One of the central assumptions of modern neuroscience research is that the brain's shape and structure affect behavior. Scientists have linked a thicker cortex (the brain's outer layer) to higher intelligence, certain brain wave patterns to better volleyball ability, and higher connectivity between parts of the brain to chess-playing skills. There's a vast number of these so-called brain-wide association studies (BWAS).

But when experts repeat these studies, they can't replicate the results.

This "replication crisis" suggests that a substantial amount of brain-behavior imaging research rests on a shaky foundation. There are myriad problems affecting this area of research, said Randy Ellis, a senior scientist at Oracle who wrote about these issues while working as a biomedical informatician at the Icahn School of Medicine at Mount Sinai in New York.

Some of these issues aren't unique to neuroscience. They begin with what Ellis called the "original sin" of science: Academics are put under huge pressure to publish positive research findings.

But some of these factors do apply specifically to this field.

The problems are big enough that they are "halting the growth and development of science and the curing of diseases," Ellis told Live Science.

Tiny differences, small samples
Several brain studies that could not be reproduced in follow-up work show how problems can creep in. Each of the original papers has over 500 citations, with the number of citations reflecting how much these studies may influence thinking in the field.

For example, a landmark study in 2007 found that the brains of kids with attention-deficit/hyperactivity disorder took longer to mature. But a study published earlier this year found that this link vanished once the different rates of aging between boys and girls were taken into account. "That's what made the whole house of cards topple," Matthew Albaugh, co-author of the replication paper and a clinical neuroscientist at the University of Vermont, previously told Live Science.