Browsing by Subject "Inter-subject covariance"

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  • Sarasjärvi, Kiira (Helsingin yliopisto, 2018)
    Objective: In the present study we investigated neuronal synchronization in post-traumatic stress disorder (PTSD) during real-time fMRI neurofeedback (rt-fMRI NF). We a used inter-subject covariance (ISC) -based method to discover model-free stimulus-response patterns that conventional GLM-analysis is not able to detect. So far, ISC has never been implemented in block-design nor rt-fMRI NF experiments, and only two studies have applied the method in a clinical sample. However, we hoped to find some distinct patterns that could disclose some new information regarding the psychopathology of PTSD and effects of neurofeedback. Methods: The study combined three previously conducted studies that focus on teaching participants to self-regulate anterior cingulate cortex (ACC) activity (HC=24, PTSD=9). The participants lay in the fMRI scanner whilst ACC activity was controlled with the help of a social avatar. The participants were measured three times within one week to examine the effect of neurofeedback. The analyses were completed by using ISC to detect the model-free brain activity. A 2x4 repeated ANOVA was used to investigate the group and neurofeedback effects. The ACC was chosen as a region of interest to investigate synchrony in the target region. An additional 3x4 repeated ANOVA was completed to examine the within and between-group ISC differences during the task. Results: We discovered a higher ISC in the PTSD group in respect to healthy controls, along with a linear decrease of ISC in both groups throughout the experiment. The same pattern was also detected in the ROI-analysis. The additional 3x4 ANOVA revealed a cluster in the orbitofrontal cortex showing a higher ISC within the groups, in respect to between the group ISC. Conclusions: ISC-analyses demonstrate a new type of information regarding the brain mechanisms and connections in respect to the conventional brain analyses. Our results indicate a stronger ISC in PTSD-groups and during the start of the experiment. Moreover, the results are reversed with comparison to the conventional GLM-method – demonstrating a new type of information regarding the brain synchrony. These results could further solidify the importance of the individual strategy used during the experiment. Furthermore, the additional analysis argues for disorder-specific synchrony in PTSD patients that could be meaningful in the psychopathology of PTSD. The thesis proves the feasibility of the ISC-method to discover direct stimulus-response relationship patterns that conventional GLM-analysis are not capable of revealing. Furthermore, it creates new research questions that have not previously existed and therefore it can be applied to neuroimaging.