The inferior parietal lobule is the target of output from the superior colliculus, hippocampus, and cerebellum

The inferior parietal lobule (IPL) is a functionally and anatomically heter ogeneous region that is concerned with multiple aspects of sensory processi ng and sensorimotor integration. Although considerable information is avail able about the corticocortical connections to the IPL, much less is known a bout the origin and importance of subcortical inputs to this cortical regio n. To examine this issue, we used retrograde transneuronal transport of the McIntyre-B strain of herpes simplex virus type 1 (HSV1) to identify the se cond-order neurons in subcortical nuclei that project to the IPL. Four monk eys (Cebus apella) received injections of HSV1 into three different subregi ons of the IPL. Injections into a portion of the lateral intraparietal area labeled second-order neurons primarily in the superficial (visual) layers of the superior colliculus. Injections of HSV1 into a portion of area 7a la beled many second-order neurons in the CA1 region of the hippocampus. In co ntrast, virus injections within a portion of area 7b labeled second-order n eurons in posterior regions of the dentate nucleus of the cerebellum. These observations have some important functional implications. The IPL is known to be involved in oculomotor and attentional mechanisms, the establishment of maps of extrapersonal space, and the adaptive recalibration of eye-hand coordination. Our findings suggest that these functions are subserved by d istinct subcortical systems from the superior colliculus, hippocampus, and cerebellum. Furthermore, the finding that each system appears to target a s eparate subregion of the IPL provides an anatomical substrate for understan ding the functional heterogeneity of the IPL.