Suppression of neural activity with high frequency stimulation.

Deep brain stimulation (DBS) has been shown to generate suppression of abnormal neural activity in patients with Parkinson's disease and epilepsy. High frequency stimulation is applied to the brain through depth electrodes in the range of 50 to 200 Hz. Yet the mechanisms underlying the suppression effect have not yet been elucidated. In order to study directly the effect of HFS in the brain, sinusoidal stimulation was applied in the in-vitro brain slice preparation. Sinusoidal stimulation was chosen in order to observe the activity during the stimulation by filtering the stimulation artifact. Sinusoidal stimulation at 50 Hz applied to the CA1 region of the hippocampus was observed to block epileptiform activity in three separate models of epilepsy induced by low-calcium, high potassium and picrotoxin (GABA A blocker). Stimulation applied to the alveus showed that activity in both the cell bodies (evoked potentials) and in the axons (compound action potentials) is suppressed. The frequency range of this effect is nearly identical to that of DBS with maximum suppression effect between 50 and 200 Hz. The effect could not be attributed to desynchronization or damage and was associated with increased extracellular potassium concentrations. These data provide new insights into the effects of HFS on neuronal elements and show that HFS can block axonal activity through non-synaptic mechanisms.