Many years ago Manny had surgery to remove a bit of the bone from his foot. Now he remembers being wheeled back to the operating room, but he has no memories of the morning spent waiting for his surgery to begin

What is the most likely explanation for this difference in his memories?
a) He is probably having a repressed memory of that morning, since he was likely to be terrified.
b) He probably experienced retrograde amnesia as a result of undergoing general anesthesia.
c) He probably experienced an increase of stress hormones right before he was taken to the operating room.
d) He probably experienced long-term potentiation immediately after he was taken back to the operating room.

ANS: C, Stress hormones such as cortisol and adrenaline can help us make and keep long-term memories. The stress probably increased as the surgery neared, which is why he can remember being taken to the operating room.