Using multiple regressions at each voxel, separately for each subject and each condition, find more we fitted the time course of the BOLD response recorded during
the first presentation of the video (e.g., the third run for the Entity video) with the time course of the BOLD response recorded in the same voxel during the second presentation of the same video (i.e., the fourth run for the Entity video; see Table S1 in Supplemental Experimental Procedures). This parameter captures the covariance between the BOLD signals at the same voxel, when the subject is presented twice with the same complex stimuli. Accordingly, IRC identifies areas responding to systematic changes within the complex stimuli, without any a priori knowledge or assumptions about the content of the stimuli and the cognitive processes associated with it (synchronization; see also Hasson et al., 2004). It should be noted that this procedure will miss any area showing learning-related effects that occur only during the first (e.g., encoding) or second (retrieval) presentation of the video and it is therefore not suitable for the investigation of memory processes. Together with the voxel-specific BOLD time
course, each regression model included the head motion realignment parameters and global signal of both fMRI runs (data and predictor runs). The regression models concerning the covert viewing conditions included losses of fixation selleck chemical as events of no interest. A cosine basis-set was included in the model to remove variance at frequencies below 0.0083 Hz. In addition, the IRC models for the Entity video included the predicted BOLD response for the human-like characters (i.e., delta functions time-locked to the characters’ onset, convolved with the HRF; separately for AG and NoAG characters), thus removing from the IRC estimation any common variance between the two runs that can be accounted for by the transient response
to these stimuli. Images resulting from the within-subject estimation Non-specific serine/threonine protein kinase entered the standard second-level analyses in SPM. These included three one-sample t tests (one for each condition: overt/covert viewing of the No_Entity video, plus covert viewing of the Entity video) assessing the statistical significance of IRC at the group level. A within-subject ANOVA was used to directly compare the IRC in the three conditions. Specifically, we compared brain synchronization during covert viewing of the Entity versus No_Entity video (i.e., the effect of video condition); and synchronization during covert versus overt viewing of No_Entity video (i.e., the effect of viewing condition). The p values were corrected for multiple comparisons at the cluster level (p-corr. < 0.05; cluster size estimated at p-unc. = 0.005), considering the whole brain as the volume of interest. As for our main hypothesis-based analyses, we also specifically assessed IRC in the rTPJ ROI.