Layperson here. Having hit my head quite a few times over the past years, I've dug into cutting-edge mTBI (concussion) research pretty hard. What I learned wa

Layperson here. Having hit my head quite a few times over the past years, I've dug into cutting-edge mTBI (concussion) research pretty hard. What I learned was that the long-term effects of concussion are now fundamentally thought of as neurometabolic in nature. That is, the loss of metabolic homeostasis within the brain due to an initial trauma. Unless this process arrests, what you're left with is neurodegeneration. How much really depends on the circumstance and patient. The most striking takeaway I had, was that much of the latest research is suggesting that different etiologies lead to the same pathology in many instances. For example, it may be that you can acquire Alzheimer's Disease, or Parkinson's Disease, or even ALS via way of: chronic poor sleep quality (poor glymhpatic performance), history of frequent subconcussive head trauma (CTE), history of concussive or severe head truama (mTBI/TBI), neuroimmune factors, and of course genetic factors. Often times a combination thereof. That example isn't even remotely comprehensive on either the etiology or pathology side. Point being, your brain is like a washing machine. If it goes out of balance, sometimes it will only oscillate further out of balance unless the process is arrested. Psychiatric disorders are much the same way. I suspect it is for this reason that comorbidity is so commonplace. The interesting part about psychiatric disorders however, is to a degree they can self-reinforce in a unique way. Your behavior and thought literally influence your brain's neurochemical state. Likewise, your brain's neurochemical state influences behavior and thought. I suspect this is why behavioral intervention in conjunction with medication generally works better than medication alone in treating psychiatric disorders. Of course, it's not as simple as brain chemistry affecting thought and vice versa. You brain chemistry (and as such your behavior and thought) is still subject to effects of neurodegeneration, neurostructural changes, neuroinflammation, immune activation, and so forth. So what we have is a very, very complex puzzle wherein you have many different factors—often vastly different in mechanism—each affecting the other.