3.1. Study of Short Duration
In this experiment, the subjects were required to listen to favorite and relaxing music. The FC of the brain in each frequency band can be observed from network density and node strength. Listening to different types of music affects the brain’s functional connectivity. Depending upon the type and genre of the music, the functional connectivity of the listener can change. The strength of some connections can either increase or decrease in different frequency bands, which in turn cause the network density to either increase or decrease. After the raw EEG signals were processed and filtered, the network density at all three stages (baseline, after listening to favorite music, and after listening to relaxing music) was calculated for each frequency band using the connectivity matrices. The thresholds used to display the connections between different frequency bands are different depending upon the IPSC values. Although the connections seem great in the delta band, the threshold used is 0.0% above the median value, while in the case of the alpha band, it is 25% above the median value. This means that the change in the alpha band is much higher than that of the delta band. Similarly, the threshold for the theta band is 8%, and for the beta band, the threshold is 11% above the median value. For the average connectivity matrix, the threshold used is 0.25% above the median value. The color code shows the strength of the connection between nodes, with blue being the weakest and red being the strongest connection in each frequency band. The strength of the connection is also reflected by the thickness of the connection on each topo-map. The color code for the connectivity matrix can be seen in
Figure 4.
Table 1 shows the original grand averaged connectivity matrix and grand-averaged weighted connectivity topo-maps after the application of the threshold for delta, theta, alpha, and beta bands and general FC, respectively. In the topo-maps, the color of the connections and the size of each node indicate the strength of the edges and nodes, respectively. The change in the number of connections and the connection strength can be seen in each figure. These findings suggest that music influences the brain’s FC.
It can be seen from the topo-maps in
Table 1 and
Table 2 that there is no change in network density and number of connections in the delta frequency band. In the theta frequency band, the number of connections increased in the case of relaxing music, while in the case of favorite music, the number of connections decreased. The network density in the alpha band increased after listening to both kinds of music, while a greater change can be seen in the case of favorite music. Similarly, the beta band network density increased after listening to favorite music but decreased after listening to relaxing music. The grand averaged connectivity over the complete frequency range shows that the network density and number of connections increased after listening to both favorite and relaxing music.
To analyze the significance of the results obtained above,
t-test and ANOVA were carried out. The results of the
t-test and ANOVA are shown in
Table 3. The edge strength is used to evaluate the test. The
p-value of 0.05 is used as a significance level. This means that if the
p > 0.05, the null hypothesis is true; otherwise, it is false. From the statistical tests, a significant change in edge strength can be seen in alpha, beta, and theta bands after listening to both types of music. In the case of the grand average and delta band, the change is not significant.
To further analyze the changes associated with listening to music, the network strength of each lobe was calculated separately, and statistical tests were applied to them to get the significance of the change.
t-test and ANOVA were carried out and the results are shown in
Table 4. The
p-value of 0.05 is used as a significance level. The results of the statistical tests indicate a significant change in the frontal lobe in all frequency bands after listening to both types of music. In the beta frequency band, a significant change can be seen in the parietal lobe after listening to favorite and relaxing music, while a significant change in edge strength can also be seen in the beta band in the occipital lobe after listening to favorite music.
3.2. Study of Long Duration
The individuals in the Music Listening Group were directed to listen to relaxing music for at least 30 min for two weeks in the long-duration study. After one and two weeks, the EEG data were recorded. The recorded EEG signals were then processed and cleaned, and the connectivity matrices were generated using ISPC. The difference in brain FC amongst the Control and Music Listening Groups can reveal the impact of music on the brain. The threshold was selected in the same way as for the short-term study.
Table 5 shows the original grand-averaged connectivity matrix and grand-averaged weighted connectivity topo-maps after the application of threshold for delta, theta, alpha, and beta bands and full-frequency-range FC, respectively, for the Control Group and the Music Listening Group. In the topo-maps, the color of the connections and the size of each node indicate the strength of the edges and nodes, respectively. The color code for the connectivity matrix can be seen in
Figure 4.
