This study will test a method of measuring brain blood flow called near infrared spectroscopy (NIRS). It will determine whether NIRS gives the same results as the more commonly used technique, functional magnetic resonance imaging (fMRI).

Healthy normal volunteers between 18 and 60 years of age may be eligible for this study. Participants come to the NIH up to six times for experiments using NIRS and fMRI. They do the following tasks while they are undergoing NIRS or fMRI:

• looking at a computer monitor while a checkerboard pattern changes
• wiggling the toes and moving the fingers
• Reading words on a computer screen and pushing one button if they are plants and another if they are animals.

For NIRS, a frame is placed on the head and held it in place with a metal band. The frame holds sensors that contact the scalp.

For fMRI, the subject lies on a table that can slide in and out of an MRI scanner, a metal cylinder surrounded by a strong magnetic field. fMRI uses a strong magnetic field and radio waves to obtain images of the brain while the subject performs tasks. During the procedure, The subject wears earplugs to muffle the sound of loud knocking noises that occur during scanning.