On 2013 Oct 23, Stephen Shea commented:

What is the basis for the statement that CO2 is odorless? Because it is to humans? This paper that the authors cite (http://www.ncbi.nlm.nih.gov/pubmed/17702944) quite convincingly demonstrated low concentration responses to CO2 in the olfactory sensory neurons and main olfactory bulb?. What reason is there to conclude that these are trigeminal in origin? Aren't these neurons the most likely source of the responses you see in cortex? I don't see how you can make your central claim without inactivation of trigeminal and olfactory sensory neurons.

On 2013 Oct 23, Stephen Shea commented:

What is the basis for the statement that CO2 is odorless? Because it is to humans? This paper that the authors cite (http://www.ncbi.nlm.nih.gov/pubmed/17702944) quite convincingly demonstrated low concentration responses to CO2 in the olfactory sensory neurons and main olfactory bulb?. What reason is there to conclude that these are trigeminal in origin? Aren't these neurons the most likely source of the responses you see in cortex? I don't see how you can make your central claim without inactivation of trigeminal and olfactory sensory neurons.