Detecting the coupling direction between both hands physiological tremors - a non-parametric directionality analysis

This study continues some previous research done on the hand physiological tremor (PT) signal - a motor phenomenon that we treated as a potential window to better understand the dynamical structures underlying the human visuomotor circuits. In order to understand how visual inputs processing interacts with limb motor system, two intermittent light stimulation (ILS) paradigms were implemented and the corresponding dynamical evolution of limbs' motor systems outputs (i.e., the hand PTs) were tracked using a non-parametric directionality approach. In the ILS paradigms two visual stimuli, of different frequencies (7 Hz and 19 Hz), were delivered first alternatively and, then, concurrently in each of the two subjects' visual hemifields. The final results point out, at least, two major aspects: (a) the repetitive visual stimulation is not a common driver for the left and the right hand PT processes and, more, (b) the visuomotor circuits of each subject should be viewed as a distinct system, endowed with a particular responding way to the external visual stimuli.