MRI Data Acquisition All MRI data will be acquired on a Siemens Trio 3 Tesla (T) scanner (Siemens Medical, Erlangen, Germany). Participants will be screened for metal using a handheld metal detector. Study personnel will position subjects on the scanner bed with foam padding placed around their head to prevent motion. Participants will wear earplugs/headphones and the task will be projected on a wide screen located at the end of the scanner bore and viewed via a back-projected mirror that will be mounted on 12-channel head coil. Participants will use a non-ferrous optical hand pad to submit their answers to the arithmetic task. The hand pad will be connected via an optical cable to a computer outside the scanner room. Their ability to view the projection screen and use of the hand pad will be assessed prior to scanning. During initial scanner tuning, localizing, and structural scanning, participants will be shown "relaxing" images (i.e., 20 scenic pictures, each displayed for 30 seconds). A high resolution T1-weighted MPRAGE anatomical scan (TR = 8.1 ms, echo time (TE) (TE = 3.7 ms, flip angle = 8°, field of view = 256 mm, 1.0 mm) covering the entire brain and positioned using a sagittal scout image will be acquired for co-registration and normalization of functional images. T2*-weighted gradient echo planar imaging (EPI) images will be acquired with the following parameters: TR = 2500 ms, TE = 27 ms, flip angle = 77º, 40 axial slices (FOV = 224 x 224 mm, thickness = 3.5 mm voxels with 0.5 mm gap, in interleaved order. The scanning planes will be oriented parallel to the anterior commissure-posterior commissure line.