A team of Japanese researchers has successfully grown miniature brain-like structures that show signs of activity similar to neural networks in the human brain, potentially leading to a better understanding of how the brain works, the alleviation of animal testing, and the advancement of disease and drug research.

Publishing their work in Stem Cell Reports, the researchers built upon the work of “cerebral organoids", artificially grown three-dimensional human tissue bundles that resemble the region of the brain called the cerebrum. This area is the largest and most complex tissue in the brain and covers a wide range of human activity, from motor and sensory skills to our thoughts and memory. 

"Because they can mimic cerebral development, cerebral organoids can be used as a substitute for the human brain to study complex developmental and neurological disorders," said study corresponding author Jun Takahashi of Kyoto University in a statement.

In their build-a-brain lab, researchers took a cluster of pluripotent stem cells and cultured them in an environment mimicking that required for brain development. Within three months, individual cells began to grow from the tissue and organize themselves into clusters and individual networks. The team then studied the calcium ion activity to see how and when neurons fired.

"In our study, we created a new functional analysis tool to assess the comprehensive dynamic change of network activity in a detected field, which reflected the activities of over 1,000 cells," said study author Hideya Sakaguchi. "The exciting thing about this study is that we were able to detect dynamic changes in calcium ion activity and visualize comprehensive cell activities."

In the beginning, they noticed that the neurons only fired individually. As networks and connections grew, they began to work together and fire in synchrony – a mechanism that scientists believe forms the foundation of brain functions. The neurons would also sometimes fire spontaneously, similar to how new connections are believed to form in the brain.

"We believe that our work introduces the possibility of a broad assessment of human cell-derived neural activity," Sakaguchi said. 

Altogether, their work may lead to the discovery of new drugs, a better understanding of neuropsychiatric disorders, and the potential for regenerating parts of the brain that might have been lost from disease or physical trauma.

Let’s be clear here: The mini brains aren’t actually capable of thinking. Ethicists are concerned that scientists could one day mimic the developmental process of the brain so well that we could create consciousness, a concern that researchers say is unlikely given cerebral organoids cannot form connections with their surrounding environments.

"Consciousness requires subjective experience, and cerebral organoids without sensory tissues will not have sensory input and motor output," Sakaguchi said.

Regardless, the manufactured brain-like bundles could help us understand how human brains function.