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Human Brain Cells Alive in Mouse Brains

The views expressed are those of the author and are not necessarily those of Scientific American.

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Into brains of newborn mice, researchers implanted human “progenitor cells.” These mature into a type of brain cell called astrocytes (see below). They grew into human astrocytes, crowding out mouse astrocytes. The mouse brains became chimeras of human and mouse, with the workhorse mouse brain cells – neurons – nurtured by billions of human astrocytes.

Neuroscience is only beginning to discover what astrocytes do in brains. One job that is known is that they help neurons build connections (synapses) with other neurons. (Firing neurotransmitter molecules across synapses is how neurons communicate.) Human astrocytes are larger and more complex than those of other mammals. Humans’ unique brain capabilities may depend on this complexity.

Human astrocytes certainly inspired the mice. Their neurons did indeed build stronger synapses. (Perhaps this was because human astrocytes signal three times faster than mouse astrocytes do.) Mouse learning sharpened, too. On the first try, for instance, altered mice perceived the connection between a noise and an electric shock (a standard learning test in mouse research). Normal mice need a few repetitions to get the idea. Memories of the doctored mice were better too: they remembered mazes, object locations, and the shock lessons longer.

Astrocytes (red) embedded among neurons (green)

Astrocytes (red) embedded among neurons (green)

The reciprocal pulsing of billions of human and mouse brain cells inside a mouse skull is a little creepy. Imagine one of these hybrid mice exploring your living room. Would you feel like a Stone Age tribesman observing a toy robot? Does the thing think?

Neuroscience has no idea – none – of how a mind rises like a genie from the fleshy human brain. It supposes, however, that the magic trick’s spoiler will turn out to reside in physics and chemistry of brain cells. That is the discipline’s fundamental assumption. Nowhere else can the mystery be hiding.

But we have no idea what’s happening as billions of human astrocytes animate rodent awareness inside the tiny skulls. And “awareness” is one quality of “mind.” Do billions of human cells have no effect on mouse awareness? That seems unlikely.


S. H. Saey, Mice get brain boost from transplanted human tissue. Science News, Vol. 183 #7, April 6, 2013

Xiaoning Han, et al., Forebrain Engraftment by Human Glial Progenitor Cells Enhances Synaptic Plasticity and Learning in Adult Mice, Cell Stem Cell, vol. 12, No.3, March 7, 2013.

John McCarthy About the Author: John McCarthy is a science writer whose site, strives to make current research on life sciences accessible to non-scientists. Science and education have been his avocations, during a long career in affordable housing. An attorney and a Yale Law graduate, he was for many years a senior executive in a non-profit that invested billions of dollars to rebuild New York City’s low-income neighborhoods after the City’s near-bankruptcy in the 1970’s. Follow on Twitter @truthfromerror.

The views expressed are those of the author and are not necessarily those of Scientific American.

Comments 8 Comments

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  1. 1. N a g n o s t i c 9:32 am 05/9/2013

    This is cool stuff. And of course mice “think” – with or without human astrocytes. The research and preliminary results here are potentially Earth-shaking, technologically and philosophically.

    I do feel some concern for the mice (hey, I’m self-aware and appreciate Mozart – stop experimenting on me), but eggs have to be cracked to get the omelette.

    I believe infusing human brains with appropriate, task-specific animal astrocytes would offer us all a way to enjoy our social welfare states without the price of inflated public employee compensation packages. Canine or bovine neuron infused ‘people’ could work for nearly nothing. Brave New World, here we come!

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  2. 2. DougAlder 12:21 pm 05/9/2013

    Sorry – can’t help it :)

    Pinky: What’ll we do tonight Brain

    Brain: Same thing we do everynight Pinky, try to take over the world

    Link to this
  3. 3. malonesq 2:15 pm 05/9/2013

    This blog piece strongly reminds me of “Flowers for Algernon” of course – that very poignant sf story later made into the movie “Charlie” with Cliff Robertson.

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  4. 4. greenhome123 2:31 pm 05/9/2013

    Most Christians believe that humans have an afterlife, but that animals don’t. So, if you want to make a Christian question their faith, simply ask them if a mouse with human brain cells in it will have an afterlife :-)

    Link to this
  5. 5. souhjiro 4:00 pm 05/9/2013

    They’re dinky
    They’re Pinky and The Brain, Brain, Brain, Brain
    Brain, Brain, Brain, Brain

    Link to this
  6. 6. zstansfi 10:47 pm 05/9/2013

    I haven’t read the article, but “billions of human astrocytes” is way off. Perhaps “millions” is correct? Even then, this would be a massive replacement of the mouse brain astrocyte population.

    Link to this
  7. 7. zstansfi 11:23 pm 05/9/2013

    Just finished a quick once-over of the paper. The authors do not formally quantify the number of transplanted astrocytes, though glancing at the figures suggests that they are widespread, but fairly sparse. Given that a mouse brain has ~70 million neurons (e.g., and many fewer astrocytes, it’s probably a better bet to say that “thousands” of astrocytes were grafted.

    Also, the effects of engraftment on behavior and synaptic function were pretty modest (in a number of cases, differences were null). Also, the authors never show that “On the first try… altered mice perceived the connection between a noise and an electric shock”. Anyways, it’s a feature of conditioning paradigms that rodents quickly detect the tone-shock relationship: that’s why they’re so popular.

    So, I think it’s a little early to speculate on the likelihood that these cells significantly alter “mouse awareness” in any powerful way.

    I will consider blogging the paper in the near future, see

    Link to this
  8. 8. stargene 5:05 am 05/10/2013

    Ummm… This may explain the rapid disappearance
    of certain items in our storage shed, along with
    little scrawled notes in a very tiny script, on
    the floorboards, about two inches off the floor.
    Possibly thank-you notes for all the missing
    bird seed and strawberry jam jars.

    Link to this

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