A monofilament stimulator is a tool that can be built into an electro-dynamic probe. With the proper modifications, it can be used to manipulate neurotransmitter levels in a Human brain.

During his investigation into Kovin's possible assault of Seven of Nine in 2374, The Doctor saw Kovin's electro-dynamic probe with a monofilament stimulator as corroboration for Seven's story. (VOY: "Retrospect")