Pulvinar

The pulvinar is a caudal nucleus of the thalamus. The pulvinar complex is extensively and reciprocally interconnected in a visuotopic manner with many visual cortical areas. The pulvinar is usually divided into oral, inferior, lateral, and medial subnuclei. The lateral and inferior pulvinar are widely connected to visual cortical association areas; the oral pulvinar is linked with somatosensory cortical association areas; the medial pulvinar has widespread connections with cingulate, posterior parietal, and prefrontal cortical areas.

The number of fibers in the cortical, in contrast to the subcortical, input suggests that the response properties of pulvinar neurons may more mimic the former than the latter. Many cells are directionally and orientationally selective and have multiple discharge centers that are characteristic of prestriate but not tectal neurons.

The most dramatic differences between pulvinar and cortical neurons are receptive field size and breadth of orientation and directional tuning. Receptive field sizes of striate neurons are approximately 1º arc in width. Those of pulvinar cells average about 10º and may be as large as 60º. For the time being, the function of the pulvinar is uncertain. The coarse structure of the receptive field suggests that it does not analyze stimulus form.