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Why does olfactory sensation need lateral inhibition? If it's not helping in spatial discrimination then why is it needed? Don't we just smell the odour which is more concentrated?

My attempt: It is said that lateral inhibition is an important part of olfaction as it aids in odour discrimination by decreasing firing in response to background odours and differentiating the responses of olfactory nerve inputs in the mitral cell layer. But we also know that sensory perception is based on the pattern of receptors activated by the stimulus. So following questions arise:

Why don't background odours laterally inhibit the target odour? Isn't there more chance of inhibition of target odour being inhibited since its concentration is less?

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  • $\begingroup$ Can you provide references to your claims? $\endgroup$ – Memming Jun 4 '17 at 14:54
  • $\begingroup$ Its in my textbook and some other information is from wikipedia. $\endgroup$ – JM97 Jun 4 '17 at 15:00
  • $\begingroup$ Can you tell us about which textbook / chapter it's from, and which wikipedia article / section you are referring to? $\endgroup$ – Memming Jun 4 '17 at 15:04
  • $\begingroup$ About lateral inhibition here en.wikipedia.org/wiki/Olfactory_bulb $\endgroup$ – JM97 Jun 4 '17 at 15:09
  • $\begingroup$ In the note below action potential goo.gl/sFAjqD $\endgroup$ – JM97 Jun 4 '17 at 15:12
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Here is the paper which directly answers your question.

Urban NN. Lateral inhibition in the olfactory bulb and in olfaction. Physiology & behavior. 2002 Dec 31;77(4):607-12.

A few salient points:

  1. It is true that the spatial gradient of sensory attributes is not as clear in the olfactory bulb-neuronal topography as it is at other places with lateral inhibition, but lateral inhibition still seems to serve a similar purpose in all these cases, namely sharpening the perceived stimuli. It is not settled how is this "edge enhancement" brought about in a nontopographical system ( "...Specific inhibitory connections between groups of cells with similar receptive fields may allow for functional lateral inhibition in such nontopographic systems, but no evidence for such specificity has been provided in the olfactory system...").

  2. Unlike say for example in the Retina, where lateral inhibition creates the on/off centres, the lateral inhibition in olfactory bulbs is more widespread. That is, the area inhibited is relatively more expansive. This fact, coupled with the highly localised excitation caused by odours, suggests that "....lateral inhibition will be most effective at suppressing signals with low spatial frequency, in other words, signals that involve activation of broad regions of the olfactory bulb...". This is what I assume was meant by your source while referring to background odours.

  3. The overall neurological effects of lateral inhibition is not settled, and the evidence is scanty. To quote the aforementioned paper, "... A simple prediction for the effects of lateral inhibition on olfactory behavior would be that impairment of lateral inhibition should impair performance on olfactory discrimination tasks, and perhaps that these effects should be strongest for tasks involving discrimination of very similar odorants. Such a result has been obtained in experiments in the honeybee in which inhibition is blocked by picrotoxin. However, in these experiments, the blockade of inhibition did not affect the odor-evoked firing rate of the cells recorded, suggesting that the impairment of discrimination ability was independent of a broadening of tuning curves..."

Have a look at the cited paper, and the papers quoted therein, for further information.

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  • $\begingroup$ Thanks for the link , but what I am unable to understand is how come background odour not inhibit the other odour? Shouldn't the inhibition be equal? If thats true then new odour must be more suppressed but its not the reality. So how can I justify this unfair treatment? $\endgroup$ – JM97 Jun 17 '17 at 15:07
  • $\begingroup$ THe suppression of background odors happens by a different mechanism, namely receptor desensitization which is a phenomenon occurring in almost all receptors. After a while, these receptors reduce their firing intensity despite the molecules still being present. If this happens, it won't affect the lateral inhibition profile in the olfactory bulb. $\endgroup$ – Satwik Pasani Jul 5 '17 at 9:49
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    $\begingroup$ Second, the paper suggests a different meaning of background odors, as odors with wide receptor specificity. These also have a different lateral inhibition effect. And one caveat that always looms overhead while studying neuroscience is that we might not know the thing perfectly well. I couldn't find any other simple papers regarding this, but if you delve a bit deeper, there might be more complicated yet explanatory papers out there $\endgroup$ – Satwik Pasani Jul 5 '17 at 9:50

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