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Last week, I read a fascinating book called The Expectation Effect: How your mindset can transform your life. I should acknowledge here that the author, David Robson, is a friend of mine, but I also wanted to get to grips with it, as I’ll be introducing his talk on the subject at New Scientist Live, which is being held from 12 March in Manchester, UK (tickets available ).

I have written previously about the placebo effect, the strange way that people’s health can improve simply because they expect it to do so – for instance, because they have taken dummy versions of pills containing no active ingredients. Doctors often deliberately harness the placebo effect, and medical researchers design randomised trials to take account of it, yet we don’t understand what causes the phenomenon.

The Expectation Effect also looks at what is sometimes called the placebo effect’s evil twin: the nocebo effect. This refers to the way people’s expectations can trigger ill health. It can involve quite extreme symptoms – even paralysis and blindness – that are psychological in origin, as I wrote about a few years ago.

These psychological conditions can spread between people like a form of social contagion, sometimes called mass hysteria – although this is an unfortunate name because it sounds dismissive. There are reports going back centuries of communities that see outbreaks of symptoms such as fainting or vomiting, often initially blamed on a new infection or toxin. In many such incidents, women and younger people seem more susceptible.

For instance, there were outbreaks of skin rashes (a very physical symptom) in some US schools soon after 9/11, with people blaming everything from mouldy library books to bioterrorist attacks. After lengthy investigations by toxicologists, a psychological cause now seems the .

More recently, you may have heard of Havana syndrome, which started affecting US diplomats in Cuba in 2016. They reported symptoms such as dizziness, ear pain and tinnitus, and blamed sonic weapons being aimed at the US embassy or their houses.

But such weapons don’t seem physically capable of producing this syndrome. Some neurologists who specialise in treating psychological symptoms are convinced it is a case of , although they tactfully try to avoid using that term.

TICS FROM TIKTOK

These days, it is even easier for reports of such outbreaks to spread, with social media adding fuel to the fire. A more recent phenomenon is “TikTok tics”, where teens and young adults acquire something resembling the tic disorder Tourette’s syndrome – when people compulsively say certain words or show repetitive movements – through watching videos of other people with tics.

The standard form of Tourette’s is itself fairly mysterious, but it seems to involve something going wrong in small structures deep within the brain called the basal ganglia, normally responsible for generating movement and turning simple actions into habits.

With Tourette’s, the tics could become habits that are very hard to break – perhaps because the basal ganglia are malfunctioning. There is no simple cure, but the condition is usually helped by medication or psychological therapy that helps retrain people out of their repetitive actions.

In the past couple of years, neurologists around the world have seen a surge of people seeking help for tics who don’t have the usual features of Tourette’s.

For instance, the tics start fairly suddenly in adolescence – and they do so after the person has been watching people on TikTok with tics. Tourette’s usually has a gradual onset, starting in young childhood.

Tourette’s is normally very rare, but a UK neurologist has told me they know of two clusters of cases of TikTok tics within secondary schools.

It is unclear exactly what is going on and not everyone accepts the psychological explanation. But in some people with the new syndrome, their tics may mimic those of their favourite TikToker, even down to repeating the same unusual words and actions. In those cases, it seems fairly hard to argue that the tics aren’t related to the videos.

People with the new kind of tics are also much more likely to be female, while Tourette’s is usually up to .

It can be uncomfortable for the people affected when neurologists tell them about the possible psychological origin of their symptoms. The doctors have to stress that a psychological cause certainly doesn’t mean anyone is faking their symptoms or could stop them if they chose.

But understanding the cause of the tics matters, because the drugs used to treat Tourette’s are strong ones and shouldn’t be taken unnecessarily. Treatment for tics with a psychological origin is different – and usually includes stopping watching tic videos. There is other advice .

If you see any videos of people with the TikTok tics, you may find it surprising that anyone could be so affected by a syndrome that is psychological in origin. But that just shows the enormous power of the mind over the body.

OTHER HEALTH STORIES

• How a sense of transcendence can make you happier and less stressed.
• One in seven premature births could be prevented by giving fish oil capsules containing omega-3 fatty acids to pregnant women.
• Covid-19 really did jump to people from animals at a Wuhan seafood market in late 2019, a new analysis has shown.
• The superbug MRSA turns even nastier when exposed to air pollution, experiments on animals and human cells suggest.

FROM THE ARCHIVE

Speaking two languages may make people better at learning, multitasking and solving problems. Eventually, it might even protect their brains against the ravages of old age. According to some studies, people’s memories, values and even their personality may change depending on which language they happen to be speaking. It is almost as if the bilingual brain houses two separate minds.

David Robson’s talk on the power of expectations is just one of many great talks at next week’s , being held in Manchester on 12 and 13 March, with a day just for schools on 14 March. You can join us in-person and virtually.

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