A 2018 study used a rigorous matched-pairs design. Thirteen yoga practitioners were each matched with a control participant of the same age and sex. Researchers confirmed the groups were similar in demographics and physical fitness, including VO2 max. Both groups completed a working memory task during functional MRI scanning.
The yoga practitioners had greater gray matter volume in their left hippocampus and higher activation of the dorsolateral prefrontal cortex. These are brain regions central to memory formation and executive function. The matched-pairs design rules out the possibility that general fitness, not yoga, explains the differences.
When the fitness levels are equal, yoga practitioners still show distinct brain advantages. The practice does something that general exercise does not.
Source: Yoga Research: Brain Structure & Function on ashtanga.tech. Original research.