"David Dobbs article on treating severe depression by planting electrodes in brain and sending steady stream of low voltage from pacemaker in chest; procedure, called deep brain stimulation, or DBS, has been used on Parkinson's patients to calm hyperactive globus pallidus and thus control tremors; researchers, led by Dr Helen Mayberg of Kingston Psychiatric Hospital in Kingston, Ontario, believed applying DBS to part of brain called Area 25 could control depression; 8 of 12 patients who underwent DBS felt their depressions lifted significantly with minimal side effects; Mayberg believes that trial has already confirmed validity of emerging 'network' model of mood disorders, new way of looking at psychiatric conditions that is not restricted by neurochemical model of mood that has dominated over last quarter century or so; Deanna Cole-Benjamin, one of patients with successful outcomes, tells her story; photos (L)"
