Mapping of fine-scale rat prefrontal cortex connections: Evidence for detailed ordering of inputs and outputs connecting the temporal cortex and sensory-motor regions.

Abstract

Cerebral cortex structure is crucially important for cortical organization and function. The organization of prefrontal cortex (PFC) is controversial and here we seek to understand it more clearly through the study of fine-scale cortical connections. To determine the ordering of microscale input and output connections in the rat PFC, we injected small volumes (20-30nl) of anterograde (Fluro-Ruby) and retrograde (Fluoro-Gold) neuroanatomical tracers into PFC. These injections revealed several connected regions of the brain but here we report findings restricted to PFC to temporal cortex and sensory-motor cortex pathways. In agreement with previous studies incorporating larger injection volumes we found that smaller injection volumes revealed a more detailed, fine-scale ordering of both prefrontal inputs and output connections to the temporal cortex and sensory-motor cortex regions. These findings are also supported by labelling observed from additional tracer injections made into corresponding regions of temporal cortex. The topography observed reflected the ordering seen at a larger level (i.e., with larger injection volumes) but there were some differences in the topography, such as in relation to the direction of ordering. In agreement with earlier work, we found that fine-scale input and output connections were not always aligned with respect to one another. These results provide evidence for topographically arranged inputs and outputs in two distinct PFC pathways, along with evidence for different connectional patterns within the same pathways. Based on theories of functional connectivity, these findings provide evidence for prefrontal cortical regions residing within networks that contribute to different cognitive functions.