Pain is very important survival and adaptive factor for living organism signalling about some injuries or disturbances. That's why many alternative pathways of pain signals transmission are existing in living organism, and all of them are important. When we are working with laboratory animals, we can evaluate the pain sensation only by resulting reaction = reaction threshold (vocalization, jumping, paw licking etc.). It is easier to evaluate a human reaction, because we can evaluate the threshold of pain sense. On physiological level tens of different factors may affect on intensity of pain, including age, body weight, type of nervous system, emotions, air temperature, depression and so on. And also we have to consider that different types of pain may involve different pathways of stimulus transmission. That's why the separation of some factors or pathways more important than others too difficult, I guess...

Erick, are you asking about pain or nociception? The answers would be very different depending on which, and the relationship between the two is complex and controversial.

Dear Sean,

You're right, there is no a strict relationship between nociception and pain. But assuming that the activity elicited by projection neurons can be associated with pain sensation, are the lamina I projection neurons more important than WDR neurons located at deeper laminae? or vice versa?

I recently developed a computational model to help explain somatosensory processing and how its disruption in the spinal cord contributes to chronic pain. Several experimental works from Lu and Perl (Lu Y, Perl ER., J Neurosci. 2003;23(25):8752–8758; J Neurosci. 2005;

25(15):3900–3907; J Clin Invest. 2013;123(9):4050–4062) take the Lamina I projection neuron as the output, but this create a conflict with the Gate Control Theory and other studies (J Neurophysiol. 1989 Aug;62(2):450-7.) which have demonstrated that WDR neurons are crucial in coding the intensity of painful stimuli.

Thank you for your concern!

Very interesting, Erick, but I'm afraid I can't help you much. There is an interesting anatomical review on spinal nocicpetive pathways that I find helpful (Brain Res 1000:40-56, 2004), but I suspect that the precision is rather less than you would need for your modelling. Nonetheless, I would be interested in knowing how your model works out.

Buena suerte!