World's oldest lab-grown human brains reach seven years old - and scientists think they may have 'recorded the passage of time'

The world's oldest lab–grown human brains have reached seven years old, scientists have revealed.These tiny peppercorn–sized lumps of human brain tissue, known as organoids, are grown directly from stem cells.Typically, organoids only live for a few months in the lab, and the previous record for the oldest artificial brain was a little under two years.Now, researchers have shattered that record, and even say their lab–grown creations may have 'recorded the passage of time'.In a new paper, published in Nature, scientists discovered that these clumps of brain cells age in a remarkably similar way to the ones in our heads.Amazingly, the scientists also claim that the cells 'retain a memory of the developmental steps already performed'.That doesn't mean organoids have a memory as we understand it, with the ability to recall events like a childhood birthday party.Instead, the researchers say the organoids' past is 'engraved' into them at a cellular level. The world's oldest lab–grown human brains (pictured) have reached seven years old, according to scientists Researchers say that these lumps of brain tissue, known as organoids, 'recorded the passage of time and retain a memory of the developmental steps already performed'Brain organoids have a much simpler structure than real human brains and don't receive any sensory input from the outside world.For these reasons, scientists widely agree they are not capable of consciousness, thought, self–awareness or any other higher–order brain functions.However, because they mimic real human brains, they are an extremely valuable 'biological model' for understanding brain development and disease.The issue for researchers has been that most organoids only last a few months, while our brains take 20 years to fully develop.That leaves a big gap in scientists' understanding that extremely long–lived artificial brains might be able to fill.In their new study, researchers kept a set of organoids alive for seven years using a special technique designed to provide the optimal conditions for growth.They then analysed these organoids using three newly developed 'genetic clocks' that allow scientists to roughly determine the biological age of cells.This revealed that the organoid cells had aged over time in roughly the same way as cells in a real brain, and bore all the normal cellular 'memory' of that development. The researchers also mixed young and old cells together, and found that the old cells 'jumped ahead' in their development What are brain organoids? Brain organoids are tiny, three–dimensional models of brain tissue grown in a laboratory from human stem cells.Brain organoids are not miniature human brains. They reproduce some aspects of brain development but lack many of the structures and complex connections found in a real brain. They can develop different types of brain cells, including neurons and supporting cells, and can reproduce some features of early human brain development.Researchers use them to study how the brain develops and what goes wrong in conditions such as neurological and neurodevelopmental diseases.Because they can be made from a patient's own cells, organoids can also be used to investigate how particular genetic mutations affect the brain. Co–author Professor Paola Arlotta, of the Harvard Stem Cell Institute, says: 'The brain can continue to develop outside the context of a person for this unprecedented amount of time.'In the future, the scientists hope this will help shed light on how a range of disorders, such as autism and schizophrenia, emerge and develop.Earlier studies have already begun to use organoids as a model for testing Alzheimer's, Parkinson's and spinal cord injuries.One promising new treatment, developed by biotechnology company Axonis Therapeutics, uses a reprogrammed virus to deliver beneficial gene therapy to central nervous system cells (CNS).Researchers tested the efficacy of these treatments using brain organoids grown aboard the International Space Station, where microgravity conditions promote rapid growth.The researchers currently aren't sure just how long brain organoids could be made to live.Since they don't have a body that can get sick or infected with disease, they could theoretically outlive a real human.However, while Professor Arlotta suspects they could be made to last longer, she admits that 'nobody really knows' organoids' lifespan at the moment.To investigate their cells' ageing further, the researchers also conducted what Professor Arlotta describes as a 'crazy experiment'.The scientists took cells from a two–year–old artificial brain and mixed them with cells from another that was just two weeks old to make a 'chimaera '.While the younger cells behaved normally, the older ones 'jumped ahead a whole chunk of development'.Right away, these cells started to make neurons that would normally take about four months to develop.Professor Arlotta says that this procedure effectively 'warped time' for brain development, adding that the results were 'super cool'.The researchers hope that this technique could be used to boost the development of brain cells for future experiments.That could let scientists study conditions which develop later in life, without needing to wait 20 years for the brain cells to reach maturity.