[fernly]

Not clear what distinction you are trying to make. They practiced mindfulness meditation according to a specific, published plan, and brain anatomy changes were noted. It doesn't seem they are making any claim other than, this series of exercises produce this effect.

The paper doesn't seem to be available, but the abstract at the author's page[0] says "Healthy but stressed individuals are randomized to either a meditation-based stress reduction intervention or health education control intervention."

[0]https://connects.catalyst.harvard.edu/Profiles/display/Perso...

[insickness]

If the control group were doing nothing for eight weeks, they would expect no change. An expectation of change can illicit substantial differences. That's the placebo effect.

When administering medication and checking for results, the control group is given a sugar pill rather than nothing. If they were given nothing it would not eliminate the placebo effect.

[danielharan]

(You mean elicit, not illicit)

Placebo might be a fair critique if we were talking about people's self-reported stress or well-being. Here we're talking about physical changes in the amygdala.

[insickness]

The brain and nervous system changes based on it's use and function. Look up neoroplasticity. This is nothing new. A placebo could certainly elicit a change within 8 weeks if participants thought it was helping them cope with stress. If you think dancing clockwise in a circle for ten minutes a day will help you, it probably will. That doesn't mean there is anything useful in the practice.