The relationship between the brain networks for time perception and social stress

One of the most fundemental parameters known to affect time perception is emotion. Changes in mood alter the perception of time. It has been shown that negative stimuli tend to be perceived longer than they are actually presented. The aim of this study was to evaluate the effect of stress on time perception by functional brain imaging and to examine the relationship between these activations and methylation levels of dopamine-related genes. For this purpose, participants were performed a time reproduction task during fMRI acquisition and psychosocial stress was applied by giving false feedback that they performed poorly in half of the sessions during the acquisition. Cortisol samples were taken at 5 different times during fMRI session. A space reproduction task was used as a control condition. The time task required reproducing the duration of a circle remaining on the screen for a total of 5 target duraions ranging from 2 to 3.5 seconds, and the space task required reproducing the size of circles ranging from 100 to 175 pixels in radius. A total of 48 healthy adults aged 18-35 years participated in the study, and data from 45 participants were analysed (22 females and 23 males, age = 23.73 ± 3.85 years). Images were analysed by repeated measures ANOVA including task (time and space) and stress (stressed and non-stressed) conditions in MATLAB SPM12. No significant differences were observed in behavioural data. In the activations, the time main effect caused widespread frontoparietal activations, especially in the supplementary motor area (SMA). The stress main effect caused activations in the left hippocampus (HPC) and left ventral posterior cingulate cortex (vPCC), which are prominent in the regulation of stress. Stress and time interactions were observed in the inferior frontal gyrus and intraparietal sulcus. These activations were impaired only during the time perception task under stressful conditions, while activations related to space perception were not affected by stress. These findings indicate that high-level cognitive processing related to time perception is impaired in the presence of stressors. Activated areas were identified as ROIs and their relationship with methylation levels of dopamin related COMT, TH, DRD2, SLC6A3 genes, and glucocorticoid receptor gene (NRC3C1) was analysed. Significant relationships were observed between HPC and vPCC activations and methylations of genes related to the dopaminergic system. Rapid cortisol increase was found to be associated with lower vPCC activity. A negative correlation was observed between SMA activation and SLC6A3 gene methylation level. This relationship contributes to studies on the role of dopamine in time perception by indicating that SMA activation decreases in the time task as more dopamine is present in the synaptic cleft. With these findings, the specific effects of stress on time perception in the brain and its relationship with epigenetic mechanisms have been demonstrated for the first time in the literature.