Cortical neurons were cultured to construct functionally active neural networks in vitro. The cortical tissues were dissected from E18 SD rats (Koatech, Republic of Korea) and immersed into HBSS (14175, Gibco, California). After dissociating the tissue into the single cells, we centrifuged the suspension at 1000 rpm for 2 min. Supernatant was then gently removed, and the plating medium [Neurobasal medium (21103, Gibco, California) supplemented with B27 (17504-044, Gibco, California), 2 mM GlutaMAX-1 (35050, Gibco, California, L-glutamate (L-Glutamic acid, nonanimal source, G8415, Sigma, Missori, and 1% (v/v) penicillin-streptomycin (15140, Gibco, California)] was re-filled to suspend cells. Cells were cultured on the substrate with the density of , and half of medium was changed with the maintenance medium (as same as the plating medium without L-glutamate) twice a week. All procedures of cultivation were performed according to the approved animal use protocols of the KAIST Institutional Animal Care and Use Committee.