For the purpose of studying the mechanism of the propagated sensation along channels (PSC) and clarifying the relationship between PSC and the central neuvous system

this paper was designed to observe the chara- cteristics of cortical somatosensory evoked potentials (SEP) in the subjects with marked PSC. The investigation was performed on 10 subjects

whose PSC was kept stable

distinct and could reach the head

and 16 subjects without PSC. Electrical stimulation was delivered to the Jiaxi or Hegu. SEP were recorded simultaneously from four scalp points: corresponding to the areas of foot

arm representation contralateral to the stimulated side and bilateral face representation of somatosory area I(SI). The results are shown as follows: 1. In addition to the PSC perceived by the subject

a complex poten- tial consisting of 5 elements (P_1

N_1

P_2

N_2

P_3) could be recorded from the point corresponding to the contralateral foot representation in stimu- lating Jiaxi in the subjects with marked PSC. Their mean peak latencies were 45.1±4.63

57.1±5.71

72.9±7.34

84.8±11.1 and 106±10.4 msec

respectively. The mean amplitudes of components C_1

C_2

C_3

C_4

C_5

which were composed of N_0-P_1

P_1-N_1

N_1-P_2

P_2-N_2

N_2-P_2

were 0.47± 0.19

0.87±0.47

0.98±0.52

1.68±1.24

1.41±0.16μv

respectively. View- ing on the distribution characteristics of SEP

the amplitude was the lar- gest in contralateral foot representation area but decreased markedly in other areas. The similar distribution was observed in 16 subjects without PSC. 2. Comparing the SEP from the foot representation area of the sub- jects with marked PSC with that of the subjects without PSC

the ampli- tudes of the majority of the components in the former were smaller than those in the latter

but there was no significant difference (P>0.05) bet- ween the two groups except for components C_4-C_5. The amplitude of com- ponents C_4-C_5 in the subjects with marked PSC was 2.6±1.59μv

while in the subjects without PSC was 4.24±1.83

the difference was signifi- cant (P<0.05). In accordance with the reports that the components C_4- C-5 might have a close relation to the perceptive procese of the somatic stimulation

we also found that there was a positive correlation between componets C_4-C_5 and the intensity of the needling sensation. 3. The results similar to those mentioned above were also observed when hegu was stimulated. 4. Observation on imitation of PSC was carried out in 10 subjects without PSC. The method of imitation was as follows: a soft painting bru- sh was moved repeatedly along the Gall Blabder Channel from foot to fa- ce at a speed of 20 cm per sec. The mean amplitude of components C_4-C_5 was 2.84±0.57μv during imitation. The control values derived from the recording before and after imitation were 4.45±0.7 and 4.85±1.02μv

re- spectively. The amplitude of component C_4-C_5 was markedly decreased during imitation (P<0.01) but recovered completely after imitation. The results demonstrated that the amplitude of components C_4-C_5 in the subje- cts with marked PSC was nearly the same as that in the subjects without PSC during imitation (P>0.5). The decrement of the amplitude during imitation was just equal to the difference between the two groups. The results mentioned above revealed that SEP in the subjects with marked PSC differed from that in the subjects without PSC. Components C_4 -C_5 of the former were much smaller than those of the latter. It seem that during the advance of PSC the functional activities of SI of the cere- bral cortex were interfered by some factors

which led to the decrease of the amplitude of SEP. This is a sensory physiological evidence of the existence of the PSC in reality. However

the cause of the interference remains to be further carified. Based on the results of imitation of PSC and the fact that the irradiation of excitation is limited by the surround inhibition and other mechanisms in somatosensory system

of which this is an important characteristic feature

it could be expected that the inter- ference of the functional activities of SI may be a reflection of the ac- tivation of the peripheral nerve fibers and receptors insequence by a certain agent advancing along the channels.