Brain fog is one of the most frustrating—and often least visible—symptoms reported by people with postural orthostatic tachycardia syndrome (POTS). New research is helping scientists investigate what may be happening in the brain.

You know the information.

You know the word you're trying to say.

But suddenly you can't find it.

You reread the same paragraph several times. Following a conversation becomes exhausting. Planning something that should be simple feels strangely complicated. After concentrating for a while, you feel as though you've done something physically strenuous—even though you've barely moved.

People with POTS often call this brain fog.

The phrase can sound deceptively mild. But the cognitive difficulties associated with POTS can interfere with school, work, conversations, reading, driving and everyday decision-making.

And researchers are increasingly investigating whether some of those cognitive symptoms may be connected to changes in cerebral blood flow and autonomic regulation inside the brain.

POTS Is About More Than Heart Rate

POTS is a chronic disorder of the autonomic nervous system characterized by an excessive increase in heart rate when a person becomes upright, together with symptoms of orthostatic intolerance.

But heart rate is only one part of the condition.

People with POTS may experience symptoms involving multiple systems, including dizziness, palpitations, fatigue, exercise intolerance, gastrointestinal symptoms, temperature-regulation difficulties and cognitive dysfunction.

A major review published in JAMA in August 2026 describes POTS as a chronic autonomic disorder with multisystem symptoms.

That broader view is important.

The autonomic nervous system helps regulate many processes that happen without conscious effort—including heart rate, blood pressure, digestion, temperature regulation and aspects of circulation.

That includes maintaining an adequate supply of blood to the brain as conditions change.

What Happens to Circulation When You Stand?

Standing looks simple.

Physiologically, it isn't.

When you move from lying down to standing, gravity shifts blood toward the lower part of the body. Your cardiovascular and autonomic systems respond rapidly to help maintain circulation and blood pressure.

Blood vessels constrict. Heart function adjusts. Multiple reflex systems coordinate to keep blood moving where it needs to go.

In POTS, some of that regulation doesn't function normally.

That is one reason researchers have become interested in a seemingly simple question:

What is happening to blood flow in the brain?

New Research Is Giving Scientists a Closer Look

A 2026 study published in Heart Rhythm used advanced brain imaging to investigate the central nervous system in people with POTS.

Researchers compared 18 people with POTS with 20 healthy controls.

They used MRI and functional MRI to examine brain structure, cerebral blood flow and neural responses while participants underwent several challenges involving autonomic regulation.

Those included passive leg raising, an isometric handgrip exercise and something particularly interesting:

mental arithmetic.

Researchers weren't only examining what happened during physical stress.

They examined what happened while participants were thinking.

What Did Researchers Find?

General cognitive screening scores were similar between the POTS and control groups.

That is an important finding by itself.

People experiencing brain fog don't necessarily lose their overall intellectual abilities.

However, when researchers looked at executive functioning, differences appeared. Participants with POTS were slower on a test involving executive function.

Researchers also identified reduced cerebral blood flow, structural differences in certain brain regions and altered neural responses during the autonomic challenges.

Those altered responses were observed during physical challenges—and during mental arithmetic.

The authors suggested that abnormalities in central autonomic regulation could contribute to the cardiovascular dysregulation associated with POTS.

This doesn't mean researchers have discovered the single cause of POTS brain fog.

But it adds another important piece to the puzzle.

What Is Cerebral Blood Flow?

Cerebral blood flow simply refers to the blood circulating through the brain.

Your brain requires a continuous supply of oxygen and nutrients, so the body has sophisticated mechanisms for regulating that circulation.

Normally, cerebral circulation adapts as you stand, move, exercise, concentrate and encounter changes in blood pressure.

Because POTS involves abnormal autonomic regulation, researchers have been investigating whether altered regulation of cerebral circulation might contribute to symptoms such as dizziness and cognitive dysfunction.

And the 2026 study isn't the first to explore this connection.

Earlier Research Found Something Fascinating About Mental Exertion

In an earlier study, researchers examined people with POTS while they completed prolonged cognitive testing while seated.

