Taking a closer look at blood flow in the brain

When talking about dementia we often focus on nerve cells – they are, after all, in charge of everything we do and think. But nerve cells aren’t lone rangers. Just like there’s no Sherlock Holmes without Watson, no Starsky without Hutch and no Ant without Dec, nerve cells and the blood vessels that supply the brain, go hand in hand. Today, we heard from two researchers exploring the relationship between nerve cells and blood vessels – and what can go wrong in dementia.

Nerve cell communication requires huge amounts of oxygen, delivered by intricate networks of blood vessels in the brain. It’s important that blood flow can meet the demands of nerve cells across the brain and this is controlled by a process called ‘neurovascular coupling’.

Neurovascular coupling is a ‘conversation’ between nerve cells and blood vessels. The conversation is orchestrated by cells known as astrocytes and pericytes. When this process goes awry, nerve cells can’t communicate properly. From studying human brain tissue, researchers have found that neurovascular coupling is disrupted in Alzheimer’s, but the reasons behind it aren’t entirely clear.

When Alzheimer’s Research UK-funded student, Jessica Duncombe, began her PhD studies at the University of Edinburgh, she set out to understand how a toxic Alzheimer’s protein called amyloid disrupts neurovascular coupling. Surprisingly, she found that changes in neurovascular coupling occurred in older mice, even in those without amyloid in the brain. In the older mice, she found that astrocytes were damaged and there were fewer pericytes – all with knock-on consequences for nerve cell health. These changes could help explain why some people develop memory and thinking difficulties when they get older and highlights a possible driving force in vascular dementia – the second leading cause of dementia in the UK.  Now, Jessica will try and understand why these changes occur and whether drugs that boost blood flow to the brain could help improve memory and thinking skills.

From the lab to the clinic

Dr Laura Parkes from the University of Manchester shared her latest research using special imaging techniques to explore changes in neurovascular coupling in people. MRI scans can tell us lots of information about the structure of the brain. Using these scans, clinicians can look at changes in the brain that could help guide a diagnosis of dementia. But changes in structure are just one part of the puzzle. Changes in blood flow and alterations in the amount of oxygen used by the brain can tell us huge amounts of information about brain health.

Dr Parkes uses a sophisticated brain imaging technique called functional MRI to zero in on small vessel disease (SVD) – a cause of vascular dementia where tiny blood vessels that serve the brain are damaged. She asked volunteers in the earliest stages of small vessel disease and healthy people of a similar age, to complete the Stroop test while in an MRI scanner. You may have had a go at the tricky Stroop test yourself at some point – volunteers are shown the name of a colour, presented in a different colour.  They are asked to name the colour of the word. How quickly can you do it?

This type of task challenges certain parts of your brain and is a good test of thinking skills.

She found that the brains of older volunteers used less oxygen than younger people – a sign of lower nerve cell activity. This difference was particularly obvious in people who struggled with the Stroop test and could explain their difficulties with the task. Dr Parkes is now using the technique to investigate neurovascular coupling in people with small vessel disease to understand how changes in blood vessels impact on brain health.

Dr Parkes’ work also highlighted an important point for researchers to consider. Many of the sophisticated techniques used to analyse brain scans were developed in young healthy people. The assumption that the brain works in a similar way in health and disease, and in young and old, could mean that brain scans are misinterpreted. It’s important that researchers refine analysis techniques to make sure they’re not missing crucial information that could help guide diagnosis and treatment strategies.

It is clear from today’s talks that to understand dementia we can’t just focus on nerve cells – we need to understand their complex relationship with a whole host of other brain cells and how this changes with age and in dementia. We are currently funding Dr Jason Berwick at the University of Sheffield to get to grips with neurovascular coupling in Alzheimer’s and understand how we can use changes in this important process for the early detection of dementia. You can learn more about this important study in an interview with Dr Berwick on the blog.