- A new study reveals how brains of individuals who had an entire hemisphere removed during childhood continue to function.
- The remaining half of the brain reorganizes itself and learns to take additional responsibilities to perform everyday tasks.
A few neurological conditions such as perinatal infarction (stroke) and malformations of cortical development require hemispherectomy, a very rare surgical procedure in which a cerebral hemisphere (half of the brain) is disconnected or removed.
Hemispherectomy was first performed in 1928 to treat the most aggressive cancer, glioblastoma. However, the procedure was later adopted to treat children who have intractable seizures and brain malformations where damage is confined to half of the brain.
After the surgery, most of the children are able to talk, read, walk and do everyday tasks. In 20% of cases, they retain astonishingly high levels of cognitive and sensorimotor abilities.
Recently, an international team of researchers revealed why some people recover exceptionally well from the hemispherectomy. Actually, the remaining half of the brain reorganizes itself. They were able to identify various networks that pick up the slack for the removed/disconnected tissue.
Comparing ‘Full Brain’ With ‘Half Brain’
A healthy brain is comprised of a reliable set of functional networks that is responsible for cognition, emotion, and behavior.
For the first time, researchers analyzed the resting-state functional networks across the entire hemisphere in 6 adults who had childhood hemispherectomy. To obtained detailed scans of their brain, the team used state-of-the-art high-resolution neuroimaging techniques.
They then compared the intrinsic functional architecture in the single hemisphere of healthy adults and hemispherectomy cases. To achieve the highest sensitivity to individual anatomy, they used a surface-based registration approach.
MRI of an adult’s brain who had an entire hemisphere removed in childhood | Caltech Brain Imaging Center
They found a striking similarity of connectivity patterns that define typical resting-state functional networks in adults with hemispherectomy. That’s why people who had hemispherectomy in childhood behave like other typically developed adults.
Reference: Cell Report | DOI:10.1016/j.celrep.2019.10.067
It’s quite surprising because most brain networks require both hemispheres to function. For example, processing cognitively challenging information requires both sides of the cerebral cortex.
The hemispheres communicate with each other via a thick band of 250 million never fibers known as the corpus callosum. The right hemisphere controls the left side of the body while the left hemisphere controls the right side of the body. The bottom line is you need both to get synchronized and perform a task.
Results Are Encouraging
However, the team discovered that while the brain networks remained the same in adults with just one hemisphere, different parts (within a hemisphere) strengthened the existing connections. These parts (which are responsible for different functions such as face recognition, processing sensorimotor information) learned to communicate with each other more frequently than normal brains.
In other words, parts of the one hemisphere have gradually learned to take additional responsibilities to perform most of the everyday tasks.
The findings are encouraging for families and scientists studying the aftereffects of hemispherectomy. In the next study, researchers will include more patients with a broad range of brain disorders and injuries, to better understand the intrinsic mechanisms of brain organization.