This laboratory has made use of a novel finding concerning the effects of intracellular pH on membrane excitability in squid giant axons. Under certain conditions these preparations either fire action potentials in a rhythmic, spontaneous manner, or they are quiescent, i.e., they are bistable. We have injected computer generated noise in these axons to investigate the transitions between the two stable states. Membrane noise is a ubiquitous feature of neurons in the central nervous system, especially neurons in the brain. Bistability has been hypothesized to occur in neurons in areas of the brain undergoing epiliptic seizures. Brief duration current pulses applied at a critical point in the spontaneous firing cycle of one of these cells can terminate the activity, that is, it can reset the neuron to its stable rest state. Membrane noise may be a more efficacious way of accomplishing this result, since a small amplitude noise signal is sufficient, and the timing of the noise pulse is not as critical as in the case of a current pulse. These results might have relevance in the design of implantable devices in the brain as one way of controlling seizure activity.
