Brain balls sound like something straight out of a Tim Burton movie: starting as stem cells harvested from patients, they eventually develop into masses of living neurons, jumbled together in misshapen blobs.

Just like the developing brain, these neurons stretch and grow, reaching out skinny branches that grab onto others to form synapses—junctions where one neuron talks with the next.

And they do talk: previous attempts at growing these “brain organoids” found that they spark with electrical activity, much like the webs of neurons inside our heads that lead to thoughts and memories.

• Researchers have constructed a laboratory model for a unique neurological disorder by transforming patients’ own cells using stem cell technology.
• This innovation could also benefit the research of other neurological disorders that may also have roots in a dysfunctional blood-brain barrier, like Alzheimer’s disease and Huntington’s disease.

The human body is a melding of different systems designed to function well together. In some cases, however, a mechanism that protects the body can also cause it harm, like with the specialized shield of endothelial cells — called the blood-brain barrier — that keeps toxins in the blood from entering the brain.