Figure 4. Extracellular potassium measurements during attempts to suppress activity with 50 Hz sinusoidal fields.

A, during low-Ca²⁺ epileptiform activity, subthreshold stimulation resulted in a transient increase in extracellular potassium. As the potassium increase decayed, spontaneous activity resumed. B, in the same slice, application of suprathreshold stimulation resulted in a larger potassium increase during stimulation and suppression of activity. C, during picrotoxin epileptiform activity suprathreshold stimulation resulted in similar transients in extracellular potassium.