Our brains may learn more from rare events than from repetition

Associative learning in the brain relies more on the timing and rarity of cue-reward pairings than on repetition. Mice learned associations just as effectively from infrequent, widely spaced rewards as from frequent ones, with dopamine responses emerging after fewer rare events. These findings suggest that rare or intermittent experiences can drive rapid learning, challenging traditional repetition-based models.
More than a century ago, Pavlov trained his dog to associate the sound of a bell with food. Ever since, scientists have assumed the dog learned this through repetition. The more times the dog heard the bell and then got fed, the better it learned that the sound meant food would soon follow.
Now, scientists are upending this 100-year-old assumption about associative learning. The new theory asserts that it depends less on how many times something happens and more on how much time passes between rewards.
It turns out that the time between these cue-reward pairings helps the brain determine how much to learn from that experience.
When the experiences happen closer together, the brain learns less from each instance and this could explain why students who cram for exams don't do as well as those who studied throughout the semester.
Scientists have traditionally thought of associative learning as a process of trial and error. Once the brain has detected that certain cues might lead to rewards, it begins to predict them. Scientists have postulated that at first the brain only releases dopamine when a reward like tasty food arrives.

But if the reward arrives often enough, the brain begins to anticipate it with a release of dopamine as soon as it gets the cue. The dopamine hit refines the brain's prediction, the theory goes, strengthening the link with the cue if the reward arrives—or weakening it if the reward fails to appear.
The findings could shift the way we look at learning and addiction. Smoking, for example, is intermittent and can involve cues—like the sight or smell of cigarettes—that increase the urge to smoke. Because a nicotine patch delivers nicotine constantly, it may disrupt the brain's association between nicotine and the resulting dopamine reward, blunting the urge to smoke and making it easier to quit.

Dennis A. Burke et al, Duration between rewards controls the rate of behavioral and dopaminergic learning, Nature Neuroscience (2026). DOI: 10.1038/s41593-026-02206-2

Air pollution may directly contribute to Alzheimer's disease—new study
Higher exposure to fine particulate air pollution (PM2.5) is associated with an increased risk of Alzheimer's disease, independent of other risk factors such as high blood pressure, stroke, and depression. PM2.5 particles, primarily from fossil fuel combustion and wildfires, may contribute to brain inflammation and oxidative stress. Global regions with elevated PM2.5 levels face rising dementia rates.

https://journals.plos.org/plosmedicine/article?id=10.1371/journal.p...

Heart attack study reveals 'survival paradox'
Analysis of over 900,000 heart attack patients shows that while severe frailty is more common in women, frail men have a higher one-year mortality risk. This "sex-frailty paradox" indicates that frailty impacts outcomes differently by sex, challenging current risk assessments and highlighting the need for sex-specific care pathways and frailty assessment tools in acute myocardial infarction management.

New Research challenges the "one-size-fits-all" approach to heart attack care, adding critical nuance to the debate on sex disparities. A new study involving more than 900,000 patients has revealed a "sex-frailty paradox" in heart attack outcomes, challenging the prevailing narrative that high clinical risk is predominantly a female issue.
While considerable focus has rightly been placed on addressing the fact that women are often undertreated compared to men after a heart attack, this new research, published in The Lancet Regional Health—Europe, highlights a hidden and profound vulnerability in men.
The study found that while severe frailty is indeed more common in women following a heart attack (acute myocardial infarction, or AMI), the actual risk of dying within one year is significantly higher for frail men.

This creates a complex picture where women face inequalities in access to care, but frail men face a "malignant" prognosis that current standard treatments are failing to address.

The study is the largest of its kind, analyzing national data over a 15-year period to disentangle the relationship between sex, frailty, and survival.
It challenges current risk assessments including patient frailty and age used by clinicians to determine treatment strategies, highlighting the need for sex informed care pathways to be included.

Patient frailty has long been an indicator of poorer outcomes, including mortality, rehospitalization and recurrent cardiovascular events, with frailty scores underpinning treatment decisions.

Hasan Mohiaddin et al, Sex–specific associations between frailty and long-term outcomes in patients with acute myocardial infarction: a national population-based study, The Lancet Regional Health - Europe (2026). DOI: 10.1016/j.lanepe.2026.101612