Dean Burnett

The brain has to deal with a lot of information at every given moment, and to do this effectively it maintains a mental model of how the world is meant to work. Beliefs, experiences, expectations, assumptions, calculations – all of these are combined into a constantly updated general understanding of how things happen, so we know what to expect and how to react without having to figure it out again each time. As a result, we’re not constantly surprised by the world around us.

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.

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 behaviour (for instance someone muttering to herself in a shop as you pass) as suspicious and threatening, provoking delusions of mysterious plots against them.