Effects of wrist oscillations on contralateral neurological postural tremor using a new myohaptic device ('wristalyzer')

Upper limb postural tremor consists of distinct oscillations, mainly mechanical-reflex and central-neurogenic. These oscillations are superimposed upon a background of irregular fluctuations in muscle force. Muscle spindles play key-roles in the information flow to supra-spinal and spinal generators. Oscillations were delivered using a new generation portable myohaptic device, called 'wristalyzer', which takes into account the ergonomy of upper limbs allowing a fine adjustment to each configuration of upper limb segments. The nominal torque of the device is 4 Nm, with a maximal rotation velocity of 300 degrees/s and a range of motion of +45 to -45 degrees. Reliability was assessed in basal condition and during loading conditions. We assessed the effects of wrist oscillations upon contralateral postural tremor in 6 control subjects and in 7 neurological patients exhibiting a postural tremor in upper limbs. Patients exhibited an increased variability of postural tremor during fast oscillations (13.3 Hz). One patient with overactivity of the olivocerebellar pathways exhibited a drop in the peak frequency of more than 20 %. The relative power of the 8-12 Hz subband was significantly higher in controls both in basal condition and during oscillations (p = 0.028 and p = 0.015, respectively). This new device could be used to increase our knowledge of the responsiveness of tremor generators to stimulation of muscle spindles. It has also several potential applications for telemedicine in neurological rehabilitation.