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.
Mean ± SEM numbers of heroin-reinforced lever presses for the first 15 training sessions in subgroups of the symmetric lesion condition. Effective lesions were defined as those that caused self-administration rates 2 SD lower than those of the sham-lesioned animals (shown with those of the asymmetric-lesioned animals in dotted lines). Stars indicate data points significantly (p < 0.05) different from the corresponding point for the sham-lesioned animals.
