One theory claims the retinae of SAD patients may fail to adjust to less light in winter

Read Norman Rosenthal’s original 1984 paper describing SAD

The study helped formalize research and diagnosis of seasonal affective disorder, catalyzing the development of therapies (like bright light) and leading to broader adoption of effective treatments. It also helped connect the influence of light and seasons on biological mechanisms in the human body, spurring exploration of circadian rhythms.

10 percent of SAD cases occur in the summer

Despite its significantly lower incidence, summer-risk SAD is as significant as its winter counterpart. Rather than being prompted by less light, the summer version is typically spurred by high temperatures, strong light, distinct summer time social pressures (appearing in a bathing suit, for example), and pollen. Common treatments include keeping cool and prioritizing sleep.

SAD disrupts melatonin secretion, producing it longer in the morning

The hormone is secreted from the pineal gland in the brain and is key to the timing of sleep. However, the substance does not generate sleep itself. With seasonal affective disorder, the body misperceives the photoperiod—the time with light—and the cycle of sleeping and waking gets off-phase, leading to issues with circadian rhythms.

Lack of sunlight during Arctic winters can fuel a winter slump and a circadian disconnect

Sunlight typically tells our brain to stop producing melatonin, a hormone that makes us sleepy, but in dark Arctic winters humans must adapt to life without much sunlight. Scientists in this video provide tips that include trying to increase the amount of light around you, even if it’s just table lamps.

SAD uniquely affects people with attention-deficit hyperactivity disorder

Those with ADHD—chronic issues with attention and executive function—are primed for SAD. Many are disproportionately evening chronotypes (more awake in the evening), have a delayed sleep phase, and have low sensitivity to light in the morning. This podcast explores the overlap between these two groups.

The side effects of falling back and springing forward

Daylight saving time can interfere with a person’s sleep schedule, but it also has been linked to increased rates of depression, heart attack, stroke, cancer, and car accidents. UT Southwestern’s Dr. Joseph Takahashi explains why the time change is bad for your brain and health.

Animals get SAD—especially those in zoos, like pandas

Giant pandas in locations outside their evolved latitudinal range (from southeast Asia to northern regions around Beijing) exhibit more sluggish behavior, even when they were born there. Researchers have observed that similar sensitivities to "photoperiods" (or time with light) impacts many animals, including birds, insects, and our pets. (Nautilus imposes a metered paywall.)

Circadian rhythms shift as we age—making older adults want to go to bed earlier

Throughout our lives our internal biological clocks shift. Early-to-rise toddlers become hard-to-wake teens and eventually early-to-sleep seniors. Circadian rhythm fluctuations throughout our life cycle explain some of these changes.

Proteins with limited light sensitivity prevent humans from seeing all types of light

Specialized photoreceptor cells in the retina called cones each possess photopigments that activate when exposed to three ranges of visible light. Other forms of electromagnetic radiation outside the activation range do not generate signals for processing in the brain, thereby limiting average human vision to approximately 10 million colors.

Light pollution is giving oysters insomnia

Oysters, bivalve mollusks that have light-detecting cells along their skin, can't sleep with all this artificial light. According to a 2022 study, oysters' sleep cycles are disturbed by light dimmer than that provided by the full moon. As with humans, it's possible that these bouts of insomnia could have adverse health effects and contribute to the development of disease over time.

The science of spring fever

Researchers have confirmed what people have sensed for ages: Our emotions during the springtime can go a little wild. This piece breaks down the impact of the seasonal transition on our bodies and prescribes a few ways to mitigate the effects.

Studies suggest when you sleep is as important as how much you get, and syncing with your circadian rhythms may lead to less fatigue and improved long-term health outcomes

LIghter-colored eyes have heightened risks for macular degeneration

People with blue eyes appear to be at elevated risk of developing the disorder, perhaps because more light can penetrate their eyes. But the most significant modifiable factor heightening the risk for macular degeneration is smoking.

Usher Syndrome, a rare genetic disorder, causes progressive hearing and vision loss

People with one of the subtypes of this condition have a genetic mutation that starves cells in the inner ear and the retina of proteins required for detecting sound and light. Gene therapy in animals has seemed like a promising treatment for the condition.

What pupils can reveal about a person’s thoughts and feelings

Eyes have long been said to be the window to the soul. In this article, a psychologist and pupillometrist explores research demonstrating pupils as a window into the mind. Pupils tell us how intensely someone is exerting mental effort, or even reveal what a person is imagining. Read this article for insight into the field of pupillometry and how it can offer insights into our psyches.

Examining self-diagnosed synesthesia

A growing number of people on social media claim to have a perceptual condition that lets them smell colors, see music, or taste sounds. But do they really?

