489 Intern. J. Neuroscience, 112:489–499, 2002 Copyright  2002 Taylor & Francis 0020-7454/02 $12.00 + .00 DOI: 10.1080/00207450290025608 Brief Communication Received 3 January 2002. Address correspondence to Prof. Dr. Uner Tan, Department of Physiology, BlackSea Tech- nical University Medical School, Trabzon, Turkey. E-mail: unertan@meds.ktu.edu.tr or unertan100@ netscape.net VALIDITY OF SPECTRAL ANALYSIS OF EVOKED POTENTIALS IN BRAIN RESEARCH ALEXANDER V. KRAMARENKO Central Clinic Hospital N5 Kharkov, Ukraine UNER TAN Department of Physiology BlackSea Technical University Medical School Trabzon, Turkey The averaged electronencephologram (EEG) response of the brain to an external stimulus (evoked potential, EP) is usually subjected to spec- tral analysis using the fast Fourier transform (FFT), especially to dis- cover the relation of cognitive ability to so-called brain dynamics. There is indeed a discrepancy between these two systems, because the brain is a highly complex nonlinear system, analyzed by a linear system (FFT). We present in this work some inaccuracies that occurred when EPs are subjected to spectral analysis, using a model signal. First of all, the EP power spectra depended upon the number of samples used for averag- ing; the input EP (model signal) and the output EP (from the system) seemed to be similar in forms, but they exhibited completely different spectral power curves. It was concluded that the spectral analysis of evoked responses by using FFT (linear system analysis) in relation to brain (highly complex nonlinear system) may mislead neuroscientists. Keywords brain, cognition, evoked potential, linear system, nonlinear system, spectral analysis