A neural parasite was an alien lifeform that attached itself to the nervous system of a host creature. The host creature nourished the parasite, as in standard parasitism. A neural parasite took parasitism a step further: it was an intelligent creature (or colony of such creatures), and used the host for more than just food purposes. By infiltrating the host's nervous system, it could use the host for any purpose it wished.
There have been several different species encountered by the Federation that fall under this category.
- In 2154, the Xindi-Reptilians used a neural parasitic species to brainwash Hoshi Sato. (ENT: "Countdown")
- In 2267, the USS Enterprise encountered a neural parasitic species at the Deneva colony. (TOS: "Operation -- Annihilate!")
- In 2364, the USS Enterprise-D encountered a neural parasitic species attempting to infiltrate Starfleet Command. (TNG: "Conspiracy")