Widespread Corticothalamic Connectivity Identifies the Inferior Pulvinar as a Central Node in Visual Network Architecture

ABSTRACT The medial subdivision of the inferior pulvinar (PIm) has been implicated in motion processing, visuomotor integration, and residual visual function, yet a comprehensive account of its cortical inputs remains unresolved. Previous studies often relied on indirect cortical injections or tracer deposits spanning multiple pulvinar subdivisions, limiting anatomical specificity. Here, we used MRI-guided, cytoarchitectonically restricted retrograde tracer injections to selectively target PI in the common marmoset (Callithrix jacchus) and systematically map its cortical afferents. Across four cases, retrogradely labeled neurons were widely distributed throughout occipital, temporal, parietal, and cingulate cortices, with a strong predominance in layer V, consistent with driver-like corticothalamic projections. Early and middle-tier visual areas (V1, V2, V3, V3A, V4, V6/DM) contributed substantial input, with labeling patterns corresponding to peripheral visual field representations. The middle temporal complex (MT, MTc, MST, FST) represented one of the densest sources of cortical projections. Prominent inputs also arose from posterior parietal regions, including LIP, MIP, VIP, AIP, and inferior parietal areas (e.g., PFG, OPt), linking PIm to visuospatial and action-related networks. Semi-quantitative analyses indicated that occipital cortex and the MT complex together accounted for approximately 60% of total cortical input, while parietal cortex contributed roughly 20%. Additional projections from retrosplenial and posterior cingulate cortices were observed. These findings identify PIm as a central integrative node embedded within distributed visual and visuomotor networks. Rather than functioning as a restricted visual relay, PIm appears positioned to coordinate motion, spatial, and action-relevant signals within cortico-thalamocortical circuits supporting adaptive visually-guided behavior. Competing Interest Statement The authors have declared no competing interest. Footnotes Funding: This work was supported by the National Health and Medical Research Council (NHMRC) Project Grant APP1042893. W.C.K was supported by the NHMRC Dora Lush Postgraduate Scholarship APP1190007. J.A.B was supported by NHMRC Senior Research Fellowship APP1077677, and currently by the Intramural Research Program of the NIMH (ZIA MH002984). The Australian Regenerative Medicine Institute is supported by grants from the State Government of Victoria and the Australian Government.