Electroencephalography and clinical neurophysiology. Supplement
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Electroencephalogr Clin Neurophysiol Suppl · Jan 1996
ReviewMagnetic resonance imaging studies of functional brain activation: analysis and interpretation.
We have demonstrated that a time series of echoplanar images can contain low frequency noise components which confound analysis of functional MRI data. In simulated tasks of long duration, the false positive rate from t-test analyses greatly exceeded the statistical probability level. As task durations were shortened, the false positive rate declined. ⋯ Many of the advantages of the procedures described here are due to the alternation of short duration tasks rather than the application of frequency domain techniques per se. However, the success of these techniques in isolating periodic task-related signal changes suggest that a more complex design with concurrent stimulation presented at different frequencies might be feasible. Such designs may have advantages in that categories of stimuli would not be presented in isolation but against a changing ba
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Electroencephalogr Clin Neurophysiol Suppl · Jan 1991
Mechanisms of peripheral nervous system stimulation using the magnetic coil.
We measured the distribution of the electric fields induced within isotropic and anisotropic volume conductors by figure '8' and round magnetic coils (MCs). For various MC orientations maximal electric fields were induced parallel to the inner surface of the volume conductor. Predictions from physical models roughly approximating human forearm and vertebral column were then tested by MC stimulation of distal median nerve at the wrist and nerve roots at the cervical spine, respectively. ⋯ This site most likely corresponds to the vicinity of the neuroforamina where the induced electric field is most intense and the first spatial derivatives peak. By contrast, the low value of the first derivative in the longitudinal axis of the vertebral canal implies that long tracts in the spinal cord are not likely to be excited using commercially available MCs. Our study also indicates that intracranial stimulation of facial nerve occurs at a selected low threshold location, probably reflecting focusing of induced current.