Computerized odor psychophysical testing in mice

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Abstract
An automated odor psychophysical procedure was developed and used to determine absolute sensitivity to n-amyl acetate. Mice were trained to initiate a trial by interrupting a photobeam at the rear of the test chamber, then sample an odor port and indicate the presence or absence of odorant by either quickly withdrawing from the port or by continuing to sample the port. Once the air dilution olfactometer had been adjusted prior to a training or testing session, a microcomputer was used to record all responses by the animal, to control the delivery of stimuli to the odor port and to control all events in the test chamber. Correct reponses on both odor and control trials were reinforced and incorrect responses on both types of trials were punished with a forced ''time-out'' period. The odor sensitivity of all mice was estimated, using a tracking procedure, and was then studied in detail using schedules in which odor concentrations were presented in ascending, descending and random order. With all three schedules, thresholds to n-amyl acetate were between 1 .times. 10-12 and 1 .times. 10-13 M. Threshold estimates obtained from two of these same animals more than 1 year later were within 0.25 log units of the original values. This method should prove valuable in future studies of nasal chemoreception in mice.