Dutch researchers charted changes in T1-weighted MR images of young to middle-age adults over three time points and found a statistically significant increase in intracranial volume between the ages of 20 and 35. That trend reverses, however, and intracranial volume begins to decrease by the time adults are in their 40s.
"Intracranial volume is a key biological marker, and changes in the intracranial volume during the lifespan can teach us about the biology of development, aging, and gene X environment interactions," wrote lead author Yaron Caspi, PhD, and colleagues from University Medical Center Utrecht. "However, whether intracranial volume changes with age in adulthood is not resolved."
Intracranial volume has long served as a way to evaluate medical and physiological conditions such as schizophrenia and dementia. However, to what degree intracranial volume might fluctuate during adulthood and how those changes might influence brain activity and function has not been explored in depth.
Thus, Caspi and colleagues set out to see if such changes occurred in this longitudinal study, in which they used their own internally created algorithm to measure the intracranial volume of young and middle-aged adults who had undergone T1-weighted imaging on a 1.5-tesla MRI scanner (Philips Healthcare) at three different time points.
The subjects came from a previous study on schizophrenia and were divided into three groups: a healthy control group, patients diagnosed with schizophrenia, and children of schizophrenics. The data included a total of 528 T1-weighted images from the first MRI scan, 378 images from the second scan, and 309 results from the third and final scan. The age span at the first time point was between 16 and 55 years, with an average period between consecutive follow-up scans of 3.32 (± 0.3) years.
Overall, the researchers found no significant changes in the individual intracranial volume between young adults and people in their 50s. The finding "suggests that if longitudinal changes in the intracranial volume between early adulthood to the sixth decade of life exist, they are minimal and amount to a value of the order of 0.1% per year of the total intracranial volume," Caspi and colleagues wrote.
Between the ages of 20 and 35, however, the researchers found statistically significant changes, with a total average intracranial volume increase of 2.9 ml, or approximately 0.5 ml (0.03%) per year beginning immediately at age 20. By age 55, total average intracranial volume began to decrease at a rate of 1.3 ml (0.09%) per year.
"Interestingly, the decade of life where we found the intracranial volume to change direction between growth and decline corresponds well to the decade of life where the amount of white matter in the brain stops growing and starts shrinking or starts accelerated shrinking," the researchers added. "This raises the possibility that these two processes result from a shared genetic cause, which will be interesting hypothesis to check in future works."
Caspi and colleagues concluded by hoping their research will "inspire future longitudinal analysis of intracranial volume and other brain biomarkers aging-trajectories, especially using big data cohorts. We believe that conducting longitudinal-designed studies over multiple conditions and in multiple populations is the most trustworthy method to obtain accurate measures of brain aging and its dependency on various genetic and environmental factors."
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