One of the standard arguments to come up whenever there's an evidence-based discussion of life after death is the so-called transmission theory, first proposed by William James, which views the brain as a receiver of the "signal" of consciousness (not an actual electromagnetic signal — it's a metaphor). The transmission theory stands in opposition to the production theory, which holds that the brain produces consciousness.
The essential point underlying the transmission theory is that correlation is not causation - that the admittedly obvious correlation between brain states and mental states does not establish that the brain causes the mind to come into being. The usual modern analogy is of a television set; damage to its components will compromise the picture and sound in predictable ways, but this does not mean that the TV actually produces the content it displays. The content actually originates as a signal, and the signal will continue uninterrupted and unimpaired even if the set is turned off or destroyed.
Though objections to the transmission theory today are usually dressed up in the latest findings of neuroscience, there's really nothing new here. Even in James's day (and long before) it was well understood that brain damage or the ingestion of alcohol or certain drugs could alter mental states. No one disputes this; the question is whether the changes to the brain affect the brain's ability to produce consciousness or affect the brain's ability to receive and decode the signal of consciousness, which comes from an outside source.
Another common Skeptical objection is that the transmission theory is unfalsifiable — i.e., that it cannot be disproven even in principle, rendering it untestable and unscientific. Let's take a closer look at this argument.
First, it should be pointed out that neither the transmission theory nor the production theory really deserves the name of "theory." Both ideas are thumbnail sketches, vague starting points for a possible theory that has yet to be developed. Though there has been some effort to explain the mechanism of transmission in terms of quantum tunneling and microtubules, the work is still in a preliminary phase and is very controversial. Meanwhile, no one on the production side of the debate has ventured to solve the "hard problem" of neuroscience - how electrochemical activities in the brain become qualia and self-awareness.
Though I'll continue to use the term "theory" for convenience, it might be more accurate to describe both production and transmission as hypotheses — or even as suggestions, notions, or speculations.
But what about unfalsifiability? Is it true that the transmission theory is inherently impossible to disprove?
Probably, yes. No matter how many correlations are found between brain and mind, the transmission theory can always insist that the mind's true source lies elsewhere. Even if the source is never found, advocates of transmission can maintain that it's out there ... somewhere. And even if artificial intelligence someday replicates human intelligence, it will be possible to argue that AI is only a simulation lacking true self-awareness — a masterful imitation but not the real thing.
So if transmission is unfalsifiable, where does that leave us? Well, it means we need to take a hard look at production. Is that theory falsifiable in principle?
Answer: yes. It could be falsified by any convincing evidence that consciousness can operate when the brain is shut down or permanently defunct. After all, if consciousness persists when the brain is flatlining or dead, then it cannot depend on the brain's activity for its existence (even if it does require the brain to mediate its interaction with the physical world).
Now, I would argue that there already is convincing evidence on exactly this point. The best documented cases of NDEs, mediumship, and spontaneous reincarnation memories (among other things) strongly suggest — and arguably prove — that consciousness does, in fact, continue even when the brain is temporarily or permanently offline.
In other words, it can be argued that while transmission is indeed unfalsifiable, production has already been falsified. Production cannot cover all the data — it cannot explain, and is not consistent with, the parapsychological evidence — and therefore it must be wrong.
This, in itself, does not prove that the transmission theory is correct. Perhaps there is some third alternative. Perhaps any form of dualism is wrong, and consciousness is all there is. Who can say?
But while we can't say definitively that transmission is true, we can — if we accept the evidence from parapsychology — say definitively that production is false. To overturn that conclusion, Skeptics would have to show that all the empirical evidence indicative of postmortem survival can be explained by deception, delusion, mistaken observation, faulty memory, and so forth. I wish them luck!