The various spontaneous electrical patterns persisting in the isolated neuronal mass were observed for investigating the synchronous regularity. The regularity among the properties of electrical activities is discussed in relation to the activity of neuronal chains and the mechanism generating it is supposed on the basis of the change in excitability. The synchronous regular activity is presumably due to the mass activity of neuronal chains i. e. a regular rhythmical electrical activity, manifesting in the absence of afferent impulses and driven by the large shifting of excitability, would be dependent upon the waxing and waning due to activity in the neuronal chains. The author wishes to acknowledge his indebtedness to the members of Department of Physiology for their helpful advice.