Can ants get into brains?

No. Ants do not enter the brain. However, fire ants inject an alkaloid venom called solenopsin - into the skin or any membranes that they come in contact with. This can be quite painful.
Not in the U.S. The typical ants in the U.S. Cannot get into the brain of a normal, healthy person. The ants have to reason to try to do that.