Use the adjective prefrontal when you're talking about the very front part of the brain. Take care of your prefrontal cortex; it controls your personality.
In an anatomy class, you'd gain a lot of information about the prefrontal cortex, since it's a vital section of the brain. The word prefrontal comes up in discussions of non-human animals as well, usually describing their brains, but sometimes in discussions of the skull, specifically the bones in front of a bird's or reptile's eye socket. Prefrontal combines pre-, "before," with frontal, "being in front," emphasizing the far forward location.