Time constraint and error corrections contribute to the increase of hand postural tremor during mental calculation

Hand postural physiological tremor increases during arithmetic computation. The present work aims at investigating whether this could be attributed to a raise in stress for having to provide a correct answer within a constrained period of time, or to voice vibration for having to speak to report the answer.

In 16 participants tremor was recorded by using a 3-axial accelerometer during 5 min of a hand postural task performed simultaneously while: 1) subtracting 13 from a 3-digit number within 4 s and with mistakes correction (intervention: math stress task), 2) same as for the "intervention task" but without time limit and mistakes correction (intervention: math nonstress task), 3) adding 1 to a 3-digit number (intervention: voice vibration task), and 4) only postural task while keeping quiet (control task). Electromyographic (EMG) activity from the extensor carpi radialis was measured during the hand postural task.

Compared to control, tremor increased during both math interventions (+30.9 % p = 0.002, math stress; +15.0 % p = 0.01, math nonstress), but not during the voice vibration task (+12.2 % p = 0.239). During the math stress trial tremor was greater compared to both the voice vibration trial (+21.0 % p = 0.021), and the math nonstress trial (+13.5 % p = 0.01). EMG activity was not affected.

The results suggest that during arithmetic computation the "stress component" contributes only partially to the observed increase in hand postural tremor, and that this increase cannot be attributed to voice vibrations.