[Study on the derivation of P300 with reference electrode in the oral cavity]

The event related potential P300 is useful as an index of the fall of the cognitive function attends by aging and the diagnosis of dementia. If the generator of P300 is assumed to be equivalent current dipole (ECD), the negative wave should be recorded at other sites which polarity differs from the positive wave on the scalp. This study is to determine the most suitable reference electrode site for P300 recording and to improve S/N of P300. In order to record the P300 or N300 potential which spread on the scalp, earlobe (A1), oral (X1) and under site of the nose(X2) was used as a reference electrode. Auditory oddball paradigm which consists of the acoustic sound of 2000 Hz (targets) and 1000 Hz (standards) was used for the measurement of P300. In this results, P300 or N300 was measured by using earlobe(A1) site as a reference electrode. P300 wave was detected by Cz-A1 derivation and also the negative wave of N300 was detected by X1-A1 and X2-A1 derivation. These results demonstrate that there is an ECD which goes to the parietal region from internal focal area as a source of P300, and also suggest that P300 amplitude with Cz-X1 or Cz-X2 derivation is higher than that with Cz-A1 derivation. Therefore, it was speculated that the most suitable reference electrode sites for the improvement of the S/N in the P300 are oral (X1) or under the nose (X2) that show the negative potentials (N300).