Researchers have been able to look inside the human brain thanks to MRI images. Furthermore, the technique is excellent at revealing stroke damage or areas that light up when we view a face. However, brain scan research has yet to provide much insight into the basis of personality qualities such as intellect or mental health problems such as anxiety and depression. A major explanation for this is that these studies require thousands of brain scans rather than the hundreds generally employed, according to a team that published their findings in the journal Nature on March 16. Dr Nico Dosenbach, one of the study’s authors and an associate professor of neurology at Washington University in St. Louis, adds that a large sample is required, and larger samples are preferable. According to Paul Thompson, a neuroscientist at the University of Southern California who was not involved in the study, this is a lesson that the area of genetics has previously learned. According to Thompson, geneticists eventually solved the problem by increasing the size of their research from a few dozens to millions of people. Neuroscientists now look to be in a similar situation, which will force them to rethink the findings of several tiny investigations.
- A fascinating investigation of intelligence
The latest article on brain scan studies sprang out of a 2018 initiative to learn more about how toddlers acquire cognitive abilities, or intelligence. A group led by Scott Marek, a Washington University researcher in Dosenbach’s lab, intended to use data from a federal study that scanned the brains of thousands of adolescents. Intelligence is closely linked to the thickness of the brain’s outermost layer and the strength of connections between certain brain regions, according to a previous study. As a result, Marek and his colleagues examined almost 1,000 brain scans from the federal study. Then they double-checked their work with a thousand distinct scans. In one series of scans, an area or connection that seemed significant may appear unimportant in the next. The results became more credible only after they extended the sample size to thousands of brains.
- Small sample size’s dangers
One limitation of small studies is that they can only identify brain traits that have a significant impact on mood, behaviour, or mental abilities. It’s easy to demonstrate that hippocampal atrophy is followed by a significant loss of memory in Alzheimer’s disease, for example. Variations in the brain that are linked to mental disease are significantly less visible and far more contentious. Some studies have discovered that persons with major depressive disorder had reduced activity in the frontal lobe of the brain. However, the strength of that link varies a lot from one study to the next. And there’s no way to tell how someone is feeling just by looking at their frontal lobe activity. Another issue with short studies is a phenomenon known as publication bias. If numerous groups conduct similar research with limited samples, one or more of the groups may produce a meaningful result, according to Dosenbach. And that’s exactly what will be reported. When a large number of similar studies are published, a false conclusion can become common knowledge. However, this does not rule out the possibility that tiny studies are flawed. As a result, headlines extrapolating the results of a small MRI research to the entire population should be avoided.
- “Aftershocks” in a study
Many brain experts are still digesting the notion that human behaviour studies could necessitate tens of thousands of scans. The remedy, according to Thompson, is obvious and attainable: Combine scans from several small studies into one or more large databases, then examine the results. “There are huge differences all over the brain in schizophrenia,” Thompson explains. “Hallucinations are caused by abnormalities in the auditory centres. Memory and vision systems are both undergoing changes.” However, because the variations are so slight, it may take even larger research to discover the brain areas and connections linked to mental diseases like depression and bipolar disorder. Some of these research projects are already in the works. For example, the National Institutes of Health has enrolled almost 11,000 teenagers in a study on adolescent brain development, which scans their brains on a regular basis to follow changes. According to Terry Jernigan, a brain scientist at the University of California, San Diego and one of the study’s primary investigators, the study’s large scale is in part an effort to solve issues observed in smaller research. But, according to Jernigan, including thousands of people in brain scan research isn’t enough; the studies must be more diverse than they are now. She explains that you want to know how generalizable your findings are to all of our society’s different groupings.