Using structural and functional MRI to assess the effects of ethnicity on healthy ageing in the human brain

Abstract

In the last decade, several large multi-institutional neuroimaging studies have emerged, the chief amongst them being the Alzheimer's Disease Neuroimaging Initiative (ADNI). The data obtained from these studies are free to access for researchers, and are an invaluable resource in areas where getting a large enough cohort takes too long or becomes too expensive to fund. However, one should proceed with caution as the sample consists mostly of highly educated American Caucasians, reducing its generalisability to other countries. For those who have an interest in cross-ethnicity differences however, the ADNI dataset is ideal for this purpose.

This thesis begins with a cross-sectional look at cognitively normal, elderly Hong Kong Chinese subjects and matched ADNI Caucasian ones. When comparing total cortical grey matter volumes and the summed volumes of cortex that are often associated with Alzheimer's disease, it was found that Chinese subjects had significantly smaller cortical volumes than American Caucasians, even after adjusting for brain volume, despite having similar cognitive test scores. Unable to control for extrinsic factors such as environment and culture, however, no strong conclusions could be made.

The second study of this thesis consists of a replication of the first, this time using American Chinese and American Caucasian subjects, all long-time residents of San Francisco. The same results were found regarding total cortical grey matter volume, leading to the implication that the Chinese population have inherently smaller cortices than Caucasians, but with no obvious cognitive detriment.

Having found that ethnicity can have an effect on brain structure, the focus then shifts to how the brain changes during healthy ageing. The concept of healthy ageing has been gaining in popularity in recent years, especially as more and more age-related diseases are being thought of as "pathological ageing". In order to help diagnose and monitor diseases related to ageing, it is therefore important to understand the trajectory and effects of normal ageing. As such, a pilot fMRI study was conducted to try and see how attention and increased vulnerability to interference from presented stimuli changed with age.

The results from the pilot study matched generally well with the literature and opens up the door towards using cognitive paradigms in neuroimaging to act as baseline markers of cognitive function, which can then be correlated with other measures to paint a more detailed portrait of the healthy ageing brain.