Understanding individual differences in brain function is one of the fundamental goals of neuroscience. Natural stimulus imaging induces individual differences in brain responses in near-life scenarios. The natural stimulus paradigm is more similar to the external world and has better ecological validity than the paradigm of multiple repetitions of simple stimuli, making it a promising paradigm for individualized research. The search for biomarkers that characterize individual differences in mental or psychological traits is an important task in cognitive neuroscience, and the reliability is a fundamental prerequisite for biomarkers to be widely recognized and applied. This dissertation reports three studies designed to test the reliability of individual differences reflected by the natural stimulus imaging method and to test the ability of the method to reflect individual differences and identify different groups in clinical psychological research.
Study 1 used repeated measures data to examine the reliability of individual differences in brain activity reflected by naturalistic stimulus imaging and to compare the differences in the reliability of naturalistic scenery and social-emotional content in reflecting individual differences. 24 healthy subjects were recruited and their resting-state, brain imaging data from viewing natural stimuli (Movie A: natural scenery, Movie B: emotionally rich clips) and a series of behavioral data were collected twice a week apart. The Mantel test was used to examine the reliability of inter-individual relationships expressed by the inter-subject correlation in the naturalistic imaging and to compare the reliability of the brain imaging data with that of the behavioral test. The results showed that: (1) The certain brain regions were stable in characterizing inter-subject correlation and the superior temporal lobe showed comparable stability to the state subscale of the State and Trait Anxiety Inventory (STAI); (2) brain regions that were highly stable in expressing individual differences could maintain this ability in emotional movies with different content and thus may reflect individual "traits"; and (3) social-emotional content contributes to the reliability of individual differences in natural stimulus expression of brain activity.
Study 2 used the above test-retest data to verify the reliability and individual discrimination of the typicality coefficient, an individual indicator of naturalistic imaging. The typicality coefficient reflects the similarity of individual and group- averaged time series. We investigated the ability to identify whether two sessions were of the same subject under different stimulus conditions (resting-state, natural scenery, and emotionally rich clips) at the region of interest scale and network scale for functional connectivity, reho, alff, time series, and subject typicality coefficients, respectively. The results showed that: (1) The certain brain regions could consistently characterize subject typicality coefficient, and in these regions, the relative position of subjects in the group remained consistent; (2) the correct recognition rates of functional connectivity, reho, and alff were higher than those of time series and typicality coefficient at either spatial scale, but there were no significant differences in the three different stimulus conditions, while time series and typicality coefficients showed higher recognition accuracy in movies with emotionally rich clips than those with natural scenery; (3) The recognition accuracy of functional connectivity, reho, and alff were more susceptible to spatial scale.
Study 3 applied the natural stimulus paradigm to a study of brain function in participants experiencing a major stressful event and tested the ability of the natural stimulus paradigm to reflect individual differences and group differences. In this study, brain imaging data and a series of behavioral scales were collected from 44 participants experiencing the same major stressful event (experiment group) and 39 participants with the same occupation and age range (control group) while watching 5 movie clips, 2 of which were movie material related to first-hand experiences of the experiment group. We compared the differences in inter-subject correlation across the groups. The results showed that: (1) Different brain regions in different movie clips characterized inter-subject correlation differences between the groups; (2) the above-mentioned regions of interest also reflected higher functional connectivity when they had higher inter-subject correlation; (3) using subject typicality coefficient to predict the participants’ group was slightly more accurate than using behavioral scores; (4) some of these brain areas associated with traumatic experiences recovered to a similar level as control group after six months, and some did not; (5) the activity in these brain regions associated with traumatic experiences was also associated with specific behaviors.
The results of these studies support the ability of the natural stimulus imaging methods to reflect individual differences stably and effectively in brain activity, providing an important basis for the clinical application of natural stimulus imaging. The reliable brain regions identified in the study suggest target regions for future studies of individual differences in brain function and the realization of neuroimaging-based diagnosis of mental disorders. We also verified the advantages of the natural stimulation paradigm in clinical psychological applications.