Different conditions of gait ignition freezing, spontaneous freezing during walking and turning freezing on encountering obstacle will be investigated in fMRI study to examine whether different regions of brain will be involved under different conditions of freezing. We hypothesize that anterior cortical regions will engage in gait ignition failure, deep locomotion regions will be responsible for spontaneous freezing and schema regions will be involved in the generation of turning freezing on seeing the barrier. In the third part of the project, we will deliver a 5-day session of transcranial direct current stimulation (tDCS) to the motor cortex of the FOG patients to examine whether the intervention will benefit the patients. Based on the signal source findings, we will investigate whether the possible tDCS beneficial effect will be different or similar in patients with different electric sources. In addition, how long the possible beneficial effect of tDCS can be consolidated after the 5-day course of stimulation is crucial and requires to be elucidated under the research project. We aim to peep the myth of FOG in PD by the multi-modality approach and hope the study will benefit the long suffering patients.

Inclusion Criteria:

The diagnosis of freezing of gait will be made by the following criteria:

1. Without video:Is there any feeling that your feet are transiently glued to the floor while trying to initiate walking, making a turn or when walking through narrow spaces or in crowded places? (Sometimes it can be accompanied with trembling of the legs and small shuffling steps.)
2. Additional instructions with video:We will watch a short video together to see the many ways in which freezing can occur. Also, look carefully for how long these episodes last, as you can expect some questions on this later.
3. Patient is diagnosed to have freezing of gait if "I have experienced such a feeling or episode over the past month" was answered.

Exclusion Criteria:

1. Impairment of cognition that leads unable to fully cooperate with the oral commands during examinations.
2. Moderate to severe medical disorders such as functional III or above congestive heart failure, or cancer with distant metastasis etc.
3. Hoehn and Yahr stage 5.