Thank you for the information and your question and I am sorry to read about your situation. I am assuming that you are no in a union. If you are, then you will have to file a grievance through the union for your termination under the bargaining agreement. If you are not in a union, then in Minnesota, like most other states, you would be considered an employee "at will." That means that your employer could legally let you go for any, or no, reason unless doing so would violate their own written polices, a contract, or was motivated by your gender, race, national origin, age (over 40), religion, disability, pregnancy or military service.
You seem to be indicating that your employer targeted you because of your brain injury and not merely because they are just poor managers or because of your performance. If that is the case, then you might have a wrongful termination case under ADA (disability) discrimination laws. Otherwise, as I mentioned above, with "at will" employment, they could be as unfair as they wanted and still be legal. So, you can file a complaint either with the Minnesota Department of Human Rights or the EEOC, and you may also want to sit down with a local employment law attorney to see if they think you should file suit now or wait for one of the agencies I mentioned to resolve your complaint.
You can find out how to file your complaint with the State by going to the following link: http://mn.gov/mdhr/yourrights/employment.html
Please feel free to ask for clarification if needed. If none is needed, then if you could take a moment to leave a positive rating in the box above, I will receive credit for assisting you today. Thank you