Building a better brain
It's never too late for renovation
By AMY ADAMS
Growing a brain is like following a blueprint for any construction project — the design scheme leaves plenty of room for improvements. Want some added functionality?
Enhanced math skills? Superior problem-solving abilities? Just make your request early enough and the human brain will happily adjust to accommodate the request.
The only problem is timing.
Most major brain construction takes place before we are born, leaving only a few key areas unfinished. Our ability to use vision to distinguish objects in the world around us isn’t hammered out for several months. Likewise, our abilities to learn languages, coordinate movements and solve puzzles gradually mature as we age.
The question is what, if anything, can we do to influence the neuronal wiring in the areas of the brain that make these behaviors possible? And what’s the likelihood of successful remodeling projects in adulthood, after construction has officially completed?
That depends, says Eric Knudsen, PhD, a professor of neurobiology, who investigates brain development using barn owls as study subjects. In his work, he has found that barn owls learn certain skills best when they are young. However, they can still pick up new skills well into their golden years, especially if their brains are primed with the best early experiences. Although barn owls clearly don’t mimic the range of human skills and emotions, this work does suggest that life experiences physically alter the way the brain is constructed.
Knudsen and his colleagues are piecing together how influences such as a supportive environment or a well-chosen toy can alter how the brain itself is wired in a permanent way. This work could help parents and teachers build the best possible brains in their young charges. It also hints at ways adults can pick up new skills long after they are done playing with mind-expanding toys.
Laying the foundation
Early in the brain’s formation, the neurons interconnect to form a communications web. This network allows the brain to quickly carry out complicated information-processing tasks. For an example, look at vision. These neural connections allow signals to travel from the eye to the vision center in the back of the brain and on to other brain regions that are able to name the image (tree), understand the meaning of the image (low branch), and make appropriate decisions (duck!).
Each connection, called a synapse, adds to the brain’s computing power, so it’s no surprise that humans generally have more synapses than our less-intellectual cousins in the animal kingdom.
But despite their obvious importance, the molecules that allow these new synapses to form were unknown until neurobiology professor Ben Barres, MD, PhD, found them just recently. Developing mouse brains hold lots of these molecules, called thrombospondins. Mature mouse brains, which make few new synapses, have almost none. Studies have also found at least one thrombospondin in much higher quantities in the brains of adult humans compared with adult chimpanzees. Barres says this could be one explanation for our longer-lasting ability to learn new skills throughout life.
Modifying the blueprint
The synapses that form as the brain develops aren’t hard-wired. Rather than providing a precise blueprint, our genes simply lay out which groups of neurons should probably keep in touch. The specifics of which neurons form which connections is a mystery Stephen Smith, PhD, a Stanford professor of molecular and cellular physiology, has started unraveling. He has discovered some rules that govern why one neuron makes a certain connection and its neighbor doesn’t. It all comes down to noise.
Smith and his colleagues have built a high-energy laser microscope that fills an entire room to make digital movies of brain cells growing in a tiny, see-through fish barely larger than a pinhead. These stunningly detailed movies are providing the first glimpses of processes fundamental to the “wiring up” of all brains. In recent experiments reported in the April 21, 2005, Nature, Smith’s graduate student Jackie Hua combined this movie-making capability with DNA engineering to explore how experience in a newborn animal can guide its brain’s growth. In the studies, Hua held a 3-day-old fish in a slab of breathable gelatin and filmed individual neurons, altered to be less electrically active and to glow green.
At first, these neurons sent exploratory projections in all directions, just like their neighbors. And with their quieter demeanor, these glowing neurons eventually pulled back most of their projections without forming many new synapses. But when Hua chemically quieted the neighboring neurons, the green cells had a fighting chance and formed a more substantial network of connections.
According to Smith, this system is a miniature model for how human brains form and react to experiences. Neurons that are regularly active — such as those getting called upon to solve tasks or make particular language-related sounds — will then form more extensive connections throughout the brain. In Smith’s fish, a nerve with more connections will help the fish see whatever shape or movement that neuron detects. The same logic applies to parts of the brain that process language or solve problems: that is, the more use those neurons get when they are developing, the more total brainpower they’ll contribute.
A matter of timing
But no amount of reading quadratic equations to a newborn will help the child’s math skills — the math-processing neurons just aren’t ready yet. Neurons can’t respond to potentially brain-altering events until they are at the right developmental stage. And for now, determining the precise moment a particular person is ready to learn any particular skill is impossible.
But that’s OK, says Knudsen.
His work with owls suggests that building the best possible brain is all about preparation. True, a child can’t learn algebra until the brain is ready. But how well the child picks up that new skill can be altered by early experiences that prime those neurons and their connections for action.
Knudsen’s work involves prism lenses that shift the owl’s vision to the right or left. Young owls easily adjust to a slightly shifted world and manage to hunt successfully. Older owls can learn to navigate the world with the lenses on, but only if Knudsen and his colleagues use prisms that shift the owl’s vision in small increments.
Most remarkably, Knudsen found that after hunting with the lenses as juveniles, the owls could quickly readjust as adults — unlike their less-experienced peers. Within the brain, he found that neurons from a sensory region had formed synapses with two places in a navigation center. One location was the same as in owls that had never used the lenses. The other was a location in the navigation center that allowed the owls to compensate for the shifted lenses. The early experience had forever altered the owl’s internal wiring.
Knudsen says the owls’ early hunting experiences suggest what a rich, stimulating environment provides for a child’s developing brain. Those fancy toys with colors, sounds, textures and puzzles aren’t exactly the same as teaching a child to play Mozart. But the extra synapses formed because of those experiences might help with both Mozart and math later on. Research over the past few decades also shows that kids who have the richest environment growing up are also more emotionally stable and able to form normal relationships.
That brain-building environment doesn’t follow a simple recipe, Knudsen says. But in the lab, animals that have the most stimulating environment with toys and distractions are the best learners. “If you want to promote higher-order processing, the building blocks have to be in place,” he says. These building blocks include brain cells poised for future learning with a dense network of interconnections.
As a member of the National Scientific Council on the Developing Child, which disseminates research findings on early childhood development to the media, public and policy-makers, Knudsen recommends that kids spend time in environments that stimulate all parts of the brain. “Exposing young kids to enriching experiences is perfect,” Knudsen says. There’s no timeline for these experiences. It’s the cumulative impact of a rich childhood that adds up to a brawny brain, not any one experience or any particular toy or game at a set time.
“The brain has tremendous potential to learn during the early phases of development. If you take advantage of that you can do amazing things,” he says.
What all this research adds up to is good news for those who had rich and rewarding early experiences. Their brains are primed for learning new skills throughout life. As for adults hoping to make late-term modifications to their brains’ wiring, all hope isn’t lost. Knudsen’s work shows that older owls can still learn, if somewhat more slowly than juveniles. As with any remodel, it’s less efficient than starting from scratch, but with patience even fully mature brains can squeeze out some new connections.
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