Children and adolescents with a higher body mass index show distinct differences in their brain activity and the ways different brain regions communicate with one another. These neurological patterns point to a reduction in the brain’s natural inhibitory systems, which might make it harder for to change deeply ingrained habits. The findings were recently published in Clinical Neurophysiology.
The human brain continues to develop and rewire itself heavily throughout childhood and adolescence. The frontal cortex, a brain area responsible for impulse control and complex decision making, is among the last regions to fully mature. During this lengthy developmental window, the brain is highly sensitive to environmental factors. Such external influences include nutrition, physical activity, and overall body weight.
Animal models have shown that diets high in fat and sugar can disrupt the delicate equilibrium of the brain. Brain cells communicate using a mix of excitatory signals that increase activity and inhibitory signals that quiet activity down. Proper brain function relies on maintaining a steady balance between these two forces.
In rodents, researchers found that obesity related diets damaged specialized inhibitory cells in the frontal cortex. These cells are typically wrapped in a protective mesh called a perineuronal net. High fat diets appeared to erode this protective mesh, leaving the inhibitory cells vulnerable to damage.
When these inhibitory cells fail to function properly, the brain loses its ability to hit the neurological brakes. This results in a state of hyper-excitability. A research team wanted to see if human youths with higher body weights exhibited neurological patterns similar to this disinhibited state.
Amy C. Reichelt, a researcher at Western University and the University of Adelaide, led the investigation. She worked alongside Benjamin T. Dunkley from the Hospital for Sick Children in Toronto, as well as a team of other specialists. Together, they designed a study to directly measure brain activity in young volunteers.
The researchers recruited 32 children and teenagers, ranging in age from eight to 19 years old. They calculated each participant’s body mass index, a standard medical metric based on a ratio of height to weight. The cohort was divided into two groups based on how their body mass index compared to standard growth charts for their specific age and sex.
One group consisted of 15 youths with a lower body mass index, falling within average ranges. The other group included 17 youths with a higher body mass index, falling into the overweight or obese categories. Both groups were matched as closely as possible for age and height.
To measure brain activity, the team used a noninvasive imaging technique called magnetoencephalography. This technology relies on highly sensitive sensors to detect the tiny magnetic fields generated by the electrical activity of neurons. This method offers incredibly detailed information about the timing and rapid frequency of brain waves. It can track neural oscillations millisecond by millisecond.
Instead of asking participants to perform an active cognitive puzzle, the researchers had them undergo a resting state scan. Participants laid in the scanner and watched a computer generated, abstract video landscape for five minutes. This neutral video helped the subjects stay still while allowing their minds to wander naturally. The approach allowed the scientists to record the brain’s spontaneous background activity.
The researchers analyzed the resulting brain wave data, focusing on rhythmic oscillations. They found that the youths with a higher body mass index exhibited notable differences in high frequency rhythms known as gamma brain waves. Gamma waves are fast electrical rhythms generated when excitatory and inhibitory cells engage with one another.
In the higher body weight group, gamma activity was highly elevated across many different cortical lobes. The researchers found the boldest effects in the posteromedial cortex and the temporoparietal junction, which are areas involved in directing attention. Elevated gamma activity is often interpreted as a sign that the brain’s natural inhibitory systems are not exerting enough control.
The team also looked at aperiodic activity, which is the constant background electrical static in the brain. They measured the slope of this background noise, a common metric that scientists use to gauge the overall balance of excitation and inhibition in neural tissues. The higher weight group had a shallower slope, pointing to a relative lack of neural inhibition.
These background noise differences were most prominent in the frontal cortex and midline parietal regions. The frontal cortex is deeply involved in top down cognitive control and mental flexibility. Alterations here suggest a potential difficulty in regulating impulses and adjusting to new rules.
Beyond isolating localized brain areas, the researchers examined how specialized brain networks communicated with each other. The brain relies on interconnected webs of regions passing information back and forth. For example, the default mode network is active during internal thought, while the central executive network handles focused working memory tasks.
The salience network is another structural web, responsible for detecting relevant stimuli in the environment and deciding what the brain should pay attention to. The researchers mapped the connections between these distinct networks by looking at how their signals synchronized. In youths with a higher body mass index, they observed weakened communication in lower frequency brain waves like delta and theta rhythms.
Specifically, there were reduced connections between the salience network and networks responsible for driving motivated behaviors. Conversely, the same group showed unusually strong connections in high frequency gamma waves. These tighter high frequency bonds appeared between the default mode network and the central executive network.
This specific combination of weakened low frequency bonds and enhanced high frequency bonds points to an overall loss of efficiency. The typical pathways used to coordinate thoughts and behaviors appeared reorganized in the higher weight group. This could mean the brain is working harder to transmit the same amount of information.
The researchers note several caveats to their experimental approach. Body mass index is an imperfect tool, taking only height and weight into account. It cannot distinguish between muscle mass and adipose tissue. This means it does not always provide an exact reflection of an individual’s body fat percentage.
The relatively small number of participants also means these results should be viewed as preliminary. The observational design of the study means that the researchers cannot state that a higher body mass index caused the brain functioning changes. It remains entirely possible that preexisting brain differences made certain youths more susceptible to excess weight gain.
The scientists also did not track the participants’ daily diets, physical activity levels, or perform behavioral cognitive tests. As a result, the real world implications of these neural shifts are not yet known. It remains a mystery how these specific brain wave patterns translate to daily decision making, academic performance, or emotional regulation.
Future research could incorporate detailed dietary tracking and extensive cognitive assessments alongside brain imaging. The researchers suggest that weakened inhibitory signaling in the frontal cortex could directly influence decision making around food over the long term. Without robust inhibitory control, individuals might find it much harder to resist eating highly palatable foods.
Over time, this could create a feedback loop where dietary habits alter brain development, which in turn entrenches those same dietary habits. Understanding how body weight relates to adolescent brain development might eventually help medical professionals design better strategies for supporting both mental and physical health.
The study, “Elevated body mass index in youth is associated with neural disinhibition and internetwork functional dysconnectivity: A magnetoencephalography study,” was authored by A.C. Reichelt, E. Daskalakis, J. Cohen, K.G. Solar, M. Saberi, M. Ventresca, M. Ali, R. Zamyadi, V. Bhat, S.E. Scratch, J. Hamilton, and B.T. Dunkley.
