Xindi neural parasite
From Memory Alpha, the free Star Trek reference
The Xindi neural parasites are organisms used by the Xindi-Reptilians to ensure cooperativeness in their captives. They invade the neocortex and reconfigure the synaptic pathways of their victim to ensure compliance. If untreated, the parasites lead to permanent neural damage.
Commander Dolim had Hoshi Sato injected with parasites to force her to decode the third launch code for the Xindi superweapon. When Sato was recovered by Enterprise forces, the parasites proved no match for Doctor Phlox's osmotic eel. (ENT: "Countdown")
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