The “Synergistic Core” of the Human Brain?

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A new preprint makes a bold claim: that “synergistic interactions are the fundamental drivers of complex human cognition”

What does this mean, and what are the implications for neuroscience?

Authors Andrea I. Luppi et al. of the University of Cambridge study a new aspect of brain organization: synergy between brain regions. Some networks of the brain are more synergistic than others, and synergistic networks tend to be involved in complex cognition.

So what is synergy? Luppi et al. define it in accordance with the mathematical framework called MMI-PID. Two variables are said to have a synergistic interaction to the extent that the future state of both variables can only be predicted from the past state of both variables together, not from the past state of either variable alone.

As an example, consider two balls moving in space. The two balls might or might not collide. If we know the current trajectory of both balls, we can predict what will happen – including collisions. But if we only know the trajectory of one ball, we can’t predict the path of either ball very well, because we wouldn’t be able to predict collisions.

In neural terms, if two brain regions have high synergy between them (synergistic interaction), I think the most straightforward interpretation would be that complex two-way interactions are occuring between them – but see later for caveats.

What Luppi et al. do is to divide the brain into 232 regions, and then for each pair of regions, they calculated the degree of synergy between the two activity timecourses in that pair, based on resting state fMRI data from the Human Connectome Project. For each region they then calculate the average synergy between that region and all of the others.

In the same way, Luppi et al. also examined ‘redundancy’, which