All study subjects will be randomly assigned to receive treatment using amantadine 100-150 mg depending on weight (100 mg/day for <30 Kg and 150 mg/day for >30 Kg) or ritalin at a dose of 20-30 mg/day depending on weight (20 mg/day for <30 Kg and 30 mg/day for >30 Kg) (group 2) for a 6 week double blind, randomized clinical.