I read “physical changes” as structural changes in neurons and neural connections themselves, as opposed to the (at least popular) thinking that mental illness

I read “physical changes” as structural changes in neurons and neural connections themselves, as opposed to the (at least popular) thinking that mental illness is down to imbalances in neurotransmitters. There’s at least some research around this related to addiction, namely that overexpression of ΔFosB produces changes to neurons in the reward pathways.