Regional head tissue conductivity estimation for improved EEG analysis

Abstract

We develop a method for estimating regional head tissue conductivities in vivo, by injecting small (1-10 microA) electric currents into the scalp, and measuring the potentials at the remaining electrodes of a dense-array electroencephalography net. We first derive analytic expressions for the potentials generated by scalp current injection in a four-sphere model of the human head. We then use a multistart downhill simplex algorithm to find regional tissue conductivities which minimize the error between measured and computed scalp potentials. Two error functions are studied, with similar results. The results show that, despite the low skull conductivity and expected shunting by the scalp, all four regional conductivities can be determined to within a few percent error. The method is robust to the noise levels expected in practice. To obtain accurate results the cerebrospinal fluid must be included in the forward solution, but may be treated as a known parameter in the inverse solution.

A Developmental Study of the Feedback-Related Negativity From 10–17 Years: Age and Sex Effects for Reward Versus Non-Reward

“…A whole-head CT scan of this same individual, whose Talairach-transformed head closely matches the Montreal Neurological Institute average MRI (MNI305), was also used. Within the FDM, conductivity values were 0.25 S/m(Siemens/meter) for the brain, 1.8 S/mfor the cerebral spinal fluid, 0.018 S/m for the skull, and 0.44 S/m for the scalp (Ferree, Eriksen, & Tucker, 2000). Distributed dipole placement relied on the probabilistic map of the MNI305 average brain.…”

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“…Because the effects of varying conductivities for common tissue types such as bone, scalp, GM and WM have been widely explored elsewhere (Chen et al, 2010; Ferree et al, 2000; Pohlmeier et al, 1997; Zhang et al, 2006) and are relatively better understood than the effect of pathology, this type of analysis is not reproduced here. In the case of pathology, Fig.…”