Head direction cells

Many mammals possess Head Direction cells (HDCs): Neurons that are active only when the animal's head points in a specific direction within an environment. HDC firing is independent of the animal's body position relative to the head. The system is related to the Place cell system, which is mostly orientation-invariant and location-specific, while Head Direction Cells are mostly orientation-specific and location-invariant. Head Direction Cells don't require a functional hippocampus, as Place cells do. They are found in the post-subiculum, retrosplenial cortex, anterior Thalamic Nucleus, lateral dorsal Thalamic Nucleus, lateral mammillary nucleus, dorsal tegmental nucleus, and striatum. HDCs are not sensitive to geomagnetic field, neither purely driven nor independent of sensory input, and strongly depend on the vestibular system. Some HDCs exhibit anticipatory behaviour: best match between HD activity and the animals' actual head direction was found to be up to 95 ms in future. They show no firing rate adaptation, the baseline firing rate is around 45 deg from the preferred orientation. When an animal is put in a novel environment, HDCs often shift to a new preferred orientation, and shift back to the old reference frame in known environments. For a review on the HD system and Place Field system, see Muller(1996)