Deep brain stimulation of the NST is effective for cardinal motor signs in patients with idiopathic Parkinson's disease (IPD), its effects on gait disturbances, especially freezing of gait-FOG, and falls are variable from one patient to another, in part depending on the location of the NST-stimulating contact. The ability to change the shape of the current field, and thus the volume of activated tissue, with a directional stimulation electrode is a new treatment option for NSC SCP patients with Parkinson's disease. In this pilot research program, the main objective is to determine the impact of directional DBS on gait and balance issues for PD patients implanted in the STN, using previously described anatomical and functional data for gait disturbances to guide directional programming. Ten patients with Patients with severe form of Parkinson's disease eligible to deep brain stimulation of the subthalamic nucleus, will be included in two French sites.

Inclusion Criteria:

1. Age between 18 and 70 years
2. Diagnosis of Parkinson's Disease; as defined by the United Kingdom Parkinson's Disease Society Brain Bank (UKPDSBB) criteria
3. Patients eligible for subthalamic bilateral deep brain stimulation (STN-DBS) according to local inclusion criteria;
4. Freezing of gait in the OFF-dopa condition with item 2.13 of the MDS-UPDRS > 0 in usual life;
5. Patient having read and understood the information letter and signed the Informed Consent Form
6. Patient affiliated with, or beneficiary of a social security category
7. Stability of others medical disorders or that do not interfere with the research protocol.
8. Woman of childbearing potential with effective contraception according to WHO definition (estrogen-progestin or intra-uterine device or tubal ligation) since at least 3 months (negative urinary pregnancy test at inclusion)

Exclusion Criteria:

1. Actual and severe psychiatric pathology or other neurological disorder
2. Dementia (MMS <24/30)
3. Contraindication to research MRI (without contrast product) such as claustrophobia, metallic splinters in the eyes, ferromagnetic foreign bodies close to nerve structures, cardiac, ORL and neurological devices not MRI compatible, wearing of osteosynthseis equipment prior to 1980, metal prostheses, bypass valves ventriculoperitoneal neurosurgery, tattoos containing iron particles…
4. Contraindication to surgery: hemostasis trouble, anticoagulants or antiagregants treatment, ongoing infection
5. Hypersensitivity to contrasts agents
6. Persons under guardianship, tutorship or any other administrative or judicial measure of deprivation of rights and liberty
7. Subject at the time of exclusion from other biomedical research or participating in any other biomedical research or therapeutic trial
8. Pregnant or parturient or lactating woman or lack of proven and effective contraception according to WHO definition (estrogen-progestin or intra-uterine device or tubal ligation) (for women of childbearing age)