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What would Stuart Little make of it? Mice have been created whose brains are half-human. As a result, the animals are smarter than their siblings. The idea is not to mimic fiction but to advance understanding of human brain diseases by studying them in whole mouse brains rather than in laboratory dishes.

The altered mice still have mouse neurons - the thinking cells that make up around half of all their brain cells. But practically all their glial cells, the ones that support the neurons, are human.

It’s still a mouse brain, not a human brain, says Steve Goldman of the University of Rochester Medical Center in New York. But all the non-neuronal cells are human.

A new study out today in the Journal of Neuroscience shows that traumatic brain injury can disrupt the function of the brain's waste removal system. When this occurs, toxic proteins may accumulate in the brain, setting the stage for the onset of neurodegenerative diseases such as Alzheimer’s and chronic traumatic encephalopathy.

We know that traumatic brain injury early in life is a risk factor for the early development of dementia in the decades that follow, said Maiken Nedergaard, M.D., D.M.Sc., co-director of the University of Rochester Center for Translational Neuromedicine and senior author of the article. This study shows that these injuries set into motion a cascading series of events that impair the brain's ability to clear waste, allowing proteins like tau to spread throughout the brain and eventually reach toxic levels.

The findings are the latest in a series of new insights that are fundamentally changing the way scientists understand neurological disorders. These discoveries are possible due to a study published in 2012 in which Nedergaard and her colleagues described a previously unknown system of waste removal that is unique to the brain which researchers have dubbed the glymphatic system.