The theatre form that tried to capture the inner workings of the human mind is a soliloquy.
Soliloquy is the act of talking to oneself; speaking one's thoughts aloud regardless of any hearers. This technique is used as a device in drama or theatre to let the character's thoughts known to the audience without speaking directly to them.
A soliloquy is different from a monologue. The monologue is a speech spoken by a character that's addressed to a hearer, while a soliloquy is not addressed to anyone.
The most famous soliloquy is Hamlet's "To be or not to be" speech written by Shakespeare.
