̽��ֱ�� of Cambridge - Kamen Tsvetanov

Strongest evidence to date of brain’s ability to compensate for age-related cognitive decline

cjb250 — Tue, 06 Feb 2024 14:00:20 +0000

As we age, our brain gradually atrophies, losing nerve cells and connections and this can lead to a decline in brain function. It’s not fully understood why some people appear to maintain better brain function than others, and how we can protect ourselves from cognitive decline.

A widely accepted notion is that some people’s brains are able to compensate for the deterioration in brain tissue by recruiting other areas of the brain to help perform tasks. While brain imaging studies have shown that the brain does recruit other areas, until now it has not been clear whether this makes any difference to performance on a task, or whether it provides any additional information about how to perform that task.

In a study published in the journal eLife, a team led by scientists at the ̽��ֱ�� of Cambridge in collaboration with the ̽��ֱ�� of Sussex have shown that when the brain recruits other areas, it improves performance specifically in the brains of older people.

Study lead Dr Kamen Tsvetanov, an Alzheimer's Society Dementia Research Leader Fellow in the Department of Clinical Neurosciences, ̽��ֱ�� of Cambridge, said: “Our ability to solve abstract problems is a sign of so-called ‘fluid intelligence’, but as we get older, this ability begins to show significant decline. Some people manage to maintain this ability better than others. We wanted to ask why that was the case – are they able to recruit other areas of the brain to overcome changes in the brain that would otherwise be detrimental?”

Brain imaging studies have shown that fluid intelligence tasks engage the ‘multiple demand network’ (MDN), a brain network involving regions both at the front and rear of the brain, but its activity decreases with age. To see whether the brain compensated for this decrease in activity, the Cambridge team looked at imaging data from 223 adults between 19 and 87 years of age who had been recruited by the Cambridge Centre for Ageing & Neuroscience (Cam-CAN).

̽��ֱ��volunteers were asked to identify the odd one out in a series of puzzles of varying difficulty, while lying in a functional magnetic resonance imaging (fMRI) scanner, so that the researchers could look at patterns of brain activity by measuring changes in blood flow.

As anticipated, in general the ability to solve the problems decreased with age. ̽��ֱ��MDN was particularly active, as were regions of the brain involved in processing visual information.

When the team analysed the images further using machine-learning, they found two areas of the brain that showed greater activity in the brains of older people, and also correlated with better performance on the task. These areas were the cuneus, at the rear of the brain, and a region in the frontal cortex. But of the two, only activity in the cuneus region was related to performance of the task more strongly in the older than younger volunteers, and contained extra information about the task beyond the MDN.

Although it is not clear exactly why the cuneus should be recruited for this task, the researchers point out that this brain region is usually good at helping us stay focused on what we see. Older adults often have a harder time briefly remembering information that they have just seen, like the complex puzzle pieces used in the task. ̽��ֱ��increased activity in the cuneus might reflect a change in how often older adults look at these pieces, as a strategy to make up for their poorer visual memory.

Dr Ethan Knights from the Medical Research Council Cognition and Brain Sciences Unit at Cambridge said: “Now that we’ve seen this compensation happening, we can start to ask questions about why it happens for some older people, but not others, and in some tasks, but not others. Is there something special about these people – their education or lifestyle, for example – and if so, is there a way we can intervene to help others see similar benefits?”

Dr Alexa Morcom from the ̽��ֱ�� of Sussex’s School of Psychology and Sussex Neuroscience research centre said: “This new finding also hints that compensation in later life does not rely on the multiple demand network as previously assumed, but recruits areas whose function is preserved in ageing.”

̽��ֱ��research was supported by the Medical Research Council, the Biotechnology and Biological Sciences Research Council, the European Union’s Horizon 2020 research and innovation programme, the Guarantors of Brain, and the Alzheimer’s Society.

