Introduction of a new synchronization index by correlating Leg Movements and overall activity distinguishes subjects with normal cognitive functioning from those with MCI: Preliminary results

Abstract

AbstractBackgroundExploratory data analysis was performed, looking after correlations of Leg Movement (LMs) against the 22 full‐EEG polysomnography during sleep. The EEG signals were recorded with the 19 derivations from the traditional International 10/20 electrode placement, chin electromyography (EMG), and electrooculogram (EOG). Nine subjects were considered: six in the Mild Cognitive Impairment (MCI) group, and three controls (CTRL). In line with the hypothesis about phasic activity reorganizing cerebral processing, lower correlations were expected for MCI, during REM sleep.MethodFor each subject, the first rotation (PC1) of the Principal Component Analysis (PCA) decomposition of the data (22 channels) was generated. This accounts for the direction of the maximal variance. The proportion of variance explained by PC1 was very high (Table 2). In view of this, pairing the LMs and the PC1 time series allowed for reliable comparisons. As expected, there was no linear relation between the LMs and each of the channels: out of 198 pairs (22 for each subject), the maximal correlation coefficient was 0.0194. Therefore, it was natural to look for nonlinear relationships. The metric considered, was the total variation, at 5‐second intervals. The total variation corresponds with the arclength of the graph and is a measure of variability of a time series. For each subject, correlation coefficients were calculated for the total variations for LM versus PC1.ResultThe mean coefficients for the CTRL group were higher than those for the MCI group for all the sleep epochs (Table 1). The difference was highest for REM sleep. In Table 2, the coefficients of the PC1 for each subject and variable (PC1) are presented (variations of one subject, Fig. 1).ConclusionDue to the small size of the sample, it is not possible to draw any actual conclusions. However, anecdotal evidence was found for differences in synchronic activity between groups. This was most notorious for REM sleep, with decreased correlations for the MCI group. It would be of interest to replicate this study with a much larger sample.