Changes in vision or eye pain can be early MS symptoms

This occurs due to myelin degradation around the optic nerve, impairing its ability to transmit visual information to the brain. Individuals may especially experience eye symptoms after exercising or taking a hot shower because boosted body temperatures slow down nerve function in nerves already damaged by MS.

Restoring vision in impaired patients via CRISPR

Since CRISPR was revealed as a gene editing tool in 2012, it has been on an accelerated track to real-world applications. Among other clinical demonstrations, doctors have now injected a CRISPR treatment directly into eye cells, helping vision-impaired patients see shapes and colors again.

Why we have different seasons

Visualize just how exactly seasons come to be with this animation of the earth in relation to the sun, and see how earth's tilt determines our seasons.

A deeper walk through of the four stages of sleep

In this TED video, sleep expert Matthew Walker carefully breaks down the sleep stages along with a description of why each is important. He finishes the discussion by examining the consequences of altered or decreased sleep, and why seemingly small alterations in our sleep patterns can have outsized effects.

During the fall, chlorophyll breakdown in leaves produces color changes

With shorter days and less sunlight, the concentration of the green pigment diminishes, revealing yellow and orange pigments. Red leaves result from trapped sugars, producing new pigments called anthocyanins, which weren't present in leaves during the growing season.

Watch how doctors examine leprosy patients for signs of vision impairment

Clinicians must screen for symptoms of eye and vision damage in leprosy patients, including loss of sensation, reduced blink reflex, and inability to close or keep the eyes closed.

'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.

The emotional regression that happens when we visit home

Despite how mature we might like to think we are, returning home for the holidays often results in reverting to our moodier, angstier childhood selves. This story in the conversation dives into the root of this phenomenon, which can largely be explained by attachment theory. Read along to understand how your past experiences and attachment style can influence your current behaviors and for advice on how to cope with regression.

Relative motion between a source and an observer shifts the color of observed light

The phenomenon, known as the Doppler effect, is the result of experiencing an increase in the frequency of observed waves when approaching a source and a decrease when moving away. Because this property corresponds to color, approaching objects appear bluer than normal—blueshift—and receding objects appear redder than usual—redshift.

Sharp wave ripples in the brain tag experiences for long-term memory storage

These ripples were known to quickly replay neuronal sequences during sleep for consolidation. While awake, they help the brain prioritize memories to remember, and their disruption can impair memory formation.

All rainbows are 'raincircles' caused by water droplets separating white sunlight into a spectrum of colors, but Earth's surface blocks the bottom half of the circle from our line of sight.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

Poison ivy can cause rashes year-round since all parts of the plant contain urushiol, the oil that triggers our allergic response.

In recent years a child anxiety expert has created and tested a novel phobia and anxiety treatment approach for children, focused on changing how parents respond to the fears.

After 25 people used virtual reality headsets to practice flying with virtual wings—flapping their arms—their visual cortex responded to the wings almost as if they were real arms, treating them as body parts.

Crows are believed to have intelligence on par with a seven-year-old child and demonstrate complex behaviors, from problem-solving with tools to recognizing human faces.

Ebola infects and disables immune cells, triggering a cascade of events that leads to small blood clots throughout the body, weakening blood vessels and interrupting blood flow to key organs.

Discover the catastrophic consequences of a failure of the US electrical grid—something that is more likely than many Americans think.

When caught in the mouths of cardinal fish, seed shrimp release glowing, bioluminescent chemicals, which alert predators of the cardinal fish, prompting the shrimp's ejection.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

See images of medical cases of firework injuries shared on this 'Instagram for doctors.' (Warning: Graphic content)

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

The Great Salt Lake's distinct dual coloration results from high-salinity organisms that only live in the northern portion and produce a purple protein.

Human-to-human transmission of hantavirus remains extremely rare, so the 2026 hantavirus cruise ship outbreak doesn't mean we're facing a COVID-style pandemic risk.

Explore the known asteroids, comets, and spacecraft involved in asteroid studies within our solar system with 'Eyes on Asteroids,' a 3D visualization from NASA.

Salvador Dalí believed he was his own dead brother, who had died nine months before he was born

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

El Niño, Spanish for 'the boy,' was named after Jesus Christ because the phenomenon resembled the weather changes observed around Christmastime.

Up to a million Girl Scouts sell about 200 million cookie boxes every spring, generating $800 million, largely because refusing a child is frowned upon

The 19th-century painters of the Hudson River School were among the first American romantics, with portraits that displayed the natural beauty of the young country.

In 1939, baseball star Lou Gehrig delivered his inspirational 'Luckiest Man' speech after retiring due to the health condition that now bears his name.

The distributor behind 'Rocky Horror' pulled the film from its scheduled national release, believing it would be a failure, though it eventually amassed a dedicated fanbase through midnight showings, a trend that continues over 50 years later.

In 2026, Finland was named the world's happiest country for the ninth consecutive year based on its wealth, social safety network, and high life expectancy, among other factors.