Brain Organoids Show Promising Results Integrating into Visual Cortex

A recent paper in the journal Cell Stem Cell reveals that brain organoids—clumps of lab-grown neurons—can integrate with the injured visual cortex of adult rats and respond to visual stimulation like flashing lights. This is the first time human brain organoids have successfully integrated with a host brain's visual system.

H. Isaac Chen, a physician and Assistant Professor of Neurosurgery at the University of Pennsylvania, and his team cultivated human stem cell-derived neurons in the lab for around 80 days before transplanting them into the brains of adult rats that had sustained injuries to their visual cortex. 

The results showed that the grafted organoids had integrated with their host's brain within just three months, becoming vascularized, growing in size and number, sending out neuronal projections, and forming synapses with the host's neurons.

The research group detected the physical connections between the organoid and the brain cells of the host rat using fluorescent-tagged viruses that traced the connections along synapses from neuron to neuron. The activity of individual neurons within the organoid was then measured using electrode probes when the animals were exposed to flashing lights and alternating white and black bars.

The scientists found that numerous neurons within the organoid responded to specific orientations of light, demonstrating that the organoid neurons had integrated with the visual system and had adopted specific functions of the visual cortex.

The team was surprised by the degree of integration they saw within only three months, as previous studies had shown that even nine or ten months after transplanting human neurons into a rodent, they were still not fully mature. This study highlights the potential of brain organoids as a promising approach for brain repair and their ability to adopt sophisticated functions after being inserted into large injury cavities in the brain.

These findings demonstrate the potential for human brain organoids to integrate with and replace large cortical cavities in the brain and support the use of pluripotent stem cell-derived neural tissues to repair brain circuitry.

The next step for the research team is to understand how organoids could be used in other areas of the cortex, as well as the rules that guide their integration with the brain, so that the process can be better controlled and made to happen faster.