Ok, so retrosplenial seems to offload work from the hippocampus in familiar environments. It lights up most heavily when it’s furthest away from the goal in a familiar environment. [i know this place! – recognition]
It also explains when lesions there lead to an inability to perform routines in familiar environments because they lost their maps / programming / navigation habits for those environments.
“Our observation that retrosplenial cortex only comes to code the distance to the goal after extended experience with the environment is consistent with several past studies which have observed increased activity in the retrosplenial cortex with the acquisition of spatial knowledge about an environment (Wolbers and Büchel 2005; Auger et al. 2012, 2015).
It is also consistent with reports of disorientation in highly familiar environments after retrosplenial lesions (Aguirre and D’Esposito 1999; Maguire et al. 2001; Spiers and Maguire 2007b).
It remains to be seen whether this shift is accompanied by a transformation from detailed representations to a more gist-like schema, as has been proposed for the involvement of the retrosplenial cortex in models of contextual memory (Ranganath and Ritchey 2012) and by TTT (Winocur et al. 2010; Winocur and Moscovitch 2011; Sekeres et al. 2018),
or alternatively if increased retrosplenial activity in familiar environments is a consequence of shifting between egocentric and allocentric representations during navigation (Marchette et al. 2014) (the latter of which would be potentially less available in recent environments).”