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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 1.

Figure 1

Flow chart showing contingencies for the free-choice trials in the variable-ratio task. Definitions: VR, variable ratio; FR, fixed-ratio. Free-choice trials allow the rat to make a selection between the VR lever, which delivers the large reinforcer (100Hz) immediately after the required number of presses is completed and the FR lever that delivers the small reinforcer (50Hz) immediately after 3 presses. If no selection is made within 28s, the levers are withdrawn, and a new trial begins 2s later.