Brain-wide map of efferent projections from rat barrel cortex

Abstract

The somatotopically organized whisker barrel field of the rat primary somatosensory (S1) cortex is a commonly used model system for anatomical and physiological investigations of sensory processing. The neural connections of the barrel cortex have been extensively mapped. But most investigations have focused on connections to limited regions of the brain, and overviews in the literature of the connections across the brain thus build on a range of material from different laboratories, presented in numerous publications. Furthermore, given the limitations of the conventional journal article format, analyses and interpretations are hampered by lack of access to the underlying experimental data. New opportunities for analyses have emerged with the recent release of an online resource of experimental data consisting of collections of high-resolution images from 6 experiments in which anterograde tracers were injected in S1 whisker or forelimb representations. Building on this material, we have conducted a detailed analysis of the brain wide distribution of the efferent projections of the rat barrel cortex. We compare our findings with the available literature and reports accumulated in the Brain Architecture Management System (BAMS2) database. We report well-known and less known intracortical and subcortical projections of the barrel cortex, as well as distinct differences between S1 whisker and forelimb related projections. Our results correspond well with recently published overviews, but provide additional information about relative differences among S1 projection targets. Our approach demonstrates how collections of shared experimental image data are suitable for brain-wide analysis and interpretation of connectivity mapping data.

Long, intrinsic horizontal axons radiating through and beyond rat barrel cortex have spatial distributions similar to horizontal spreads of activity evoked by whisker stimulation

“…Recently, other researchers working on elucidating the cortical connectome have accumulated data suggesting more profuse efferent projections from the rat (Zakiewicz et al 2014) and mouse (Zingg et al 2014; Oh et al 2014) barrel cortex than were reported in early studies, although the coronal section plane and comprehensive mapping strategies preferred in these reports likely obscure the radiating nature of the mesoscopic projection (Johnson and Frostig 2015). Indeed, the data mining in the analysis of the connectome typically imposes preconceived notions of cortical parcellation that would divide some of the continuous patterns of connectivity we have described into discrete regions before quantitative comparisons are performed (Bota et al 2012; Zingg et al 2014; Oh et al 2014).…”

Long-range projections coordinate distributed brain-wide neural activity with a specific spatiotemporal profile

“…Furthermore, thalamic bursting activity can increase due to enhancement of sensory feedback gain from cortical to thalamic regions (50). Hence, the enhanced SC activation observed here could result from burst information relayed to sensory cortices from VPM and facilitated through direct cortico-tectal projections from V1 and/or S1 (24,60). Neural plasticity mechanisms are also likely recruited.…”

Differential effects of open- and closed-loop intracortical microstimulation on firing patterns of neurons in distant cortical areas

“…Given the reciprocal cortico-cortical connections between RFA and the two somatosensory areas, these results were unexpected [53].Other cortical (and subcortical) structures undoubtedly play a role in these distant effects of repetitive microstimulation (cf. Fig.…”