HOW CHILDREN'S BRAINS MEMORIZE MATHS FACTS
As children learn
basic arithmetic, they gradually switch from solving problems by counting on
their fingers to pulling facts from memory. The shift comes more easily for
some kids than for others, but no one knows why.
Now, new brain-imaging
research gives the first evidence drawn from a longitudinal study to explain
how the brain reorganizes itself as children learn math facts. A precisely
orchestrated group of brain changes, many involving the memory center known as the
hippocampus, are essential to the transformation, according to a study from the
Stanford University School of Medicine.
The results, which
will be published online Aug. 17 inNature Neuroscience, explain brain
reorganization during normal development of cognitive skills and will serve as
a point of comparison for future studies of what goes awry in the brains of
children with learning disabilities.
"We wanted to
understand how children acquire new knowledge, and determine why some children
learn to retrieve facts from memory better than others," said Vinod Menon,
PhD, professor of psychiatry and behavioral sciences and the senior author of
the study. "This work provides insight into the dynamic changes that occur
over the course of cognitive development in each child."
The study also adds to
prior research into the differences between how children's and adults' brains
solve math problems. Children use certain brain regions, including the
hippocampus and the prefrontal cortex, very differently from adults when the
two groups are solving the same types of math problems, the study showed.
"It was
surprising to us that the hippocampal and prefrontal contributions to
memory-based problem-solving during childhood don't look anything like what we
would have expected for the adult brain," said postdoctoral scholar
Shaozheng Qin, PhD, who is the paper's lead author.
Charting the Shifting
Strategy
In the study, 28
children solved simple math problems while receiving two functional magnetic
resonance imaging brain scans; the scans were done about 1.2 years apart. The
researchers also scanned 20 adolescents and 20 adults at a single time point.
At the start of the study, the children were ages 7-9. The adolescents were
14-17 and the adults were 19-22. The participants had normal IQs. Because the
study examined normal math learning, potential participants with math-related
learning disabilities and attention deficit hyperactivity disorder were
excluded. The children and adolescents were studying math in school; the
researchers did not provide any math instruction.
During the study, as
the children aged from an average of 8.2 to 9.4 years, they became faster and
more accurate at solving math problems, and relied more on retrieving math
facts from memory and less on counting. As these shifts in strategy took place,
the researchers saw several changes in the children's brains. The hippocampus,
a region with many roles in shaping new memories, was activated more in children's
brains after one year. Regions involved in counting, including parts of the
prefrontal and parietal cortex, were activated less.
The scientists also
saw changes in the degree to which the hippocampus was connected to other parts
of children's brains, with several parts of the prefrontal, anterior temporal
cortex and parietal cortex more strongly connected to the hippocampus after one
year. Crucially, the stronger these connections, the greater was each
individual child's ability to retrieve math facts from memory, a finding that
suggests a starting point for future studies of math-learning disabilities.
Although children were
using their hippocampus more after a year, adolescents and adults made minimal
use of their hippocampus while solving math problems. Instead, they pulled math
facts from well-developed information stores in the neocortex.
Memory Scaffold
"What this means
is that the hippocampus is providing a scaffold for learning and consolidating
facts into long-term memory in children," Menon said. Children's brains
are building a schema for mathematical knowledge. The hippocampus helps support
other parts of the brain as adultlike neural connections for solving math
problems are being constructed. "In adults this scaffold is not needed because
memory for math facts has most likely been consolidated into the
neocortex," he said. Interestingly, the research also showed that,
although the adult hippocampus is not as strongly engaged as in children, it
seems to keep a backup copy of the math information that adults usually draw
from the neocortex.
The researchers
compared the level of variation in patterns of brain activity as children,
adolescents and adults correctly solved math problems. The brain's activity
patterns were more stable in adolescents and adults than in children,
suggesting that as the brain gets better at solving math problems its activity
becomes more consistent.
The next step, Menon
said, is to compare the new findings about normal math learning to what happens
in children with math-learning disabilities.
"In children with
math-learning disabilities, we know that the ability to retrieve facts fluently
is a basic problem, and remains a bottleneck for them in high school and
college," he said. "Is it that the hippocampus can't provide a
reliable scaffold to build good representations of math facts in other parts of
the brain during the early stages of learning, and so the child continues to
use inefficient strategies to solve math problems? We want to test this."
Other Stanford
co-authors of the study are former postdoctoral scholar Soohyun Cho, PhD;
postdoctoral scholar Tianwen Chen, PhD; and Miriam Rosenberg-Lee, PhD,
instructor in psychiatry and behavioral sciences.
The research was
supported by the National Institutes of Health (grants HD047520, HD059205 and
MH101394), Stanford's Child Health Research Institute, the Lucile Packard
Foundation for Children's Health, Stanford's Clinical and Translational Science
Award (grant UL1RR025744) and the Netherlands Organization for Scientific Research.
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