A banned Ferengi device, a glowing sphere that projects thoughts and pain into a victim's mind, used by DaiMon Bok against Picard in The Battle.
The thought maker is a mind-altering device regarded as illegal even by the Ferengi. It consists of a sphere, with a matching unit that can be hidden near the target, and lets its operator impose headaches, memories and delusions on a chosen person.
It appears in the first-season Next Generation episode The Battle. DaiMon Bok presents Picard with the wreck of his old command, the USS Stargazer, having concealed one of the spheres in the captain's belongings. Bok blames Picard for the death of his son at the Battle of Maxia and uses the device to make him relive that fight and turn the Stargazer on the Enterprise-D.
With help from Riker and Data, Picard realises what is happening and destroys the sphere with a phaser. Bok's own officers relieve him of command for an unprofitable vendetta.