Psicofisica e correlati elettrofisiologici (sLORETA) delle illusioni di movimento indotte da vibrazione

[Autom. eng. transl.] The vibratory stimulation of the tendons that anchor the skeletal joints induces an illusory perception of movement in most people. This stimulation is, in fact, able to activate the muscle spindles and selectively elicit trains of action potentials in the primary endings connected to the afferent fibers Ia, generating signals erroneously traced back to movements of the body segment concerned. Although the anatomical network that mediates these illusions is partly known, their functional and psychophysiological correlates are still being studied. The aim of the present research is to investigate the illusory perceptions of vibration-induced movement by measuring their electrophysiological correlates (EEG) and qualifying them from a psychophysical point of view in terms of frequency, intensity and duration of the perceived illusion. Seventeen right-hand volunteers took part in the study. Two participants never perceived the illusions of movement and were therefore excluded from the analysis. After mounting a 28-channel EEG system and an adaptable wrist splint, the vibration stimulator was positioned at the flexor tendons of the right wrist, perpendicular to their course. Finally, the limb was hidden from view by a screen. The experimental design involved the reiteration of 15 trials with baseline and stimulation periods, at the end of which participants were asked to report and describe any perception of movement that affected the right hand. The EEG traces were analyzed in the frequency domain by extracting power data used for the signal source localization procedure (sLORETA). The analysis of psychophysical data has shown significant correlations between the frequency and average intensity of illusory perceptions, and between the intensity of these perceptions and their estimated duration. The comparison analysis of the EEG data related to the baseline and to the stimulation periods characterized by the presence of illusory perceptions showed a significant decrease of the upper-alpha component (cortical activation), in particular at the expense of the insular and prefrontal regions. Finally, correlation analyzes between psychophysical data and data on intra-cerebral current density distribution have highlighted significant relationships between the activation of parietal regions and the frequency of illusory perceptions. The integrated analysis of psychophysical and electrophysiological data shows a clear consonance between the conscious experiential level and the electrophysiological modulations that induce the phenomenon of motor illusions, and suggests that pre- and post-central structures play different roles in their definition. In particular, the thorough investigation of the EEG components can help to clarify the contribution of the upper parietal areas in the conscious experience of illusory movement.