Detecting and correcting for head movements in neuromagnetic measurements.

Head movements during neuromagnetic measurements may cause a significant error in the estimated locations of active brain areas. In this study we present a fast method for measuring the head position while neuromagnetic data are acquired. We then compare two methods for removing the effect of the movements in neuromagnetic source estimation and magnetic field alignment: minimum-norm estimate alignment and forward calculation correction. Simulations and a test measurement show that the proposed head position measurement method works with millimeter precision and that incorporating the effect of the head movements into the magnetic field forward calculations is an efficient and a sufficiently accurate method for correcting for the head movements. Copyright 2001 Academic Press.