Therapeutic deep brain stimulation in Parkinsonian rats directly influences motor cortex.

Much recent discussion about the origin of Parkinsonian symptoms has centered around the idea that they arise with the increase of beta frequency waves in the EEG. This activity may be closely related to an oscillation between subthalamic nucleus (STN) and globus pallidus. Since STN is the target of deep brain stimulation, it had been assumed that its action is on the nucleus itself. By means of simultaneous recordings of the firing activities from populations of neurons and the local field potentials in the motor cortex of freely moving Parkinsonian rats, this study casts doubt on this assumption. Instead, we found evidence that the corrective action is upon the cortex, where stochastic antidromic spikes originating from the STN directly modify the firing probability of the corticofugal projection neurons, destroy the dominance of beta rhythm, and thus restore motor control to the subjects, be they patients or rodents.