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Elizabeth Sowell, Ph.D
Assistant Professor of Neurology
Laboratory of Neuro Imaging, UCLA
Email: esowell@loni.ucla.edu
Mapping Maturational Brain Change |
| Understanding normative changes in brain structure through the various stages of development is paramount to understanding cognitive changes. Considerable progress has been made in these endeavors during the last few decades, given the availability of non-invasive imaging tools such as magnetic resonance imaging (MRI). This revolutionary technological advance allows us to study normally developing children and adolescents because it is virtually without risk, produces exquisite anatomical resolution, and provides the unprecedented opportunity to study individuals at multiple time points. Prior to the advent of these powerful imaging tools, researchers were forced to infer brain changes from post mortem data.
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Figure 1
We used structural MRI and computer image analyses to measure brain changes that occur between childhood and young adulthood. The figures (Figure 1a) show continued brain development between childhood and adolescence on the top, and between adolescence and adulthood on the bottom. Shown in purple are frontal lobe regions that continue to develop during the age ranges studied. Note the dramatic increase in frontal lobe (purple) development that occurs after adolescence (i.e., between adolescence and adulthood).
The movie (Figure 1b, size: 18.0 M) illustrates and explains how the computerized brain image analyses were conducted.
Now we have mapped the spatial and temporal patterns of brain development
between childhood and young adulthood throughout the entire brain in vivo. Our discoveries, particularly of post-adolescent frontal lobe maturation potentially provide new insight for interpreting the occasionally troublesome human behavior through the adolescent years. Teens in typical Western society are notorious for being poor planners, having difficulty interpreting potential consequences of their actions, having difficulty controlling their emotions, and having trouble inhibiting inappropriate behaviors, to name a few of their less endearing qualities. Notably, the frontal lobes are responsible for planning, organization, and impulse control, all functions typically under-developed during adolescence. Previously, erratic behavior during the teen years has been attributed largely to the influx of steroidal hormones around puberty. Our results suggest that on-going changes in brain structure may also play a role.
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Mapping Cortical Change Across the Human Life Span
 
Figure 2
Patterns of cortical maturation and degeneration between childhood and old age likely reflect changing behavioral functions and cognitive abilities across the human life span. Here we used computerized brain image analyses to create 3-dimensional, maps of gray matter change in the human cerebral cortex across 9 decades (7 to 87 years) in 176 normal individuals recruited from the community and studied with MRI. The brain images shown here are maps of the gray matter loss and increases that occur over the human life span. One of the images (on the top), actually shows the age at which the maximal change in any given brain region occurs. Note that gray matter in the green regions in the figure on the top actually increase until about age 30, whereas the regions in purple, pink and blue decrease to a minimum according to the color bar. Presumably, gray matter loss is observed because synaptic pruning, and continued myelination occur during the adolescent period. Both synaptic pruning, and increased myelination are cellular changes that result in a more fine-tuned, efficient brain. Patterns of gray matter loss were most rapid between 7 and 60 years of age after which it was more gradual. Gray matter increases were actually observed in the left posterior temporal region (primary brain language region, shown in white in the figure on the left), where subtle gray matter gain was observed up to age 30 followed by relatively dramatic losses. Results from this study show that the trajectory of maturational and aging effects vary considerably over the cortex, with primary visual, auditory, and limbic cortices, known to myelinate relatively early in development, showing a more linear pattern of aging, than the frontal and parietal neocortex which continue myelination into adulthood. Further, these findings suggest that the posterior temporal cortices, primarily in the left hemisphere where language functions are typically dominant, have a more protracted course of maturation than any other cortical region, and its age-related degeneration may be delayed as well.
The movie shows when and where gray matter is increasing and decreasing across the human life span.
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Sowell ER et al.
In vivo evidence for post-adolescent brain maturation in frontal and striatal regions.
Nature Neuroscience 1999 Oct;2(10):859-61. {Download paper}
Sowell ER et al.
Mapping cortical change across the human life span.
Nat Neurosci. 2003 Mar;6(3):309-15. {Download paper}
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