The compass and the map: how does the brain orient itself in the environment?
As we navigate the world, it is crucial to maintain a robust sense of where we are. Head-direction (HD) cells serve as the brain’s internal ‘compass’ and each of them is tuned to the specific direction the animal is facing, independently of its location and ongoing behavior. Theoretical models have long suggested that the HD network is governed by ‘attractor dynamics’ ensuring the transmission of a reliable and unambiguous HD signal. By recording from large ensembles of neurons in the HD neuronal circuit of freely moving animals, and across brain states, we have provided experimental evidence for this theoretical prediction. In turn, the HD signal is believed to be a crucial input to the entorhinal-hippocampal network where boundary vector, grid and place cells form the brain’s navigational system that allows to identify the animal’s current location. However, how these neuronal correlates of space arise remains unclear. I will show how the combination of the HD signal - anchored to the absolute reference frame - with other sensory inputs relative to a body-centered reference frame may constitute one of the building blocks of spatial coding in the brain.