1. An apparatus for assessing consciousness comprising: an electroencephalographic sensor collecting electrical signals from firing neurons within a patient's brain; a neural stimulator for promoting a localized excitation of neurons within the patient's brain at a location and time using transcranial magnetic stimulation; and an electronic computer receiving the electrical signals from the electroencephalographic sensor and executing a stored program to: (i) measure neural activity indicated by the electrical signals following the localized excitation of neurons by the neural stimulation, and (ii) output an indication of consciousness based on the measured activity.