A rat will readily learn to discriminate between non-biological odors to receive rewards.  Figure 1 shows the behavioral apparatus used in the odor discrimination task.  This apparatus consists of an odor sampling port (white circle) and a fluid delivery well (black circle).  On each trial, the rats sample odors presented at the odor port (Figure 2a) and then must decide, based on the identity of the odor, whether to make a ‘go’ response at a nearby fluid well (Figure 2b) to receive a sucrose reward or whether to withhold that same response (Figure 2c) to avoid a penalty (quinine or a prolonged time-out period).  The video clip below shows the behavior of a rat during learning regarding new odor cues.

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Figure 1

Photograph of odor port and fluid well on polycarbonate insert that the rat below is using in the odor discrimination task.  This insert is bolted into the wall of a cubical aluminum training chamber pictured below.

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Figure 2

Still photographs and schematics showing the behaviors in the discrimination task.  The photographs were taken by a low-light video camera mounted in the side-wall of the behavioral chamber.  The camera is located on wall to the left of the photograph in Figure 1.

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The video clip below shows a rat learning to discriminate a novel pair of odors.   Note that the rat begins the session responding at the well after both positive and negative odors.  Initially responses to both odors occur rapidly, and then the rat begins to respond differently on trials after sampling the negative cue.  A slower response latency is evident after odor sampling on trials 20, 25, 34, and 40.  On Trial 20, the rat investigates the front of the well before responding.  On Trial 40, the rat responds but does not remain in the well long enough to register a response.  These changes in the response on negative trials indicate that the associations between the odors and the reinforcers have been learned.  Several trials later, the rat decides to withhold responses altogether on negative trials.  Shortly thereafter the rat reaches a criterion on the discrimination of 90% performance in a moving block of 20 trials.  Our analyses of neural activity during discrimination performance have been focused on encoding within these different phases related to learning and choice behavior.  

Web Content from:  Schoenbaum, G.  Olfactory Learning and the Neurophysiological Study of Rat Prefrontal Function.  In: CRC Series: Methods and Frontiers in Neuroscience.  Edited by S.A. Simon and M.A.L. Nicolelis, CRC Press, NY, 2000.