How do brain scans work?

A beginner's guide to the brain

Small but powerful, the brain constitutes only about 2 percent of the human body. However, it runs jus about everything, day and night, all year round. Learn about the different parts of the human brain, as well as its unique defenses, like the blood brain barrier in this four-minute video.

Explore an interactive 3D model of the brain

The brain contains about 86 billion neurons—nervous system cells—and controls vital bodily functions via electrochemical signals. Neurons form circuits through axons, and different brain regions use these circuits to perform specific tasks.

Can brain scans help with processing trauma?

MRIs and brain monitoring therapies are becoming increasingly popular for those looking to process trauma and address mental health conditions, including PTSD and depression. This article details how these therapies quantify mental health, giving users another way to measure and manage their mental and emotional needs through brain mapping and other methods.

Everything scientists could learn by looking at your skull

Our skulls are all unique, but they also share characteristics across groups of people. In the absence of fingerprints, forensic scientists can learn a lot about you just from your skull.

Schizophrenia is being studied with pea-sized 'mini-brains'

Brain organoid research is enabling researchers to study distinct electrical firing patterns associated with schizophrenia. These "mini-brains" that are constructed in the lab from patients' cells could lead to better diagnosis approaches and drug development.

Like fingerprints, brain anatomy is unique too

Researchers have discovered that a combination of experiences and genetic factors shape the anatomy of the human brain. They found even quick experiences affect the brain’s genetic makeup, which—over time—means every person develops a completely unique brain anatomy. While brain imaging could be used to identify individuals, it remains much more expensive than fingerprinting for now. Read to found out more about this study from the University of Zurich.

The study of dreams, formally called oneirology, has evolved over the centuries, from anecdotal interpretations to advanced brain imaging.

An interesting perspective on whether (and how) brain size matters in cognitive ability

Some brains are bigger than others, but what is the relevance, if any, to brain size and intelligence? This Scientific American article explores the question and offers examples. It also visually compares frontal slices of several mammals' brains, showing that humans don't necessarily have the biggest cerebrums on the block.

The evolution of the human brain

The human brain, in all its staggering complexity, is the product of millions of years of evolution. Read on to find out about brain size and intelligence, language and brain development, and more.

How can octopuses and MDMA help scientists understand the human brain?

Research shows that psychedelics may induce something called "critical periods" in the adult brain, which can make our brains more open to learning and changing, like they once were back in early childhood. Psychedelics similarly change how social creatures like octopuses behave, which demonstrates that these animals could help us better understand our own neurobiology.

How helium enables MRI machines to look inside organisms

By cooling the machine's magnets with liquid helium to extremely low temperatures, they can generate and maintain powerful magnetic fields that align the hydrogen atoms in living things to point toward a patient's head or feet. A radio pulse nudges these atoms, which realign and induce a measurable signal in nearby electrical coils. These signals are captured in slices and then stacked into a 3D reconstruction.

The dreaming brain, as understood by scientists

Technology has advanced to where the seemingly separate fields of psychology and neuroscience are asking the same questions about dreams, such as whether they're more closely related to perception or visualization. Some field-intersecting findings include research that shows people with impaired face perception don't dream of faces, those with brain legion-related cognition difficulties deal with similar issues in dreams, and children's dreams change in parallel to their cognitive development.

Brain wave-reading earbuds are being used by companies to study workplace performance

Limited safeguards prevent governments from accessing and companies from sharing brain data. Foreign governments may also be developing technology to spy on and potentially disrupt human thoughts.

Scientists are studying dying patients' brain activity in the final moments of life

In the final moments of life there are distinctive bursts of coordinated neural activity. Researchers are interested in parsing that data to better understand the dying process and also exploring how this data relates to our understanding of consciousness.

Computed tomography scans use X-rays to create 3D internal images

Just as shadows can reveal the shape of obstacles blocking visible light, the donut-shaped CT scanner measures how X-rays are blocked, revealing the shape of bones, organs, tissue, and other matter along a cross-section. As it rotates, the scanner combines these cross-sections to build a model of the internal structure.

