4–12 Hz oscillatory activity is suppressed during deep brain stimulation in patients with phasic dystonia

Aims: Enhanced low frequency (4–12 Hz) activity is found in pallidal local field potential (LFP) recordings in patients with dystonia and has been related mainly to phasic involuntary movements. Deep brain stimulation (DBS) of the globus pallidus internus (GPi) may suppress pathological synchronized activity leading to improvement of motor symptoms. Here, we investigate changes in 4–12 Hz oscillatory activity during DBS in patients with dystonia.

Methods: LFPs were recorded from DBS electrodes implanted in 10 GPi of 9 dystonia patients using a specially designed amplifier, allowing simultaneous stimulation and recordings. The paradigm consisted of a 150 s pre-stimulation baseline recording, and 3 runs of 150s LFP recordings during unilateral monopolar stimulation (130 Hz, 2.5–3.5 V), followed by 150s of LFP recordings after cessation of DBS. Spectral LFP power was analyzed for each condition and expressed as percentage change from baseline.

Results: Spectral power was enhanced in the 4–12 Hz band in all patients. During DBS, we found a significant decrease of 4–12 Hz activity with a mean suppression of 34.3% of peak power in patients with predominantly phasic dystonia. The suppression was still ongoing after cessation of DBS (mean decrease of 27.5%; p<0.05). In contrast, a significant increase of 4–12 Hz activity occurred during DBS (19.1% increase in peak power; p<0.05) in patients with tonic dystonia but did not last after stimulation was turned off.

Conclusion: Our results suggest that DBS may suppress pathologically enhanced low frequency activity in patients with phasic dystonia. The phasic components are the quickest to respond to DBS. Suppression of 4–12 Hz activity might therefore afford a biomarker for effective DBS for phasic dystonia. Amelioration of tonic dystonic movements may be related to longer term plastic changes in the neuronal network similar to the delayed clinical response.