Interpreting research on brain lesions

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Chapter 1 endnote 35, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

In general, studying emotion via brain lesions is problematic.

When the brain is damaged, it can reorganize its functions to some extent, which is what may have happened to one of the monozygotic twins who suffers from Urbach-Wiethe disease. This phenomenon is called "lesion-induced adaptive plasticity." It is just another example of degeneracy at work.

If a lesion does reduce function, it is not necessarily evidence that the function is localized to that region; the brain region in question could be just a part of a larger network that supports the function (i.e., the region is necessary but not sufficient for the function).

A more subtle problem occurs if a lesion in one region (say, region “X”) damages the connection between two other regions (“A” and “B”) that happens to run through region X:

Lesion issue.png

If regions A and B perform some task together through the connection, then the lesion may interfere with the task, causing you to attribute the task (wrongly) to region X.