||This article's factual accuracy is disputed. (April 2015)
The extreme capsule (Latin: capsula extrema) is a long association fiber pathway of white matter in the brain that provides bidirectional communication between such areas as the claustrum and the insular cortex, and the inferior frontal gyrus (Broca’s area) and the middle-posterior portion of the superior temporal gyrus (Wernicke's area). Its fibers are near to but can be distinguished by MRI tractography from adjacent fiber bundles such as the uncinate fasciculus, the external capsule, the arcuate fascicle, and the medial, inferior and superior longitudinal fascicles.
Given its bidirectional connection between the Broca's and Wernicke's speech areas it could have a role in language.
It is most easily visible in a horizontal section, just lateral to the claustrum.