# Use of Covariance Analysis in Electroencephalogram Reveals Abnormalities in Parkinson's Disease
## 4 Results
### Outlier Controls of Average Profile: Are They Potential Subjects of Risk? In this section, we show two cases that were notably different in comparison with other members of their groups: CL04 <60 and CL07 >60. These EEGs were obtained from subjects considered clinically healthy with no symptoms related to PD; however, as per our analysis, these two could be potentially in a prodromal state of neurological illness or in a condition other than the resting state at the time of data acquisition. Figure 7 shows the general wavelet profiles of both outliers. Figure 7A shows the global wavelet curves profile for CL04 <60. A main \(\delta\) brainwave was observed with a frequency value of 2.52 \(\pm\) 1.48 Hz and a power of 0.94 microV\({}^{2}\). A secondary \(\alpha\) brainwave was also identified with a frequency of 11.33 \(\pm\) 2.85 Hz and a power of 0.66 microV\({}^{2}\). Figure 7B shows the main frequencies profile for CL04 <60; the representative brainwave was \(\delta\), with frequency values of 2.12, 2.24, 2.38, 2.52, 2.67, 2.83 and 3.00 Hz, instead of the \(\alpha\) brainwave, which was the predominant in the members of the group. In this participant, the \(\alpha\) frequencies were also higher than the others, at 11.33 and 12.00 Hz. Figure 7C shows the power anomalies profile for CL04 <60. Negative anomalies were observed in the Fp and P channels with mean values of \(-\)1.8 and \(-\)0.1, respectively. Positive anomalies were identified in the F, T, C and O channels with mean values of 0.3, 1.3, 0.2 and 0.4, respectively. In comparison with our general wavelet profile of CL <60, we found opposite anomalies in the Fp and O channels. The anteroposterior gradient was observed from low to high power with a slope of 0.05. Figure 7D represents the brainwave power profile for CL04 <60; the \(\delta\) brainwave presented the highest power instead of the \(\alpha\) brainwave as it was observed in the CL <60 group. For this participant, the \(\alpha\) brainwave had the half of the \(\delta\) power, the \(\theta\) brainwave had less than half and the \(\beta\) brainwave had one-eighth the \(\delta\) power; the power values were 0.55, 0.49 and 0.12, respectively. In respect with the above mentioned, the results found in this participant showed more similarities with the general wavelet profile of PD patient >60 than with its own group. However, \(\delta\) frequency values obtained from this EEG were between 2.12 and  
Figure 7: Outliers’ profiles. (**A**) The global wavelet curves profile for CL04 <60. (**B**) The main frequencies profile for CL04 <60. (**C**) The power anomalies profile for CL04 <60. (**D**) The brainwave power profile for CL04 <60. (**E**) The global wavelet curves profile for CL07 >60. (**F**) The main frequencies profile for CL07 >60. (**G**) The power anomalies profile for CL07 >60. (**H**) The brainwave power profile for CL07 >60. 3.00 Hz instead of 2.38 Hz and 2.67 Hz, and the \(\alpha\) frequencies were between 11.33 and 12.00 Hz instead of 8.99 Hz. Figure 7E shows the global wavelet curves profile for CL07 >60. The main brainwave was \(\alpha\) with a frequency of 8.01 \(\pm\) 2.35 Hz and a power of 0.98 microV\({}^{2}\). The secondary brainwave was \(\delta\) with a frequency of 2.67 \(\pm\) 0.67 Hz and a power of 0.84 microV\({}^{2}\). In this participant, the \(\alpha\) peak was observed at the limit of the \(\theta\) brainwave. Figure 7F shows the main frequencies profile of the outlier CL07 >60; the \(\alpha\), \(\delta\) and \(\theta\) brainwaves were observed, instead of solely the \(\alpha\) brainwave as in the general wavelet profile of CL >60. Some \(\alpha\) frequency values in this participant were lower than those observed in the profile. The frequency values of the \(\delta\) brainwave were 2.52 and 2.67 Hz and the \(\theta\) frequency value was 7.56 Hz. Figure 7G shows the power anomalies profile for CL07 >60; positive anomalies in the Fp and C channels were observed, with mean values of 1.2 and 0.2, respectively.