Figure 1.

Fear extinction requires posttraining NR2B activation. (a) Percent freezing during conditioning (first trial and averages of 2–4 and 5–7 tone–footshock trials on Day 1), trial-by-trial extinction training (20 tone-alone trials on Day 2), and extinction test (5 tone-alone trials on Day 3). Vehicle (white circles) or ifenprodil (black circles) injections were administered immediately after extinction training (arrow); No-Ext control group (No-Ext; gray triangles). (b) Averaged percent freezing across all extinction test trials for vehicle-treated (white bar), ifenprodil-treated (black bar), and No-Ext (gray bar) rats. *P < 0.05 relative to control groups (vehicle and No-Ext) in the same session. +P < 0.05 relative to ifenprodil and vehicle groups in the same session.