eub | Zou, Li, and Buck: Odor maps in the olfactory cortex

Reading the paper posted by

aquaeri in comments to this interesting post.

(PNAS++ for making the article available online. Oh, ah, they manage that by charging the authors $1000 to exercise the Open Access option. authors++)

What I got:

A given odorant excites a widespread clumpy pattern over the anterior piriform cortex (APC).
Similar odorants have similar patterns.
Even different odorants have overlapping swathes. (I.e. they hit some neurons very near each other.)

Still up in the air:

For all I can see here, the patterns in APC could be just scramblings of the clustered odorant responses seen in olfactory bulb.
For example, do we know that any APC neuron receives inputs from two distinct receptor clones?
When similar odorants have similar patterns in APC, is that simply because they light up similar sets of olfactory receptors upstream? (The authors mention this for future work.)
Is there any kind of processing being done in APC?
Does position within the APC mean anything?

I'd love love love to see this paper's measurements of APC taken along
with ones of olfactory bulb. *That* could get you somewhere.

"single cortical neurons are likely to receive signals derived from combinations of ORs [cite]. Based on the findings presented here, we speculate that neurons in the OC require combinatorial OR signals for activation." --
That's reasonable speculation, but how is it based on these findings?

What is the shape of the APC?
Layers I, II, III shown in Fig 1 coronal sections, but what is their orientation?
Is APC your six-layer flavor of cortex? Where are IV+ in this picture? And does it have inhibitory interneurons and suchlike?
Fig 2 reducing APC to 2 dimensions -- collapsing away the lateral axis?
Can't figure out how layers would show up on Fig 2 maps.

Hierarchical clustering: "stimuli viewed as vector variables determined by number and distribution of c-Fos+ cells" -- well, heck, determined *how*? I say feh to the hierarchical clustering.

They slam the mouse with a lot of odorant and see every neuron light up. Would this identical measurement show up with a high concentration of a different odorant? I bet the *mouse* can tell overwhelming thiol from overwhelming ester.