On day four, the time spent by the animal in each compartment was recorded for 30 min. In the second phase (conditioning), animals were conditioned with MDMA or saline through four pairings with the non-preferred or preferred compartment respectively.
In the second phase (conditioning), animals were conditioned with saline, MDMA, WIN or both drugs through four pairings with the respective compartment (one pairing each day).
Experiments with lights and metronomes failed to reveal the following important principle of conditioning: animals appear to have built-in biases toward associating some classes of stimuli with certain classes of consequences.
In classical conditioning, animals (or humans) are given a cue to perform a task and then rewarded with a treat.
For NaCl conditioning, animals were exposed to 25 mM NaCl in CTX buffer for 4 hours.
24 h after fear conditioning animals were tested for their ability to express learned fear.
For conditioning, animals were grown at the indicated temperature for 2 days and starved for 4 hrs before testing.
LFP recordings were obtained for the entire 24 h period and analyzed in the same method as the odor shock conditioning animals.
Following conditioning, animals were allowed to move freely for another 10 min without light stimulation to determine their post-stimulation preference.
After conditioning, animals were introduced to the apparatus and restrained in a plexiglass chamber with an angled base, such that each hind paw rested on a separate force plate connected to a load cell.
