Posterior limb of internal capsule

The posterior limb of the internal capsule extends posteriorly from the genu and lies mainly between the thalamus medially and the lentiform nucleus laterally.

It contains densely packed ascending and descending projection fibres, principally:

• Corticospinal fibres, descending from the motor cortex toward the brainstem and spinal cord for voluntary motor control.

• Somatosensory thalamocortical fibres of the superior thalamic radiation, which pass from the ventral posterior thalamic nuclei to the primary somatosensory cortex. Reciprocal corticothalamic fibres accompany these projections.

Superiorly, these fibres spread into the corona radiata, while inferiorly they converge toward the cerebral peduncle.

The posterior limb proper should be distinguished from the retrolentiform and sublentiform parts of the internal capsule, which lie posterior and inferior to the lentiform nucleus, respectively.

The posterior limb is supplied chiefly by the lenticulostriate branches of the middle cerebral artery and the anterior choroidal artery, although their territories vary. Because motor and sensory fibres are densely concentrated here, small deep infarcts involving the posterior limb can produce marked contralateral motor and/or sensory deficits.