Dr Drechmeyer says in Cafe Diem "They're here!" In clear reference to the movie Poltergeist (1982) since the episode is about "ghosts".
The episode contains the series-recurrent 1970s song "Car Wash" - this time sung by the mail carrier in the elevator.
First appearance of Jaime Ray Newman as Tess Fontana.
The episode title Insane in the P-Brain is based on the Cypress Hill song title Insane in the Membrane.
The RADAR tracking the P-Brane activity is the first direct confirmation that Eureka is in Oregon.