After several labs successfully implanted human brain organoids into rats, many scientists are questioning the ethical implications of the experiment, STAT News reports.

Nearly four years ago, scientists in Vienna discovered that they could create organoids – lentil-sized blobs of human brain tissue – from stem cells. The revolutionary discovery has helped advance research on human brain development, Alzheimer’s, and Zika virus.

These human brain organoids existed solely in test tubes, until this past weekend, when two teams of neuroscientists reported successfully implanting these cells into the brains of rats and mice.

The scientists also observed neurological activity – when they shone a light in the rodent’s eyes, connected neurons lit up in the implanted organoid.

Other labs reported connecting the human brain organoids to blood vessels in the rodents.

Despite the discovery’s potential medical contributions, many scientists are questioning the ethics of this controversial experiment.

‘It brings up some pretty interesting questions about what allows us, ethically, to do research on mice in the first place – namely, that they’re not human,’ biologist Josephine Johnston of The Hastings Centre told STAT News. ‘If we give them human cerebral organoids, ‘what does that do to their intelligence, their level of consciousness, even their species identity?’

Currently, the restrictions on such experimentation are blurry and the National Institutes of Health has issued no ban on implanting human brain organoids.

‘We are entering totally new ground here,’ said Christof Koch, president of the Allen Institute for Brain Science in Seattle in an interview with STAT News. ‘The science is advancing so rapidly, the ethics can’t keep up.’

While skeptics question the future consequences of creating more human-like rodents, other scientists believe that the research is not yet advanced enough to create an ethical or moral dilemma.

‘Some of what people warn about is still science fiction,’ Dr. Isaac Chen, a neurosurgeon at the University of Pennsylvania, said. ‘Right now, the organoids are so crude we probably decrease the rats’ brain function.’

Chen believes that organoid experimentation is invaluable, as it could be used to treat brain injury, stroke and potentially, schizophrenia and autism.

Legal Scholar and bioethicist at Stanford University Hank Greely says that even though these organoids are extremely restricted within the confines of a small mouse brain, scientists still must consider the rights of something ‘human-ish’ and determine what that means.

At this point, scientists doubt that these organoids could create the feeling of ‘a human trapped in a rodent’s body,’ but some believe that an eventual ‘Frankenstein’ situation is not entirely unlikely.

‘At some future point, it could be that what you’ve built is entitled to some kind of respect,’ Greely said.

Noting Mary Shelley’s novel, Greely added, ‘I think that story is relevant to what we’re talking about.’