Intersubject Synchronization of Cortical Activity During Natural Vision

Uri Hasson, Yuval Nir, Ifat Levy, Galit Fuhrmann, Rafael Malach

To what extent do all brains work alike during natural conditions? We explored this question by letting five subjects freely view half an hour of a popular movie while undergoing functional brain imaging. Applying an unbiased analysis in which spatiotemporal activity patterns in one brain were used to "model" activity in another brain, we found a striking level of voxel-by-voxel synchronization between individuals, not only in primary and secondary visual and auditory areas but also in association cortices. The results reveal a surprising tendency of individual brains to "tick collectively" during natural vision. The intersubject synchronization consisted of a widespread cortical activation pattern correlated with emotionally arousing scenes and regionally selective components. The characteristics of these activations were revealed with the use of an open-ended "reverse-correlation" approach, which inverts the conventional analysis by letting the brain signals themselves "pick up" the optimal stimuli for each specialized cortical area.



http://www.sciencemag.org/cgi/content/short/303/5664/1634

Can this be our next journal club topic?

Jen

Hi all,

So what I think is most interesting about this article is how really uninteresting this really is. (sorry to any fans). As far as I can tell, there is no information in this study. These guys show that regions previously shown to be driven by stimulus features are driven by the stimulus features of a film. For example, when faces appear on screen, voxels in the fusiform face area are driven accross subjects. Of course they are. This has been shown in hundereds of studies an hardly qualifys as a Science paper!

It may have been interesting is they had shown coherence in regions of the brain we know to be responsible for more abstract thinking, for example limbic or prefrontal cortices, rather than stimulus features. Then they could make some claim that the these complex stimuli were provocing similar thoughts in different subjects (maybe). However, they do not show coherence in any part of the brain that isn't driven by stimulus features.

Anyway, for any of those intersted, these are my thoughts.

Jen

I thought it was an entertaining article. Initially, as I first started reading it, I was expecting the authors to sensationalize their findings, but they did a pretty good job of not going overboard. As they note in the discussion, the sluggish time courses of the BOLD signal are problematic.... you can't conclude from their study that inter-subject coherence will occur at finer timescales, like on the order of milliseconds. I found it interesting that the authors discerned regional non-specific intersubject correlations (which they thought might relate to correlated levels of movie-induced arousal), in addition to the regionally-specific ones. The averaging over FFA's across subjects before applying the reverse-correlation to predict movie scenes based on "averaged FFA" BOLD signals seemed a bit sketchy to me because I think there's too much inter-subject variability in the location of the FFA, even after Talairach transformation, to make this averaging legitimate or useful. I don't think they ever say what delta t (temporal precision) they used for scanning....you would expect that scanning parameters would be set to optimize temporal resolution of the BOLD signal for purposes of their inter-subject correlation computations, but I don't think they ever make it clear in the article whether they do this or not. If they don't, and have scan time resolutions of 2 or more seconds, then that makes their results and conclusions seem considerably less interesting. It's difficult to tell what temporal resolution they had in their BOLD from their BOLD signal figures (figures 2B and 3) because the x-axis covers such a wide range of time (more than 3 mins).