Delusions result when this system undergoes alteration. A well-known type of delusion is Capgras delusion, where people genuinely believe someone close to them (spouse, parent, sibling, friend, pet) has been replaced by an identical impostor.31 Usually when you see a loved one, this triggers multiple memories and emotions: love, affection, fondness, frustration, irritation (depending on length of relationship).
But suppose you see your partner and experience none of the usual emotional associations? Damage to areas of the frontal lobes can cause this to happen. Based on all your memories and experiences, your brain anticipates a strong emotional response to the sight of your partner, but this doesn’t happen. This results in uncertainty: that’s my long-term partner, I have many feelings about my long-term partner, feelings I’m now not experiencing. Why not? One way to resolve this inconsistency is the conclusion that they aren’t your partner, but a physically identical impostor. This conclusion allows the brain to reconcile the disharmony it’s experiencing, thus ending uncertainty. This is Capgras delusion.
The trouble is, it’s clearly wrong, but the individual’s brain doesn’t recognize it as such. Objective proof of their partner’s identity just makes the lack of emotional connection worse, so the conclusion that they’re an impostor is even more “reassuring.” Thus a delusion is sustained in the face of evidence.
This is the basic process believed to underlie delusions in general; the brain expects something to happen, it perceives something different happening, the expectations and occurrence don’t match, a solution to this mismatch must be found. It starts to become problematic if solutions rely on ridiculous or unlikely conclusions.
Thanks to other stresses and factors upsetting the delicate systems of our brain, things we perceive that would usually be dismissed as innocuous or irrelevant end up being processed as far more significant. The delusions themselves can in fact suggest the nature of the problem producing them.32 For example, excessive anxiety and paranoia would mean an individual is experiencing unexplained activation of the threat-detection and other defensive systems, so it would try to reconcile this by finding a source for the mysterious threat, and thus interpret harmless behavior (for instance someone muttering to herself in a store as you pass) as suspicious and threatening, provoking delusions of mysterious plots against them. Depression invokes inexplicable low mood, so any experiences that are even slightly negative (perhaps someone leaving a table just as you sit down next to them) become significant and are interpreted as people intensly disliking you due to your awfulness, and thus delusions occur.
Things that don’t conform to our mental model of how the world works are often downplayed or suppressed; they don’t conform to our expectations or predictions, and the best explanation is that they’re wrong, so can be ignored. You might believe there is no such thing as aliens, so anyone claiming to have seen UFOs or been abducted is dismissed as a raving idiot. Someone else’s claims don’t prove your beliefs are wrong. This works up to a point; should you then be abducted by aliens and vigorously probed, your conclusions are likely to change. But, in delusional states, the experiences that contradict your own conclusions can be even more suppressed than normal.
Current theories about the neurological systems responsible propose a frighteningly complex arrangement, stemming from another widespread network of brain areas (parietal lobe regions, prefrontal cortex, temporal gyrus, striatum, amygdala, cerebellum, mesocorticolimbic regions, and so on).33 There’s also evidence suggesting those prone to delusions show an excess of the excitatory (producing more activity) neurotransmitter glutamate, which may explain innocuous stimulation becoming overly significant.34 Too much activity also exhausts neuronal resources, reducing neuronal plasticity, so the brain is less able to change and adapt the affected areas, making delusions more persistent again.
A word of caution: this section has focused on hallucinations and delusions being caused by disruptions and problems with the brain’s processes, which does suggest that they’re due only to disorders or illnesses. This isn’t the case. You may think someone is “deluded” if they believe the earth is only six thousand years old and dinosaurs never existed, but millions of people genuinely believe this. Similarly, some people genuinely believe their deceased relatives are talking to them. Are they sick? Grieving? Is this a coping mechanism? A spiritual thing? There are many possible explanations other than “poor mental health.”
Our brains determine what’s real or not based on our experiences, and if we grow up in a context where objectively impossible things are seen as normal, then our brains conclude they are normal, and judge everything else accordingly. Even people not brought up in the more extreme belief system are susceptible—the “just world” bias described in Chapter 7 is incredibly common, and often leads to conclusions, beliefs and assumptions about people experiencing hardships that aren’t correct.
This is why unrealistic beliefs are classed as delusions only if they’re not consistent with the person’s existing belief system and views. The experience of a devout evangelist from the American Bible Belt saying he can hear the voice of God is not considered a delusion. An agnostic trainee accountant from Sunderland saying she can hear the voice of God? Yes, she’ll probably be classed as delusional.
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The brain provides us with an impressive perception of reality but, as we’ve seen repeatedly throughout this book, much of this perception is based on calculations, extrapolations and sometimes outright guesswork on the brain’s part. Given every possible thing that can affect how the brain does things, it’s easy to see how such processes might go a bit awry, especially considering how what’s “normal” is more general consensus than fundamental fact. It’s amazing how humans get anything done, really.
That’s assuming they actually do get anything done. Maybe that’s just what we tell ourselves for reassurance. Maybe nothing is real? Maybe this whole book has been a hallucination? All things being equal, I hope it isn’t, or I’ve wasted quite a considerable amount of time and effort.
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