The researchers measured cerebral blood-flow velocity before and after approximately 30 minutes of sustained cognitive stress.

Both the POTS group and healthy controls experienced some reduction in cerebral blood-flow velocity.

But the decrease was significantly greater in the POTS group.

The average reduction was approximately:

7.8% in the POTS group

compared with

1.8% in healthy controls.

The researchers also observed worsening cognitive performance.

Perhaps most interestingly, the cerebral blood-flow reduction following prolonged cognitive stress in participants with POTS was comparable to what researchers observed after standing.

That raises an intriguing possibility:

Mental exertion itself may create meaningful physiological demands in POTS.

Why Can Thinking Feel Physically Exhausting?

We often divide activity into two categories.

Physical activity is walking, standing, cleaning or exercising.

Mental activity is reading, working, studying, planning or talking.

Biologically, the distinction isn't nearly that simple.

Your brain is part of your body.

Concentrating requires neural activity, energy metabolism, oxygen delivery and regulation of cerebral circulation.

For someone living with autonomic dysfunction, demanding cognitive activity may therefore represent a genuine physiological load.

That could help explain an experience many people with chronic illness struggle to describe:

“I didn't do anything today. Why am I so exhausted?”

But perhaps you did.

You worked.

You studied.

You navigated appointments.

You processed information.

You held conversations.

You made decisions.

You concentrated.

Those activities may not involve many steps on a fitness tracker, but that doesn't mean they require no physiological resources.

Thinking isn't physiologically free.

Brain Fog Doesn't Mean You're Less Intelligent

This distinction deserves more attention.

The 2026 study found similar general cognitive screening scores between the POTS and control groups even though differences emerged in more specific measures of executive function.

That may help explain why POTS brain fog can feel so strange.

You may know that you know something while temporarily struggling to retrieve it.

You may understand a complex subject but need substantially longer to process information.

You may be capable of performing a task but unable to sustain that level of concentration for very long.

Brain fog can involve difficulties with things such as:

• attention

• working memory

• processing speed

• word retrieval

• executive functioning

• sustained concentration

• mental stamina

Those problems are not synonymous with intelligence.

A highly capable person can experience significant cognitive dysfunction.

Is All POTS Brain Fog Caused by Reduced Cerebral Blood Flow?

No.

This is where emerging research needs to be interpreted carefully.

The 2026 neuroimaging study was small, involving only 18 participants with POTS.

Earlier studies have also produced somewhat different results.

For example, another small study found measurable problems with short-term memory and alertness in people with POTS but did not find significant differences in the particular cerebral blood-flow measurements researchers examined.

That's not unusual in an evolving area of science.

Different studies use different imaging techniques, cognitive tests, body positions, autonomic challenges and patient populations.

POTS itself is also heterogeneous.

There may not be one mechanism responsible for every person's cognitive symptoms.

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

The current research therefore doesn't establish:

POTS brain fog = low blood flow to the brain.

Instead, it tells us that cerebral circulation and central autonomic regulation are important areas of investigation.

Why Can Brain Fog Happen Even While Sitting?

This is another important question.

It might seem logical that cognitive problems associated with POTS would disappear when someone sits down.

But that isn't necessarily what people experience—or what researchers have observed.

The sustained cognitive-stress study specifically examined participants while they were seated.

Cerebral blood-flow velocity still declined more in the POTS group during prolonged mental work.

That suggests cognitive symptoms can't necessarily be understood only as something that happens when a person stands.

Posture matters enormously in POTS.

But cognitive workload may matter too.

Brain Fog May Also Change Throughout the Day

Another reason brain fog can be difficult to understand is that it may not remain constant.

A person might think clearly in the morning but struggle after several hours of activity.

They may tolerate a short conversation but become cognitively depleted during a long appointment.

They may read for ten minutes comfortably but struggle after an hour.

That means one brief cognitive test in a clinical setting may not necessarily reproduce the difficulties someone experiences after sustained activity in everyday life.

