Comatose patients would be so relieved to be able to communicate with the outside world
Most previous brain signal translation has been adaptions of typing in some form. This is directly translating signals intended for vocal cords, IE for vocal speech, into text.
https://www.brain-injury-law-center.com/blog/brain-activity-...
A complete lack of brain activity is brain death. Brain activity is often slowed in comatose patients, but that varies from patient to patient.
https://www.mayoclinic.org/diseases-conditions/traumatic-bra...