Inter-subject correlation


This method is motivated by recent findings in two disparate fields. First, electrophysiological studies indicate that neuronal responses are more reliable (reproducible) under naturalistic stimulus conditions than under conventional laboratory conditions using artificial stimuli (Belitski et al., 2008; Mechler et al., 1998; Yao et al., 2007). Second, our human fMRI studies indicate that some natural stimuli evoke highly reliable, selective, and time-locked activity across a wide network of brain areas. The data are analyzed by comparing the neural (e.g., fMRI, ECOG) response timecourses across different subjects over the course of the natural stimulation (e.g. listening to a story or watching a movie). We called this correlation method inter-subject correlation (ISC; Figure 3A). The ISC analysis method differs from conventional fMRI data analysis methods in that it circumvents the need to specify a model for the neuronal processes in any given brain region during movie watching. Instead, the ISC method uses the subject’s brain responses to naturalistic stimuli as a model to predict brain responses within other subjects.


Read more:

1. Hasson U, Nir Y, Levy I, Fuhrmann G, Malach R (2004) Intersubject synchronization of cortical activity during natural vision. Science 303:1634-1640. [PDF]

2. Mukamel R, Gelbard H, Arieli A, Hasson U, Fried I, Malach R (2005) Coupling between neuronal firing, field potentials, and FMRI in human auditory cortex. Science. [PDF]

3. Hasson U, Malach R, Heeger DJ (2010) Reliability of cortical activity during natural stimulation. Trends Cogn Sci 14:40-48. [PDF]

4. Ben-Yakov A, Honey CJ, Lerner Y, Hasson U (2012) Loss of reliable temporal structure in event-related averaging of naturalistic stimuli. NeuroImage 63:501-506. [PDF]





Inter-subject functional correlation


Standard functional connectivity (FC) analysis is a measure of the temporal correlation across different brain areas within an individual. The inter-subject functional coherence (ISFC) differs from standard FC analysis in one crucial way: it is calculated across brains rather than within brains. The ISFC method provides a novel way to isolate the stimulus-locked response component of each functional network, by correlating the response timecourse across brains. Intrinsic neural dynamics during the resting and task conditions that are not related to the processing of stimuli, as well as non-neuronal artifacts (e.g., respiratory rate, motion), can only influence the pattern of connectivity within each task trial, but cannot induce correlations between trials. In contrast, neural processes that are locked to the structure of the stimulus can be correlated across brains. Thus, the ISFC method allows us to track the stimulus-locked brain processes within a network during the processing of real-life stimuli and to study the dynamical evolution of network architectures during real-life information processing.
Read more:
1. Simony E, Honey CJ, Chen J, Lositsky O, Yeshurun Y, Wiesel A, Hasson U (2016) Dynamic reconfiguration of the default mode network during narrative comprehension. Nat Commun 7. [PDF,   PDF+ Supp]