Linking brain structure to behavior
How reliable are claims that link brain structure to behavior from studies using small sample sizes?
All human brains share the same basic structure. But no two brains are exactly alike. Brain scans can reveal differences between people in the organization and activity of individual brain regions. Studies have suggested that these differences give rise to variation in personality, intelligence and even political preferences. But recent attempts to replicate some of these findings have failed, questioning the existence of such a direct link, specifically between brain structure and human behavior. This had led some disagreements whether there is a general replication crisis in psychology, or if the replication studies themselves are flawed.
Kharabian Masouleh et al. have now used brain scans from hundreds of healthy volunteers from an already available dataset to try to resolve the issue. The volunteers had previously completed several psychological tests. These measured cognitive and behavioral aspects such as attention, memory, anxiety and personality traits. Kharabian Masouleh et al. performed more than 10,000 analyzes on their dataset to look for relationships between brain structure and psychological traits. But the results revealed very few statistically significant relationships. Moreover, the relationships that were identified proved difficult to replicate in independent samples.
By contrast, the same analyzes demonstrated robust links between brain structure and memory in patients with Alzheimer’s disease. They also showed connections between brain structure and non-psychological traits, such as age. This confirms that the analysis techniques do work. So why did the new study find so few relationships between brain structure and psychological traits, when so many links have been reported previously? One possibility is publication bias. Researchers and journals may be more likely to publish positive findings than negative ones.
Another factor could be that that most studies use too few participants to be able to reliably detect relationships between brain structure and behavior, and that studies with 200 to 300 participants are still too small. Therefore, future studies should use samples with many hundreds of participants, or more. This will be possible if more groups make their data available for others to analyze. Researchers and journals must also be more willing to publish negative findings. This will help provide an accurate view of relationships between brain structure and behavior.
Originally published at https://elifesciences.org/digests/43464.
