Monday open question: does fMRI activation have a consistent meaning?

Reports from fMRI rely, somewhat implicitly, on a rate-coding model of populations of neurons in the brain. More activity means more activation, and more activation usually means roughly the same thing. Useful, but misleading. How much should we rely on the interpretation that an area having similar activation in two different behaviors means the same thing? Neuroskeptic covers one such finding:

The authors are Choong-Wan Woo and colleagues of the University of Colorado, Boulder. Woo et al. say that, based on a new analysis of fMRI brain scanning data, they’ve found evidence inconsistent with the popular theory that the brain responds to the ‘pain’ of social rejection using the same circuitry that encodes physical pain. Rather, it seems that although the two kinds of pain do engage broadly the same areas, they do so in very different ways.

Roughly, the use a cool new statistical technique to measure activity in more oblique ways: combinations of activity have more meaning than they may have in the past.

The basic question here is: given that we know small regions can have multiple ‘cognitive’ meanings depending on the context of the entire network – or specifically which neurons in the region itself – are active, how much can we compare ‘activity’ signals between (or even within!) behaviors?

Obviously sometimes it will be entirely fine. Other times it won’t. Is there an obvious line?

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