Researchers at Harvard used MRI scans to examine the brains of participants before and after an 8-week meditation program. The results showed measurable increases in gray matter density in the hippocampus, a region tied to learning and memory. Increases were also found in structures associated with self-awareness and compassion.
Equally significant, gray matter decreased in the amygdala, the region associated with fear and stress responses. Participants reported lower stress levels, and the brain scans confirmed the subjective experience with physical evidence.
This study is frequently cited because of the short timeline. Eight weeks is not a lifetime of practice. It suggests that even relatively new practitioners may be experiencing structural brain changes they cannot perceive directly but that are nonetheless occurring.
Source: Yoga Research: Brain Structure & Function on ashtanga.tech. Original research.