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Variable anisotropic brain electrical conductivities in epileptogenic foci.

Akhtari M, Mandelkern M, Bui D, Salamon N, Vinters HV, Mathern GW - Brain Topogr (2010)

Bottom Line: Electrical conductivities perpendicular and parallel to the pial surface of neocortex and subcortical white matter (n = 15) were measured using the 4-electrode technique and compared with clinical variables.A perpendicular principal axis was associated with normal, while isotropy and parallel principal axes were linked with epileptogenic lesions by MRI.Electrical conductivities were decreased in patients with cortical dysplasia compared with non-dysplasia etiologies.

View Article: PubMed Central - PubMed

Affiliation: Neuropsychiatric Institutes, David Geffen School of Medicine, University of California, Los Angeles, CA 90015, USA. Akhtarim@ucla.edu

ABSTRACT
Source localization models assume brain electrical conductivities are isotropic at about 0.33 S/m. These assumptions have not been confirmed ex vivo in humans. This study determined bidirectional electrical conductivities from pediatric epilepsy surgery patients. Electrical conductivities perpendicular and parallel to the pial surface of neocortex and subcortical white matter (n = 15) were measured using the 4-electrode technique and compared with clinical variables. Mean (+/-SD) electrical conductivities were 0.10 +/- 0.01 S/m, and varied by 243% from patient to patient. Perpendicular and parallel conductivities differed by 45%, and the larger values were perpendicular to the pial surface in 47% and parallel in 40% of patients. A perpendicular principal axis was associated with normal, while isotropy and parallel principal axes were linked with epileptogenic lesions by MRI. Electrical conductivities were decreased in patients with cortical dysplasia compared with non-dysplasia etiologies. The electrical conductivity values of freshly excised human brain tissues were approximately 30% of assumed values, varied by over 200% from patient to patient, and had erratic anisotropic and isotropic shapes if the MRI showed a lesion. Understanding brain electrical conductivity and ways to non-invasively measure them are probably necessary to enhance the ability to localize EEG sources from epilepsy surgery patients.

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Line graphs showing the relationship between the percent change in electrical conductivity by axis (calculated as (((Cond. Perp. − Cond. Par.)/Cond. Perp.)) × 100)) compared with conductivity velocities perpendicular (a) and parallel (b) to the pial surface by patient. Conductivities perpendicular (vertical) to the pial surface positively correlated with percent change (P = 0.0069) while conductivities parallel (horizontal) to the pial surface did not (P = 0.496). The changes in electrical conductivities relative to axis direction are illustrated in the oval shapes at the top of (a) (line above ovals represents the pial surface). Negative percent change indicate greater anisotropic shapes with the main axis horizontal to the pial surface, values near zero indicate isotropic shapes, and positive percent changes reflect anisotropic shapes with the main axis and vertical to the pial surface
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Fig3: Line graphs showing the relationship between the percent change in electrical conductivity by axis (calculated as (((Cond. Perp. − Cond. Par.)/Cond. Perp.)) × 100)) compared with conductivity velocities perpendicular (a) and parallel (b) to the pial surface by patient. Conductivities perpendicular (vertical) to the pial surface positively correlated with percent change (P = 0.0069) while conductivities parallel (horizontal) to the pial surface did not (P = 0.496). The changes in electrical conductivities relative to axis direction are illustrated in the oval shapes at the top of (a) (line above ovals represents the pial surface). Negative percent change indicate greater anisotropic shapes with the main axis horizontal to the pial surface, values near zero indicate isotropic shapes, and positive percent changes reflect anisotropic shapes with the main axis and vertical to the pial surface

