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Newborn mice implanted with human brain cells grew up to be significantly more intelligent than normal mice, according to a new study.

The latest findings published in the journal Cell Stem Cell revealed that grafting human glial cells, star-shaped cells that surround and support the brain's neurons, into the brains of mice "sharply enhanced" the rodents' cognitive abilities.

The new study revealed that these newly engineered mice significantly outperformed their normal counterparts on learning and memory tests, leading scientists to suggest that supportive astrocytes or glial cells played a major role in the evolution of the modern human brain.  Besides providing insight into the development of the human brain, investigators believe the latest findings could also have major implications for the treatment of neurological and psychiatric disorders in humans.

Researchers say that as the human brain evolved, supportive glial cells became larger and more varied than those in the brains of rodents. Unlike neurons, glial cells do not conduct electrical impulses.  Instead, they maintain homeostasis, form insulating myelin and provide support and protection for neurons in the brain. 

Researchers theorized that the development of larger and more complex glial cells allowed the human brain to develop more connections and process more complicated signals.

Scientists tested their theory by transplanting stem cells that produce human glial cells into the brains of mice before birth. As the mice grew into adulthood, a network of human glial cells developed along with their normal brain cells.

"The human glia cells essentially took over to the point where virtually all of the glial progenitor cells and a large proportion of the astrocytes in the mice were of human origin, and essentially developed and behaved as they would have in a person's brain," co-author Dr. Steven Goldman of the University of Rochester Medical Center said in a university release.

After conducting a series of brain scans, researchers found that experimental mice had brain signals that traveled significantly faster than normal mice and responded more quickly to electrical stimulation. 

Researchers also performed a series behavioral experiments designed to test memory and learning ability.  They found that the experimental mouse, which researchers dubbed the human glial chimeric mouse, was also better at finding its way through a maze and at recognizing familiar objects when placed in new locations.  What's more, experimental mice learned to fear a particular noise, which was always followed by an electric shock whereas normal mice could not associate one with the other.

"The bottom line is that these mice demonstrated an increase in plasticity and learning within their existing neural networks, essentially changing their functional capabilities," said Goldman.

"This tells us that human glia have a species-specific role in intellectual capability and cognitive processing. While we've suspected for a while that this might be the case, this is really the first proof of this point," he added.

Previously, Goldman and his team also found a way to generate stem cells that produced glial cells from the skin of human patients with certain brain diseases. The technique would allow researchers to study a number of human psychiatric and neurological disorders.  Researchers explain that by implanting these glial stem cells into mice, they would be able to assess the role of glial cells in these disorders, as well as test different treatment strategies that target abnormal glial function.  Researchers are currently testing these experiments with cells from patients with schizophrenia and Huntington's disease.