Brown Institute for Brain Science

Olfactory Habituation and Cross-Habituation Task

Rationale of Test

Neurobiologists interested in sensory function have developed methods based upon innate novelty preferences to assess olfactory sensory acuity. This task relies upon the principle that when a stimulus is repeatedly presented, investigation of that stimulus decreases. When a novel stimulus is then presented, interest is again engaged, and the animal spends a greater period of time investigating the new stimulus. The cross-habituation experiment tests how different the odorant has to be from the habituated odorant before the animal will treat it as a new odorant and increase investigation.

Apparatus

Procedure

Five odor sets of four odorants each are used for the cross-habituation experiment. All odorants are diluted in mineral oil so as to theoretically emit a steady-state vapor phase partial pressure of 0.01 Pa (Cleland et al., 2002). Each odor set consists of a homologous series of three unbranched aliphatic molecules (Ohab, S1, S2) and a dissimilar control odorant (D). In each set, odorants are selected so that the most similar odorant S1 has a chain length that differed by one carbon atom from the habituation odorant Ohab, the moderately similar odorant S2 differs from Ohab by two carbon atoms, and odorant D is structurally and perceptually dissimilar to all of the others. At the odorant concentration used, perceptual similarity correlates with structural similarity within straight-chain aliphatic series (Cleland et al., 2002; Cleland and Narla, 2003). Odors are presented by placing 60 ┬Ál of the diluted odor stimulus onto a filter paper disc (Whatman #1) contained within a tea ball that is placed in the cage. Each test session is preceded by one 50-second presentation of plain mineral oil. Test sessions comprise four 50-second presentations of the habituation odorant at five-minute intervals, followed by one 50-second presentation of each of the test odorants (S1, S2 and D) in a randomized and counterbalanced order. The amount of time that the mice spent actively investigating each presented odorant is measured. Active investigation was defined as directed sniffing within 1 cm of the odor source. Behavioral testing is repeated over the course of 5 separate days using 5 different odor sets. Time spent sniffing is coded during testing, with the experimenter blind to odorant identity as well as the genotype of mice or using Ethovision Observer and coding sniffing behavior from digital video files. Data from the 5 separate days of testing is then averaged within subjects.

Interpretation

Relevant Controls

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