Reference

Knights, E et al. Neural Evidence of Functional Compensation for Fluid Intelligence Decline in Healthy Ageing. eLife; 6 Feb 2024; DOI: 10.7554/eLife.93327

Scientists have found the strongest evidence yet that our brains can compensate for age-related deterioration by recruiting other areas to help with brain function and maintain cognitive performance.

Now that we’ve seen this compensation happening, we can start to ask questions about why it happens for some older people, but not others - is there something special about these people?

Ethan Knights

CDC

Woman in purple and white floral shirt washing a carrot

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Your brain might not be as ‘old’ as you think

cjb250 — Mon, 09 Mar 2015 09:22:10 +0000

How ‘old’ is your brain? Put another way, how ‘aged’ is your brain? ̽��ֱ��standard, scientific answer, suggests that the older you get, the greater the changes in the activity of your neurons. In fact, my colleagues and I have found out that this isn’t necessarily the case: older brains may be more similar to younger brains than we’d previously thought.

In our study, published recently in the journal Human Brain Mapping, we’ve shown that changes in the ageing brain previously observed using functional magnetic resonance imaging (fMRI) – one of the standard ways of measuring brain activity – may be due to changes in our blood vessels, rather than changes in the activity of our nerve cells, our neurons. Given the large number of fMRI studies used to assess the ageing brain, this has important consequences for understanding how the brain changes with age and it challenges current theories of ageing.

̽��ֱ��fundamental problem of fMRI is that it measures the activity of our neurons indirectly through changes in regional blood flow. Without careful correction for age differences in how the blood vessels respond, differences in fMRI signals may be erroneously regarded as differences in our neurons.

An important line of research focuses on controlling for noise in fMRI signals using additional baseline measures of vascular (blood vessel) function, for example involving experimental manipulations of carbon dioxide levels in blood. However, such methods have not been widely used, possibly because they are impractical to implement in studies of ageing.

An alternative way of correcting makes use of the resting state, ’task-free’, fMRI measurement, which is easy to acquire and available in most fMRI experiments. While this method has been difficult to validate in the past, the unique combination of an impressively detailed data set across 335 healthy volunteers over the lifespan, as part of the Cambridge Centre for Ageing and Neuroscience (CamCAN) project, has allowed us to probe the true nature of the effects of ageing on resting state fMRI signal amplitude. This showed that age differences in signal amplitude at rest – in other words, while volunteers perform no task during the scan – originate from our blood vessels, not our nerve cells. We believe we can use this as a robust correction factor to control for vascular differences in fMRI studies of ageing.

A number of research studies have previously found reduced brain activity in the areas of the brain related to our senses and movement during tasks that study these aspects. Using conventional methods, we replicated these findings, but, after correction, we found that it is more likely to be vascular health, not brain function, that accounts for most age-related differences in fMRI signals in sensory areas. In other words, neuroscientists may have been overestimating age differences in brain activity in previous fMRI studies.

Why is this important? We’re an ageing society, with more and more people living into old age, so it’s crucial that we understand how age affects how the brain functions. We clearly need to refine our fMRI experiments, otherwise we risk creating a misleading picture of activity in the brain as we age. Without refinement, such fMRI studies may misinterpret the effect of age as a cognitive phenomenon, when really it has more to do with our blood vessels.

Dr Tsvetanov is funded by the Biotechnology and Biological Sciences Research Council (BBSRC).

Reference

Tsvetanov, KA et al. ̽��ֱ��effect of ageing on fMRI: correction for the confounding effects of vascular reactivity evaluated by joint fMRI and MEG in 335 adults. Human Brain Mapping; 27 February 2015

Our standard way of measuring brain activity could be giving us a misleading picture of how our brains age, argues Dr Kamen Tsvetanov from the Department of Psychology.

We’re an ageing society, with more and more people living into old age, so it’s crucial that we understand how age affects how the brain functions

Kamen Tsvetanov

Brain areas with rich blood supply lower their vascular reactivity with ageing

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