Study maps changes in brain’s ‘neural noise’ from childhood to adulthood

For over a century, neuroscientists and psychologists have been trying to understand the neurophysiological mechanisms underpinning the human brain’s development from birth to late adulthood. While past studies have shed light on some of these mechanisms, several aspects of the brain’s maturation remain poorly understood.

Researchers at Northwestern University and other institutes carried out a study aimed at shedding new light on how brain signals that do not follow a rhythmic patternwhich are broadly referred to as aperiodic activity, vary and develop across the human lifespan.

Their findings, published in Nature Human Behaviouroffer new insight into the neural mechanism supporting the maturation of attention and memory processes during adolescence.

“Understanding how the brain develops from childhood into adulthood is central to understanding healthy age- and disease-related changes in attention, memory, and learning across our lives,” Dr. Zachariah R. Cross, first author of the paper, told Medical Xpress.

“Most of what we know comes from studies using MRI or scalp EEG in small samples, often with limited age ranges. Our team sought to take a more comprehensive approach.”

As part of their study, the researchers monitored the brain activity of study participants using a technique known as intracranial electroencephalography (iEEG), which involves electrodes implanted in the brain to directly track electrical activity in the brain with a high resolution.

iEEG is not as commonly used as scalp EEG or functional magnetic resonance imaging (fMRI) because it requires the recruitment of study participants that have already had electrodes implanted for the treatment of epilepsy or other neurological conditions. Cross and his colleagues analyzed iEEG recordings collected from a large group of children and adults aged five to 54 years.

“This allowed us to track how a specific form of brain activity known as aperiodic activity, a ubiquitous but often ignored measure thought to reflect ‘neural noise,’ differs with age and relates to memory and brain structure,” said Cross.

“The study grew out of a broader effort to map brain development more precisely and identify reliable neural markers of cognitive function across the lifespan.”

Instead of looking at brain activity at large, the researchers focused on so-called aperiodic activity, or, in other words, “neural noise” that does not follow a rhythmic pattern. To do this, they analyzed the so-called power spectral density (PSD) of the electrical signals in the brains of the individuals involved in the study.

“Specifically, we measured the aperiodic slope, where a steeper slope indicates less neural noise and a flatter slope suggests more noise,” explained Cross.

“This allowed us to track how neural noise differs with age across various brain regions. Participants also completed cognitive tasks to assess memory performance, and we explored how these were related to the aperiodic slope.

“Additionally, we used structural magnetic resonance imaging (MRI) scans to measure gray matter volume in regions like the medial temporal lobe (MTL) and prefrontal cortex (PFC), which are crucial for memory and executive function.”

Combining iEEG with the completion of cognitive tasks and MRI data, the researchers were able to gain insight into how neural noise in the brains of people at different stages of development relate to their cognitive abilities and brain structure.

Interestingly, they discovered that neural noise increased into early adulthood across some brain regions (i.e., sensorimotor and association cortices). This observation challenges a long-standing hypothesis in the neuroscience research community, namely, that areas in the brain supporting sensory and motor functions mature earlier than brain regions linked to cognitive functions like attention and memory.

“In an association area called the prefrontal cortex—a brain region particularly important for attention and memory—age-related differences in neural noise depended on attentional state: adults had less noise during tasks, while children had more,” said Cross.

“Yet, increased neural noise in this region during tasks was linked to better memory performance as the brain matured into adulthood, revealing a ‘Goldilocks’ effect. These findings suggest that the balance of neural noise plays a critical role in cognitive development and offer a window into understanding developmental conditions and age-related cognitive decline.”

Overall, the results gathered by this research team highlight the importance of studying the brain’s development across the entire lifespan, rather than just in young adults.

By examining brain signals of people in real-world conditions and how they develop over time, Cross and his colleagues could also identify patterns of neurotypical development and signs of dysfunction.

As part of their recent study, they looked at the aperiodic activity in the brains of distinct individuals who were different ages when the iEEG recordings were collected. In the future, however, they also hope to track activity in the brain of the same individuals as they age.

“Another avenue for future research will be to investigate clinical populations with the goal of identifying early markers of cognitive difficulties and supporting targeted interventions during development,” added Cross.

“This is an especially promising avenue because atypical neural noise has been linked to conditions like ADHD and schizophrenia.

“Finally, we are currently preparing a sibling study of periodic activity aimed at mapping the development of theta oscillations, which are key brain rhythms in memory and attention, from childhood through adulthood.”

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