Few minutes of focal vibration (FV) on limb muscles can improve motor control in neurological (stroke, Parkinson) patients for unknown underlying neurophysiological mechanisms. Previous results showed that FV increased excitability in the primary sensorimotor cortex (S1-M1) during an isometric contraction of the stimulated muscle (Lopez et al., 2017). Here, we will use the same archive data used in the reference study to evaluate whether FV is also able to modulate the cortical functional connectivity among S1-M1 and other brain regions in healthy subjects. To this aim, electroencephalographic (EEG) data recorded in 20 healthy young volunteers will be used. The design included an initial control condition with no FV stimulation (Baseline) as well as three short experimental sessions of FV and a Sham (fake) session in a pseudo-random order. In the Baseline condition and immediately after those sessions, EEG activity was recorded during a mild isometric muscle contraction of the right arm. We predict that, compared to the Baseline (no FV) or Sham stimulation, the first two FV sessions may show a cumulative modulation of functional connectivity between contralateral S1-M1 and the other cortical regions. These results would suggest a specific effect of vibration on the excitability and functional connectivity of contralateral S1-M1 generating EEG ``mu¿ rhythms. The expected outcome may help to explain the clinical effects of vibratory rehabilitation in neurological patients with motor deficits.
In line with the classical neurophysiological model describing the reduction of the ¿mu¿ rhythms during the execution of a voluntary movement, in a previous study (Lopez et al., 2016) bilateral alpha and beta MRPD during the isometric muscle contraction of the right arm was found. This effect might be due to several neurophysiological mechanisms, as shown by a bulk of literature evidence with several brain research techniques. Furthermore, we found that muscle FV induced an involvement of both somatosensory and motor neuronal circuits as revealed by the modulation of Rolandic alpha rhythms after the repetition of the FV. However, in that previous study, the authors could only provide a short discussion of the literature and a tentative explanation at the present early stage of the research. A deeper exploration of the neurophysiological mechanisms underlying to the cortical information processing in S1, M1, and premotor areas associated with sensorimotor events should be performed. In this framework, in the present study, we will conduct a re-analysis of the existing database to evaluate the functional connectivity among the S1-M1 contralateral and ipsilateral and other brain areas to assess the directionality of somatosensory information processing along FV protocol. The results of the present study will complement the previous one in providing a complete overview of which may be the neurophysiological model for the explanation of the long-lasting clinical effects of vibratory rehabilitation in neurological patients with motor deficits.