ReviewHabituation and adaptation to odors in humans

- With regard to the field of olfaction several of the principles of habituation have either not been tested or need more research: potentiation of habituation, dishabituation, habituation of dishabituation, and long-term habituation.
- The impact of odor valence on adaptation is still not clearly understood and more research is needed in this area.
- Adaptation of odor perception is relatively fast with the onset of cortical adaptation being more pronounced than peripheral adaptation.
- Olfactory adaptation is a distributed process involving adaptation at both peripheral and cortical level, and more studies looking at feedback between these two systems (including the olfactory bulb) are needed.

Habituation, or decreased behavioral response, to odors is created by repeated exposure and several detailed characteristics, whereas adaptation relates to the neural processes that constitute this decrease in a behavioral response. As with all senses, the olfactory system continually encounters an enormous variety of odorants which is why mechanisms must exist to segment them and respond to changes. Although most olfactory habitation studies have focused on animal models, this non-systematic review provides an overview of olfactory habituation and adaptation in humans, and techniques that have been used to measure them. Thus far, psychophysics in combination with modern techniques of neural measurement indicate that habituation to odors, or decrease of intensity, is relatively fast with adaptation occurring more quickly at higher cerebral processes than peripheral adaptation. Similarly, it has been demonstrated that many of the characteristics of habitation apply to human olfaction; yet, evidence for some characteristics such as potentiation of habituation or habituation of dishabituation need more support. Additionally, standard experimental designs should be used to minimize variance across studies, and more research is needed to define peripheral-cerebral feedback loops involved in decreased responsiveness to environmental stimuli.