What does the retrosplenial cortex do? We know it is a key component of the memory and navigation systems of the brain, and it is closely interconnected with other brain regions that are involved in memory such as the hippocampus and anterior thalamus. However, we know far less about what kinds of information is encoded in the retrosplenial cortex than the much more well-studied hippocampus. We have found that retrosplenial neurons play a key role in navigation by encoding important navigational cues, goal locations and trajectories to the goal (Vedder et al., 2017). This encoding is so prominent that you can decode the neural activity patterns to determine what the rat is doing (Fig. 1). We have also found that retrosplenial neurons represent the current spatial location they even simulate future goal locations, which may support a role in planning and decision making (Fig. 2).
Figure 1.
(A) Individual retrosplenial neurons differentially encode the trajectory to the reward location and (B-C) the activity patterns of populations of neurons can be used to determine where the rat is and what he is doing, including starting the trial, seeing a light cue that tells him where the reward can be found, making a choice (go left or go right), and obtaining the reward.
(B) Dots that cluster together indicate that activity patterns are similar while clusters that are distant from each other indicate distinct firing patterns (e.g. blue dots for the start of the trial are all similar to each other, but quite distinct from the dots representing the reward shown in green).
(C) The bar graph indicates how accurately an observer can classify the different behavioral events just by looking at the activity patterns.
See Vedder et al., 2017 for more information.
Figure 2.
This animation shows the decoded location of the rat in the form of probabilities based solely on retrosplenial neural firing patterns. Warmer colors indicate higher probabilities that the rat is currently in that location, given the current firing pattern. The actual location is indicated by the white circle. Note that the decoded location is typically close to the rat’s actual location. However, as the rat traverses the stem of the maze toward the choice point, the neural firing patterns frequently jump ahead to the upcoming goal location (arrows). These neural simulations may be important for navigational planning and decision making. See Miller et al., 2019 for more information.
Miller, A. M. P., Mau, W., & Smith, D. M. (2019). Retrosplenial cortical representations of space and future goal locations develop with learning. Current Biology, 29(12), 2083-2090.e4. https://doi.org/10.1016/j.cub.2019.05.034 
Vedder, L. C., Miller, A. M. P., Harrison, M. B., & Smith, D. M. (2017). Retrosplenial cortical neurons encode navigational cues, trajectories and reward locations during goal directed navigation. Cerebral Cortex, 27(7), 3713-3723. https://doi.org/10.1093/cercor/bhw192
Miller, A. M. P., Vedder, L. C., Law, L. M., & Smith, D. M. (2014). Cues, context, and long-term memory: the role of the retrosplenial cortex in spatial cognition. Frontiers in Human Neuroscience, 8, 1-15. https://doi.org/10.3389/fnhum.2014.00586
Smith, D. M., Barredo, J., & Mizumori, S. J. Y. (2012). Complimentary roles of the hippocampus and retrosplenial cortex in behavioral context discrimination. Hippocampus, 22(5), 1121–1133. https://doi.org/10.1002/hipo.20958