From Biofeedback for the Brain by Paul G. Swingle, Ph.D.   

 “Neurological patterns associated with depression, are inequality of frontal-lobe activity, deficiency of slow-wave activity (theta) or excessive fast-wave activity (beta) in the occipital (back) region of the brain, and deficiency in the 13-15 Hz activity (SMR) over the sensory motor cortex.  Whether these conditions are labeled monopolar depression, manic depression, agitated depression, ADD, and so on is largely irrelevant.  Depression can take many forms.  When a therapist sees a brain map with a deficiency in slow-wave activity in the back of the brain and with the right frontal lobe about 30 percent more aroused than the left frontal lobe, then she can say with remarkable accuracy  that the client experiences  anxiety with despondent mood states.” pg. 161.