Physiological Tremor: Does Handedness Make a Difference?

Abstract

The purpose of this study was to quantify with precision the characteristics of normal physiological tremor in the dominant and nondominant hand of a group of right-handed females. Twenty-two right-handed females (aged 20 to 40) gave informed consent to participate. Manual dominance determined with a questionnaire had to be equal to, or above 90%, for subjects to be accepted in the study. While the subjects kept their eyes closed, tremor was recorded simultaneously in the two extended index fingers during 40s. Preceding the recording of postural tremor there was a period during which the subjects were asked to relax (control condition); to exert a pressure with the two index fingers on two strain gauges (static condition); or to press on and off with both index fingers on two strain gauges (dynamic condition). Each condition was recorded twice with two helium neon velocity lasers. This procedure was repeated after permutation of the lasers, thus a total of twelve sweeps of data were recorded. Seven parameters were used to analyze the tremor signal including measures of harmonicity, median frequency, proportional power in the 7–12 Hz range, amplitude, waveform morphology, entropy, and nonlinearity. Significant differences between hands were found in three parameters (median frequency, power in 7–12 Hz and entropy) but not in tremor amplitude (RMS). In addition, significant differences were found in five out of seven characteristics between conditions. These results suggest that neuromotor activity preceding the recording of tremor has a significant influence on tremor characteristics and that some of these characteristics are significantly different between the right and left hand in right-handed females.

Key Words:

• Handedness
• physiological tremor
• laterality
• neuromotor activity
• manual dominance