Human brain cells reshape mouse cortex in Stanford study

Stanford neuroscientist Sergiu Pașca and colleagues reported in Nature that human brain organoids can grow extensively inside genetically modified mice whose cortex and hippocampus do not fully develop. The altered animals created room for the implanted tissue to divide, expand and connect with the mouse nervous system, with one mouse described as having nearly half its brain volume replaced with human cells.

The mice missing brain tissue appeared broadly normal in basic behavior, including walking and squeaking, but showed memory problems in a maze test. Mice that received added human cells performed better, suggesting the transplanted tissue was contributing to cognition. Pașca calls the animals “xenocortical mice” and sees potential for studying brain injuries.

The research adds momentum to wider efforts involving brain organoids, including experiments connecting them to computers and proposals to use them as replacement tissue for stroke patients. It also raises ethical questions about consciousness, dubious therapy clinics and species boundaries. Pașca said he is not concerned that the rodents have human cognitive capacities, but warned that placing human brain organoids into engineered primates would cross a clear red line.