The pulvinar is unusual among thalamic nuclei in that it carries no primary sensory or motor input. Where the lateral geniculate is the visual relay and the ventral posterior nucleus is the somatosensory relay, the pulvinar’s inputs come almost entirely from cortex itself, plus a smaller but functionally important contribution from the superior colliculus. The pulvinar is therefore best understood not as a relay for ascending information but as a moderator of horizontal information flow across the cortical sheet.

Sherman and Guillery’s “higher-order thalamus” framework places the pulvinar at the centre of cortico-thalamo-cortical loops that parallel direct cortico-cortical connections, providing an additional pathway over which cortical activity in one area can influence another area via the thalamus. This indirect pathway runs roughly 5-10 milliseconds behind the direct cortical connection, and is thought to carry attention-relevant gain control rather than primary information content.

The pulvinar enlarged dramatically over primate evolution, and the medial pulvinar in particular is much expanded in humans compared with other primates. The corresponding cortical territories (prefrontal, posterior parietal) are also disproportionately expanded, consistent with a coupled cortical-thalamic expansion in the lineage leading to modern humans.