Many cultures have seen a close connection between mysticism and madness — and in fact, there are significant similarities between behaviors associated with some forms of mental illness and the behaviors associated with mediumship (trance mediumship in particular). There are also areas of overlap between the intellectual fixations of some mental patients and the accounts of near-death experiencers.

Critics see these parallels as evidence that paranormal states of consciousness can be explained as instances of a psychological or neurological problem. Basically they say, “You’d have to be crazy to believe this stuff.”

I don’t agree with that assessment. But I do think it’s interesting and instructive to examine these similarities, which some people with spiritual inclinations may find troubling.

Anyone who's had the opportunity to spend time with a person suffering from delirium, schizophrenia, or dementia may have noticed some or all of the following behaviors:

Incessant talk about God, visiting heaven, and meeting with deceased relatives, often expressed with intense emotion.

Belief in out-of-body experiences and heavenly communications, including direct contact with God.

Periods of communication with an unseen presence, in which the patient will talk, with eyes closed, to someone who “isn’t there.”

Grandiose projects intended to save the world – projects that are admirably altruistic but mostly impractical.

Stream-of-consciousness speech, incredibly loquacious and verbose; the rapid production of large blocks of words, at a rate that would challenge the skills of a stenographer.

The insistence that everything is connected and is all part of a larger plan; the connections cited are trivial, random, and arbitrary, but are interpreted as profoundly meaningful.

The claim that “time is running out” and that some amazing, transformational event is about to take place, for which the world must be prepared.

The assurance that all these revelations are startlingly clear and make perfect sense, even though they seem nonsensical to observers.

I have personally observed all of the above.

Now, if we look at parapsychological phenomena, we can easily see areas of overlap with the behaviors listed above. Mediums, by definition, spend time talking to someone who “isn’t there,” at least in a mundane sense. Trance mediums who practice automatic writing are known for their incredible output, producing thousands of words with little apparent effort and with minimal need for revision. It has often been noted that those on "the other side" have no shortage of altruistic plans and projects, but that these schemes are generally impractical. There is also no shortage of failed predictions by mediums, usually involving some momentous event of world-shaking import.

Near-death experiencers often report that while they were out of their body, they understood that everything that happens is interconnected in a vast, beautiful, and perfect design. Some also report having had access to all knowledge with astonishing clarity, yet they are rarely, if ever, able to convey this clarity after being revived.

Such parallels go a long way toward explaining why mainstream psychiatrists, who often encounter delirious, schizophrenic, or senile patients, are generally skeptical of phenomena like mediumship and NDEs. There are, however, crucial differences that shouldn't be glossed over. The best cases of mediumship involve verifiable details that the medium had no normal way of knowing, and in some cases involve actually re-creating the characteristic mannerisms, gestures, facial expressions, and verbal tics of a deceased person unknown to the medium. The best NDE cases include veridical observations of things that took place while the patient was deeply unconscious or even clinically dead.

Even though it would be a mistake to conflate mental breakdown and paranormal mindsets in a simplistic way, the obvious similarities still require an explanation. Why should madness and mysticism be so closely linked?

My best guess is that the "mental filter" hypothesis popularized by Aldous Huxley in such books as The Doors of Perception is at least partially correct. This hypothesis holds that consciousness exists outside of the brain, rather than being created by the brain; the brain serves as a filter that shuts out the greater part of consciousness, allowing us to focus on narrower, more specific objectives consistent with survival on earth.

If the brain is damaged or its chemistry is altered, the filter starts to break down and normally restricted input begins to trickle in. The result is a subjective sense of mind expansion, a conviction of direct contact with "the beyond," and an urgent desire to communicate ineffable ideas. Unfortunately, there is a severe downside: the person's ability to function in the everyday world is seriously compromised. (Remember that the need to function in ordinary reality is the reason for the filter mechanism in the first place.)

Moreover, whatever legitimate input may be coming to the person’s attention is mixed together with erroneous or irrelevant thoughts – what William James called “bosh" in connection with the mediumship of Mrs. Piper. (As Michael Tymn notes in Resurrecting Leonora Piper, James characterized a great deal of what Mrs. Piper had to say while in trance as bosh or nonsense, while acknowledging that a smaller portion of what she said was not explicable by any normal means. It was this smaller portion that fascinated him and other investigators.)

The filter hypothesis is very ably explained and defended in Chapter 2 of Bernardo Kastrup’s new book, rather combatively titled Why Materialism Is Baloney. Kastrup, who maintains a blog arguing for philosophical idealism, notes that the filter hypothesis implies two important predictions. The first is that:

The subjective experiences that are filtered out become the so-called 'unconscious' mind of the respective ego. Since each ego allows in only an infinitesimally small part of all potential experiences – given the unfathomable variety of conscious perspectives that exist in potentiality – the 'unconscious' minds of different egos will differ only minimally, the vast majority of the 'unconscious' being identical across egos. As such, the filter hypothesis, unlike materialism, predicts the existence of a 'collective unconscious,' a shared repository of potential experiences that far transcends mere genetic predispositions of a species.

He finds evidence supporting this prediction in the work of analyst Carl Jung and the whole field of transpersonal psychology.

