(NYT) – The animals may help reveal the causes of brain disease in people and point the way to treatments. But researchers already are calling for new ethical guidelines.

In order to learn more about brain disorders, scientists reported on Wednesday that they had created extraordinary mice whose brains are filled with millions of human neurons. The work marks a startling advance in replicating the complexities of the human brain outside the body.

The research, described in the journal Nature, also poses some profound questions. “Will there be some enhancement of function?” asked Dr. Sergiu Pașca, the Stanford University neuroscientist who led the work. “Will they do better than other mice?” (Read More)