posted at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3368527/ (read the full research)
David M. Coppola *
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Unilateral naris occlusion has long been the method of choice for effecting stimulus deprivation in studies of olfactory plasticity. A significant body of literature speaks to the myriad consequences of this manipulation on the ipsilateral olfactory pathway. Early experiments emphasized naris occlusion's deleterious and age-critical effects. More recent studies have focused on life-long vulnerability, particularly on neurogenesis, and compensatory responses to deprivation. Despite the abundance of empirical data, a theoretical framework in which to understand the many sequelae of naris occlusion on olfaction has been elusive. This paper focuses on recent data, new theories, and underappreciated caveats related to the use of this technique in studies of olfactory plasticity.
5.2. Olfactory Perceptual Learning
This is a phenomenon that in some ways is reminiscent of olfactory induction (reviewed by ). After a period of passive exposure to certain binary mixtures of pure odorants, rats begin to discriminate components that had not been discriminated prior to the exposure period . However, unlike induction, this phenomenon is thought to have a bulbar origin because blocking neurogenesis in the bulb with drug infusion before and during the odorant exposure period prevents the improvement in discrimination .
5.3. Compensation Redux
From an evolutionary perspective the compensatory processes discussed previously, which appear to be implemented at various levels of the olfactory system, seem quite logical. Given their finite dynamic range, nature has designed sufficient plasticity into sensory systems to continuously adjust their output to maximize the useful information transferred by them about the environment to the brain .