Given the complexity of the human body, it’s no surprise that we’re still making new discoveries about the different parts we’re made up of – and scientists have just made a new discovery about the cerebellum at the back of the brain.

Already known as being important for properly controlling our movements, it now appears that this brain region also has a key role to play when it comes to remembering positive and negative emotional experiences.

These types of emotional experiences are particularly well remembered by the brain, not least because it helps the survival of our species to be able to remember times when we were in danger and times when we prospered.

Human brain tissue has been successfully transplanted into the brains of rats using a cutting-edge experimental procedure, say researchers. They envision the achievement as a promising new frontier in medical research.

Groups of living human nerve cells have become integrated into the brains of laboratory rats, creating hybrid brain circuits that can be activated through input from the rats’ senses, the scientists reported Wednesday.

Further, experiments have shown that the human tissue forms a two-way connection within the rat brain, also sending out signals that can potentially alter the rat’s behavior, the researchers said.

Last year, the pharmaceutical company Biogen released a drug called Aduhelm. It was the first new Alzheimer’s drug approved by the FDA in almost 20 years, but its rollout was mired in controversy — vast swaths of experts decried its approval, claiming there simply wasn’t enough evidence to support its efficacy, while the Journal of American Medicine (JAMA) rejected Biogen’s key Aduhelm paper. Shortly thereafter, Medicare chose to limit coverage of the drug.

All that is to say that given last year’s Aduhelm spectacle, you’d be forgiven for doubting what appears to be a promising development in Biogen’s continued Alzheimer’s drug development. And that’s just what it announced with a collaborator, fellow pharmaceutical maker Eisai, on Tuesday. But that being said, initial data suggests that the new drug is actually proving quite successful in late-stage clinical trials — enough so that Biogen might have a redemption arc, after all.

That new drug, lecanemab, is an anti-amyloid medication. An amyloid is a type of protein, and a normal one for brains to produce. An overabundance of amyloids, however, is believed to be caused by a disruption in a healthy brain’s built-in protein disposal system, resulting in a plaque; although our understanding is still fuzzy, brains with Alzheimer’s are shown to have abnormal plaque levels, so the idea is that anti-amyloid lecenameb, administered intravenously, could scrub that plaque away.

When lab-grown clumps of human neurons are transplanted into newborn rats, they grow with the animals. The research raises some tricky ethical questions.