## 1 Introduction  
Several studies have used functional magnetic resonance imaging (fMRI), electroencephalogram (EEG), and magnetoencephalogram (MEG) to investigate the level of nerve activation in regions that respond to vibrations, such as the primary somatosensory area (S1) and Brodmann area 3 (BA3). A considerable degree of activation has been noted in these areas after stimulation with low-frequency vibration (<80 Hz), particularly in Meissner's corpuscle. Some studies have also compared the degree of activation on applying low-frequency vibration stimulation to the first phalange of a given finger [1; 2; 3; 4; 5; 6; 7; 8]. It was reported that the activation area of the little finger was larger than that of other fingers, and that the activation area of the index finger was larger than that of the middle and ring fingers. In addition, several studies have compared the level of brain activation in response to low-frequency vibration stimulation applied to the first phalange of all five fingers [9; 10; 11; 12; 13]. In these studies, from the analysis of peak coordinates for the activation area, the distance increased in radial form for each finger based on the distal phalanx (P1) of the thumb. The distance between the distal phalanx (P1) of the thumb and P1 of the little finger was the largest. From these results, it was derived that the activation distance corresponding to each finger could be observed. One study compared the level of activation by presenting vibration stimulation to all phalanges of all five fingers [14]. In these studies, peak coordinates at BA3 were formed in the order of index finger, middle finger, and hand finger in the lateral to medial direction and inferior to superior direction for each finger. For each phalanx, it was reported that the peak coordinates in BA3 appeared only in the index and handhelds in the order of P1, intermediate (P2), and proximal (P3) in the anterior to posterior direction. Thus, several studies have reported the characteristics of neuronal activation in the S1 and BA3 regions in response to low-frequency vibration stimulation on all fingers and phalanges. The difference in the number of voxels in the activated somatosensory area according to the vibration stimulation is used in most tactile studies because it allows visually intuitive expression and quantitative analysis of the position, area, and size of the activation for each finger and phalanx. Studies have been also conducted to observe the level of neural activation in the S1 and BA3 areas when the fingers are presented with high-frequency (>100 Hz) vibrational stimuli sensitive to the Pacinian corpuscle. Namely, one study compared activation characteristics of these areas when presenting the high-frequency vibration stimulus to all phalanges of the index finger [15], and another study compared the degree of activation when applying the high-frequency vibration stimulus to the first phalange of the index finger and the little finger [16]. In these previous studies, the activation area of the little finger was larger than that of other fingers, and the activation area of the second finger was larger than that of the first and third nodes. For each finger, peak coordinates at BA3 were formed in the order of index finger, middle finger, ring finger, and hand finger in the lateral to medial direction. For each phalange, peak coordinates were shown in BA3 from anterior to posterior and inferior to superior in the order of P1, P2, and P3 for all fingers. Compared with a low-frequency vibration stimulus, studies using high-frequency vibration stimulation have only been conducted on a specific finger or phalange; thus, there is a need for more research on the effects of high-frequency vibration stimulation on various fingers and phalanges. In tactile studies, BA3 is referred to as the primary somatosensory cortex, and it has been reported that it is activated by most tactile stimuli such as vibration and pressure stimulation [17; 18].