Human neurons implanted in a rat’s brain respond to flashing lights

Laboratory-grown neurons were transplanted into the brains of rats with damaged visual cortex. After two months, the neurons responded when the rats saw flashing lights

from Jason Arunn Murugesu

Human neurons have been integrated into the brains of adult rats with damaged visual cortex, even taking over some functions of the organs’ visual system.

Isaac Chen of the University of Pennsylvania and his colleagues wondered if transplanting a clump of lab-grown neurons, called organoids, into the brains of rats with a damaged visual cortex would restore the area’s function.

They first cultured human stem cells, which can develop into many different cell types, for 80 days, creating a three-dimensional tissue culture of cerebral cortex cells. These form the outer layer of the brain and play key roles in several functions such as vision.

Next, the team removed part of the visual cortex in 46 rats before transferring the organoids to these damaged cortices.

The rats were studied for three months. After two months, the organoids showed a neuronal response. This was measured by inserting an electrode into their transplanted organoid while the animals viewed a series of images on a screen.

One set of images consisted of blinking lights, while another featured alternating black and white lines in various orientations, such as horizontal and diagonal.

The neuronal response of the organoids changed alongside the blinking lights and depending on the orientation of the black and white lines. This suggests that the neurons are integrating into the rats’ brains and taking over some of the function of their visual system, says Chen.

In another part of the experiment, the researchers compared the rats with the transplanted organoids to rats without damage to the visual cortex. The neuronal responses were relatively similar, but fewer neurons responded to the light in the rats with the organoid grafts compared to their undamaged counterparts, Chen says.

The researchers did not measure whether the organoid grafts improved the rats’ vision.

“There is definitely room for improvement in understanding what factors are driving this integration and how we can potentially optimize this integration,” says Chen.

The next step is to repeat this experiment by removing other cortices in a rat’s brain, such as the motor cortex, he says. “We hope that this study will move us in the direction of restoring function using these organoids and, in the long term, lead to transplanting organoids in patients with brain injuries,” says Chen.

“This study shows that transplanted organoids not only integrate into the host tissue, but are also able to restore lost complex functions,” says Laura Ferraiuolo from the University of Sheffield, UK.