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. Author manuscript; available in PMC: 2018 Jul 3.
Published in final edited form as: Prog Neuropsychopharmacol Biol Psychiatry. 2017 Apr 12;77:178–184. doi: 10.1016/j.pnpbp.2017.03.027

Figure 2.

Figure 2

Rats press for the positive reinforcer, independent of lever presentation. (A) Lever-pressing in Phase 2. Presses during training for FR3 when only one lever is extended (either left or right). Rats (n=15) self-stimulated equally, independent of which lever was extended. (B) Lever-pressing during Phase 3. Both levers were extended, and the rats selected the preferred reinforcer. Data shown verify that rats (n=14) preferred the large reinforcer when associated with either the right or left lever. (C) Rats (n=11) exerted high physical effort to obtain the large reinforcer in a forced VR10. A similar number of reinforcers were delivered, regardless of the lever assignment. On the left y-axis is the number of lever presses averaged across two consecutive sessions. On the right y-axis is the average number of large reinforcers received. Paired t-test, p>0.05.