Researchers are beginning to study these dynamic responses rather than looking only at a single measurement taken at rest.

That could be important for understanding conditions in which capacity changes with exertion.

POTS Brain Fog and PEM Aren't Necessarily the Same Thing

There is another distinction worth making.

People with POTS may experience cognitive symptoms during orthostatic stress or prolonged mental activity.

People with ME/CFS and some people with Long COVID may experience post-exertional malaise (PEM)—a broader worsening of symptoms following physical, cognitive, emotional or social exertion that can be delayed and may last for days or longer.

Because these conditions can overlap, it can become difficult to determine what is causing a particular episode of cognitive exhaustion.

Immediate difficulty thinking while upright isn't necessarily the same phenomenon as delayed PEM.

Understanding that distinction is an important area for both research and patient education.

What This Research Does Not Tell Us

Emerging research can easily become exaggerated online, so several limitations are important.

These studies do not currently show that:

• cerebral blood-flow testing can diagnose POTS brain fog

• everyone with POTS has reduced cerebral blood flow

• every episode of brain fog has the same cause

• brain imaging is routinely needed for POTS

• a particular supplement, medication or hydration strategy will correct cognitive dysfunction

• researchers have identified a single mechanism responsible for POTS brain fog

The findings are clues.

They are not a finished explanation.

Why This Research Matters Anyway

For a long time, POTS was frequently reduced to a simple description:

“Your heart rate goes up when you stand.”

But modern POTS research is revealing a considerably more complicated disorder involving interactions among the cardiovascular system, autonomic nervous system and brain.

The newest research doesn't provide all the answers.

What it does provide is something important:

A reason to investigate brain fog as a physiological symptom rather than dismissing it as simply being tired, distracted or anxious.

And that changes the question.

Instead of asking:

“Why can't I just concentrate?”

Researchers can begin asking:

“What happens to autonomic regulation, cerebral circulation and cognitive performance when a person with POTS has to think for an extended period of time?”

That's a much more useful scientific question.

And we're beginning to get answers.

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The Bottom Line

Brain fog is a recognized and potentially disabling part of POTS.

Emerging research suggests that cerebral blood flow and central autonomic regulation may contribute to cognitive dysfunction in at least some people with the condition.

Researchers have also found something particularly interesting: sustained cognitive activity itself may produce measurable physiological changes in people with POTS.

But the science is still developing.

We don't yet have one explanation for POTS brain fog, and cerebral blood flow is unlikely to be the entire story.

What the research increasingly demonstrates is that thinking, circulation and autonomic regulation are interconnected.

For people living with POTS, that may help explain something they have understood intuitively for a long time:

Mental activity is still activity.

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A Note From Complexa Wellness

Complex chronic illness rarely fits neatly into one body system. Understanding the connections between the nervous system, circulation, energy demands, nutrition and everyday function can make complicated health information easier to navigate.

At Complexa Wellness, our goal is to translate emerging chronic-illness research into accessible education—without turning early findings into miracle claims or pretending science knows more than it does.

Wellness made simpler.

This article is for educational purposes only and is not intended to diagnose, treat, cure or prevent any disease. Brain fog and new or worsening cognitive symptoms can have many causes. Discuss significant or changing symptoms with an appropriate healthcare professional.

References

Malik V, Roy B, Sarkar A, 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.

Chung TH, Raj SR. Postural Orthostatic Tachycardia Syndrome (POTS): A Review. JAMA. Published online August 24, 2026. doi:10.1001/jama.2026.14809.

Wells R, Paterson F, Bacchi S, et al. Cerebral Blood Flow and Cognitive Performance in Postural Tachycardia Syndrome: Insights From Sustained Cognitive Stress Test. Journal of the American Heart Association. 2020.

Anderson JW, Lambert EA, Sari CI, et al. Brain fog in postural tachycardia syndrome: An objective cerebral blood flow and neurocognitive analysis. Journal of Arrhythmia. 2020.