Physiological changes to the brain on LSD can be captured via MRI

Psychedelics like LSD often take users on novel experiences that can result in lasting shifts in perspective and behavior. See how LSD affects brain activity in this video that details how scientists visually captured the psychedelic's effect for the first time.

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

The science of optical illusions

The human brain has developed cognitive shortcuts to help us navigate in a world where our visual senses are constantly bombarded of information. But these shortcuts can also be exploited, tricking the brain into telling us something is happening when it really isn't. This short video unpacks the neuroscience behind some of the most common (but perplexing) optical illusions.

Your brain appears to age in five distinct stages, with the pattern of connections inside your brain shifting, on average, around ages 9, 32, 66, and 83.

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.

Depression changes the brain, causing distinct structural alterations visible on brain scans, but effective treatment can eventually make a depressed brain resemble a healthy one.

Watch this 2021 video demonstrating a full brain death examination

This video and accompanying article in the peer-reviewed New England Journal of Medicine show the then-standard steps of a full brain death examination—demonstrating the process on a medical dummy to search for pain, blinking, eye movement, cough, gagging, or other forms of responsiveness. (May need to sign up for a free account to view.)

What is the blood brain barrier?

Every blood vessel is lined with endothelial cells that act as filters between blood and the rest of the body. In the brain, these cells are tightly packed together to keep a close watch on what substances can access the vital organ. This protective measure poses an obstacle to drugmakers looking to deliver drugs to the well-defended brain for conditions like Alzheimer's. Watch a quick overview here.

Take a deep dive into the neuron

Neurons are the basic unit of the brain and nervous system—electrically excitable cells that sends signals throughout the body. They can communicate with each other, fire in sequence, and conspire to do everything from drive body movement to help form memories. Check out this intro-level overview to learn more about their structure and how they work.

Brain implants are restoring movement and communication in early human trials

Several companies developing brain-computer interfaces have begun testing on humans with promising results. These implants have helped reanimate paralyzed limbs and enable communication, though ethical concerns remain about data privacy.

Dream interpretation has evolved from ancient mystical explanations, to dream reports, to tracking electrical activity in the brain and more.

How MS is diagnosed with brain and spinal cord MRIs and eye tests

There's no definitive test for MS, but to make a diagnosis doctors typically use MRIs of the brain and spinal cord to hunt for telltale lesions. Also, optic nerve tests to see how quickly information travels down the optic nerve—since degraded myelin sheaths will slow electrical signals between the eye and brain.

The human brain only uses 5% more energy during active tasks versus resting

Despite only being 2% of the weight of a human body, the average adult brain consumes 20% of its energy, with the majority of it spent on maintaining homeostasis—the stable equilibrium conditions of temperature, acidity, blood sugar, and other properties in the body. For infants, the consumption is closer to 50%.

Open brain surgery is not required for BCIs inserted via blood vessel injection

Synchron's brain-computer interface, the Synchron Switch, takes advantage of preexisting medical devices, such as stents and catheters. Cells grow over the device over a 90-day period, incorporating it into the vessel wall and minimizing clots.

Brain-computer interfaces create a direct link between the brain and external devices

The technology enables users to control prosthetics, computers, or even games using only their thoughts. In 2021, a monkey played table tennis using only its brain, thanks to a Neuralink device, marking a major milestone before human trials began in 2024.

The inner life of a cell

White blood cells are responsible for protecting the human body from infection. This video uses biophysical data from Harvard researchers to accurately demonstrate what goes on inside one white blood cell as it works within the immune system.

Can you guess which ancient human skull is which?

When scientists discover a new fossil skull, they compare it to skulls that have already been identified as particular early human species. In this activity, you get the chance to be the scientist! Choose a mystery skull to identify by clicking on it.

