Vibration applied on the muscle belly after 'motor block' onset

Vibration applied on a bony mark after 'motor block' onset

Vibration applied on a bony mark before 'motor block' onset

Vibration applied on the muscle belly after 'motor block' onset

Local vibration will be applied using a custom-made vibratory system (named Vibrators) consisted of small vibratory devices (constructed using DC micro motors (Faulhaber® - Switzerland) bearing an eccentric load, enclosure on a PVC involucre). Vibrators measure 4.5cm x 2cm x 2cm and weight 27-31g each. Vibrators were custom-made especially for this study and therefore do not have a trade name.

Vibrators will be positioned either on the extensor carpi radialis brevis (ECRB) muscle belly or on the olecranon region. Devices will be kept in place using regular elbow elastic supports.

Participants will be comfortably seated, while both forearms rest on a table with hands facing down. Then, the right arm should slowly and actively be moved to a certain target angle indicated by the test leader. This target angle should be memorized while holding their arm at this position for 4s, after which participants slowly return their arm to the starting position. After 3s, participants will be asked to actively reproduce the previous target position with the same limb. All trials will be conducted while participants maintain their eyes closed and with their elbow off the table surface. The limb position will be recorded by using 7 MX-T20 optoelectronic cameras (Vicon, Oxford Metrics, UK). For this 3D movement analysis, each participant will be instrumented with 10 spherical reflective markers positioned on participants' right shoulder, arm, elbow, forearm and hand.

For this test a dual channel nerve stimulator (TENS) will be used (CEFAR PRIMO PRO - CEFAR Medical AB®). Participants will be seated in a standardized and comfortable way, allowing them to observe the entire procedure. Two individual electrodes (3cm of diameter) will be placed on bulb of the index finger (anode) and on the tenar region of the same limb (cathode). A constant current of 40Hz with single square pulses with 80μs of duration will be used. The current amplitude will be increased in steps of 0.5mA at every 2 seconds. The participant will be instructed to say "now" when they feel a slight tingling sensation. Three trials will be used for both hands. The Perceptual Threshold of Touch will be considered as the average of the three trials. It is expected that subjects will feel a slight itching and painless sensation. To avoid any discomfort, the test will be interrupted whenever an involuntary movement is seen, since the Motor Threshold always precedes the Pain Threshold.

The paradigm consists of performing a task on a 16.5cm length tablet (Fujitsu Componentes Europe®) .The device is powered by a regular laptop. To maximize participants' comfort the tablet screen is squared. The task consists of a 'freezing-provoking task'. This 'freezing-provoking' task has already been tested in people with PD in a current writing study at the Neuromotor Research Group . This task has been shown to be highly successful to elicit motor blocks in the upper limbs in PD patients (data submitted for publication). Each trial will last 30 seconds and as much trials as needed will be provided before the data collection to ensure participants have learned the task.