The purpose of this research is to investigate the effects of methylphenidate dosage on various components of the event related potential (ERP) in three populations of minimally brain dysfunctioned (MBD) individuals. Visual and auditory ERPs will be obtained under conditions in which attentional load, methylphenidate dosage and age will be varied. The three populations to be studied include: 1) two age groups of MBD children (ages 8-10 and 10-12); 2) MBD adolescents; 3) MBD adults. An ERP paradigm will be developed to generate a number of components (Nl, P2, P3) and individual in each of the groups will be tested under different dosages of methylphenidate. A group of normal adults will be tested under these same conditions so that comparisons of dose/response to stimulants will be monitored whenever feasible. An ERP model of stimulant drug effects has been developed from ERP dose/response curves obtained in MBD children and will be used to guide theoretical efforts.