Fig. 1

Experimental procedure. The place preference test was performed in a dark environment. To make a clear contrast between the test chambers, we selected two different floor materials: wood chips and plastic boards. Test chambers were connected with a tube with a gate kept open during pre-conditioning measurement on day 1 and the test period on day 4. On day 2 and day 3, mice received a piece of chocolate in one chamber, and regular chow in the other with the gate closed. Another set of animals was conditioned using an instinctively aversive odorant, 2-methyl-2-thiazoline (2MT), and distilled water as the control. The method section contains a detailed description