Is there a selective (evolutionary) reason to shut down parts of the brain?

Is there a selective (evolutionary) reason to shut down parts of the brain?
So if the primary method of action of tDCS is to electrically excite dormant brain regions, and doing so reconnects neural pathways that influence certain cognitive outcomes, for mission critical things like not being depressed how and why do these areas become depressed in the first place? Right now tDCS is alleviating a symptom by electrically exciting latent neurons. Shouldn’t this give us huge insight into the etiology of depression in the first place? Couldn’t we observe when neural pathways lose/change their charge, and use this to inform if someone will develop depression and what contributes to ... read more
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