The implanted system was composed of four silver ball electrodes placed in the burr hole of the skull, a reference placed subcutaneously near the nose, two electrodes for EMG, and a ground. The dural attachment was 0.1 mm in diameter. A cassette connector was placed on the back. Implanted cables between the cassette connector and all electrodes consist of twisted fine wires placed in a silicone tube 0.5 mm in diameter. The implanted electrode system weighed 0.8 g. The outlet cables were of the same materials used for implanted cables and placed in a silicone tube 1.5 mm in diameter. The impedance matching between these cables was successful and assured the minimum contamination of artifacts in the EEG recording of freely moving mice. Long-term (4-5 weeks) recording, thus, became possible without damage to the implanted materials. Monopolar recordings demonstrated the localized paroxysmal discharges during general tonic clonic convulsion in El mice. Several artifacts are presented.