Olfactory Adaptation

Behavioral Characteristics

Historically, there have been two terms to describe a decrease in response to a stimulus following repeated presentation of that stimulus: adaptation and habituation. The original use of these terms defined the decrease in behavioral response as habituation, and one potential neural mechanism of this habituation—a decrease in the response of those neurons that initially received the stimulus (e.g., receptor neurons in the eye, skin, or nose) as adaptation. However, it has become increasingly clear that behavioral habituation may involve adaptation at both the receptors and within the central nervous system. This has led to a blurring of the lines between what is meant by habituation and adaptation. Within the sensory physiology and psychophysics literature, adaptation has become the more common term to describe both decreased behavioral response and its potential underlying neural cause. Within the learning and memory literature, habituation and adaptation still tend to be used in somewhat different contexts closer to their historical usage. Here, olfactory adaptation refers to both the reduced behavioral/perceptual response and its presumed underlying neural cause.

Either repeated or prolonged exposure to an odor reduces subsequent responsiveness to that odor. This adaptation can be measured as either an increase in detection threshold (i.e., how strong the odor needs to be before it is noticeable), or as a decrease in response magnitude to strong odors (i.e., the intensity rating of an odor that is detectable). Depending on the conditions, as described next, olfactory adaptation can occur within seconds or minutes of exposure, or may take much longer if stimulus presentations are spaced over time or depending on the context or odor identity.

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