Abandon the philosopical concept of an independent thinking mind capable of evaluating something by itself.
“Decisions” and “Thoughts” don’t exist without the environment, as they’re a succession of neuronal activation cascades in response to the current state of all stimulus, the previous connections formed in your brain, and reinforced patterns.
Leave a human being in an empty void and their thoughts will be built by severely boosting sensitivity and then responding to random sensory noise. Sever all sensory connections and the mind shuts down.