New research reveals that a specific brain network — known to be the last to develop and the first to show signs of neurodegeneration — is more vulnerable to unhealthy aging as well as to disorders that emerge in young people, shedding light on conditions such as Alzheimer’s disease and schizophrenia.
The research, led by Dr. Gwenaëlle Douaud at the Oxford University Functional MRI of the Brain (FMRIB) Center in the UK, sheds light on potential genetic and environmental factors that may occur early in life, causing lifelong consequences. The findings are published in the journal Proceedings of the National Academy of Sciences.
For the study, the team focused on grey matter in the brain — a network of nerve cells that coordinate information from different senses
Grey matter does not fully develop until late adolescence or early adulthood, and it is linked with both intellectual capacity and long-term memory — mental abilities that become impaired in people with schizophrenia or Alzheimer’s disease.
A theory from the 1880’s, known as the “retrogenesis” theory of brain change, proposed that brain ability declines in reverse order to how it develops in humans and in evolutionary terms (for example, humans and chimpanzees evolving from a common ancestor).
Following these lines, the researchers used a data-driven approach to study age-related changes. So, instead of looking for a certain pattern in brain changes in a specific brain location, the team analyzed magnetic resonance imaging (MRI) scans of 484 people, ranging in age from 8-85 years, to see what patterns were revealed.
Specific brain regions ‘develop more slowly and degenerate faster’
According to the authors, their findings are the first to demonstrate the retrogenesis theory in grey matter on a large scale by using image analysis techniques.
Results from their imaging data revealed that a particular network within the grey matter links most higher order regions of the brain. Additionally, they found that this network develops later than the rest of the brain and degenerates first in older age.
Though the finding that grey matter declines with age is not new, the researchers explain that these new results show that one specific network is more vulnerable to age-related neurodegeneration, in that it degenerated sooner than other brain areas.
When the team compared this brain network in healthy individuals with those of people with Alzheimer’s and schizophrenia, they found that these brain areas likely play an important role in the two very different conditions.
“Our results show that the same specific parts of the brain not only develop more slowly, but also degenerate faster than other parts,” says Dr. Douaud. “These complex regions, which combine information coming from various senses, seem to be more vulnerable than the rest of the brain to both schizophrenia and Alzheimer’s, even though these two diseases have different origins and appear at very different, almost opposite, times of life.”
‘Results reconcile two historical hypotheses’
The authors point to previous research that has shown these regions of the brain are not as developed in chimpanzees and other primates. Because these animals do not appear to experience schizophrenia or Alzheimer’s, scientists have suggested humans’ evolved brains and extended lifespans are to blame.
“These results, which might seem surprising at first, are really exciting as they actually reconcile two historical hypotheses – until now presented completely separately in the scientific literature – that the brain damage observed in Alzheimer’s and schizophrenia is related to these higher order regions of the brain,” says Dr. Douaud.
Prof. Hugh Perry – chairman of the Medical Research Council’s Neurosciences and Mental Health Board, which funded the research – notes that long ago, doctors referred to schizophrenia as “premature dementia.” Until this study, however, there has not been any evidence that the same parts of the brain could be “associated with two such different diseases.”
He says the study “raises important issues about possible genetic and environmental factors that may occur in early life and then have lifelong consequences,” and adds: “The more we can find out about these very difficult disorders, the closer we will come to helping sufferers and their families.”