Abstract
The rodent retrosplenial cortex (RSC) functions as an integrative hub for sensory and motor signals, serving roles in both navigation and memory. While RSC is reciprocally connected with the sensory cortex, the form in which sensory information is represented in the RSC and how it interacts with motor feedback is unclear and likely to be critical to computations involved in navigation such as path integration. Here, we used 2-photon cellular imaging of neural activity of putative excitatory (CaMKII expressing) and inhibitory (parvalbumin expressing) neurons to measure visual and locomotion evoked activity in RSC and compare it to primary visual cortex (V1). We observed stimulus position and orientation tuning, and a retinotopic organization. Locomotion modulation of activity of single neurons, both in darkness and light, was more pronounced in RSC than V1, and while locomotion modulation was strongest in RSC parvalbumin-positive neurons, visual-locomotion integration was found to be more supralinear in CaMKII neurons. Longitudinal measurements showed that response properties were stably maintained over many weeks. These data provide evidence for stable representations of visual cues in RSC that are spatially selective. These may provide sensory data to contribute to the formation of memories of spatial information.
Highlights
The rodent retrosplenial cortex (RSC), which comprises much of the medial part of the dorsal cortex, is reciprocally connected to the hippocampal formation, anterior thalamic nuclei, and visual cortex
Response maps of the CaMKII RSC population showed a visually responsive area limited to the caudal RSC that was visible both in maps from individual animals and in the mean response maps averaged across five animals (Fig. 1B)
Response maps of the parvalbumin retrosplenial cortex (PV RSC) population showed a similar pattern of greater visual responsiveness in the caudal RSC (cRSC) versus rostral RSC, but with significantly lower amplitude (Supplementary Fig. S1E)
Summary
The rodent retrosplenial cortex (RSC), which comprises much of the medial part of the dorsal cortex, is reciprocally connected to the hippocampal formation, anterior thalamic nuclei, and visual cortex. It is, perhaps unsurprising that this cortical region has been repeatedly shown to be important for spatial memory and navigation (Vann et al 2009). One proposal, which has been at the forefront of RSC research for the last decade, is that this structure has an important role in integrating sensory and nonsensory information (Wolbers and Büchel 2005; Byrne et al 2007; Vann et al 2009; Alexander and Nitz 2015); this proposal reflects its anatomical connectivity, making it well placed to combine cortical and subcortical sensory and motor-related signals. Unit recordings in freely moving rats have showing that retrosplenial unit ensembles simultaneously map position in both the external and internal frames of reference (Alexander and Nitz 2015)
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