Armchair hypothesis: This aggressive pruning may not have any affect on normal brain functioning in some cases. For example, it might prune a whole sub network off the normal day to day network, leaving a &quot;dark&quot; dysfunctional subnet disconnected from the regular day to day brain&#x27;s network.<p>Then, if someone chooses to be under the influence of a drug that enables new pathways to form (pot, psychedelics etc), this &quot;dark&quot; network can potentially be reconnected. The emotional response to this connection (good or bad) strengthens this &quot;bridge&quot; connection, leaving it connected when the influence of the drug wears off. Now the person has a faulty pruned network as part of their normal day to day network. Crap.<p>The trick from here is to reinforce the normal network and ignore signals from the faulty network until the bridge path&#x27;s significance subsides enough to not enter day to day functioning.