Neural rhythms shape how we move, focus, remember, and interact with the world

Millions of neurons in the brain produce rhythmic electrical signals, or brain waves, that guide physical movement and help form and store memories. Researchers also use these rhythms to create brain-computer interfaces, letting people control devices using only their thoughts.

The secret lives of cells

Cutting-edge microscopy has revealed previously unseen interactions of biological molecules within their cellular environment, enabling scientists to observe and analyze the molecules in a holistic view. This podcast explains the minute advancements made over the last few decades in observing cells, revealing how scientists have come and what the future holds for the field.

Animal brain studies show brain activity similar to what we'd expect during dreams, but parsing whether animals are truly dreaming depends on how one defines dreaming and how scientists could prove it.

An essay exploring how living day-to-day with a brain implant helps restore a sense of identity

Companies like Neuralink are experimenting with volunteers who have lost control over their bodies. Many of the program's participants claim the most significant benefit from the tool is the ability to perform simple, mundane tasks, such as playing video games or shaking hands, rather than more obvious milestones like walking or eating. This essay explores what it's like, day to day, to use a brain implant.

What is the brain up to when the mind wanders?

As you stare into the distance while washing your home's seemingly never-ending pile of dishes, the brain activates its default mode network. This collection of "task-negative" brain regions associated with memory, reward, action consideration, and prediction alight with activity when humans mentally turn inward, possibly giving rise to the brain's ability to wander and humans' ability to construct internal narratives about the world.

What happens in a dying brain?

Near-death experiences usually happen during death or on the border of life and death when a person isn't understood to be conscious. This article details the science of what's going on with the brain during NDEs.

Dreams largely occur during REM sleep (but not entirely).

PET scans create images of the body by detecting light emitted from the annihilation of matter and antimatter, with the latter produced by custom chemicals containing radioactive atoms.

How four types of psychedelics affect the brain

Brain imaging shows that ayahuasca, MDMA, DMT, and psilocybin profoundly affect neural activity, giving rise to higher states of introspection and consciousness. This article details exactly how each of these drugs physically affects the brain and what that means for mental health treatment. Some of these drugs quiet the brain or trigger the release of neurochemicals associated with mood regulation and learning.

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.

The debate on why humans are conscious—and what that means

Understanding what consciousness is, and why and how it evolved, is perhaps the greatest mystery known to science. Watch interviews with the world's leading experts on what it is and whether we'll ever know.

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.

What a tiny marine worm can tell us about our brains

Meet the amphioxus, a small eel-like animal that has a lot to teach us about brain evolution. The genetic roots of our brains can be seen in these unusual creatures. This three-minute educational video focuses on the evolutionary history of the human brain through these odd little critters with a 500-million-year-old history.

This is the human brain on the world's strongest psychedelic

Within seconds of inhaling a high dose of vaporized synthetic 5-MeO-DMT—a lab-produced substance that otherwise is naturally derived from the glands of the Colorado River toad—it induced slow brain waves. Such waves are typically associated with unconsciousness due to a coma or anesthesia, perhaps explaining why users describe feeling like everything falls away. The compound is currently in clinical trials for treating depression.

Research studies can be conducted inside or outside of living samples

While "in vitro" experiments occur outside living organisms for cost-effectiveness, "in vivo" experiments take place inside them, providing real-life insights at a higher cost and with increased ethical concerns. Alternatively, "in silico" methods use computational simulations.

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.

Exploring bird skulls

Birds inspire us to fly—but what about bird skulls? This collection of various birds' preserved skulls offers a peculiar "bird's-eye" view. See the many surprising shapes of beaks and eyeholes, from mockingbirds to turkeys, in this fascinating visual collection.

'Susan's Brain': what happens to the brain during addiction

This engaging animation from Harvard Online breaks down the neuroscience of addiction through the story of “Susan’s brain,” demonstrating how addictive substances hijack normal reward pathways. Through clear visual metaphors and approachable narration, it explains complex brain chemistry in understandable terms.