1. In a system for tracking neural activity in a user and using an electrical signal based on said tracked activity for controlling computer controlled functions, a system for preventing neural activity during said user's sleep from being used for controlling said functions comprising: means for predetermining a neural activity pattern indicative of the transition of a user from awake to asleep; means for monitoring the neural activity of said user for said predetermined neural activity pattern; and means responsive to the detection of said predetermined neural activity pattern for terminating said use of said electrical signals based on said tracked neural activity.