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How does the brain change with age? Part #2: MRI brain imaging

How does the brain change with age? Part #2: MRI brain imaging - 23 July 2013. BBSRC

A suite of videos explores a major BBSRC programme to study ageing and cognition in healthy adults.
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  How does the brain change with age? Part #2: MRI brain imaging.

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A central part of the Cam-Can Project (see below 'The resilience of the brain') is the use of advanced brain imaging studies.

Resting state data and a short audio-visual task is obtained from 700 individuals in an MRI scanner (magnetic resonance imaging). From that pool, 280 are selected for an extensive variety of fMRI studies (functional MRI) to test activity in a wide variety of cognitive domains such as emotion, memory, language, attention and motor function; each individual test is designed by an expert in the field.

MRI is a considered one the most accurate and safest brain imaging techniques because it does not have the risks associated with the X-rays or radioactive tracer compounds used in CT (computed tomography) or PET (positron emission tomography) scanners. Instead, MRI scanners use hugely powerful electromagnets to measure changes in hydrogen protons as harmless radio waves are applied to the body. Because the human body contains lots water, the hydrogen protons are an ideal vehicle to measure soft tissues such as the brain.

Cam-CAN Assistant Director Professor Rik Henson says MRI neuroimaging can tell us many different things about the brain, in terms of both its structure and function. "More specifically, we can use MRI to measure things like grey- and white-matter volume (using so-called T1- and T2-weighted images); direction and integrity of major white-matter fibres (using so-called diffusion-weighted images) and the degree of myelination of white-matter (using so-called magnetisation transfer images)," Henson explains. "All of these things change – quite dramatically – as we age."

To look more at the brain as it functions, as opposed to just the structure, Henson and colleagues are using fMRI which maps activity of the brain's neurons using blood flow as a proxy – the more active the neurons are, the more blood flows to them. "We can use fMRI to measure local changes in blood oxygenation over time (caused when parts of the brain are 'busy'), which can then be related to changes in the task performed by the person, i.e., to changes in different cognitive functions", says Henson.

"We can also measure the degree of functional connectivity between brain regions, which we believe is an important aspect of reorganisation of function in the face of the dramatic structural change over the years," he says. Henson and his colleagues have examined patterns of connectivity using fMRI, as well as using another safe technique called magneto-encephalography (MEG), while people rest with their eyes closed. The data show that younger brains show a greater clustering of connections, with greater fragmentation in local brain connectivity as people grow older.

"We are now examining how this 'disconnection' pattern relates to changes in structural connections in the brain (using various other types of MRI data) and to functional connectivity patterns during more active cognitive tasks," says Henson, "since older brains may still be able to 're-wire' appropriately in order to perform specific functions."

The resilience of the brain

Ageing is an aspect of living common to every person, whether old or young, but what differs is how our brains and cognitive abilities change as we grow older. Some people's minds remain sharp and intact well into their 80s and 90s, whereas others can slide into early cognitive decline from their early 50s. Why such a divergence?

A major £5M grant from BBSRC has established the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) team that seeks answers to these questions. By studying the brain and its cognitive functions using advanced brain imaging techniques and cognitive experiments the team of researchers, based at the University of Cambridge and the MRC Cognition and Brain Sciences Unit, hope to unravel the mechanisms and processes of healthy brain functions.

And it's not just about old people. The Cam-CAN project's full cohort of 3000 participants spans the full adult range of 18-88. This is because recent research suggests that the brain changes throughout our lifespan – not just when we are older. Important changes are happening in midlife that set the scene for how well our brains will work in retirement years.

"The changes that take place when we are older may only be a small piece of the puzzle," says Cam-CAN director Professor Lorraine Tyler from the University of Cambridge. "Individual brains may change at different rates at different ages, so a model of only the later years may be inadequate, and also would not help us to generate predictive models which may be needed to enable us to develop interventions early in life."

Hence, along with studying healthy rather than diseased states in all ages constitutes a novel and ambitious approach that could change our perspective of ageing processes, and reveal why abilities such as language are retained while others are lost.

In time, biomarkers for health can also be compared with the biomarkers from disease states, and interventions designed and implemented that in the future might restore the balance and well-being that every person wants.

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