Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Experimental designs are read from left to right. Each phase of behavior is separated by 24 h; however, infusions occurred immediately prior to testing in both Experiments 1 and 2. A, B, C, experimental contexts; T, tone CS; +, US; −, no US.
