Brain hemispheres control opposite sides of the body without either dominating

Although distinctions exist between the two halves—language processing is left-oriented, and emotions are right-oriented—signals are sent along neural pathways between the hemispheres and across different regions to collectively process information about external stimuli.

Someone suffers from a stroke every 40 seconds

Every 40 seconds, someone in the US experiences a stroke—and every minute without treatment destroys millions of brain cells. This explainer breaks down the two main types of strokes, their risk factors, and how early detection could change outcomes in the future.

An estimated 2 million brain cells die each minute a stroke goes untreated

Modern stroke treatment is a delicate balance between obtaining an accurate diagnosis and delivering treatment quickly. Each stroke has its own cause, and the appropriate treatment must be paired with the correct diagnosis to prevent further harm. Typical treatments pair emergency surgery to relieve the affected area and long-term regimens to avoid recurrence.

A brain scientist's experience with a stroke

What happens when a leading brain scientist has a stroke of her own? Dr. Jill Bolte Taylor recounts moment by moment watching her brain function slow and then cease, followed by a prolonged recovery. Through this experience, she details what she learned about the phenomenon of stroke and how it has impacted her research ever since.

Visualize a stroke at the microscopic level.

Medical recognition of strokes stretches back to ancient Greece

Every minute, 750 milliliters of blood flows to the brain, supplying 20% of the body’s oxygen. A sudden disruption—whether from a clot (ischemic stroke) or a bleed (hemorrhagic stroke)—can be life-threatening. From ancient Greek theories to modern CT and MRI scans, here’s how stroke science has evolved over time.

A stroke occurs when blood flow to part of the brain is suddenly interrupted, either by a blockage (ischemic stroke) or bleeding when a blood vessel in the brain breaks and bleeds (hemorrhagic stroke).

Research suggests the brain maintains connections to lost limbs

Decades-old research suggested brain reorganization after amputations, but brain scans show unchanged limb representations. Phantom limb pain may result from such unchanged brain maps, which may enhance prosthetic limb control in brain-computer interface technology.

Hemorrhagic strokes make up roughly 13% of stroke events

A hemorrhagic stroke occurs when a faulty blood vessel within the brain bleeds. Though this is less common than an ischemic stroke, it is often far more deadly. This in-depth resource from the American Stroke Association provides a comprehensive overview of the two main subtypes of hemorrhagic stroke along with a useful animation of the condition.

Recent research found that the brain doesn't seem to massively rewire following amputation—upending earlier beliefs about the cause of phantom limb pain.

Take a quiz to discover your brain care score

Each year, nearly 800,000 Americans have a stroke. With such a high occurrence rate, you may be asking yourself what you could do now to prevent a future stroke. Researchers at Harvard collaborated to answer this question by coming up with a "Brain Care" scoring system. Take the quiz to learn the quality of your brain health today and pick up helpful insights to lower your risk of stroke and dementia well into the future.

Prolonged stress impairs the prefrontal cortex

Burnout isn't just a feeling—it physically affects the brain. Prolonged stress impairs regions of the brain responsible for decision-making, emotional control, memory, and more. It can also lead to chemical imbalances, like reduced dopamine and norepinephrine levels, that worsen these effects.

Stress and the brain

While an acute stress response is a normal bodily function, the effects of chronic stress can be extremely damaging to the human body. This is particularly true with regard to the brain. This article explores the effects of stress on the human brain, including how chronic stress may lead to psychological conditions such as depression and memory loss.

Visualize the difference between a healthy brain and one with Alzheimer's.

The brain has three main parts—the cerebrum, brain stem, and cerebellum—each combining to control the entirety of the body's operations. Alzheimer's progressively deteriorates the circuitry in these structures, resulting in what we see as the symptoms of the disease.

'FAST': An acronym to remember stroke symptoms to look for

The primary factor in surviving a stroke is how quickly one gets the appropriate medical treatment. “FAST” refers to the four most noticeable symptoms of a stroke: face-dropping ("F"), arm weakness ("A"), speech difficulty ("S"), and "time to call 911" ("T").

Brain death is a uniquely modern problem stemming from modern ventilators.

Exercise improves brain blood flow, stimulates neural growth, and more.

Research advances suggest death takes much longer than we realized

Recent research indicates that organs, including the brain, are better at handling a lack of oxygen after the heart stops beating than previously known. Such findings may open up possibilities that include someday reversing certain death processes and expanding the availability of organs available for organ donations. (Some users may experience a paywall.)

Stroke risk doubles each decade after age 55

While age is the greatest risk factor, genetics, diet, and overall health play a prominent role in determining individual stroke risk. Prevention focuses heavily on modifiable risk factors. High blood pressure is the single most important controllable risk factor, contributing to both types of stroke.

