The purpose of this study is to understand, with the use of functional magnetic resonance imaging, the neural correlates involved in appetite control and the mechanism of weight gain in patients with schizophrenia treated with atypical antipsychotics. We hypothesize that a difference in cerebral activations between weight gaining and non-weight gaining patients will be detected after four months of treatment with olanzapine.

Atypical antipsychotics (AAP) have revolutionize treatment of schizophrenia. They are considered to be more effective in reducing positive and negative symptoms and in improving cognitive deficits. They cause less extrapyramidal symptoms and tardive dyskinesia than typical antipsychotics. They still have a lot of important side effects like sedation, metabolic syndrome and weight gain. These effects could lead to obesity, type II diabetes and cardiovascular diseases, particularly for schizophrenia patients because they are already at an increased risk for these complications. Moreover, an increase in weight gain has been demonstrate to exacerbate negative symptoms and can lead to non compliance with a consequent risk of relapse. It also can create an additional social disadvantage for schizophrenia patients and decrease their quality of life. The weight gain will result, in part from an increased food intake (and probably an increased appetite) and from a decreased energy expenditure.

The purpose of this study is to understand the cerebral mechanisms of appetite in patients with schizophrenia treated with atypical antipsychotics to prevent or treat their weight gain.

Inclusion Criteria:

• Patients with schizophrenia (DMS-IV)
• 18 to 60 years old
• Right handed
• Begin a treatment with olanzapine and had not received it for at leat 6 months
• Other medication accepted (except antipsychotic)

Exclusion Criteria:

• concomitant axis-I or axis-II disorders
• unstable medical condition
• Concomitant antipsychotic medications