The olfactory bulb carries out concentration invariance calculations by itself and does it very quickly.

Abstract

The olfactory bulb is known to carry out computations for the olfactory perception of concentration invariance of odor recognition, a perception that is essential for life as we know it. However it is not known whether these computations require the extensive feedback to the bulb from the many brain regions which send this feedback. We have measured the concentration dependence of the mitral cell output of the bulb before and after blocking this feedback by lidocaine infusion into the medial olfactory peduncle. Surprisingly we found that the concentration dependence of the mitral cell output was unaffected by the lidocaine block of feedback. Furthermore the computation is rapid; it is complete within a single 250 msec inhalation. The computations for concentration invariance are most likely carried out within the olfactory bulb itself and they are carried out quickly.