Figure 5.

The figure demonstrates the phenomenon of coherence in a patient with psychogenic tremor of right hand. Simultaneous EMG and accelerometry were performed on both hands. The right hand was at rest (A and D) and the patient did fast tapping (B) and later slow tapping (E) on the table with the index finger of left hand. During fast tapping with left index finger, the tapping frequency as well as the right hand tremor frequency had identical peaks at 4.3 Hz with harmonics at 8.6 to 8.7 Hz. Coherence was seen at 4.5 Hz to 5.2 Hz. During slow tapping with left index finger (at around 2.3 to 2.6 Hz) the right hand tremor at rest was at 3.8 Hz with a harmonic at 7.8 Hz. The coherence between the movements of the two sides was at 2.3 Hz. This coherence test proves the entrainment of the tremor of right hand with the tapping frequency of left hand, thereby suggesting a psychogenic tremor.