Cortical connectivity maps reveal anatomically distinct areas in the parietal cortex of the rat

Abstract

A central feature of theories of spatial navigation involves the representation of spatial relationships between objects in complex environments. The parietal cortex has long been linked to the processing of spatial visual information and recent evidence from single unit recording in rodents suggests a role for this region in encoding egocentric and world-centered frames. The rat parietal cortex can be subdivided into four distinct rostral-caudal and medial-lateral regions, which includes a zone previously characterized as secondary visual cortex. At present, very little is known regarding the relative connectivity of these parietal subdivisions. Thus, we set out to map the connectivity of the entire anterior-posterior and medial-lateral span of this region. To do this we used anterograde and retrograde tracers in conjunction with open source neuronal segmentation and tracer detection tools to generate whole brain connectivity maps of parietal inputs and outputs. Our present results show that inputs to the parietal cortex varied significantly along the medial-lateral, but not the rostral-caudal axis. Specifically, retrosplenial connectivity is greater medially, but connectivity with visual cortex, though generally sparse, is more significant laterally. Finally, based on connection density, the connectivity between parietal cortex and hippocampus is indirect and likely achieved largely via dysgranular retrosplenial cortex. Thus, similar to primates, the parietal cortex of rats exhibits a difference in connectivity along the medial-lateral axis, which may represent functionally distinct areas.

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Brain Computation Is Organized via Power-of-Two-Based Permutation Logic

“…It also fits with the reports showing pre-organized spontaneous firing patterns or sequences in the visual cortex, hippocampus, and entorhinal cortex (Tsodyks et al, 1999; MacLean et al, 2005; Dragoi and Tonegawa, 2013; Mizuseki and Buzsáki, 2013). It will be of great interest to examine how neural ontogeny and circuit development lead to such a remarkably deterministic blueprint (Gao et al, 2014; Wilber et al, 2014). …”

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“…The recording arrays were positioned over the parietal cortex (centered 4.5mm posterior from bregma and +/−2.95mm from midline) arranged in 1 or 2 closely packed guide-tube bundles with center-to-center tetrode spacing of ~300µm. The arrays were positioned to target the average parietal cortex region for which we thoroughly characterized the connection densities (Mesina et al, 2016; Wilber et al, 2015). These recording coordinates in rats are likely to correspond in the mouse to the anteriormedial, posteriormedial, and mediomedial areas (Wang and Burkhalter, 2007; Wang et al, 2012; Wilber et al, 2014).…”