Alzheimer’s disease and memantine effects on NMDA-receptor blockade: non-invasive in vivo insights from magnetoencephalography

To accelerate new treatments for Alzheimer's disease, there is the need for human pathophysiological biomarkers that are sensitive to treatment and disease mechanisms. In this proof-of-concept study, we assess new biophysical models of non-invasive human MEG imaging to test the pharmacological and disease modulation of NMDA-receptor inhibition. Magnetoencephalography was recorded during an auditory mismatch negativity paradigm from (1) neurologically-healthy people on memantine or placebo (n = 19, placebo-controlled crossover design); (2) people with Alzheimer's disease at baseline and 16-months (n = 42, amyloid-biomarker positive, longitudinal observational design). Optimised dynamic causal models inferred voltage-dependent NMDA-receptor blockade using Parametric Empirical Bayes to test group effects. The mismatch negativity amplitude was attenuated when Alzheimer's disease was more severe (lower baseline mini-mental state examination) and after follow-up (versus baseline). Memantine increased NMDA-receptor inhibition, compared to placebo. Alzheimer's disease reduced NMDA-receptor inhibition in proportion to severity and over time. In line with preclinical studies, we confirm in humans that memantine and Alzheimer's disease have opposing effects on NMDA-receptor inhibition. The ability to infer such receptor dynamics and pharmacology from non-invasive physiological recordings has wide applications, including the assessment of other neurological disorders and novel drugs intended for symptomatic or disease-modifying treatments.