It is agreed that for an organism to behave appropriately it must be able to handle with discrimination the continuous barrage it receives from both its internal and external envirorunents. A mechanism must exist by which the brain picks out and transmits meaningful information. In fact, recent theories dealing with central integration and such behavioral manifestations as learning and memory, rely heavily on the characteristics of a modulated frequency input. Indeed, it has been demonstrated (E. R. John, Frontiers of Physiological Psychologyl ed. by R. W. Russell, Acad. Press, New York, 1966) that two temporal sequences of electrical stimuli, applied to the same place, equated for power and differing only in the time course of events, can be informationally distinguished by the nervous system. Thus, the sequence of events at a particular place in the brain can be informational.The present series of experiments concerns the possible elements of such a discriminatory mechanism. The results were obtained by combining the techniques of local cortical per-fusion (Davies and Grenell, Journal of Neuro-physiology, 1962) with recording of cerebral evoked responses (SCR) and “spontaneous” single-unit activity (recorded with KC1 filled capillary microelectrodes) in the supra-sylviangyrus of the cat. The alterations in such responses accompanying the presence or absence of certain ions or molecules in the perfusion fluid will be described. These involve both facilitation and inhibition in the presence of low concentrations of ouabain and choline in the first instance, or of ouabain, choline and atropine in the latter.Discussion will concern the inference to be drawn from the results and from relevant literature that depending on the nature of the input, a network can pass information or not by either releasing or not releasing a particular transmitter. That is, that the same network may under the influence of inputs with different characteristics, either: 1.Release no transmitter;2.Release transmitter A; or3.Release transmitter BFurther steps in the mechanism as well as their implications will be suggested.