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People believe strange things. Or at least they say they do.
One peculiar feature of some delusions is that they can lack manifest behavioral conviction.
Someone may protest that they are being poisoned, but nevertheless continue to eat the food provided.
They may profess their spouse has been replaced by an imposter, but make no effort to locate the spouse.
Sometimes they do act on their beliefs, with tragic consequences for the ‘imposter.'
Furthermore, not all of our non-delusional beliefs are replete with manifest conviction—I believe I should eat more healthily, drink less alcohol, exercise more, however, I often fail to act consistently with those beliefs.
Alternatively, there are people who take their beliefs to extremes—acting against their own self-interest and continued existence, sometimes perhaps without expressed intention.
Beginning in 1977, more than 100 people of South East Asian descent have died unexpectedly in their sleep, of unknown causes. These Sudden Unexplained Nocturnal Death Syndrome (SUNDS) cases were particularly common in males from Laos, particularly Hmong refugees. Nutrition, toxicology, heart disease, metabolism, and genetics were all ruled out as causes.
However, a supranormal nocturnal experience, a nightmare, may be at fault.
Not merely a bad dream, but an experience of sleep paralysis characterized by wakefulness, immobility, realistic perception of the environment, sense of a nearby evil presence, intense fear, pressure on the chest, and an inability to speak (described by Hmong who were fortunate enough to wake and recount their nightmare).
Such experiences are common across cultures. The Hmong call the spirit dab tsog, who, like other spirits, needs to be appeased with offerings of food. Violating these norms can lead to an attack, in the sleep.
We needn’t agree with the Hmong on the spirit provenance of their experiences.
We can agree on the gravity of these experiences, and posit an account wherein their beliefs, about themselves, and their new social roles, became so stressful as to manifest as cardiovascular compromise and death.
Fleeing a Communist regime, the Hmong found their way to the U.S., where their community supports were weakened, their language, skills, and culture were largely irrelevant to their new life. In an attempt to integrate and gain employment, many Hmong abandoned their rituals and converted to Christianity.
The stress and trauma of cultural dislocation coupled with the appetite to integrate may have left the Hmong uncertain and traumatized, sleeping poorly and experiencing hypnagogic and hypnopompic hallucinations, but without their rituals and practices, they had no recourse against their night terrors.
The rapidly expanding literature on cardiac interoception and placebo effects underline the profound impact that beliefs and expectations can have on our bodies and our cardiovascular system in particular. For the male Hmong refugees, the consequences were disastrous.
Sleep paralysis like the Hmong nightmare is common in non-refugees. Sometimes it manifests as the belief that one has been abducted by aliens. Abduction beliefs can be common. They are associated with conviction and distress, indeed, being exposed to scripts that describe the experience can evoke the same physiological reaction as people with Post Traumatic Stress Disorder revisiting their index trauma.
Other than curiosity for the esoteria of human belief and experience, why should we care?
There are dueling camps that disagree on the number of factors necessary to explain delusions.
One-factor theorists—led by my friend and colleague Ema Sullivan Bissett, senior lecturer in philosophy at the University of Birmingham—posit that delusions are reasonable inferences about surprising experiences. The first and only factor is the unusual experience.
Two factor theorists posit that both unusual experiences and errant reasoning (as a result of some neuropsychological deficit in belief-evaluation) are necessary for delusions, because there exist some people who have the unusual experience, but no delusions. I have argued against the evidence base and logic of these theories.
The Hmong nightmares and alien abduction beliefs also trouble two factor theory.
You see the factors under the two-factor neuropsychological account must be deficits, not biases distributed on a continuum.
There are of course people who experience sleep paralysis and dismiss it as a weird experience.
However, they are not—as far as we can tell—neuropsychologically distinct from people with abduction beliefs.
Put simply, if we can allow that sleep paralysis experiences can vary in intensity or sense of reality and beyond some threshold they demand an abduction explanation, we can make the same case for all monothematic delusions.
The same case can be made for the brain damage that underwrites those neuropsychological cases of monothematic delusion—the more damage to a brain system that implements inference, the more deranged the inferences and the more delusion-like the conclusion—distinguishing between perception and belief modules is not useful, helpful, or appropriate.
This uncovers the real disagreements between theorists of delusion. They don’t necessarily disagree about delusions, but about what delusions reveal about how the brain and mind map to one another; whether there are discrete mental modules (for perception and belief) and how information passes between them.
If it is unidirectional, from perception to belief, then we need a defect in perception and a defect in belief, to get to delusion.
If there are top-down influences of belief on perception, then we do not.
That the Hmong appear to have believed themselves to death is testimony to the power of belief, its impact on perception, and on our bodily physiology.
This is both terrifying and perhaps empowering.
Placebo treatments for severe neurological illnesses like Parkinson’s disease underline the possibility for harnessing the power of belief on the body for healing.
Regardless of whether this potential is realized, its mechanisms are powerful, as are the experiences of abduction and sleep paralysis.
As a window on to the mind and brain they should not be dismissed as mere parapsychology.
