# Quantitative Electroencephalography: Cortical Responses under Different Postural Conditions
## 1 Introduction and Fundamentals  
Quantitative electroencephalography (QEEG) differs from clinical EEG as it mathematically analyses the tracing of brain waves even in non-pathological states, without necessarily having a clinical purpose [1, 2]. Some interesting frontiers in the use of these techniques are linked to sport [3, 4, 5] or to the analysis of potential predisposing factors for neurodegenerative pathologies, with a preventive approach [6]. [PERSON] and [PERSON] indeed explain that there is still limited evidence examining cortical activity during reactive balance tasks in populations with a high risk of falling [7]. It is possible to find differences in EEG signals recorded in volunteers with closed eyes compared to those with open eyes as regards the alpha frequency band (8-13 Hz) [8, 9]. A study by [PERSON] and colleagues demonstrated that a certain decrease in the power density of the alpha band in the field of EEG signal frequencies was evident in the parietal area of volunteers standing with monopodalic support, compared to those standing with bipodalic support [10]. A recent study by [PERSON] and colleagues also demonstrated that it is possible to measure the cortical responses of volunteers engaged in postural control tasks by adding pupillary analysis to the quantitative EEG. Researchers have demonstrated that EEG can be an excellent non-invasive tool for assessing the cortical involvement of postural control. Their aim was to understand the effect of increased postural task difficulty on pupillary response and EEG outcomes, and their relationship, in young adults; however, their study used a much more complex multichannel EEG system than the onepresented in this study [11]. [PERSON] et al. explained that cortical activity involvement in postural control is well recognized; however, the role of non-visual afferents remains unclear. The parietal cortical areas are strongly implicated in vestibular-spatial functions, but topographical localization during balance tasks remains limited [12]. Concerning visual deprivation during postural tasks, [PERSON] and colleagues stated that responses to postural perturbation caused by visual occlusion are similar in nature to those observed in relation to a physical perturbation [13]. [PERSON] and colleagues also highlighted how little understanding exists of the neural mechanisms underlying the continuous control of balance, and specifically underlined the important role of frontal and parietal electrocortical activities in balance control [14]. In the present study, we highlight the differences in EEG responses between a specific posture with eyes open and with eyes closed, within the EEG spectrum of the alpha bands (8-13 Hz) and also beta (13.5-30 Hz), in agreement with the analysed literature. We investigated the exclusion of visual feedback in a sitting position with eyes open (OA task) and with eyes closed (OC task), in a bipodalic stance with eyes open (BIPOA task) and with eyes closed (BIPOC task) and, finally, in a monopodalic stance with eyes open (MONOA task) and with eyes closed (MONOC task), highlighting the differences in the previously mentioned spectra. One of the major problems in electroencephalographic analyses is the presence of artefacts, of which the myoelectric type is the most problematic; it is therefore necessary to avoid recording artefacts produced by the contraction of the superficial musculoaponeuotic system (SMAS) [15]. First, we developed a prototype headcap capable of limiting these artefacts; then, we analysed the recording of relatively long tasks so that individual peaks of myoelectric activity were averaged over the entire length of the action, significantly reducing the influence of the artefact on the result of the analysis.