The primary objective of this study is to evaluate the association between cognitive dysfunction and serum anti-pentapeptide Ab. Magnetic resonance imaging (MRI) will be performed for evaluation of potentially confounding central nervous system (CNS) disease such as cerebral infarction, and of blood brain barrier breakdown by employing gadolinium enhancement. Furthermore, in participants who agree, a lumbar puncture will be performed and cerebrospinal fluid will be obtained for preliminary evaluation of the intrathecal levels of the anti-pentapeptide Ab associated with cognitive dysfunction.