Parkinsonian symptoms, such as freezing of gait (FOG) or hypophonia, play a significant role in reducing quality of life for Parkinson disease (PD) patients, and are poorly responsive or can worsen with deep brain stimulation (DBS). Repeated adjustments of stimulation parameters may be beneficial however, continuous DBS (cDBS) does not adapt to the patients' rapidly fluctuating clinical status and does not take into account reliable and consistent state-trait biomarkers. These biomarkers can be recorded by the electrode itself as local field potentials (LFP). These LFPs can be used to guide stimulation output by means of a 'closed loop' or 'adaptive' DBS (aDBS). This is a pilot, two-phase, double-blinded, cross-over study of chronic Adaptive vs. Continuous STN DBS in patients with PD by using a novel implantable DBS system that can automatically adjust stimulation parameters based on the patient's clinical condition. The study will test the hypothesis that aDBS stimulation will treat motor fluctuations similarly to continuous stimulation but it will be superior to the latter in the treatment of speech, gait impairment and falls.