Fractal Dimension of the EEG in Alzheimer's Disease
Daniel Abásolo (University of Valladolid, Spain), Javier Escudero (University of Valladolid, Spain), Roberto Hornero (University of Valladolid, Spain), Pedro Espino (Hospital Clínico San Carlos, Spain) and Carlos Gómez (University of Valladolid, Spain)
Copyright: © 2008
Alzheimer’s disease (AD) is the most frequent cause of dementia in western countries, and is characterized by progressive impairments in cognition and memory, whose course lasts several years prior to death (Jeong, 2004). These clinical features are accompanied by histological changes in the brain, which include widespread cortical atrophy, intracellular deposition of neurofibrillary tangles, and extracellular deposition of senile plaques, particularly in the hippocampus and the cerebral cortex. Although a definite diagnosis is only possible by necropsy, a differential diagnosis with other types of dementia and with major depression should be attempted. Magnetic resonance imaging and computerized tomography can be normal in the early stages of AD, but a diffuse cortical atrophy is the main sign in brain scans. Mental status tests are also useful.
Key Terms in this Chapter
Fractal Dimension (FD): Statistical quantity that gives an indication of how completely a fractal appears to fill space. It can be considered a measure of signal complexity.
Electroencephalogram (EEG): Neurophysiologic recording of electrical brain activity by positioning electrodes generally on the scalp.
Alzheimer’s Disease (AD): A neurodegenerative disease characterized by progressive cognitive deterioration, together with declining activities of daily living and neuropsychiatric symptoms or behavioral changes.
Receiver Operating Characteristic (ROC) Curve: A graphical plot of the sensitivity vs. (1–specificity) for a classifier system, as its discrimination threshold is varied.
Correlation Dimension (D2): A measure of the complexity of a nonlinear system. It characterizes the distribution of points of the attractor in the phase space.
Attractor: In dynamical systems, a set to which the system evolves after a long enough time, after transients have died out.
Fractal: A self-similar structure whose geometrical and topographical features are recapitulated in miniature on finer and finer scales.
Nonlinear Analysis Techniques: Mathematical techniques to analyze nonlinear systems, whose behavior is not expressible as a sum of the behaviors of its descriptors, or signals whose behavior is nonlinear.