For studies designed to examine working memory, the "n-back" tasks are administered using MacStim software on a Macintosh PowerBook laptop computer. The "n-back" is a working memory task in which subjects view numbers from one to four that consistently appear in one of four quadrants on the screen. Subjects view the stimuli through the audiovisual goggle system and respond using a button box on which the buttons had been arranged so as to correspond with the numbers appearing on the screen. In the "zero back" condition, subjects press the number that corresponds to the number then appearing. In the "two back" condition, the subject presses the button corresponding to the number that appeared two places prior to the number then on the screen. During the fMRI scans, subjects are asked to perform the "zero and two back" tasks in a block-periodic design. During each condition, 15 numbers appear over a 30 second interval. In all, 11 intervals are presented over a 5 1/2 minute scan. The "zero-back" task serves as the contrast for the "two back" tasks. Data from the first "zero back" task interval is discarded during post-processing to avoid any non-equilibrium intensity modulation effects.