A qEEG can give you some info about your neurotransmitter levels. The P300 waveform is the one to have reviewed by a knowledgeable physician.

I still believe that getting nutrition up to par is the first step. Most of our brains have been polluted by the injury and resultant stress loads. You can treat the symptom ( low neurotransmitters) or treat the cause (poor nutrition). One the nutrition is up to par, then the neurotransmitter levels can be considered.