A new model for olfactory imprinting in salmon

Olfactory imprinting is a specialized form of unconditioned learning in which olfactory information is acquired and then used in some specific behavioral context later in life. One of the hallmarks of olfactory imprinting is that it tends to be linked to a sensitive period of development. This prerequisite thus distinguishes olfactory imprinting from other types of odor learning in which only conditioned exposure to an odor stimulus is required for learning to occur. Most investigations designed to explore the mechanisms underlying olfactory imprinting have focused on mammalian species, concentrating on synaptic events at the level of the main and accessory olfactory bulbs.¹ Recent integrative studies with salmon^2,3 and rabbits,⁴ however, provide compelling evidence that highly specific imprinted odor memories may also be retained in the periphery, i.e., at the level of the olfactory epithelium proper. These results suggest that populations of olfactory receptor neurons may be selectively tuned to respond to odor molecules present during a hormonally linked sensitive period. A potential key to the mechanism of how these peripheral odor memories become established draws on the unique ability of olfactory receptor neurons to turn over throughout an organism's life span.⁵ How hormonal and environmental factors work together to influence olfactory neurogenesis is currently only sketchily understood,⁶ but ultimately may provide important new insights not only for basic science but for salmon conservation as well.