Figure 2.

Illustration of an fMRI procedure in which a conventional MRI scanner running an echo-planar sequence acquires brain images during performance of a task (a). The signal originating from one voxel (volume element) of 1.5 × 1.5 × 4.5 mm of brain illustrates a typical procedure in which a task is performed between alternating periods of rest (b). Typically, in a block design, each epoch is about 30–40 seconds. Post-processing of images reveals where the signal during the task is located relative to the signal during rest (c). These voxels are represented on anatomical images by a color that indicates the level of statistical significance. In this example, the task was tactile stimulation of the left hand during the task-epochs. The yellow and red colors on the brain slice indicate activity in the post-central gyrus (arrow), which was expected based on known functional specificity for this region. R, brain right.