Scientists studying the brains of so-called “SuperAgers” have discovered a set of significantly enlarged neurons associated with memory. These neurons also appeared more resistant to characteristics of Alzheimer’s disease, and present as a unique biological signature that these subjects may have carried throughout their whole lives.
SuperAgers are a group of individuals over the age of 80 with exceptional episodic memory, at least as good as people 20 to 30 years younger. Studies on what makes the brains of these SuperAgers different to typical elderly brains have produced some fascinating insights in the past few years, relating not just to memory but how they may keep neurological degeneration at bay.
PET scans have shown that these brains contained far lower aggregations of toxic brain plaques and tangles associated with Alzheimer’s disease, and MRI scans have shown they feature the neural network and connectivity akin to the brains of young adults. Other studies on visual memory specifically have found their brain activity can be similar to that of a 25 year old.
Building on this is a new study from Northwestern University researchers, who focused on the entorhinal cortex, a brain region responsible for memory and one of the first impacted by Alzheimer’s disease. The team studied six post-mortem SuperAger brains and found larger, healthier neurons in one of the six layers making up this region. These neurons were compared to those in seven cognitively average elderly people, six young subjects and five subjects with early Alzheimer’s, and were found to be significantly larger.
Neurons in the entorhinal cortex are known to be very vulnerable to brain tangles made up of abnormal tau proteins, a hallmark of aging and early Alzheimer’s. But the scientists found the SuperAger neurons contained significantly fewer of these tangles, which they suspect is related to their larger size. They say the findings indicate that neurons that escape the onset of tangle formation can better maintain their structural integrity, while tau tangles appear to lead to neuronal shrinkage.
“In this study, we show that in Alzheimer’s, neuronal shrinkage (atrophy) in the entorhinal cortex appears to be a characteristic marker of the disease,” said lead author Tamar Gefen. “We suspect this process is a function of tau tangle formation in the affected cells leading to poor memory abilities in older age. Identifying this contributing factor (and every contributing factor) is crucial to the early identification of Alzheimer’s, monitoring its course and guiding treatment.”
The scientists consider these results as evidence that these larger neurons are a key pillar in the exceptional memory seen in SuperAgers. From here, they hope to dig further into why these neurons are better maintained in the brains of SuperAgers by investigating the cellular environment and underlying reasons for their resilience.
“The remarkable observation that SuperAgers showed larger neurons than their younger peers may imply that large cells were present from birth and are maintained structurally throughout their lives,” said Gefen. “We conclude that larger neurons are a biological signature of the SuperAging trajectory.”
The research was published in The Journal of Neuroscience.
Source: Northwestern University