Again, these are details for which we don’t yet have definitive answers. Here are some things to consider.
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Layer 6a projects to L4. If L6a is sufficient to allow L4 to predict its input then L6a must encode both location and orientation, because you need to know the orientation to make an accurate prediction.
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In Entorhinal Cortex there are Head Direction cells, which are a form of orientation, and there are grid cells, which encode location.
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Most of the cells in EC are a combination of both HD and grid cells, referred to as “conjunctive” cells.
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It is likely that L6a is some form of conjunctive (location plus orientation). That is what is needed to predict the input.
In the slide above I labeled L6a as orientation and L6b as location. That was my best guess at the time. I hope I said so in my talk. But, as I said above, it is more likely that L6a are conjunctive cells. We are currently working on these issues. Hopefully we can make some progress soon.