Postural Hand Tremor and the Repetitive Photic Stimulation — A Coherence Joint Time Frequency Study.

This study aims to shed light on physiological tremor signal — an output of the motor system whose origins and possible functional role are still not well understand. In order to uncover some potential hidden frequency relationship between the motor system output and, respectively, the visual system input — the last system being regarded as to bring the major sensory inputs from all sensory modalities — a repetitive photic stimulation paradigm was implemented. In order to prevent the cortical driven oscillations to interfere with the spontaneous cortical rhythm, the stimuli frequencies were particularly chosen out of the alpha frequency band. Particularly, two visual stimuli were used, being delivered at different frequency (7 Hz, 19 Hz) — either concurrently, either alternatively -, in each of the visual hemifield. The subjects were asked to look all the time at a fix central point while the steady state visual evoked potential was induced — by visual peripherical repetitive stimulation — along the visual path at both, cortical and, respectively, subcortical level. Physiological postural hand tremor was recorded bilaterally during the period of stimulation. Assuming that the visual influence could be induced in tremor signal through either the cortical or through direct subcortical paths — given the potential ability of most sensory neurons to access the motor neurons -, the relationship of the tremor waveform to the light flashes was further investigated. For this, the coherence function was calculated within a joint time-frequency analysis (JTFA) type, for all three hand signal combinations (left-right, left-left, right-right). The preliminary results show the existence of a light coherence at the frequency of interest. To validate these results further investigations will be done. [ABSTRACT FROM AUTHOR]