seemingly distinguish EOAD from HC at -3.14μV cut-off with 100.0% sensitivity and 59.0% specificity. The study findings support the use of anterior N1 amplitude as a screening test in the diagnosis of EOAD.