A subtle change in brain wave activity could predict Alzheimer’s disease more than two years before diagnosis, according to a new study.

The signal could prove to be a sensitive biomarker of cognitive decline.

Using a noninvasive imaging technique called magnetoencephalography (MEG), neuroscientists at Brown University in the US and Spain’s Complutense University of Madrid and University of La Laguna analyzed the resting brain wave activity of 85 patients diagnosed with mild cognitive impairment.