Patterned low frequency deep brain stimulation induces motor deficits and modulates cortex-basal ganglia neural activity in healthy rats.

Deep brain stimulation (DBS) is an effective therapy for movement disorders including Parkinson's disease (PD), although the mechanisms of action remain unclear. Abnormal oscillatory neural activity is correlated with motor symptoms and pharmacological or DBS treatment that alleviates motor symptoms appears to suppress abnormal oscillations. However, whether such oscillatory activity is causal of motor deficits such as tremor remains unclear. Our goal was to generate abnormal oscillatory activity in the cortex-basal ganglia loop using patterned subthalamic nucleus DBS and quantify motor behavior in awake healthy rats. Stimulation patterns were designed via model-based optimization to increase power in the low frequency (7-11 Hz) band as these oscillations are associated with the emergence of motor symptoms in the 6-OHDA lesioned rat model of parkinsonism. We measured motor activity using a head-mounted accelerometer as well as quantified neural activity in cortex and globus pallidus (GP) in response to 5 stimulation patterns which generated a range of 7-11 Hz spectral power. Stimulation patterns induced oscillatory activity in the low frequency band in the cortex and GP and caused tremor, whereas control patterns and regular 50 Hz DBS did not generate any such effects. Neural and motor evoked responses observed during stimulation were synchronous and time-locked to stimulation bursts within the patterns. These results identified elements of irregular patterns of stimulation that were correlated with tremor and tremor-related neural activity in the cortex and basal ganglia and may lead to the identification of the oscillatory activity and structures associated with the generation of tremor activity.