What New in Psychology?

A New Explanation for Memory Loss as an Early Symptom of Alzheimer’s

 Jim Windell

           Blood circulation explains many things in our body.

           For instance, if the blood flow to the heart is restricted or cut off, you will have a heart attack. If your fingers or toes fail to receive sufficient oxygen, then you will suffer damage – maybe even permanent tissue damage – of those extremities. And if your brain is deprived of oxygen-carrying blood, you will experience irreversible brain damage and – ultimately – death.

           But what if certain specific areas of the brain, such as the hippocampus, fail to receive the blood that carries the all-important oxygen needed by brain cells? The hippocampus is commonly referred to as the brain's memory center.

            Researchers at the University of Sussex wanted to find out.

           To understand why the hippocampus is so sensitive, the University of Sussex researchers, headed up by Dr Catherine Hall from the School of Psychology and Sussex Neuroscience, studied brain activity and blood flow in the hippocampus of mice. The researchers then used simulations to predict that the amount of oxygen supplied to hippocampal neurons furthest from blood vessels is only just enough for the cells to keep working normally. The results of their work is reported in Nature Communications.

           Dr Kira Shaw, a psychology researcher at the University of Sussex who undertook the main experiments, said that, “We found that blood flow and oxygen levels in the hippocampus were lower than those in the visual cortex. Also, when neurons are active, there is a large increase in blood flow and oxygen levels in the visual cortex. This provides energy to hungry neurons. But in the hippocampus, these responses were much smaller.”

           The scientists also found that blood vessels in the hippocampus contained fewer mRNA transcripts (codes for making proteins) for proteins that shape blood vessel dilation. Additionally, the cells that dilate small blood vessels, called pericytes, were a different shape in the hippocampus than in the visual cortex. Dr. Shaw and his cohorts concluded: “We think blood vessels in the hippocampus are less able to dilate than in the visual cortex.”

           The findings are said to be an important step in the search for preventative measures and treatments for Alzheimer's. Dr Catherine Hall, Senior Lecturer in Psychology at the University of Sussex, pointed out that the findings are very important because they suggest that increasing blood flow in the hippocampus might be really effective at preventing damage from happening.

           "If it's right that increasing blood flow in the hippocampus is important in protecting the brain from diseases like Alzheimer's,” Dr. Hall noted, “then it will throw further weight behind the importance of regular exercise and a low-cholesterol diet to maintain long-term brain health.”

           Dr. Hall also explained that when anything happens to decrease brain blood flow, oxygen levels in the hippocampus reduce to levels that stop neurons working. “We think that's probably why Alzheimer's disease first causes memory problems -- because the early decrease in blood flow stops the hippocampus from working properly,” she said.

           She also said that it is the same factors that put people at risk of having a heart attack make them more likely to develop dementia. “That's because our brains need enough blood flow to provide energy -- in the form of oxygen and glucose -- so brain cells can work properly,” she said, “and because blood flow can clear away waste products such as the beta amyloid proteins that build up in Alzheimer's disease.”

           Dr. Hall went on to say that they next hope to discover whether the lower blood flow and oxygen levels in the hippocampus are what causes beta amyloid to start to build up in Alzheimer's disease. “Understanding what causes early damage will be really important to help us learn how to treat or prevent the disease,” she said.

           To read the original article, find it with this reference:

K. Shaw, L. Bell, K. Boyd, D. M. Grijseels, D. Clarke, O. Bonnar, H. S. Crombag, C. N. Hall. Neurovascular coupling and oxygenation are decreased in hippocampus compared to neocortex because of microvascular differences. Nature Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-23508-y