Part-human part-mouse brain developed in science breakthrough

The research has raised questions about what it means to alter the way laboratory animals think and feel Neuroscientists in the US have successfully adapted mice to have functioning human cells inside their own brains. The researchers hope that potential treatments for psychiatric and neurodevelopmental diseases that only occur in humans could now be tested on the laboratory rodents. While mice with brains that are partly human might sound like a Kafkaesque experiment, the scientists said these are not "mice that think like humans". The animals are genetically engineered - and surgically altered - so that some of their brain tissue is human. The scientists said their work, published in the journal Nature, external, was carried out with independent ethical scrutiny. In scans of the implanted mice, researchers were able to see connections between the human brain cells and the rest of the mouse brain The aim of this ethically complicated breakthrough was to better understand the biology of brain disorders for which there are currently no effective treatments. Some conditions cannot be studied in a mouse, simply because rodents do not develop some of the brain disorders that we do. As lead researcher Prof Sergiu Pașca from Stanford University explained in a press conference, psychiatry has "one of the lowest success rates for clinical trials". "Even drugs that actually make it to clinical trial - that seem to be working really well in animal models - fail dramatically in clinic," he said in a press conference. "That tells us we're missing a lot of information about human biology and capturing that will be essential." The Stanford researchers said that, for some complex conditions, including epilepsy, autism and cerebral palsy, it has the potential to be "transformative". Pașca said: "Here we have a new model that allows us to actually capture aspects of human brain function in a way that has not been possible before." The hope is that this will provide a new way to investigate the biology of some human brain disorders The human brain is made up of billions of cells, interconnected in millions of circuits, making it difficult to understand its development and what exactly is happening – at the cellular level - when things go wrong. While this research is not the first time human neurons have been implanted in laboratory rodents, external, these scientists took that approach to a new level. First, they genetically-engineered mice to develop almost none of their own cerebral cortex – that is the outer layer of the brain sometimes referred to as "grey matter".