Amount of information gained about one signal from the measurement of another.
Published in Chapter:
Regularity Analysis of the Magnetoencephalogram Background Activity in Alzheimer's Disease Patients Using Auto Mutual Information
Carlos Gómez (University of Valladolid, Spain), Roberto Hornero (University of Valladolid, Spain), Daniel Abásolo (University of Valladolid, Spain), Alberto Fernández (Complutense University of Madrid, Spain), and Javier Escudero (University of Valladolid, Spain)
Copyright: © 2008
|Pages: 7
DOI: 10.4018/978-1-59904-889-5.ch143
Abstract
Magnetoencephalograpy (MEG) is a noninvasive technique that allows recording the magnetic fields produced by brain activity. SQUID (Superconducting QUantum Interference Device) sensors immersed in liquid helium at 4.2 K are used to detect the extremely weak brain magnetic signals. MEG provides an excellent temporal resolution, orders of magnitude better than in other methods for measuring cerebral activity, as magnetic resonance imaging, single-photon-emission computed tomography and positron-emission tomography (Hämäläinen, Hari, Ilmoniemi, Knuutila, & Lounasmaa, 1993). A good spatial resolution is also provided, although this depends on the source configuration (Hari & Forss, 1999). Moreover, this technique is independent of any reference point. In addition, magnetic fields are not distorted by the resistive properties of the skull (Hämäläinen et al., 1993). Nevertheless, the recordings are very sensitive to external artifacts. Thus, the signals must be acquired in a magnetically shielded room. In this preliminary study, we examined the MEG background activity in patients with probable AD, and in age-matched control subjects using auto mutual information (AMI). Our purpose is to test the hypothesis that an abnormal type of nonlinear dynamics is associated with AD.