Scientists at the UNC School of Medicine have mapped the
surface of the cortex of the young human brain with unprecedented resolution,
revealing the development of key functional regions from two months before
birth to two years after.
The new cortical development mapping, reported online in the
Proceedings of the National Academy of Sciences, represents a valuable resource
for further research on brain development and offers a powerful new approach to
the study of brain-development conditions such as autism and schizophrenia.
'These results provide an important reference for
exploring and understanding the dynamics of early brain development,' said
study senior author Gang Li, PhD, associate professor of radiology at the UNC
School of Medicine.
The study's first author was Ying Huang, a PhD candidate in
Li's laboratory.
The cortex is a sheet of brain cells that wraps around much
of the rest of the brain. The most evolutionarily advanced brain region, it is
proportionately larger in humans than in other mammals, and is responsible for
higher, distinctively human functions including language abilities and abstract
reasoning.
The third trimester of pregnancy through the first two years
of life is the most dynamic period in cortical development. The cortex thickens
markedly during this interval, and grows at an even faster pace in terms of
surface area, by forming complicated cortical folds.
Disruptions to cortical thickening and expansion in this
phase have been linked to autism and schizophrenia. However, neuroscientists
haven't had as detailed an understanding of this developmental phase as they
would like. In particular, they've had a need for more comprehensive,
high-resolution mapping, across the fetal-to-toddler age range, that divides or
'parcellates' the developing cortex into distinct regions with their
own growth rates -- especially surface area growth rates.
In the study, Li and colleagues performed just such a
mapping. They first gathered a set of 1,037 high-quality magnetic resonance
imaging (MRI) scans of infants in the third-trimester-to-two-year age interval.
The scans came from two other research projects, the UNC/UMN Baby Connectome
Project (BCP) and the Developing Human Connectome Project. The team analyzed
the scan data using state-of-the-art, computer-based image-processing methods,
essentially dividing the cortical surface into a virtual mesh containing
thousands of tiny circular areas, and calculating the surface expansion rate
for each of these areas.
The analysis didn't start with assumptions about the
locations of brain structures or functional regions, but this regionalization
of the brain became evident anyway from the resulting maps, based solely on the
different rates at which areas of the surface expanded. In all, the researchers
defined 18 distinct regions, which they found correlated well with what is
already known about the developing cortex's functional regions.
'All these regions show dramatic expansion in surface
area during this developmental window, with each region having a distinct
trajectory,' Li said.
The maps revealed that each region tended to have the same
developmental path as its counterpart in the cortex's opposite hemisphere. Sex
differences were apparent too. Even when controlling for sex differences in
overall surface area -- male brains having greater area -- there remained
differences in multiple regions. For example, the medial prefrontal region in
the left hemisphere, which is believed to host important functions such as
attention and working memory, became proportionately larger in males early in
the second year of postnatal life.
The analysis also showed that the patterns of cortical
surface area expansion in this early period of life were very different from
the patterns of cortical thickness development, suggesting that these two
measures of brain development involve distinct mechanisms.
All in all, Li said, the mapping provides fundamental new
insights into brain development.
He and his team now plan to extend this approach with MRI
scan datasets that start at earlier ages and end at older ones. They also hope
eventually to study scan datasets covering children who have autism-spectrum or
other neurodevelopmental conditions. Such analyses might offer not only clues
to the origins of these conditions, but also the identification of early signs
or biomarkers, which in the future could be used to administer early and more
effective treatments.
The PNAS paper titled, 'Mapping developmental
regionalization and patterns of cortical surface area from 29 post-menstrual
weeks to 2 years of age' was co-authored by Ying Huang, Zhengwang Wu, Fan
Wang, Dan Hu, Tengfei Li, Lei Guo, Li Wang, Weili Lin, and Gang Li. At
UNC-Chapel Hill, the BCP MRI scans were conducted at the UNC Biomedical Research
Imaging Center (BRIC), led by Weili Lin, PhD.
Funding was provided by the National Institutes of Health
(MH116225, MH117943, MH109773, MH123202, 1U01MH110274) and the UNC/UMN Baby
Connectome Project Consortium.
Resource: Science Daily