It was often thought that the speed of information transmitted between brain regions stabilized during early adolescence. a study in neuroscience of nature by Mayo Clinic researchers and colleagues in the Netherlands found that transmission rates continue to increase well into early adulthood.
Because problems like anxiety, depression, and bipolar disorders can emerge in late adolescence and early adulthood, a better understanding of brain development may help clinicians offer therapies to treat these disorders.
“A fundamental understanding of the developmental trajectory of brain circuitry can help identify sensitive periods of development when clinicians can offer therapies to their patients,” says Dora Hermes, Ph.D., a Mayo Clinic biomedical engineer and author study principal.
Called the human connectome, the structural system of neural pathways in the brain or nervous system develops as people age. But how structural changes affect the speed of neuronal signaling has not been well described.
“Just as the transit time of a truck would depend on the structure of the road, the speed of signal transmission between areas of the brain depends on the structure of the neural pathways,” explains Dr. Hermes. “The human connectome matures during development and aging, and can be affected by disease. All of these processes can affect the speed of information flow in the brain.” In the study, Dr. Hermes and his colleagues stimulated pairs of electrodes with a brief electrical pulse. to measure the time it took for signals to travel between brain regions in 74 research participants between the ages of 4 and 51. Intracranial measurements were performed in a small population of patients who had been implanted with electrodes for epilepsy monitoring at the University Medical Center in Utrecht, the Netherlands.
Response delays in connected brain regions showed that transmission rates in the human brain increase during childhood and even into early adulthood. They stabilize around 30 to 40 years of age.
The team’s data indicates that adults’ transmission speeds were about twice as fast compared to those typically found in children. Transmission speeds were also typically faster in subjects in their 30s or 40s compared to adolescents.
The transmission speed of the brain is measured in milliseconds, a unit of time equal to one thousandth of a second. For example, the researchers measured the neural speed of a 4-year-old patient in 45 milliseconds for a signal to travel from the frontal to the parietal regions of the brain. In a 38-year-old patient, the same pathway was measured at 20 milliseconds. For comparison, the blink of an eye takes between 100 and 400 milliseconds.
The researchers are working to characterize the connectivity driven by electrical stimulation in the human brain. One of the next steps is to better understand how transmission rates change with neurological diseases. They are collaborating with pediatric neurosurgeons and neurologists to understand how diseases change transmission rates compared to what would be considered within the normal range for a given age group.
The research is supported by the National Institute of Mental Health of the National Institutes of Health (R01MH122258).
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