Shubhangi Gautam received her MS Dual Degree in Computational Natural Sciences (CNS). Her research work was supervised by Dr. Kavita Vemuri. Here’s a summary of Shubhangi Gautam’s thesis, Investigating Differences in the Default Mode Network in Empathy Stimulus.
Empathy, a complex social skill, allows for the ability to understand the emotional and cognitive states of another. In general, empathy is crucial in the social world and for survival. Several studies have demonstrated that the default mode network (DMN) is involved in the process of internal mental simulations (also known as mind wandering) – an aspect significant for empathetic response. Researchers have found an overlap in brain regions between the social networks and the DMN. Since the DMN is activated during the mind wandering process, most of empathy literature has examined the DMN during resting state. Therefore in this thesis, we investigate the functional connectivity differences in resting state DMN and empathy-task DMN.
In this study, we apply a novel time-frequency filter method on the BOLD signal to investigate the FC of the DMN. The aim of this thesis is to demonstrate the role of the DMN in empathetic processes and to further identify the time-frequency characteristics of the DMN activations during free-viewing emotional movie clips. Specifically, we use movie clips because research has shown more intense emotions being evoked in participants during dynamic stimuli vs static stimuli. And since we want to capture the complex psychological process of empathy, we decided to use emotional movie clips to portray the naturalistic complexity of human interactions.
It must be noted that the time-frequency technique used in this thesis (the single frequency filter bank) provides a better resolution compared to traditional approaches such as sliding window. Using this novel technique, analysis on two sets of FMRI data were conducted to examine the time-frequency dynamics. To the best of our knowledge, this is the first study to explore the time-frequency characteristics of the DMN in empathy tasks.
In the first experiment, fMRI response signals from the three short diverse movie clips (Disney, Green, and Taare) were analyzed. Before the stimuli was presented, resting state data of 3 minutes was also recorded for the 8 participants. Specific scans which consisted of the most emotional scenes were chosen to conduct the comparative analysis. The results from this preliminary investigation demonstrated differences in the activations between empathetic task vs resting state. This preliminary study corroborates findings from previous studies. For example, we found highly skewed power distributions where most power was at the lowest frequencies. This has been shown in previous research as well.
In the second experiment, two longer movies (of 9 minutes) were used as the empathetic stimuli – M1 (“These Times”) and M2 (“Most” – retitled “The Bridge”). The scores on empathy response scene-wise was collected from the scanned participants in addition to the IRI Davis empathy index. Resting state data of 4.5 minutes was also collected from the participants. In this experiment, we verified the findings from the first study and dug deeper into the DMN by analyzing specific brain regions – ACC, IPL, PCC, Precuneus, and mPFC. We grouped the participants into low vs high empath groups based on their self-reported scores and analyzed the amplitude of power spectral density differences. It was interesting to find that in both movies (M1 and M2) in the 0-0.1 Hz band, we observed significant differences in the power fluctuations in the ACC, mPFC, and IPL while the PCC and Precuneus did not show significant differences. In the 0.1-0.25 Hz band, there were more fluctuations compared to the 0-0.1 Hz band for both movies. However we realized that each group (low vs high empaths) showed different fluctuations and brain activation patterns for each movie in the 0.1-0.25 Hz band. For example in M2 in this frequency band, low empaths had large fluctuations while in M1 high empaths had large fluctuations. Thus, highlighting the importance of how situational contexts (in this case, the different movie plots / storylines) can impact empathetic and brain responses and the role of DMN. Additionally, we evaluated if there were any significant differences in the resting state DMN of low vs high empaths. In the 0-0.1 Hz band, a difference was observed where high empaths had larger power and no significant differences were found in the 0.1-0.25 Hz band.
The time-frequency method (Single-frequency filter bank) applied gave better resolution to analyse the low-frequency amplitudes and its significance in FC analysis. We also demonstrate the differences between the empathy task DMN vs resting state DMN. And significant contribution is the finding of resting state DMN analysis as a potential marker for empathy. The results are preliminary (due to the small data set) and larger dataset is required to confirm the role of task-DMN and rs-DMN as markers for empathy response.