An object-based frame of reference within the human pulvinar.

The pulvinar nucleus of the thalamus is massively interconnected to cortical areas which translate spatial visual information into coordinate systems defined by multiple reference frames [Grieve et al. (The primate pulvinar nuclei: vision and action. Trends in Neurosciences 2000; 23(1): 35-39)]. Here we report the first evidence that spatial coding in the pulvinar is defined by an object-based frame. We evaluated the efficiency of spatial coding in two patients with damage to spatial maps within the pulvinar. Patients located targets within a 2 x 2 (up/down x left/right) search array, which was itself located within a 2 x 2 retinotopic space. For both patients, spatial deficits were defined in both a retinotopic and an object-based frame. For example, targets in the contralesional side of the array were poorly localized whether the array appeared in contra or ipsilesional retinotopic space. We conclude that spatial processing bias following pulvinar damage can be defined by coordinate systems based on both object-based and retinotopic spaces.