A Tour of the Growing Brain, Looking Upside Down – Harvard Gazette
As a brain develops, young neurons arise, seeking to form synaptic connections between brain regions, Harris said. If they fail to establish these links, they “commit suicide by consuming themselves”. And even if they survive this ferocious first wave, they can “get pruned, like the plants”.
During the first trimester of pregnancy, neuronal growth is exponential: about 15 to 20 million cells are born every hour, Harris said. Only about 50 percent of these original cells survive. If, for example, there is too much of one type, causing an imbalance, the excess will die out. Or, if some seem to be performing an unnecessary task, such as those attending with a closed eye, they will move on. Why waste precious neurons?
After the first period of growth, suicide and pruning ends, adult neurons survive for a lifetime. And unlike those of a cat, they remain malleable for several years. This is one of the reasons why children are particularly adept at learning new languages and why procedures aimed at correcting neurological dysfunctions, such as a lazy eye, are more likely to be successful early in life.
“Adult neurons seem to have lost some of the mojo of their youth,” Harris said. They wear down, weaken and become a little less flexible over time. Also, unlike those of fish, amphibians, and reptiles, the human brain does not regenerate much after injury because only a small number of neurons are born in adulthood.
“Fixing broken brains is one of medicine’s toughest challenges,” Harris said.
“It’s a really good time to be an autistic or Alzheimer’s mouse because we can cure you,” Sanes said during the Q&A portion of the conference. But these remedies do not translate from mouse to human. Even though brains appear remarkably similar between invertebrate species, “there are profound developmental differences between mouse and human brains,” Sanes said.
Today, scientists grow mini-brains – or rather collections of clusters of neurons formed in a Petri dish – to study neurological diseases, including the possibilities of treatments and cures, and to shed light on the development of the brain. ‘artificial intelligence. Of course, building a brain in the lab raises ethical questions. Do they treat their world? Suffering? Human?
“We need to keep our eyes, ears and ethical antennae open to this,” Sanes said. And yet, he continued, there is a moral imperative to seek treatments for brain disorders, which cause more suffering than any other class of disease.
“To understand human brains, you have to study human brains,” Harris added, “and it’s not easy.”