If you live with postural orthostatic tachycardia syndrome (POTS), you may know the feeling.

You stand up and suddenly thinking becomes harder. You lose your train of thought halfway through a sentence. Words that should be easy to find disappear. Reading the same paragraph takes three tries. A conversation that would normally be effortless feels like work.

Or perhaps the brain fog happens even when you aren't standing.

For years, people with POTS have described problems with concentration, memory, processing speed and mental stamina. “Brain fog” has become the shorthand for all of it.

Now researchers are getting a closer look at what may be happening inside the brain—and a 2026 study adds an intriguing piece to the puzzle.

Brain Fog Is a Recognized Part of POTS

POTS is usually defined by what happens to the cardiovascular system when a person becomes upright: heart rate rises abnormally and symptoms of orthostatic intolerance develop.

But POTS can affect far more than heart rate.

Fatigue, exercise intolerance, gastrointestinal symptoms, sleep problems and cognitive dysfunction are all commonly reported. A major 2026 review in JAMA includes cognitive dysfunction—often called brain fog—among the common symptoms associated with POTS.

That matters because brain fog can be profoundly disruptive even though it is difficult to see from the outside.

Someone may appear to be sitting still while their brain is struggling to keep up.

A New Study Looked Directly at the Brain

Researchers from UCLA and collaborating institutions recently used advanced brain imaging to investigate the central nervous system in people with POTS.

The study, published online in February 2026 and appearing in the August 2026 issue of Heart Rhythm, included 38 participants: 18 people with POTS and 20 healthy controls.

Researchers used MRI and functional MRI to examine brain structure, cerebral blood flow and brain responses during several challenges involving autonomic regulation.

Those challenges included:

• Passive leg raising

• Isometric handgrip

• Mental arithmetic

That last one is especially interesting.

The researchers weren't only asking what happens to the brain during a physical cardiovascular challenge.

They also looked at what happened while participants were thinking.

The Results Were Interesting

On a general cognitive screening test, the POTS and control groups performed similarly.

But when researchers tested executive function—the collection of mental abilities involved in things such as organizing information, shifting attention, planning and completing complex tasks—the POTS group was slower.

Researchers also found differences in brain structure in particular regions, reduced cerebral blood flow, and altered neural responses during the autonomic challenges.

Those altered responses appeared during the physical challenges and during mental arithmetic.

The researchers concluded that abnormalities involving central autonomic regulation may contribute to the cardiovascular dysregulation seen in POTS.

That doesn't mean scientists have discovered the cause of POTS brain fog.

But it does give researchers another physiological pathway to investigate.

What Does Cerebral Blood Flow Have to Do With Brain Fog?

Your brain is extraordinarily metabolically active.

Although it represents only a small portion of your total body weight, it requires a continuous supply of oxygen and nutrients delivered through the circulation.

Your body therefore has systems that continually regulate blood flow to the brain as you move, stand, exercise, think and encounter changes in blood pressure.

POTS involves dysfunction of the autonomic nervous system—the system responsible for regulating many of the body's automatic processes.

When you stand, gravity shifts blood downward.

Normally, the cardiovascular and autonomic systems compensate rapidly enough to maintain circulation.

In POTS, that adjustment doesn't work normally.

Scientists have therefore been investigating whether abnormalities in cerebral circulation could contribute to symptoms such as dizziness, visual disturbances and cognitive dysfunction.

This Isn't the First Study to Find a Connection

The new research builds on earlier work.

In one study of people with POTS undergoing prolonged cognitive testing while seated, researchers found that cerebral blood-flow velocity decreased more in the POTS group than in healthy controls.

Their psychomotor speed also declined more.

Remarkably, the reduction in cerebral blood-flow velocity following prolonged cognitive stress in the POTS group was similar to the reduction researchers observed after participants stood for five minutes.

In other words, sustained mental work appeared capable of producing measurable physiological changes even without standing.

Another study using SPECT brain imaging found abnormal cerebral perfusion in a substantial portion of the POTS patients with cognitive dysfunction who were studied.

The research isn't perfectly consistent. A different small study found cognitive deficits without detecting significant differences in the particular cerebral blood-flow measurements it examined.

That inconsistency is important.

Science rarely progresses through one dramatic experiment that explains everything. Different researchers study different populations, use different imaging techniques and measure different parts of an enormously complicated system.

Taken together, however, the research increasingly supports something people with POTS have been saying for years:

Brain fog deserves to be studied as part of the physiology of POTS.

Why Can Thinking Feel Physically Exhausting?

This may be one of the most interesting questions raised by the research.

We tend to divide activity into two categories:

Physical activity: walking, standing, exercising, cleaning.

Mental activity: reading, working, studying, planning, talking.

Biologically, that distinction isn't so clean.

Your brain is part of your body.

