“CRITICAL SENSITIVITY" PHENOMENA OF NEURAL FIRING PACEMAKER TO ELECTRICAL FIELD STIMULUS
神经放电起步点对电场刺激反应的“临界敏感”现象

Interspike intervals (ISIs) sequence of discharge of single fiber was recorded from the neural firing pacemaker of chronic constriction of sciatic nerve in rat. Under calcium-free condition, th e ISIs sequence entered into period-adding bifurcation, certain concentr ation of EGTA (a kind of calcium chelator) of the perfusion solution stabilized the firing pattern at period state which was far from a b ifurcation or critical state which was near a bifurcation. Relationship between the response to electrical field stimulus and bifurcation dyn amic state was analyzed. The following results were observed, the same intensity of electrical field stimulus induced a much more firing ra te increase in the critical state than that in the period state, and in the critical state electrical field stimulus often resulted in a transition of firing pattern. In the period state, during increasing of the intensity of electrical field stimulus, firing rate increased i n an approximately linear manner and there was no change of firing p attern. While in the critical state, firing rate increased obviously w ith the transition of firing pattern when the intensity of electrical field stimulus was high enough. It is concluded that the response to electrical field stimulus in the critical state, which is near a bi furcation, is more sensitive than that in the period state, this is named as "critical sensitivity"phenomena.