Scientists are fast approaching the point where they can grow a brain in a lab.

No, we're not talking about artificial intelligence, but actual gray matter — stem cells taken from human skin or blood and reprogrammed to grow into neurons in the cortex, the brain's central processing unit.

So far, researchers have developed a stripped-down version, appropriately called a mini-brain or an organoid.

And earlier this year, a University of California team announced they had grown a mini-brain with neural activity similar to that seen in a preterm infant. That lab-grown organ not only exhibited an eerie similarity to a human foetal brain at 12 to 13 weeks, but it also tried to connect itself with a nearby spinal cord and muscle tissue.

To be sure, these mini-brains have limited functionality  — they help researchers recreate specific diseases and test therapies  — leaving them a long way from what a full-sized model can do.

But sentience, the ability to feel or experience the world around them, may be just around the corner — and all the ethical implications it brings.

When scientists from around the world gathered this week for the 49th annual meeting of the Society for Neuroscience, a team led by San Diego's Green Neuroscience Laboratory issued a dire warning.

These lumps of brain may soon feel the world around them, as noted in the abstract to their presentation, there's an "urgent need" for scientists to wrap their heads around the ethical implications.

"If there's even a possibility of the organoid being sentient, we could be crossing that line," Elan Ohayon of the Green Neuroscience Laboratory tells The Guardian.

"We don't want people doing research where there is potential for something to suffer."

Indeed, imagine an existence of endless scientific torment that lasts indefinitely — without any hope of escape.

The scientists are calling for a set of criteria to be applied to organoids that would determine sentience and treat mini-brains within an ethical framework.

Think of it as a mini-brain's charter of rights.

A 3D illustration of mini-brains, or organoids. Lab-grown mini-brains are essentially stripped down versions of their human equivalents grown from reprogrammed stem cells. (Photo: Meletios Verras/Shutterstock)

For science, the appeal of a "brain on a dish" may already outstrip the ethical implications. A mini-brain can give researchers invaluable insight into the complex workings of the mind, and, along the way, develop effective treatments for what may ail it. Organoids could also save countless animals from testing in labs.

But at what point do these new creations need protection?

"The field is developing quickly, and as we continue down this path, researchers need to contribute to the creation of ethical guidelines grounded in scientific principles that define how to approach their use before and after transplantation in animals," Isaac Chen, a neuroscientist who wasn't involved with the presentation tells Science Alert.

"While today's brain organoids and brain organoid hosts do not come close to reaching any level of self-awareness, there is wisdom in understanding the relevant ethical considerations in order to avoid potential pitfalls that may arise as this technology advances."

Indeed, if we're hurtling down this road, we may have to develop the one thing that can't be grown in a lab: a conscience.

Mini-brains grown in a lab are pushing ethical boundaries
There's an 'urgent need' for rules governing the use of lab-grown brains.