In Star Trek: The Next Generation, Data’s emotion chip gives the android the ability to experience emotions.
Data’s creator, Dr. Noonien Soong, designed the chip as a way to help his android son become more human. Soong gives it to Data in the episode “Brothers,” but Data initially cannot control the intensity of the feelings it produces. The chip later becomes an important part of Data’s struggle between artificial logic and human-like experience.
The emotion chip is separate from Data’s positronic brain. The brain provides his reasoning, memory, and artificial intelligence, while the chip adds emotional responses such as fear, anger, and joy. Data can also remove or disable the chip when its effects interfere with his judgment.
The device is sometimes confused with Data’s later attempts to understand humor, art, and friendship. Those qualities develop through experience; the chip specifically supplies the biological-style emotional component.