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Accurate localization of brain activity recorded by magnetoencephalography (MEG) requires that the forward problem, i.e. the magnetic field caused by a dipolar source current in a homogeneous volume conductor, be solved precisely. We have used the Galerkin method with piecewise linear basis functions in the boundary element method to improve the solution of(More)
Sources of brain activity, e.g. epileptic foci, can be localized with Magnetoencephalography (MEG) measurements by recording the magnetic field outside the head. For a successful surgery a very high localization accuracy is needed. The most often used conductor model in the source localization is an analytic sphere, which is not always adequate, and thus a(More)
Spontaneous magnetoencephalographic activity was recorded with a 24-SQUID gradiometer over the lateral aspects of the head in 3 healthy adults. All subjects displayed 8-10 Hz rhythmic activity which was not affected by opening of the eyes but was occasionally dampened by auditory stimuli. The equivalent sources of the rhythm were in the supratemporal(More)
Medial temporal brain structures and hippocampus are associated with memory encoding and activate during registration and transfer of information within cortico-hippocampal circuits. Hippocampal dysfunction may cause learning and memory deficits as well as epileptogenesis. We monitored neuronal population activity of the human hippocampal formation with a(More)
We study the iterative solution of dense linear systems that arise from boundary element discretizations of the electrostatic integral equation in magnetoencephalography (MEG). We show that modern iterative methods can be used to decrease the total computation time by avoiding the time-consuming computation of the LU decomposition of the coefficient matrix.(More)
Sources of brain activity, e.g., epileptic foci can be localized by measuring the magnetic eld outside the head (MEG) or by recording the electric potential on the scalp (EEG). For a successful surgery a very high localization accuracy is needed. The most often used conductor model in the source localization is an analytic sphere, which is not always(More)
Magnetoencephalography (MEG) is a noninvasive technique for studying neuronal activity in the living human brain. Weak magnetic elds caused by the activity are measured from outside the head. Based on these measurements the source of the activity is located with the help of a mathematical model. A part of the localization is the repeated computation of the(More)
We recorded auditory evoked magnetic fields from 6 healthy subjects with a 122-channel whole-head neuromagnetometer. The stimuli were 200-ms 1-kHz tones delivered at 4 different intensities (40, 50, 60, and 65 dB HL). The tones were given once every second, binaurally in the first session, and monaurally to each ear in the second one. The four intensities(More)