4.2.1 Feature analysis of emotional EEG signals based on power spectrum
We decompose the EEG signal by db4 wavelet to obtain the EEG signal data in the alpha, beta, delta, and theta frequency bands, and then calculate the power values of these four EEG signal frequency bands in the frequency domain, and divide it by the EEG signal data before wavelet decomposition The power value of the signal to get the relative power value. Figure 3 shows the relative power changes of the music stimulation group before and after the test, and Fig. 4 shows the neurofeedback training group.
The relative power of the alpha frequency band in the music stimulation group is shown in Fig. 3 (a), where the relative power values of the AF3-AF4, F7-F8, FC5-FC6, and T7-T8 electrode pairs after the test were greater than those before the test. The relative power in the Beta frequency band is shown in Fig. 3 (b), where the relative power values of the AF3-AF4, F7-F8, P7-P8, O1-O2 electrode pairs after the test are greater than before the test. The relative power in the Theta frequency band is shown in Fig. 3 (c), where the relative power values of AF3-AF4, F7-F8, FC5-FC6, and T7-T8 electrode pairs after the test are greater than before the test. The relative power of the Delta frequency band is shown in Fig. 3 (d). Except for the F7 channel, the relative power values of the other channels after the test are all smaller than before the test.
The relative power of the alpha frequency band in the neurofeedback training group is shown in Fig. 4(a), where the relative power values of the AF3-AF4, P7-P8, and T7-T8 electrode pairs after the test were greater than those before the test. The relative power of the Beta frequency band is shown in Fig. 4(b), where the relative power values of AF3-AF4, F3-F4, T7-T8, O1-O2 electrode pairs after the test are greater than before the test. The relative power in the theta frequency band is shown in Fig. 4 (c), where the relative power values of the P7-P8 and O1-O2 electrode pairs after the test are greater than those before the test. The relative power of the delta frequency band is shown in Fig. 4(d). Except for the T8 channel, the relative power values of the other channels after the test are all smaller than before the test.
According to the paired sample t test, the channels with statistically significant (P < 0.05) relative power differences before and after the music stimulation group are: AF3-AF4, F4, F7-F8, T7-T8, FC5, O2 in the alpha frequency band. AF3, F3-F4, F7, T8, P7-P8, O1 in the beta band. AF3-AF4, F4, F7-F8, T7-T8, P8, FC5-FC6, O1-O2 for theta bands. All channels in the delta band. Neurofeedback training group: AF4, F7, T7, P7-P8, O2 in alpha bands. AF3, F7, P7 for beta bands. AF3, F7, T8, P8 in theta band; AF3, P8, FC5 in delta band. Only AF4 in the alpha frequency band, F7, P8 in the beta frequency band, and F3 channel in the delta frequency band had statistical significance in the blank control group.
That is, after the test, the locations where the relative power was significantly increased were concentrated in the frontal and temporal regions.
1) Music stimulation group: alpha, theta frequency band frontal area (AF3-AF4), anterior middle temporal area (F7-F8, T7-T8), central area (FC5-FC6), beta frequency band frontal area (AF3-AF4 ), front and rear temporal regions (F7-F8, P7-P8), and occipital regions (O1-O2).
2) Neurofeedback training group: alpha frequency band frontal area (AF3-AF4), middle and posterior temporal area (T7-T8, P7-P8), beta frequency band frontal area (AF3-AF4, F3-F4), theta frequency band Posterior temporal area (P7-P8).
3) All channels are averaged, except for the delta frequency band, the relative power values of the other frequency bands after the test are greater than before the test. There was no significant change in the control group.
In the study of emotion-related EEG signals, considering the asymmetry of the left and right brain regions in the emotional processing of the human brain is a commonly used analysis index. The results of our calculation of the relative power asymmetry index before and after the test are shown in Figs. 5 and 6. The blue line indicates the relative power asymmetry index before the experiment, and the red line indicates the relative power asymmetry index after the experiment. The asymmetry index was calculated as the relative power of the right hemisphere of the brain minus the relative power of the corresponding electrode in the left hemisphere.
The yellow column represents the difference between the relative power asymmetry index of the left and right hemispheres after the test minus the pre-test, that is, the difference of the asymmetry index, which is used to more intuitively observe whether the difference before and after the test is positive or negative. The difference is positive, that is, the asymmetry increases after the test, the relative power of the right brain increases or the relative power of the left brain decreases, or the increase of the right brain and the decrease of the left brain exist at the same time. All of the above tend to be negative emotions. The difference is negative, that is, the asymmetry decreases after the test, the relative power of the left brain increases or the relative power of the right brain decreases, or the increase of the left brain and the decrease of the right brain exist at the same time. All of the above tend to be positive emotions.
In summary, in this article we need to pay attention to the brain areas where the asymmetry decreases or is close to 0 after the test, that is, the asymmetry difference is negative. We averaged all the channels and calculated the relative power asymmetry difference before and after the test, as shown in Table 2. After the alpha, beta, and theta frequency band tests of the music stimulation group and the neurofeedback training group, the difference of the asymmetry index changed from positive to negative. This shows that the numerical value of the asymmetry decreases after the test, which means that the relative power of the right hemisphere increases, or the relative power of the left hemisphere decreases, or the relative power of the right hemisphere increases and the relative power of the left hemisphere decreases simultaneously. The above three situations all indicate that the subject has changed from a tendency of negative emotions to a positive emotion or a normal state. There was no significant change in the control group.
Table 2
Differences of relative power asymmetry index before and after the test
Group | Alpha | Beta | Theta | Delta |
pre | post | pre | post | pre | post | pre | post |
music stimulation | 0.0216 | -0.0289 | 0.0093 | -0.0253 | -0.0346 | -0.0093 | 0.0253 | 0.0346 |
neurofeedback training | 0.0049 | 0.0021 | 0.0021 | -0.0078 | 0.0281 | 0.0037 | -0.1427 | 0.0216 |
control | 0.0130 | 0.0075 | 0.0042 | 0.0087 | -0.0455 | -0.0249 | 0.0025 | 0.0127 |
The above conclusions show that the music stimulation test and neurofeedback training can increase the relative power value of the right hemisphere in the alpha, beta, and theta frequency bands of the subject, and reduce the relative power value of the left hemisphere, or reduce the asymmetry between the left and right hemispheres. Especially concentrated in the frontal area and the middle and posterior temporal areas. Previous studies have found that the left and right hemisphere asymmetry of the frontal lobe and parietal lobe is common in people with negative emotions such as depression, and depression has an asymmetry in which the power of the right hemisphere is greater than that of the left hemisphere. From this point of view, the relative power asymmetry index obtained in this paper is consistent with the above conclusions.