A highly specialized serological test measures the presence and quantity of IgG autoantibodies directed against the NR1 subunits of the NMDA receptor (N-methyl-D-aspartate) in serum or cerebrospinal fluid (CSF). NMDA receptors are vital for memory, learning, and communication between nerve cells. Detection of these antibodies is a diagnostic criterion for anti-NMDA receptor encephalitis, one of the most common treatable causes of autoimmune encephalitis, often associated with ovarian tumors (teratomas).