Table 6 shows the network density and number of connections for each group and each frequency band. Here, there is no change in network density of the delta band, but in the music listening group, after week 2, the edge strength is decreased. In the theta frequency band, an increase in network density was recorded, while a decrease in the number of connections can be seen in the control group. Similarly, in the alpha frequency band, a decrease in network density was recorded for the control group, while an increase in network density can be seen in the music listening group after two weeks. In the beta frequency band, a decrease in the number of connections in both the control and music listening group was recorded. The grand average of the full range of frequency shows an increase in network density after two weeks of listening to relaxing music, while in the control group, the number of connections decreased for the first week and then increased.
To analyze the significance of the results obtained above,
t-test and ANOVA were carried out. The results of the
t-test for each band are shown in
Table 7. The edge strength is used to evaluate the test. The
p-value of 0.05 is used as a significance level. The results indicate a significant change in edge strength of delta frequency band in Music Listening Group after one week. In the beta frequency band, after one and two weeks, a significant change in edge strength can be seen in the Music Listening Group. In alpha and theta frequency bands, a significant change in node strength can be seen in both groups after two weeks. The statistical analysis of the grand average of the full range of frequency bands also shows a significant change in edge strength in the Music Listening Group after two weeks.
To further analyze the changes associated with listening to music, the network strength of each lobe was calculated separately, and statistical tests were applied to them to get the significance of the change.
t-test and ANOVA were carried out, and the results are shown in
Table 8 and
Table 9. The
p-value of 0.05 is used as a significance level. The results of the statistical tests indicate a significant change in the frontal lobe in alpha, beta, and delta frequency bands after two weeks in the Music Listening Group. Similarly, a significant change in edge strength can be seen in the parietal lobe within the delta and theta frequency band of the Music Listening Group after two weeks. After two weeks, the temporal lobe also shows a significant change in edge strength within the Music Listening Group and as well as in the control group.
In the study of the long-duration effect of music over the human brain, the strength of a few connections in the frontal lobe increased significantly (FC5-F7, FC6-F8, and F3-F4). The increase in the strength of these connections was recorded not only in the complete spectrum but also in the alpha, beta, and theta bands. Similarly, an additional connection between P8 and T8 was also observed. As shown in
Table 10, the above-mentioned connections can be seen as the strongest connections. The additional connections in the frontal lobe may result in enhancement in problem-solving, judgment, planning, and attention, while the connectivity in temporal regions may indicate memory enhancement [
41,
42].
In this research, the effect of music on the human brain was explored. To further understand the effect, the response of the subject while listening to music was analyzed in different frequency bands, i.e., delta, theta, alpha, and beta, as well as in different brain lobes, i.e., frontal, parietal, temporal, and occipital lobes. In the short-duration study of the effect of music listening on the human brain, it was concluded that both favorite and relaxing music can induce change in FC of the brain. However, the change induced by the relaxing music is more significant than the change caused by favorite music. The above-mentioned results show that listening to favorite music can significantly increase alpha and beta FC and decrease theta FC. A significant change in frontal lobe connectivity in alpha, beta, and theta bands was also seen after listening to favorite music. The increase in alpha FC indicates a relaxation state and increases the ability to perform a prolonged mental effort [
43], while the increase in beta FC indicates the increase in the concentration and motor learning performance of the human subject [
44]. On the other hand, listening to relaxing music significantly increases the FC in the frontal lobe within the alpha and theta band while decreasing the FC in the frontal, parietal, and occipital lobes within the beta frequency band. This increase in alpha and decrease in beta FC indicates the induction of a relaxing state in the subject [
45]. Long-duration study of the effect of music listening on the human brain significantly increases the FC in the frontal and parietal lobe within the alpha and theta band while decreasing the FC in frontal, temporal, and occipital lobes within the beta frequency band. This increase in alpha and decrease in beta FC indicates the induction of a relaxed state in the subject [
45]. In the Control Group, this change in FC was not significant. These results are also in accordance with the experiment conducted by Nawaz et. al. [
25], in which alpha power analysis was used to study the effects of music on the human brain. In the study of the long-duration effect of music on the human brain, a significant change in delta, alpha, and beta frequency bands was observed. The increase in FC in the delta band indicates improvement in attention, homeostatic, and motivational processes [
46]. The increase in alpha FC indicates a relaxation state and increases the ability to perform a prolonged mental effort [
43]. The results of the study conducted by Nawaz et. al. also support our findings, which indicate that the said results are the effect of the listening of music rather than any flaw in the evaluation process or noise.