Making the presumption that those alleged "mediums" were communicating with disembodied spirits is fallacious, at best.
That parts of their brains shut down while they're allegedly "channeling" has been obvious to me since the first time I attended a seance. How else to explain the alleged spirits of dead people forgetting their own names, their native languages, and the nature of their own deaths?
_________________
The mere fact that science may not yet adequately explain an object, event, or experience does not mean the immediate explanation should automatically default to a conspiratorial, extraterrestrial, paranormal, or supernatural cause.