The second prediction is that there should be "a broad pattern of empirical evidence associating non-local, transpersonal experiences with procedures that reduce brain activity."

In support of this prediction he cites fainting caused by asphyxiation, pilots who lose consciousness when blood leaves the brain, hyperventilation, psychedelic substances, inhibition of brain activity via electromagnetic fields, brain damage, automatic writing practiced by trance mediums, near-death experiences, immersion in an isolation tank, and various initiatory rituals in tribal cultures. (“It is very reasonable to assume that such ordeals – like long sessions in sweat lodges, exposure to the elements, extreme exertion, and even poisoning – physically compromised brain function.”)

All of these cases, Kastrup argues, have been associated with nonlocal, transpersonal states of consciousness, strongly indicating at least a correlation between reduced or impaired brain activity and experiences of "cosmic consciousness" (to use the phrase coined by R.M. Bucke).

Kastrup notes that materialists often cite many of these cases as evidence that transpersonal experiences, being precipitated by biological changes, must be purely illusory. He counters with this argument:

Well, such an assumption is, in my view, the product of shallow thinking at best and of prejudice at worst. Just why can't a true transpersonal experience be triggered by physical intervention in the brain, given the obvious fact that mind and brain are related in some way? What is in dispute is the nature of this relationship, not its existence. If the nature of the relationship is such that the brain modulates and localizes consciousness, without causing it, it is not only reasonable but also expectable that physical interference with the brain should change one's subjective state. Not only that, partial deactivation of certain brain processes through physical means – be them psychoactive drugs, magnetic fields, hyperventilation, asphyxiation, ordeals, sensory deprivation, etc. – should allow consciousness to partially de-localize and expand, which is perfectly consistent with the types of transpersonal experience listed above … While particular reports of transpersonal experiences could possibly be explained away, the broad pattern that associates peak transpersonal experiences with reductions of brain activity clearly points to a robust and consistent phenomenon.

To change the analogy slightly, let’s look at the brain not as a filter but as a receiver. The two metaphors are closely related; each assumes that consciousness originates outside the brain, and that the brain must modulate the inflow of consciousness in some way. A radio receiver can be tuned to any number of frequencies. In effect, the tuner is designed to "filter out" unwanted frequencies and allow only the desired frequency to come through. As long as the radio is tuned to a clear signal, the information will come through with minimal distortion.

But suppose something goes wrong with the tuner. Suppose the radio starts randomly jumping from one frequency to another. It would, in one respect, be accessing more information – or at least a broader range of information – than before. Yet the resulting transmissions would be confused and chaotic, because the dial would keep slipping unpredictably from one station to another.

Or suppose the radio acquired the ability to tune in to more than one station at a time. Then two or more transmissions would come through together. If one signal was stronger than the others, it might come through clearly enough, with only faint "ghost" transmissions in the background. (The term “ghost” is an interesting one in this context.) But if all the signals were of approximately equal strength, the resulting noise would be almost impossible to interpret. Technically, more information would be coming through; but it would be indecipherable.

There's an episode of Buffy the Vampire Slayer titled “Earshot" in which Buffy develops clairaudience – she can hear other people's thoughts. At first she finds this new found talent helpful. But as the episode progresses, her clairaudience increases, until she hears a babble of voices in her head at all times, a condition that incapacitates her and threatens to drive her insane. Though I doubt it was intentional, this storyline is a good metaphor for the benefits and hazards of impairing the brain’s “filter” mechanism.

We can probably see now why mental illness and paranormal states of mind have significant areas of overlap. In both cases, the brain's function as a filter (or tuner) has been compromised, letting in a stream of information that would ordinarily be kept out. Within limits, opening up the filter can be beneficial; outside those limits, it can do more harm than good.

In short, the filter hypothesis seems to provide a pretty good explanation for the way in which mental breakdown dovetails with trance mediumship and NDEs. The alternative explanation, proffered by materialists, would be that the communications provided by mediums and the narratives recounted by NDErs are themselves instances of mental illness or temporary mental breakdown. But this viewpoint doesn’t account for the veridical aspects of these cases, or for the fact that, typically, mediums and NDErs are able to function quite normally in their everyday lives.

All that having been said, there’s one more thing to consider. Many cultures, both ancient and modern, have taboos against delving too deeply into the paranormal. It’s possible that such taboos serve a legitimate purpose, and should be violated only with caution. If the brain’s filtering activity is indeed essential to allowing us to navigate the physical world, then any impairment of the filter may reduce our survival prospects. In fact, natural selection seems to dictate that really strong psi talents would be progressively weeded out of the population, since whatever advantages psi might offer would be more than offset by the risk of being overwhelmed and disoriented by excessive mental input. (On the other hand, more moderate psi talents would not necessarily face extinction, and higher level talents could be cultivated with practice or might appear spontaneously in rare cases, either at birth or as a result of some alteration in brain function. Cultures that placed a high value on shamanic talents would look after such individuals and see to it that their everyday needs were met.)

For millennia, mystical adepts have warned casual enthusiasts not to get caught up in things beyond their ken. It’s worth keeping these injunctions in mind. The mind-brain relationship can be a fragile thing; we toy with it at our peril.