The lentil-sized grey blob of human brain cells were seen to spontaneously send out tendril-like connections to link up with the spinal cord and muscle tissue, which was taken from a mouse.
The muscles were then seen to visibly contract under the control of the so-called brain organoid.
The latest blob shows similarities, in terms of the variety of neurons and their organisation, to the human foetal brain at 12-16 weeks of pregnancy.
However, the scientists said the structure was still too small and primitive to have anything approaching thoughts, feelings or consciousness.
Alongside the organoid, the scientists added in a 1mm-long spinal cord, taken from a mouse embryo, and the surrounding back muscle.
The brain cells automatically began to send out neuronal connections, linked up with the spinal cord and began sending electrical impulses, which caused the muscles to twitch.
“It’s extremely exciting to see evidence of functional nerve tracts growing out of developing human brain tissue and innervating other tissues,” he said. »