Deep brain stimulation (DBS) of the subthalamic nucleus is a useful treatment for Parkinson's disease, but its therapeutic mechanism is unknown. There are three proposed mechanisms: (1) DBS may correct a pathological change the firing rate of basal ganglia output neurons, (2) It may correct a pathological pattern of firing (bursting), or (3) It may correct a pathological across-neurons firing pattern (synchrony).

To be effective, DBS requires high frequency stimulation (~100 Hz), well above the average firing rate of basal ganglia output neurons, (~60 spikes/s). Periodicity of DBS is also important; random stimulation patterns at the same mean frequency are ineffective.

Neither the rate nor the pattern model for the action of DBS adequately explains either the frequency or periodicity requirements. We suggest that that periodic stimulation may act to disrupt synchrony among basal ganglia output neurons. It is well known that oscillators (including neurons) driven by periodic inputs will exhibit chaotic oscillations over a specific range of stimulus frequencies and intensities. Small differences in phase among a group of forced oscillators are amplified and synchrony is disrupted. We used a one-dimensional reduction of a model basal ganglia output neuron to predict the frequency specificity of this mechanism, and its requirement for periodic stimulation.