Experts prove Long Covid is real – after finding cause of ‘brain fog’

Scientists say they have finally discovered what causes ‘brain fog’ in people with long Covid.

The finding could help explain why millions continue to experience problems with memory and concentration months or even years after infection.

Around 1.9 million Britons are thought to be living with long Covid—a term covering a range of lingering symptoms such as fatigue, breathlessness and joint pain.

But among the most debilitating is brain fog—cognitive problems including poor memory, slower thinking and difficulty focusing, which affect more than 80 per cent of sufferers.

Until now, researchers suspected Covid might trigger structural changes in the brain but had been unable to pinpoint the molecular cause.

Now, Japanese scientists have developed a way to directly visualise key receptors in the brain linked to memory and learning, revealing what may underlie the problem.

In a study published in Brain Communications, the researchers looked at AMPA receptors (AMPARs)—proteins on the surface of brain cells that help transmit signals involved in learning and memory.

Abnormal activity in AMPARs has previously been linked to conditions such as depression, bipolar disorder and dementia.

Using advanced brain scans, the researchers compared 30 long Covid patients with 80 healthy volunteers and found a significant increase in AMPAR activity among those with cognitive symptoms.

Crucially, the more severe the brain fog, the denser the receptor activity—suggesting a clear biological link with long Covid, and a potential target for future treatments.

Professor Takuya Takahashi, an expert in molecular mechanisms and study co-author, said: ‘Our findings clearly demonstrate that long Covid brain fog should be recognised as a legitimate clinical condition. 

‘This could encourage the healthcare industry to accelerate the development of diagnostic and therapeutic approaches for this disorder.’

The team were able to distinguish every long Covid patient from healthy controls using their new brain-imaging technique—a potential breakthrough for diagnosis.

Researchers now hope the technology could help develop treatments that suppress AMPAR activity, easing brain fog in future patients.

Long Covid has returned to the spotlight as two new variants—Stratus and Nimbus—sweep through the UK and US, with infection rates doubling since August.

While experts say the strains do not appear more dangerous than earlier ones, genetic changes may make them slightly more infectious.

Patients have reported familiar Covid symptoms including shortness of breath, chest tightness, sore throat, headaches, body aches and loss of taste or smell.

But the Stratus strain has been linked in particular to a persistent dry cough, tiredness and fever.

In the UK, ministers have repeatedly said they will not impose lockdowns again unless a ‘doomsday’ variant emerges.

A wall of immunity built up through repeated infections and vaccine rollouts has given officials confidence to consign pandemic-era restrictions to history—although people are still being urged to wear masks and stay at home if infected.

Spikes in Covid cases can still cause mass illness, leading to staff shortages in schools, hospitals and public transport.

However, officials no longer monitor the virus as closely as they once did, as part of the Government’s drive to return to pre-pandemic normality.