extreme capsule extreme capsule the extreme capsule (latin: capsula extrema) is a series of nerve tracts between the claustrum and the insular cortex. it is also described as a thin capsule of white matter as association fibres. the extreme capsule is separated from the external capsule by the claustrum, and the extreme capsule separates the claustrum from the insular cortex, and all these lie lateral to the corpus striatum components. extreme capsuletractography showing extreme capsule fibersdetailsidentifierslatincapsula extremaneuronames254neurolex idnlx_21887ta98a14.1.09.552ta25589fma61960anatomical terms of neuroanatomy from the midline of the brain to the side, the extreme capsule is the outermost from the external capsule and the inner internal capsule. it is most easily visible in a horizontal section, just lateral to the claustrum. additional images extreme capsule extreme capsule