It's worth highlighting that first result is *exactly* what you asked for, given...

It's worth highlighting that first result is exactly what you asked for, given all 4 of your criteria:

1. It's on adults.

2. It's longitudinal over multiple years.

3. It studies variations in brain volume.

4. It focuses on healthy individuals.

And that first hit in JAMA Open is a fabulous paper. Ten or mire yearly MRI scans for 650 subjects.