When the sense of smell is blocked, brain activity in response to scents changes, though these changes are quickly reversed once the sense of smell is restored. Previous work had suggested that the olfactory system was relatively resistant to perceptual changes following odor deprivation, however, a paper published this week in Nature Neuroscience suggests that this stability is actually due to rapid compensatory changes in the brain. Keng Nei Wu and colleagues limited odor input to participants by completely blocking their nostrils, and having them spend a week in a low-odor ward of a hospital. The perception of odor before and immediately after the experience of olfactory deprivation was largely unchanged. However, brain activation in response to odors had changed. Following deprivation, participants had increased activation in the orbitofrontal cortex and decreased activation in the primary olfactory cortex. The authors state that this combination of changes may have sustained the perceptual stability.
A week after the deprivation experience, brain responses to odors had returned to pre-experimental levels, suggesting that deprivation-induced changes are rapidly reversed. Such a rapid reversal is quite different from other sensory systems, such as sight, which typically have long lasting effect to deprivation. It has been suggested that the olfactory system is different because deprivation due to viral infection or allergies is not uncommon.