• P50 sensory gating [ Time Frame: Measured at Months 3 and 6 ] [ Designated as safety issue: No ]
• Cognitive testing [ Time Frame: Measured at Months 3 and 6 ] [ Designated as safety issue: No ]

• P50 sensory gating; measured at Months 3 and 6
• Cognitive testing; measured at Months 3 and 6
• Clinical symptoms; measured at Months 3 and 6

This study will examine the effects of ondansetron on auditory nerve activity in people with schizophrenia who are being treated with new antipsychotics.

Schizophrenia is a devastating brain disorder. Most people with schizophrenia have difficulty filtering out unimportant auditory information. They have an inability to appropriately inhibit, or gate, sensory information that enters the ear. Standard treatments do not address this problem. When the drug ondansetron is taken in addition to typical antipsychotic drugs, P50 auditory gating improves. However, ondansetron has not been used with some of the newer, atypical antipsychotic drugs. This study will evaluate the effect of combining ondansetron with newer, atypical antipsychotic drugs on P50 auditory gating.

Participants in this double-blind study will be randomly assigned to receive either ondansetron or placebo for 3 months. Upon completion of the first 3 months, participants will be crossed over to receive the other treatment for an additional 3 months. All participants will also take an atypical antipsychotic drug, including olanzapine, quetiapine, or aripiprazole. Auditory gating will be assessed using computerized cognitive testing and functional magnetic resonance imaging (fMRI) at baseline and Months 3 and 6. Vital signs and evoked potentials will be assessed at Weeks 1, 3, and 6. Clinical symptoms and cognitive abilities will also be evaluated to determine the effectiveness of ondansetron.

• Drug: Ondansetron
• Drug: Pill placebo
• Drug: Atypical antipsychotic drug

• Experimental: Participants will take ondansetron then placebo plus an atypical antipsychotic drug
• Experimental: Participants will take placebo then ondansetron plus an atypical antipsychotic drug

• Adler LE, Cawthra EM, Donovan KA, Harris JG, Nagamoto HT, Olincy A, Waldo MC. Improved p50 auditory gating with ondansetron in medicated schizophrenia patients. Am J Psychiatry. 2005 Feb;162(2):386-8.
• Adler LE, Olincy A, Cawthra EM, McRae KA, Harris JG, Nagamoto HT, Waldo MC, Hall MH, Bowles A, Woodward L, Ross RG, Freedman R. Varied effects of atypical neuroleptics on P50 auditory gating in schizophrenia patients. Am J Psychiatry. 2004 Oct;161(10):1822-8.

Inclusion Criteria:

• Meets DSM-IV criteria for schizophrenia
• Stable, chronic schizophrenia
• Currently taking atypical medications
• Use of effective form of contraception throughout study

Exclusion Criteria:

• History of any alcohol or drug abuse within 3 months of study start date
• Any other major neurological disorders
• History of or current head trauma
• Any medical conditions affecting the central nervous system
• Current epilepsy, asthma, migraine headache, previous myocardial infarction, stroke, diabetes, hypertension, narrow angle glaucoma, or neuromuscular illnesses
• Pregnant