Dec. 4—Neuroscientists at the Massachusetts Institute of Technology (MIT) have discovered by studying rats that the fMRI signal changes during the first few weeks of life, according to a study published online November 25, in the journal Nature Neuroscience.
"Our study lays a foundation for using fMRI to study development," explains senior author Alan Jasanoff, associate member of the McGovern Institute and assistant professor of nuclear science and engineering. "It establishes an approach that others can apply to investigate many aspects of neurodevelopment in very young animals."
A weak fMRI signal in young animals could mean less neural activity, or it could simply mean that MRI cannot detect that activity because of weak neurovascular coupling, Jasanoff said.
To resolve any uncertainty about fMRI signals, Jasanoff and colleagues compared fMRI signals with direct electrical recordings of neuronal activity as they stimulated rats' forepaws. In animals younger than 11 days, they could not detect fMRI signals, even though electrical recordings showed that the brain was responding to stimulation. The fMRI signals became both stronger and faster as the animals matured, until they approached adult levels by about 3 weeks of age. The age of the rodents correspond approximately to 7-8 years in terms of human brain development, according to MIT researchers.
By compensating for these age-related changes, the authors were able to track the development of connections between different touch-sensitive brain regions as the animals matured.
The results of the study suggest that a key player in brain development is carbonic anhydrase (CA), a well-known enzyme that helps remove carbon dioxide from the blood. Age-related increases in CA activity corresponded to the changes in the fMRI signal, and drugs that block the activity of this enzyme in adult animals caused the fMRI signal to "regress" to that seen in younger animals.
“CA is an important target for drugs used to treat diverse conditions, including glaucoma, altitude sickness and epilepsy, so it will be interesting to determine whether such drugs alter the relationship between activity and blood flow in the adult human brain,” Jasanoff said.