Unlocking the Brain's Secrets: Five Major Stages of Lifelong Change
The human brain, a complex and dynamic organ, undergoes significant transformations throughout life. Now, neuroscientists at the University of Cambridge have identified five distinct "epochs" in this lifelong journey, each characterized by unique patterns of rewiring that shape our thinking, learning, and behavior.
A groundbreaking study published in Nature Communications details how the brain reorganizes itself from early development to late old age. Researchers at Cambridge's MRC Cognition and Brain Sciences Unit analyzed MRI diffusion scans from 3,802 individuals, ranging from newborns to 90-year-olds. These scans track the movement of water through brain tissue, allowing scientists to map the intricate networks that connect different regions.
The study reveals four key "turning points" that divide these five phases, representing ages when the brain undergoes substantial reorganization. These findings offer a new framework for understanding how our brains evolve and adapt throughout our lives, potentially shedding light on developmental challenges, mental health conditions, and age-related cognitive decline.
From Infancy to Adolescence: A Period of Rapid Growth and Consolidation
The first epoch spans from birth to approximately age nine. During this period, the brain experiences rapid growth, characterized by the formation of an enormous number of synapses – the connections between neurons. This phase is marked by "network consolidation," where the most active connections are strengthened while weaker ones are eliminated. Grey and white matter volume increases rapidly, and the folds of the cerebral cortex stabilize, creating the characteristic ridges on the brain's surface.
The turning point around age nine coincides with rapid cognitive development, but also an increased vulnerability to certain mental health conditions. This highlights the delicate balance between growth and potential disruption during this critical period.
The Extended Adolescence: Efficiency and Organization
The second epoch, adolescence, surprisingly extends to around age 32. This phase is characterized by continued growth of white matter, leading to more refined and efficient communication networks. MRI scans reveal more orderly water movement in the tissue, reflecting stronger and more coordinated connections. This period is notable for rising efficiency in how signals move within and across brain regions, resulting in improved cognitive performance.
Dr. Alexa Mousley, a Gates Cambridge Scholar who led the research, emphasized the significance of this phase. "Neural efficiency is, as you might imagine, well connected by short paths, and the adolescent era is the only one in which this efficiency is increasing," she said.
Adulthood: Stability and Specialization
Around age 32, the brain transitions into a relatively stable adult epoch, lasting for approximately three decades. This phase aligns with observations from other studies indicating a "plateau in intelligence and personality." However, subtle changes continue to occur, including increasing "segregation" of brain regions, meaning that different areas become more specialized in their functions.
Aging: Gradual Reorganization and Regional Reliance
The next turning point, occurring around age 66, marks the beginning of an "early aging" phase. While not involving dramatic structural changes, this period is characterized by a gradual reorganization of brain networks, likely related to age-related decline in white matter connectivity. This phase also coincides with an increased risk for health conditions that can affect the brain, such as hypertension.
The final turning point arrives near age 83, signaling the start of the last brain structure epoch. During this phase, the brain becomes less globally connected and relies more heavily on specific regions. This suggests a shift towards more localized processing as the brain ages.
Implications for Understanding Brain Health
Professor Duncan Astle, Professor of Neuroinformatics at Cambridge and senior author of the study, emphasized the broader implications of these findings. "Many neurodevelopmental, mental health, and neurological conditions are linked to the way the brain is wired," he said. "Indeed, differences in brain wiring predict difficulties with attention, language, memory, and a whole host of different behaviors."
By understanding these major turning points in brain development, researchers hope to gain insights into the vulnerabilities of the brain at different stages of life, potentially leading to new strategies for preventing and treating a wide range of neurological and psychiatric disorders. The research was supported by the Medical Research Council, the Gates Foundation, and the Templeton World Charitable Foundation.
