ScienceDaily has a item (here), R.Hayman, M.Verriotis, A.Jovalekic, A.Fenton, K.Jeffery (2011) Nature Neuroscience, Anisotropic encoding of three-dimensional space by place cells and grid cells, about the coding of vertical position.
Animal’s brains are only roughly aware of how high-up they are in space, meaning that in terms of altitude the brain’s ‘map’ of space is surprisingly flat, according to new research….The study looked at two types of cells known to be involved in the brain’s representation of space: grid cells, which measure distance, and place cells, which indicate location. Scientists found that only place cells were sensitive to the animal moving upwards in altitude, and even then only weakly so… “This finding is surprising and it has implications for situations in which people have to move freely in all three dimensions — divers, pilots and astronauts for example. It also raises the question — if our map of space is flat, then how do we navigate through complex environments so effectively?”… It seems as if grid cells do not “know” how high they are…. Place cells, found in the hippocampus itself, produce single activity hotspots in the environment and seem to function to encode specific places. These neurons were only weakly sensitive to height too — but they did show some responsiveness, suggesting they received information about height from some other, possibly non-specific, source.
So, there is a lot more to learn about navigation!
Here is the abstract:
The subjective sense of space may result in part from the combined activity of place cells in the hippocampus and grid cells in posterior cortical regions such as the entorhinal cortex and pre- and parasubiculum. In horizontal planar environments, place cells provide focal positional information, whereas grid cells supply odometric (distance measuring) information. How these cells operate in three dimensions is unknown, even though the real world is three-dimensional. We investigated this issue in rats exploring two different kinds of apparatus: a climbing wall (the pegboard) and a helix. Place and grid cell firing fields had normal horizontal characteristics but were elongated vertically, with grid fields forming stripes. It seems that grid cell odometry (and be implication path integration) is impaired or absent in the vertical domain, at least when the rat itself remains horizontal. These finding suggest that the mammalian encoding of three-dimensional space is anisotropic.