Brain activity in baby girls seems to be more complex than that in baby boys, a new study has found. For the research, Joel Frohlich at the University of Tubingen in Germany and his colleagues used an imaging technique called magnetoencephalography (MEG) to measure the magnetic fields produced by the brain's electrical currents in fetuses and babies to sound stimuli. The team found that the complexity of signals in the brain seems to decrease as the nervous system develops in fetuses and babies - and does so significantly faster in males compared with females.
According to New Scientist, the researchers used MEG in 43 third-trimester fetuses and 20 babies, aged between 13 and 59 days old. The sound stimuli consisted of various arrangements of beeps. One sequence was made up of four beeps, each lasting 200 milliseconds and separated by 400 millisecond intervals. This was played to the fetuses via a "sound balloon" squeezed between the pregnant person's abdomen and the MEG sensors.
The team then recorded their magnetic brain activity upon hearing the sound stimuli. They calculated several different measures that reflect the complexity of the MEG signal, using algorithms that determine, for example, how difficult it is to process.
The researchers explained that in adults with no known health conditions, higher levels of neural complexity are associated with better performance and faster reaction times in various executive functions, such as planning and decision-making. On the other hand, low levels are associated with states in which the capacity for information processing is reduced, such as while under general anaesthesia and during non-rapid eye movement sleep.
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Therefore, the researchers hypothesised that MEG signal complexity would rise among the fetuses as gestation progressed and among the babies as they aged. However, they were surprised to find the decrease occurring significantly faster among the male fetuses and babies than the female ones.
The reason for this decrease is unclear, but experts believe that one possible explanation is that neural complexity measures different processes as the brain develops. "The developing brain eliminates cells and connections that are unnecessary, constraining the number of ways in which the brain can respond to a stimulus," said Mr Frohlich.
"As the brain matures, it moves toward ordered patterns of neural connections, which tell it how to respond to stimuli, such as the beeps in our experiment. A more developed brain has fewer ways of responding to that stimulus, and thus lower complexity. If we were to look at spontaneous activity, we might see something different.," he explained.
The team suspects the variation between the sexes might be due to "underlying differences in how the nervous system develops in boys and girls". However, the researchers did not follow the babies beyond the end of the study and it is therefore unclear whether this variation persists.
