| Mice are randomly assigned to test groups (paired and unpaired)
||Groups are tested for sign-tracking and goal-tracking
||Sign-tracking and goal tracking (rate and duration)
- Conditioning chambers (16 Med Associates, St. Albans VT, model ENV-307W)
- Enclosed in sound attenuating cubicles (ENV-022V)
- The floor of each chamber consists of bars which are completely covered by a single piece of acrylic to facilitate cleaning and mouse ambulation
- A retractable response lever (ENV-312-2W) is mounted to the left front wall 18 mm above the chamber floor and 28 mm away from the adjacent wall; contains infrared detectors
- A pellet dispenser (ENV-203-20) delivers 20 mg Bio-Serv (Flemington NJ) Dustless Precision Pellets (F0071) into a pellet receptacle (ENV-303W)
- The receptacle is mounted to the right front wall 3 mm above the chamber floor, 28 mm away from the adjacent wall, and 125 mm away from the lever; contains infrared detectors
- A house light (ENV-315W) with bulb (CM1820, Chicago Miniature, Novi MI) is mounted outside and behind the rear wall of the chamber
- A monochrome micro video camera (Noldus Information Technology, Leesburg VA) is mounted to the ceiling of the sound attenuating cubicle directly above the chamber.
- The camera is connected to a video capture card in a Windows PC (Noldus Information Technology) which is used to record mouse behavior during testing
- Med Associates MED-PC IV software (St. Albans VT) controls the chambers
- The ST/GT program was written in-house in MEDState notation
- 70% ethanol for cleaning between testing sessions
Procedure: Pavlovian conditioned approach testing
- Mice are randomly assigned to either a paired or an unpaired condition; mice in paired condition receive PCA training in which pellet delivery is paired predictably with lever extension and retraction (pellet delivery and retraction occur simultaneously 10 s following lever extension); mice in the unpaired condition receive identical training with the exception that pellet delivery is randomized relative to lever extension and retraction.
- Testing is conducted between 1100 and 1600h. The house light is illuminated throughout the session. Sessions consist of 25 trials. Each trial is followed by an inter-trial interval (ITI) of random duration ranging from 30 to 150 s.
- The lever is extended and retracted at the beginning and end, respectively, of each 10 s trial.
- For mice in the paired group, a pellet is delivered concurrently with lever retraction; for mice in the unpaired group, a pellet is delivered at a random time between the beginning of each ITI and the end of the subsequent trial.
- All mice receive 25 pellets during each session.
- The number of lever presses and pellet-receptacle head entries during the trial and ITI are recorded automatically for each session by means of infrared detectors built into the levers and pellet receptacles.
- Because many mice show evidence of 1) lever contact that does not result in lever depression and 2) shallow pellet-receptacle head entry that does not result in an infrared beam break, the entire session is recorded for all mice of the final test day (session 15).
- Video data are subsequently scored to quantify approach to the lever and pellet receptacle during the trial and ITI on session 15.
- Goal-tracking rate for paired and unpaired conditions (15 sessions)
- Goal-tracking duration for paired and unpaired conditions for trial period and ITI (25 trials of last session)
- Sign-tracking rate for paired and unpaired conditions (15 sessions)
- Sign-tracking duration for paired and unpaired conditions for trial period and ITI (25 trials of last session)
- Pellet head entry for paired and unpaired conditions for ITI period
All data are available in the Dickson1 supplementary data file
Summary plots are available here