On the possible nature of the processes induced by unconditioned stimulation in the cerebral cortex.

Tetanic stimulation of the cortex elicits in some cortical neurons a hyperpolarizing change of the membrane potential and inhibition of impulse activity; after cessation of stimulation often an enhanced discharge occurs. Other neurons respond to stimulation with high-frequency discharges. At the site of stimulation [K+]o is increased more than by 2 mM. If tetanic stimulations are applied at less than 2 min intervals they result in an attenuated K+ release. During tetanic stimulation of the cortex a depolarizing shift of the glial cell membrane potential develops at all strata of the cortex. It is known that conditioned reflex may be elaborated when the electrical stimulation of the motor cortex is used as unconditioned stimulus if the intertrial intervals are not too short. It is hypothesized that the effectiveness of the stimulation of the cortex in eliciting the K+ release and in promoting a conditioned reflex acquisition are interrelated. According to this hypothesis an increase in [K+]o is a signal for myelin formation, and myelination of the naked axonic terminals which convey conditioned signal is the basis for the conversion of the potential connections into the actual ones.