The enigma inside our heads — scientists unlock new secrets as brain research deepens

While the revelations help humans better understand the inside workings of the brain, some of these could help unlock clues to neurodegenerative conditions such as Alzheimer’s.

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Bengaluru: In periods of anxiety, your heart and brain get in touch for a little chat, French researchers said in a study published Wednesday.

Last month, an article published in Nature Mental Health dove into research that suggests genetic predisposition to obesity impacts the brain physically and the individual behaviorally. 

In December last year, researchers from the US and Germany found that some bacteria in the gut stimulate a gut-brain pathway that enhances the effects of dopamine and improves the effects of exercise. 

The human brain, an organ that weighs barely 1.3 kg, hides many secrets. However, slowly and surely, some manner of demystification is at play. Just over the last two years, multiple studies into the brain have revealed details that scientists weren’t privy to before. 

While all of these revelations help humans better understand the inside workings of the brain, some of these could help unlock clues to neurodegenerative conditions such as Alzheimer’s, and possibly aid in their prevention and cure.

In January, for instance, researchers from Harvard Medical School in Boston, in collaboration with other institutes, found that specific mutations in some types of cells speed up more than in others during ageing, providing clues to neurodegeneration from age and onset of tumours in the brain. This study, however, has not been formally peer-reviewed. 

Last year, an international group of researchers, led by teams from the University of Cambridge and the University of Pennsylvania, collected data on how the brain changes as humans age.

Growth metrics like height and weight, physical development, and even behavioral changes are well-documented as people age. With the help of MRIs, this study attempted to do so for the brain. 

Its findings include that the human brain’s white matter, which connects different parts of the brain, peaks at age 28, after which it starts to decline. 

Its grey matter, which is associated with information processing, peaks as early as age 6. Cerebrospinal fluid — which cushions the brain and spinal cord from injury and provides nutrients — seems to increase until age 2, then plateau until 30, then increase again, growing exponentially in the 60s, the researchers said.

Findings from this study — the first to be documented cohesively and making up the largest neuroimaging dataset ever — are expected to be used as a reference or standard for further studies that use neuroimaging, including those on neurodegenerative disorders, atypical brain development, learning disabilities, mental health disorders, and more. 

The methodology and details of the findings have been published as a study in the journal Nature. The MRI data has been uploaded as an interactive reference chart here. 

Another study from last year, this one by researchers from MIT, found that sometimes in the brain, not enough receptors are activated for new neural connections, and they require activity over life to wake up.

Learning more about the brain

One of the larger brain studies from the pandemic centred on the creation of a compendium on how the brain ages.

To understand how the brain physically changes as a person ages, researchers studied brain scans of over 101,457 people at all stages of life and brain development, from multiple studies. The youngest brain in the study was from a 16-week-old foetus, while the oldest was from a 100-year-old. 

“The present work proves the principle that building normative charts to benchmark individual differences in brain structure is already achievable at global scale and over the entire life-course; and provides a suite of open science resources for the neuroimaging research community to accelerate further progress in the direction of standardised quantitative assessment of MRI data,” write the scientists in the paper. 

Among other things, the study found that the outermost layer of the brain, called the cerebral cortex, which is associated with consciousness and language, reaches its maximum thickness before the age of 2. It is believed that increased cortical thickness is linked to higher intelligence. 

It also suggested that the surface area of the brain peaks at about 11 years of age, while the total volume of the cerebrum does so at 12 years.

The observed patterns showed a high degree of stability across individuals, although the authors acknowledged limitations to the findings owing to limitations in MRI data and extreme sensitivity of other instruments. 

It also found a number of rapid degenerative changes at older ages, such as increase in the size of ventricles, which hold fluids and are associated with neurodegenerative diseases. 

Other parts of the brain were found to change variably as a person grows old, likely depending on daily life and major life experiences. For example, regions of the brain associated with senses reach different levels in different people at different times, the study says, but peak in volume first and fall rapidly as compared to other parts of the brain. 

Apart from patterns in grey and white matter and thickness of parts of the brain, the team also found previously unreported neurodevelopmental milestones as the brain ages. 

For example, the rate of increase of the total cerebral volume, or the size of the brain, peaks when an adolescent reaches their maximum height.

While it is well-established that males have larger brain-tissue volumes than females in absolute terms, the study found no difference in clinical or cognitive outcomes. 

Limitations

The brain and all its neurons are created at birth, but the development in size and neural networks change over a person’s lifetime, shaped by life experiences. 

Recent advancements in the technology of neuroimaging have enabled scientists to document the human brain better. This has led to a slew of discoveries, which are ever-increasing as they build upon each other.

However, several studies have many limitations that the authors highlight. 

For example, despite the compendium being the largest dataset of MRI scans, the data was biased towards European and North American ancestry groups, the researchers said. 

The data available was also not well-distributed across age groups, and data for foetal, neonatal (newborn), and mid-adulthood (ages 30-40) was lacking. The authors also stressed that their study could not eliminate any bias that existed in the primary studies they evaluated.

(Edited by Sunanda Ranjan)