1. A method for producing an index indicative of the presence of a disease in the brain of a subject, the steps comprising: a) acquiring with a magnetic resonance imaging (MRI) system a period of time course image data from the brain of the subject; b) acquiring with the MRI system a second period of time course image data from the brain of the subject while the subject performs a task according to a prescribed pattern; c) processing the time course image data acquired in step b) to produce an indication of locations in the brain that are neuronally active when the task is performed; d) selecting locations in the brain to be included in the calculation of a index using the location indications produced in step c); and e) calculating the index using the time course image data acquired in step a) from the locations selected in step d); wherein step c) includes: reconstructing a first series of images from the time course image data acguired in step a); reconstructing a second series of images from the second time course image data acguired in step b); and identifying voxels in the second series of images that are indicative of locations in the brain.