Expected results are 1) an improvement of gait, postural and balance disturbance, due to PPN-DBS. 2) Identification of the optimal PPN-DBS parameters, improving most the axial PD symptoms, will allow to abbreviate the adjustment period, by using as default setting these parameters when turning on the stimulator for the first time; 3) Identification of the axial signs which are the most improved will allow to select patients that could most benefit from PPN-DBS 4) The use of diverse specific rating scales and quantitative gait analysis will allow to determine the most relevant clinical criteria to be evaluated in further studies.