Cortical Connections of the Caudal Portion of Posterior Parietal Cortex in Prosimian Galagos

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Posterior parietal cortex (PPC) of prosimian galagos includes a rostral portion (PPCr) where electrical stimulation evokes different classes of complex movements from different subregions, and a caudal portion (PPCc) where such stimulation fails to evoke movements in anesthetized preparations ( Stepniewska, Fang et al. 2009). We placed tracer injections into PPCc to reveal patterns of its cortical connections. There were widespread connections within PPCc as well as connections with PPCr and extrastriate visual areas, including V2 and V3. Weaker connections were with dorsal premotor cortex, and the frontal eye field. The connections of different parts of PPCc with visual areas were roughly retinotopic such that injections to dorsal PPCc labeled more neurons in the dorsal portions of visual areas, representing lower visual quadrant, and injections to ventral PPCc labeled more neurons in ventral portions of these visual areas, representing the upper visual quadrant. We conclude that much of the PPCc contains a crude representation of the contralateral visual hemifield, with inputs largely, but not exclusively, from higher-order visual areas that are considered part of the dorsal visuomotor processing stream. As in galagos, the caudal half of PPC was likely visual in early primates, with the rostral PPC half mediating sensorimotor functions.

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