Complex cognitive activity requires neural processing, energy, oxygen delivery, regulation of cerebral circulation and coordination between multiple physiological systems.

For someone whose autonomic regulation is already under strain, demanding cognitive work may therefore represent a meaningful physiological load.

That could help explain an experience frequently described by people with dysautonomia:

“I didn't do anything today. I was just working on my computer. Why am I exhausted?”

You did do something.

You were thinking.

And thinking isn't physiologically free.

Brain Fog Isn't the Same Thing as Intelligence

There's another important distinction.

Cognitive dysfunction doesn't necessarily mean that someone's underlying intellectual ability has disappeared.

In the 2026 study, general cognitive screening scores were similar between people with POTS and healthy controls.

The differences became apparent when researchers examined more specific aspects of cognitive performance.

That distinction may help explain another frustrating experience:

Knowing that you know something while temporarily being unable to access or organize it efficiently.

A person can be knowledgeable, capable and intelligent while simultaneously experiencing impaired processing speed, attention, working memory or executive function.

Those things aren't contradictions.

Does This Mean Every Case of POTS Brain Fog Is Caused by Low Brain Blood Flow?

No.

This is where we need to be careful.

The 2026 neuroimaging study included only 18 participants with POTS. That's valuable research, but it's nowhere near enough to establish a universal explanation for millions of individual experiences.

POTS is also heterogeneous.

Brain fog could potentially be influenced by multiple factors, including autonomic dysfunction, cerebral circulation, sleep disruption, medications, pain, nutritional status, fatigue and coexisting illnesses.

Different mechanisms may dominate in different people.

Research showing an association between cerebral blood flow and cognitive performance therefore does not mean that every episode of brain fog is caused by inadequate blood flow to the brain.

It also doesn't mean that brain imaging can currently diagnose POTS brain fog.

These findings are clues—not a finished explanation.

Why This Research Still Matters

For someone living with POTS, being told that testing is “normal” can be incredibly confusing when everyday cognitive tasks have become noticeably harder.

Studies like these demonstrate why researchers increasingly need to look beyond broad screening tests.

A person can perform normally on one general cognitive assessment while experiencing meaningful difficulties with executive function, sustained cognitive exertion or autonomic regulation.

The emerging picture is more complicated than:

POTS = fast heart rate when standing.

POTS involves autonomic regulation, and the autonomic nervous system interacts with circulation, digestion, temperature regulation, exercise responses—and the brain.

Understanding those connections may eventually help researchers develop better ways to identify different POTS subtypes and determine why symptoms vary so dramatically between people.

The Bigger Question: What Happens When the Brain Has to Work Hard?

Perhaps the most interesting part of this research isn't simply that investigators found differences in people with POTS.

It's when some of those differences appeared.

Mental arithmetic was enough to produce altered neural responses in the new study.

Earlier research found measurable cerebral blood-flow changes following prolonged cognitive stress.

Together, those findings raise an important question for future research:

Could cognitive exertion itself place a measurable physiological demand on an already dysregulated autonomic system?

We don't have the complete answer yet.

But it's a question worth asking—particularly for people who find that concentrating, studying, working at a computer, holding long conversations or processing large amounts of information can noticeably worsen their symptoms.

The science of POTS is moving beyond simply measuring heart rate.

Researchers are increasingly examining what happens throughout the body—and the brain.

And that may eventually help explain why something as invisible as “brain fog” can have such a visible impact on everyday life.

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A Note From Complexa Wellness

Complex chronic illness rarely fits neatly into a single body system. At Complexa Wellness, we believe people deserve accessible explanations of emerging research without hype, miracle claims or oversimplification.

We follow developing research in POTS, dysautonomia, ME/CFS, Long COVID, mast-cell disorders, hypermobility and related chronic conditions and translate it into practical, understandable education.

Wellness made simpler.

This article is for educational purposes only and is not medical advice. New or worsening cognitive symptoms can have many causes and should be discussed with an appropriate healthcare professional.

Sources

Malik V, Roy B, et al. Brain tissue changes, network dysfunction, and cerebral hemodynamic deficits in postural orthostatic tachycardia syndrome. Heart Rhythm. 2026;23(8):e1617-e1627. doi:10.1016/j.hrthm.2026.02.020.

Postural Orthostatic Tachycardia Syndrome (POTS): A Review. JAMA. Published August 24, 2026.

Wells R, et al. Cerebral Blood Flow and Cognitive Performance in Postural Tachycardia Syndrome: Insights from Sustained Cognitive Stress Test.

Novel brain SPECT imaging unravels abnormal cerebral perfusion in patients with postural orthostatic tachycardia syndrome and cognitive dysfunction.

Brain fog in postural tachycardia syndrome: An objective cerebral blood flow and neurocognitive analysis.