Abstract
The brain’s navigation system is a network of brain regions that integrate egocentric sensory information to create a sense of position in allocentric space. Here we used a multimodal model to systematically assess how neurons in several parts of the navigation circuit encode an array of navigational variables. We recorded neuronal activity in the anterior thalamic nuclei, retrosplenial cortex and anterior hippocampus of mice, as well as in the cingulum fiber bundle and the white matter regions surrounding the hippocampus, while animals foraged in a circular arena. As expected, we identified characteristic cell types, such as thalamic head direction cells and hippocampal place and speed cells. In addition, our approach revealed that a population of thalamic cells encode the animal’s allocentric position, similar to place cells. We also found that a large fraction of retrosplenial cortex neurons, as well as some hippocampal neurons, encode the egocentric position of the arena’s boundary. Neuronal activity in the cingulum fiber bundle, recorded at the level of the anterior retrosplenial cortex, resembled a combination of antero-dorsal thalamus and retrosplenial cortex responses. Fibers travelling through the white matter in the vicinity of the hippocamps carried a mixture of navigation variables. Our results draw a new picture of the signals carried and outputted by the anterior thalamus and retrosplenial cortex, and offer new insights on navigational variables represented in the hippocampus and its vicinity.