## 4 Discussion
From a clinical perspective it has been noted that vestibular patients whose dizzy symptoms are unleashed by certain visual scenarios (i.e., visual vertigo) also demonstrate increased VD when evaluated with conventional approaches [27]. In agreement with this notion, an impaired vestibular modality in MCS patients would have led to an enhanced reliance on visual input, inducing subjects to upregulate this process and to increase VD by a sensory re-weighting [53; 27; 54]. To this end, the ability to adapt sensory-motor control to challenging circumstances by selection and weighting of alternative reference frames was postulated as one of the main aspects of postural control [55; 56]. Moreover, theoretical models of multisensory combination based on neurophysiological [57], perceptual [58] and behavioural evidence [59] proposed that adaptation to environmental changes would rely on sensory re-weighting to optimize both the relevance of individual sensory inputs and the reliability of estimates [48]. This kind of phenomenon is thought to be determined by maximum likelihood estimation so that the conscious and non-conscious brain processing appears as a near-optimal Bayesian estimator of object properties [56; 60]. Furthermore, recent findings have demonstrated disorders of vestibular function as characterized by complex perceptual, sensorimotor and behavioural deficits that exceed basic perceptions of head acceleration or motor responses, such as VOR or vestibulo-spinal reflexes [61; 62]. In order to thoroughly study these aspects of perceptual complexity, PCA was usefully performed to reduce the information dimensionality from the vast data arrays and to minimize the loss of information, relying on the fact that most of the descriptors are inter-correlated and these correlations in some instances are high [63; 64]. In accordance with these aspects, a rearrangement of the dimensions, clusters and contributions of the variables within PC1 and PC2 in MCS was found to be a conceivable model of re-weighting along vestibular sensory processing. In particular, in Figure 5A-C varimax rotation highlighted that although vHIT and VD parameters were almost equally clustered in both groups, MCS patients showed a positive correlation of FFT parameters in PC1 and classical posturography parameters in PC2. Moreover, together with vHIT parameters, VD parameters were found to be negatively correlated within PC2. In turn, HC subjects demonstrated a positive correlation of VD and classical posturography parameters in PC1, FFT PS in PC2 and vHIT values in PC3. Possible explanations for the rearranged model along vestibular processing and symptoms cohort referred to by MCS patients could be considered to reside within pathophysiological cascades, such as those involving limbic structures in the natural history of MCS [1; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15]. According to these notions, repeated exposure to MCS inducing agents were found to provide in MCS subjects both time-dependent sensitization and kindling, especially within hippocampal and limbic areas [65]. In turn, recent advances have postulated that additional \"higher\" vestibular dysfunctional aspects could really result from an impaired integration of the vestibular network within these areas [62]. This integration comprises both the internal representation of the body scheme and the internal model of the surrounding space as well as multisensory motion perception, attention, spatial memory, and navigation [62; 66]. In conclusion, although disorders of vestibular function integration remain to be completely elucidated, the present data would consider the MCS re-weighting process along bottom-up and top-down vestibular streams as possibly (i) related to MCS physiopathological cascades involving vestibular network at multiple levels; and (ii) underpinning the symptoms of dizziness referred to by the patients.