Frequency domain source localization shows state-dependent diazepam effects in 47-channel EEG

Abstract

The topic of this study was to evaluate state-dependent effects of diazepam on the frequency characteristics of 47-channel spontaneous EEG maps. A novel method, the FFT-Dipole-Approximation (Lehmann and Michel, 1990), was used to study effects on the strength and the topography of the maps in the different frequency bands. Map topography was characterized by the 3-dimensional location of the equivalent dipole source and map strength was defined as the spatial standard deviation (the Global Field Power) of the maps of each frequency point. The Global Field Power can be considered as a measure of the amount of energy produced by the system, while the source location gives an estimate of the center of gravity of all sources in the brain that were active at a certain frequency. State-dependency was studied by evaluating the drug effects before and after a continuous performance task of 25 min duration. Clear interactions between drug (diazepam vs. placebo) and time after drug intake (before and after the task) were found, especially in the inferior-superior location of the dipole sources. It supports the hypothesis that diazepam, like other drugs, has different effects on brain functions depending on the momentary functional state of the brain. In addition to the drug effects, clearly different source locations and Global Field Power were found for the different frequency bands, replicating earlier reports (Michel et al., 1992).

Frequency domain EEG source localization of ictal epileptiform activity in patients with partial complex epilepsy of temporal lobe origin

“…Since polarity is arbitrarily chosen with the FFT approximation method, the grand averages were calculated by computing the first principal component map, i.e. the best fitting map in a global sense (Michel et al, 1995).…”

“…This method, called 'FFT dipole approximation' (Lehmann and Michel, 1990), is based on the approximation of a phasecorrected voltage map for each frequency point by considering the amplitude as well as the phase information of all recorded channels. Theoretical considerations (Lütken-höhner, 1992;Valdés et al, 1992), as well as applications to normal EEG (Michel et al, 1992;Tesche and Kajola, 1993), EEG in schizophrenic patients , and EEG after medication (Dierks et al, 1993;Kinoshita et al, 1994;Michel et al, 1995) have shown the potential power of this method to localize specific brain activities. The aim of the present study was to investigate whether the FFT dipole approximation method could be applied to extracranial ictal recordings in patients with partial complex seizures, in order to determine the initiation and spread of seizure activity.…”

Temporal and spatial determination of EEG-seizure onset in the frequency domain

“…The FFT-Approximation method provides ± in contrary to the analysis of power maps ± voltage maps with positive and negative values (as the raw EEG-data). This method as been applied in different data sets (Michel et al, 1992(Michel et al, , 1995Dierks et al, 1993;Lehmann et al, 1993) including EEG of epileptic patients Michel et al, 1999). Fore each seizure in each patient, the 7 FFT-approximated epochs following the ESO were averaged.…”

“…Frequencies below 2.5 Hz were considered to be mainly due to eye artifacts, and were therefore excluded from the analysis. The frequency with maximal global ®eld power (GFP, Michel et al, 1995) which were consistent across the three evaluated seizures were identi®ed in each patient and subsequently analyzed. The range of consistency was de®ned as the frequencies within^0.5 Hz around the prominent power peak in the frequency spectrum of each seizure (see Fig.…”

Uniform decrease of alpha-global field power induced by intermittent photic stimulation of healthy subjects

“…Brain mapping results are influenced by drugs and medications (5). Michel et al (6) reported that GFP is influenced by diazepam and that the extent of influence depends on the functional state of the central nervous system. GFP analysis can serve to monitor treatment of Alzheimers disease with tacrine or related drugs (7).…”