The present study examined the topographical characteristics for the typical nine EEG patterns during the hypnagogic state. Spectral analysis of the 12 scalp EEGs (F_ , _ , F_7,F_8,F_z, C_3,C_4,P_z, T_5,T_6,O_1 and O_2) was carried out on 10 male students (20-25yr). Topographic maps from consecutive samples of 30sec period for six frequency bands (delta : 2.0-3.8Hz, theta : 4.0-7.4Hz, alpha 1 : ... [Show full abstract] 7.6-9.4Hz, alpha 2 : 9.6-11.4Hz, alpha 3 : 11.6-13.4Hz, sigma : 13.0-14.8Hz) were studied from the light off to the stage 3 onset, which was scored by standard sleep stage criterion. Topographic maps demonstrated that the dominant areas of alpha band activities moved from the posterior area (P_z, T_5,T_6,O_1,O_2) to the anterior area (F_ , F_ , F_z, F_7,F_8) on the midline of scalp in association with the progress of hypnagogic EEG stages, which were scored by the criterion of Hori et al. (1991). On the other hand, the dominant area of delta, theta and sigma bands activities were on the central area (F_z, C_3,C_4,P_z) of scalp. The differences of EEG activities between the central and the peripheral areas (F_ , F_ , F_7,F_8,T_5,T_6,O_1,O_2) increased as a function of EEG stages. To describe the topographical characteristics of EEG stages quantitatively, the EEG anterior-posterior (A/P) indexes and the EEG central-peripheral (C/P) indexes were computed for each frequency band and for each stage. The A/P indexes in alpha band started to increase from stage 1 to stage 9 as a function of EEG stages. On the other hand, the sigma band C/P indexes did not increse in early stages, but started to increase rapidly after stage 7. These results show that the sigma C/P indexes are sensitive to detect the EEG changes in later process of hypnagogic state, especially to the vertex sharp wave and spindle activities. The results of this study suggest that the alpha band A/P index and the sigma band C/P index would be good objective indicators to describe the hypnagogic EEG activities.