Using AI to restore speech 30 years after a stroke

Through a novel surgical procedure involving electrodes implanted in the brain, along with the help of artificial intelligence, a stroke patient is regaining her ability to speak. This technology converts her thoughts into speech through a digital avatar, allowing her to verbally express herself for the first time in decades.

Brain death is a top source of organ donation

Brain death is a significant source of organ donations because patients declared brain dead and hooked up to intensive care unit machines will still have oxygen flowing to organs like the heart, lungs, and kidneys—preserving those organs.

Humans can have brain damage after four minutes without blood flow.

Brain death is a top source of organ donation

Brain death is a significant source of organ donations—approximately 40% of organs in the US and the UK are recovered from people who experience brain death. Patients declared brain dead and hooked up to intensive care unit machines will still have oxygen flowing to organs like the heart, lungs, and kidneys—preserving those organs.

Long-term memory issues among West Nile survivors may be from the body's immune response, not the viral infection.

Brain activity sometimes goes into overdrive around the point of death according to researchers' recent analysis of patients' brains before and after they were taken off their ventilators.

Vertigo can last for minutes—or months—and may occur periodically

Vertigo can be caused by a variety of conditions, including as a side effect of medication, but if it comes on suddenly and is accompanied by other symptoms including difficulty with speech or weakness on one side of the body it's important to go to the emergency room to get checked for a stroke. For recurring vertigo, care teams can teach patients exercises to limit panic, lessen nausea and teach the brain to better tolerate head movements.

These areas of the brain are hard-hit in depression—but the changes are reversible

Depressed brains can have certain characteristic changes, including an overactive amygdala, reduced hippocampus size, and changes to the thalamus and neuromodulating chemicals in the brain.

Being struck by lightning has a mortality rate of about 10%

Near-immediate deaths are the result of electrical disruptions in the heart and nervous system, causing cardiac arrest, but severe skin burns, temporary paralysis, and blown eardrums are more common. About 74% of survivors are left with a long-term disability, which includes brain damage and changes in memory and mood.

Brain-reading devices are helping paralyzed people to touch

In clinical trials, implanted brain-computer interfaces are allowing dozens of individuals with paralysis to control prosthetics that are restoring a range of skills, including drinking coffee and feeding oneself. One area of related prosthetic research is creating a synthetic sense of touch—coupling the brain implant with pressure sensors in prosthetic robotic fingertips to enable an approximation of a sense of touch.

How tPA, which helps dissolve blood clots, can lessen the severity of a stroke

One of the most exciting recent advances in treating stroke is a medication known as tissue plasminogen activator, or tPA. It is only effective for use in some ischemic strokes, and it must be delivered within 4.5 hours of symptom onset to have a chance at working.

Pig brain cellular activity was restarted hours after death in study published in 2019

Yale University scientists restored basic cellular activity and circulatory function in pig brains about four hours after death with a synthetic cocktail of preservatives and nutrients. This work— which didn't restart electricity activity in the brain or consciousness—could help advance future human stroke and brain injury treatments.

Four in 10 CPR patients report consciousness not captured by standard measures.

Brain death is a medical diagnosis without any wiggle room

Seeking to resolve long-standing variations between hospitals and state procedures, in 2023 several expert groups published comprehensive step-by-step guidance for clinicians to follow when determining brain death in kids and adults. Among other guidelines, it stated that doctors don't need to get family consent to do the tests needed to make this determination.

Grief rewires the human brain

The human brain handles stress and emotional traumas similarly. In response to the emotional stress of a situation like the death of a loved one, divorce, or abuse, the brain may strengthen or weaken connections between nerves to form new neural connections. Over time, chronic stress can diminish brainpower, reducing overall nerve growth and memory to shift resources to enable elevated fear responses and enable humans to survive.

Hearing loss is linked with brain volume reductions

The brain looks different as a result of hearing loss, with reductions in brain volume overall and in specific areas, and these changes are hypothesized to impact cognition. Exactly why hearing loss alters cognition is an active area of research, but theories include that the elevated cognitive load of straining to hear affects brain power available for thinking and memory and that hearing loss leads to social isolation which boosts dementia risk.

Phantom limb pain may often match the pain or contortion of the injury that led to the limb loss.

The hippocampus, located deep inside the temporal lobe, appears to play a central role in dreaming and memory, according to recent research on dreaming and damage to that area of the brain.

The brain will attempt to rest itself in periods of chronic sleep deprivation

Skimping on sleep lengthens reaction times and blunts decision-making skills. At a certain point, the brain will try to sneak sleep where it can, shifting sections offline even as you remain awake. Going without sleep raises blood pressure, undermines the immune system, and increases one's risk of dementia.