To show how the procedure could be valuable for research, the scientists created brain organoids from healthy human cells and others from patients with a genetic disorder called Timothy syndrome and transplanted them into rat brains. The scientists later trained the rats to expect a drink of water when the human cells in their brains were activated, showing that the human cells could affect the rats’ behaviour.

But the human neurons flickered with activity when air was blown across the rats’ whiskers, showing a melding between rat and human brain tissue. Tests on the animals found no evidence that they performed any better, or suffered ill-effects. Some rats received two organoids, one on each side of the brain. Once grown, each organoid added about 5m human neurons to the rat’s 30m.

The human brain cells did not replace rat brain tissue but instead wired into it. The 1.5mm-wide balls of tissue were then transplanted into newborn rat brains, specifically a region called the somatosensory cortex, which processes tactile sensations such as whisker movement.įive months later, MRI scans showed that the clumps of human brain tissue had grown six to eight times larger and hooked up to the animal’s blood supply. To overcome these latter problems, Pasca and his colleagues grew human brain organoids in a dish until they comprised between 500,000 and 1m neurons. Part of the problem is that organoids are not bathed in nutrients from a blood supply and not wired into the broader brain circuitry. One practical issue facing the field is that lumps of brain tissue grown in the lab behave differently to neurons in the brain. Researchers have used organoids to probe brain development, autism, and the impact of infections such as Zika virus, but some have asked how scientists will know if organoids ever reach a point that they suffer or become conscious. The work is the latest advance in the ethically complex field of brain organoids, in which scientists grow tiny balls of human brain cells in the laboratory. “We see patients and patients’ families that are desperate. “Psychiatric disorders are a huge burden on society and it is very, very clear that we need better models for studying them,” said Sergiu Pasca, a professor of psychiatry who led the research at Stanford University. The groundbreaking procedure means scientists can now study how brain cells from patients with neuropsychiatric disorders malfunction in a living brain, and assess the impact of drugs in real time.

Brain neuron