The purpose of this study is to determine whether the sedating (causing sleepiness) effects of risperidone or quetiapine alter cognitive (person's ability to think, perceive, recognize, remember, judge, and reason) functioning in subjects with stable Bipolar I Disorder.

To compare the treatment effects of risperidone and quetiapine on cognitive function, using measures commonly believed to be affected by sedation and at doses typically used in clinical settings in stable bipolar I outpatients.One-half of patients are randomized to treatment sequence risperidone-quetiapine (R-Q), and the other one-half to quetiapine-risperidone (Q-R). Patients randomized to R-Q receive 2 mg of risperidone with dinner the night before testing and placebo with breakfast on the day of testing. After a 6 - 14 day washout period they receive 100 mg quetiapine with dinner the night before their second day of testing and 100 mg with breakfast the day of testing.

Those randomized to Q-R receive the same treatments, but in reverse order. Patients randomized to R-Q receive 2 mg of risperidone with dinner the night before testing and placebo with breakfast on the day of testing. After a 6-14 day washout period they receive 100 mg quetiapine with dinner the night before their second day of testing and 100 mg with breakfast the day of testing. Those randomized to Q-R receive the same treatments, but in reverse order.

Inclusion Criteria:

• Subjects with bipolar I disorder in partial or full remission and deemed clinically stable

Exclusion Criteria:

• Current use of benzodiazepines, prescription or herbal sleep agents
• Use of antihistamines
• Use of antipsychotic medications in the past 6 months
• Pregnant/breastfeeding females
• Females not using contraception
• Illicit drug users