Theory of Magnetic Detection of the Heart's Electrical Activity

Baule, Gerhard; McFee, Richard

doi:10.1063/1.1714404

Cited by 103 publications

(24 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Perhaps the most drastic effect of the secondary E field for a spherically symmetric volume conductor was immediately re-derived: independent of the TMS coil position, orientation, and shape, the radial component of the total E field is zero inside the volume conductor. This reflects the well-known fact that radial primary currents in a spherically symmetric volume conductor do not produce external magnetic fields (Baule and McFee, 1965, Grynszpan and Geselowitz, 1973). This theoretical prediction has also been experimentally confirmed (Cohen and Cuffin, 1991, Yunokuchi and Cohen, 1991).…”

Section: Introductionmentioning

confidence: 55%

Comparison of spherical and realistically shaped boundary element head models for transcranial magnetic stimulation navigation

Nummenmaa¹,

Stenroos²,

Ilmoniemi³

et al. 2013

Clinical Neurophysiology

View full text Add to dashboard Cite

Objective MRI-guided real-time transcranial magnetic stimulation (TMS) navigators that apply electromagnetic modeling have improved the utility of TMS. However, their accuracy and speed depends on the assumed volume conductor geometry. Spherical models found in present navigators are computationally fast but may be inaccurate in some areas. Realistically-shaped boundary-element models (BEMs) could increase accuracy at a moderate computational cost, but it is unknown which model features have the largest influence on accuracy. Thus, we compared different types of spherical models and BEMs. Methods Globally and locally fitted spherical models and different BEMs with either one or three compartments and with different skull-to-brain conductivity ratios (1/1 – 1/80) were compared against a reference BEM. Results The one-compartment BEM at inner skull surface was almost as accurate as the reference BEM. Skull/brain conductivity ratio in the range 1/10 – 1/80 had only a minor influence. BEMs were superior to spherical models especially in frontal and temporal areas (up to 20 mm localization and 40% intensity improvement); in motor cortex all models provided similar results. Conclusions One-compartment BEMs offer a good balance between accuracy and computational cost. Significance Realistically-shaped BEMs may increase TMS navigation accuracy in several brain areas, such as in prefrontal regions often targeted in clinical applications.

show abstract

Section: Introductionmentioning

confidence: 55%

Comparison of spherical and realistically shaped boundary element head models for transcranial magnetic stimulation navigation

Nummenmaa¹,

Stenroos²,

Ilmoniemi³

et al. 2013

Clinical Neurophysiology

View full text Add to dashboard Cite

show abstract

“…In that study, the effect to the coerced (vs. non-coerced) complement nouns was more anteriorly distributed (localizing to an anterior midline field) while that to the animacy violated (vs. non-coerced) complement nouns had a more posterior distribution (localizing to temporal sources). The reasons for this discrepancy are unclear but it is important to note that MEG and ERP measures at the surface of the scalp can be differentially sensitive to a given underlying neural source: for example, the contribution of radially oriented sources, prominent in EEG, are weak in MEG (Baule & McFee, 1965; Sharon, Hamalainen, Tootell, Halgren, & Belliveau, 2007). 6…”

Section: Discussionmentioning

confidence: 99%

Electrophysiological Correlates of Complement Coercion

Kuperberg

Choi

Cohn

et al. 2010

Journal of Cognitive Neuroscience

152

View full text Add to dashboard Cite

This study examined the electrophysiological correlates of complement coercion. Event-related potentials (ERPs) were measured as participants read and made acceptability judgments about plausible coerced sentences, plausible non-coerced sentences, and highly implausible animacy violated sentences (“The journalist began/wrote/astonished the article before his coffee break”). Relative to non-coerced complement nouns, the coerced nouns evoked an N400 effect. This effect was not modulated by the number of possible activities implied by the coerced nouns (e.g. began reading the article; began writing the article), and did not differ in either magnitude or scalp distribution from the N400 effect evoked by the animacy violated complement nouns. We suggest that the N400 modulation to both coerced and the animacy violated complement nouns reflected different types of mismatches between the semantic restrictions of the verb and the semantic properties of the incoming complement noun. This is consistent with models holding that a verb’s semantic argument structure is represented and stored at a distinct level from its syntactic argument structure. Unlike the coerced complement noun, the animacy violated nouns also evoked a robust P600 effect, which may have been triggered by the judgments of the highly implausible (syntactically-determined) meanings of the animacy violated propositions. No additional ERP effects were seen in the coerced sentences until the sentence-final word which, relative to sentence-final words in the non-coerced sentences, evoked a sustained anteriorly-distributed positivity. We suggest that this effect reflected delayed attempts to retrieve the specific event(s) implied by coerced complement nouns.

show abstract

“…Theoretically, a radially oriented current dipole produces no magnetic field outside a spherically symmetric volume conductor (Baule and McFee 1965; Grynszpan and Geselowitz 1973). However, since the human head is not exactly spherically symmetric, the radial orientation is not well defined, and an approximately radial source in the brain is not necessarily silent in MEG (Cuffin 1990).…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of MEG and EEG to Source Orientation

et al. 2010

View full text Add to dashboard Cite

An important difference between magnetoencephalography (MEG) and electroencephalography (EEG) is that MEG is insensitive to radially oriented sources. We quantified computationally the dependency of MEG and EEG on the source orientation using a forward model with realistic tissue boundaries. Similar to the simpler case of a spherical head model, in which MEG cannot see radial sources at all, for most cortical locations there was a source orientation to which MEG was insensitive. The median value for the ratio of the signal magnitude for the source orientation of the lowest and the highest sensitivity was 0.06 for MEG and 0.63 for EEG. The difference in the sensitivity to the source orientation is expected to contribute to systematic differences in the signal-to-noise ratio between MEG and EEG.

show abstract

Theory of Magnetic Detection of the Heart's Electrical Activity

Cited by 103 publications

References 5 publications

Comparison of spherical and realistically shaped boundary element head models for transcranial magnetic stimulation navigation

Comparison of spherical and realistically shaped boundary element head models for transcranial magnetic stimulation navigation

Electrophysiological Correlates of Complement Coercion

Sensitivity of MEG and EEG to Source Orientation

Contact Info

Product

Resources

About