Seven years ago, researchers at Stanford University started an ambitious experiment: They began growing miniature, simplified versions of the human brain from stem cells inside a lab, then later injected that tissue into the brains of newborn rats.
Their results, published Wednesday in the journal Nature, showed that the brain-like human tissue integrated with the rat tissue, then continued to mature.
Those brain cells, in turn, seemed to influence the rats’ behavior.
The researchers injected the human tissue into the rats’ somatosensory cortexes — regions that receive and process sensory information like touch or pain. After about two weeks of training, the rats began to lick a spout in search of water whenever the researchers stimulated the human neurons (they did this using blue light lasers). The researchers also used a puff of air to prod the rats’ whiskers, then observed how the human neurons responded.
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"We found that human neurons respond very quickly after we stimulated the whiskers. In fact, more than 70% of the human neurons are engaged in some form of activity within a second or so of that stimulation, so that tells us that they’re probably connected," Sergiu Pașca, one of the study’s authors and a professor of psychiatry and behavioral sciences at Stanford, said on a call with reporters.