It’s time for a Reality Check: The neuroscience of Delusions


Every now and then, an experience comes along that tests our confidence in our perceptions of reality. It may be a hallucination, a feeling of déjà vu – a sense that a new place or experience is strangely familiar. It may be the reverse, jamais vu, the sense of extreme unfamiliarity evoked by what is supposed to be a familiar place or face. Normally, we are able to discern reality from the imaginary. We wake up and appreciate that it was all a dream. We overlook those strange feelings of déjà vu or jamais vu and pass them off as a perceptual gaffe. But some people are unable to perform this reality check – those of us who suffer from delusions or psychiatric disorders.

It turns out reality testing isn’t just a trivial task; it isn’t dependent on how intelligent or perceptive you think you are, but on how your brain is hardwired to respond to illusory situations. In fact, there is a common link in the cognitive processes involved in delusions and in dreams, where it can be impossible to tell fact from fiction. Professor Phillip Gerrans, a Professor in the Philosophy Department at the University of Adelaide, has been examining studies looking at the neural activity of people with delusions. His research, published in the journal Frontiers in Psychology, has demonstrated that one’s ability to execute reality testing properly is associated with an error correction system instinctively performed by the brain.

Why need an error correction system to begin with? Shouldn’t the brain be capable of distinguishing fact from fiction from the offset?

According to Professor Gerrans – who was part of a group of international philosophers picked to be trained in cognitive neuroscience at the Swiss Centre for Affective Sciences – we are made to perform a reality check when one of the brain’s components which is critical for cognition, The Default Mode Network (DMN), inadvertently deceives us while doing its thing. The DMN is a network of circuits which is linked to imagination and self-introspection, and it allows us to perform mental time travel, a feature which is unique to the human brain. Unlike other animals, we are able to mentally relive the past, due to our very competent episodic memory, and use those memories to guide us through the future. The DMN is always switched on, and runs in the background whenever other cognitive processes are also running (as if in screensaver mode). It keeps track of all the experiences we have and collates them to generate an ongoing narrative about who we are.

The DMN has been theorised as being the center of our stream of consciousness. It operates when the mind isn’t focusing on its immediate environment. A 2011 study demonstrated a link between meditation and increased DMN connectivity.

One of the theorised functions of the DMN is to give a kind of autobiographical context to our experiences by running them through to generate our self-narrative. This informs, more or less, how we are supposed to act and what to expect in certain situations. But what happens when something abnormal occurs; and the brain processes information which is inconsistent with the background knowledge we have about what should happen?

This doesn’t occur infrequently. We only have to look at the common experience of déjà vu to appreciate this. But there are some people who experience abnormal events more than others, for one reason or another. “In delusions of misidentification,” Professor Gerrans writes in his paper, “people report seeing “doubles,” imposters, people in disguise, people changing appearance and identity”. This is the result of an inability for normal face-processing activities in the brain to link up elements which are usually bound together, such as the recognition of a person’s face, name or identity and the unconscious response the brain generates to determine the familiarity of that person.

One example of such a delusion Professor Gerrans makes in his study is the “Capgras delusion“, the delusion of “doubles”. In one instance, a man who suffered a serious brain injury returned home after spending over a year in hospital, only to state repetitively that his family had been replaced by impostors.

When normal elements of face recognition become dissociated, as they are for people suffering delusions of misidentification, the DMN responds by trying to make sense of the new information and fit them in with the overall context of the person’s self-narrative. It is, after all, the DMN’s job to treat these experiences as elements of the story it is trying to maintain about the self, even if they don’t make sense given the background knowledge we have about them. In the example of the man suffering from Capgras delusion, “his family looked familiar but didn’t feel familiar, and the story in his head made sense of that feeling,” Professor Gerrans explains. “It didn’t matter how much people tried to point out that his family was the same, in his mind they had been completely replaced by impostors.”

According to Professor Gerrans’ research, the brain has a way of overriding this cognitive mistake though: it performs a process of decontextualisation. An error signal is sent across the brain, triggering a higher-order cognitive process whereby the brain evaluates the accuracy of the incident. Professor Gerrans describes this process as a “tribunal of the mind”, and the story element is treated as a hypothesis to be weighed up against the evidence. This mental trial determines whether the experience should be kept or discarded within the overall narrative framework, in effect completing the reality check.

Another “delusion of doubles” is called the Fregoli delusion, named after an Italian actor famous for being a master of disguise. People who have the disorder may believe different people are in fact the same person, only in disguise.

The process appears simple on a superficial level – when a strange occurrence happens, a healthy-minded person will perhaps double-back, question what had just happened and then reassure him-or her-self that it was nothing. A delusional person would continue to believe the significance of the unusual event, even in spite of evidence contradicting it.

However, Professor Gerrans’ research implies that a more complex neurochemical process occurs underneath the surface. The decontextualisation process seems to be activated in the region of the brain called the right dorsolateral prefrontal cortex. “When [it] is hypo or inactive,” Professor Gerrans’ paper says, “the mind is hostage to the functioning of the DMN”. In other words, if there is a problem with the neural activity in this part of the brain, the mind will be unable to decontexualise and correct the erroneous narrative being weaved by the DMN. Professor Gerrans also suggests that an overactive DMN may also overpower the corrective function of the right prefrontal cortex.

This is the same thing that occurs during the dreams we have that seem bizarre, yet in which the dreamer is unaware they are dreaming, accepting everything that happens as ordinary. These dreams occur during rapid eye movement (REM) sleep, when the DMN seems as active as it is in wakefulness. The DMN is disconnected with other areas of the brain during these dreams, rendering its monitoring system in the right prefrontal cortex deactivated. It can be argued then that a delusional person is in a constant state of unregulated mind-wandering, as people are when they are in this REM state of dreaming.

What does this mean for psychiatrists? Professor Gerrans believes it goes to show that there should be new ways to manage patients suffering from delusions. These should work at “dampening down, or quietening down, activity in these narrative site systems that conjure stories out of experiences” in order to allow “other information and new alternatives to, as it were, get a hearing at the tribunal of the mind,” Professor Gerrans says. One way to do this is to alter how cognitive behavioural therapy is practiced. These are based on challenging the person’s beliefs and trying to replace them with more accurate ones, but Professor Gerrans thinks this “makes delusional people and psychiatric patients actually more defensive about their condition”. And justifiably so, if their brains are fixated on the stories they have created to make sense of their experiences.

As for the more philosophical of the study’s implications, Professor Gerrans argues that it shows that “in the normal case, seeing is believing”. “Our sensory experiences pretty much get the world right,” he says, “but it’s that further, extra step that’s very important to compare those experiences to what we know about reality from other sources, from other people’s testimonies.”

“That seems to go wrong in a lot of psychiatric disorders, not just delusion, but I think you’ll find in general that people with psychiatric disorders find it very hard to put aside the thoughts suggested by experience and tend to live as though their experience is all there is to reality; other than the world outside or reality as experienced by other people.”

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