Mentions: There were differences as to which axis relative to the pial surface had higher conductivities, and whether conductivities were isotropic or anisotropic. This was reflected in the percent change calculation comparing the perpendicular and parallel conductivities. These varied by 45% (+25.3% to −19.7%; Table 1). Positive percent change indicates anisotropic shapes with the long axis perpendicular (vertical) to the pial surface, values near zero indicate isotropic conductivities, and negative percent change indicates anisotropic shapes with the long axis parallel (horizontal) to the pial surface (see ovals at the top of Fig. 3a). Anisotropy in the perpendicular orientation was observed in seven (47%) patients (Table 1; Cases 1–7; P < 0.002), isotropic shapes were seen in two patients (13%; Cases 7 and 8), and anisotropy with a parallel orientation was seen in six (40%) patients (Cases 10–15; P < 0.031). Hence, anisotropic brain electrical conductivities were noted in 87% of epilepsy surgery patients in this cohort but with different orientations of the long axis.Fig. 3


Variable anisotropic brain electrical conductivities in epileptogenic foci.

Akhtari M, Mandelkern M, Bui D, Salamon N, Vinters HV, Mathern GW - Brain Topogr (2010)

Line graphs showing the relationship between the percent change in electrical conductivity by axis (calculated as (((Cond. Perp. − Cond. Par.)/Cond. Perp.)) × 100)) compared with conductivity velocities perpendicular (a) and parallel (b) to the pial surface by patient. Conductivities perpendicular (vertical) to the pial surface positively correlated with percent change (P = 0.0069) while conductivities parallel (horizontal) to the pial surface did not (P = 0.496). The changes in electrical conductivities relative to axis direction are illustrated in the oval shapes at the top of (a) (line above ovals represents the pial surface). Negative percent change indicate greater anisotropic shapes with the main axis horizontal to the pial surface, values near zero indicate isotropic shapes, and positive percent changes reflect anisotropic shapes with the main axis and vertical to the pial surface
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2914871&req=5

Fig3: Line graphs showing the relationship between the percent change in electrical conductivity by axis (calculated as (((Cond. Perp. − Cond. Par.)/Cond. Perp.)) × 100)) compared with conductivity velocities perpendicular (a) and parallel (b) to the pial surface by patient. Conductivities perpendicular (vertical) to the pial surface positively correlated with percent change (P = 0.0069) while conductivities parallel (horizontal) to the pial surface did not (P = 0.496). The changes in electrical conductivities relative to axis direction are illustrated in the oval shapes at the top of (a) (line above ovals represents the pial surface). Negative percent change indicate greater anisotropic shapes with the main axis horizontal to the pial surface, values near zero indicate isotropic shapes, and positive percent changes reflect anisotropic shapes with the main axis and vertical to the pial surface
Mentions: There were differences as to which axis relative to the pial surface had higher conductivities, and whether conductivities were isotropic or anisotropic. This was reflected in the percent change calculation comparing the perpendicular and parallel conductivities. These varied by 45% (+25.3% to −19.7%; Table 1). Positive percent change indicates anisotropic shapes with the long axis perpendicular (vertical) to the pial surface, values near zero indicate isotropic conductivities, and negative percent change indicates anisotropic shapes with the long axis parallel (horizontal) to the pial surface (see ovals at the top of Fig. 3a). Anisotropy in the perpendicular orientation was observed in seven (47%) patients (Table 1; Cases 1–7; P < 0.002), isotropic shapes were seen in two patients (13%; Cases 7 and 8), and anisotropy with a parallel orientation was seen in six (40%) patients (Cases 10–15; P < 0.031). Hence, anisotropic brain electrical conductivities were noted in 87% of epilepsy surgery patients in this cohort but with different orientations of the long axis.Fig. 3

Bottom Line: Electrical conductivities perpendicular and parallel to the pial surface of neocortex and subcortical white matter (n = 15) were measured using the 4-electrode technique and compared with clinical variables.A perpendicular principal axis was associated with normal, while isotropy and parallel principal axes were linked with epileptogenic lesions by MRI.Electrical conductivities were decreased in patients with cortical dysplasia compared with non-dysplasia etiologies.

View Article: PubMed Central - PubMed

Affiliation: Neuropsychiatric Institutes, David Geffen School of Medicine, University of California, Los Angeles, CA 90015, USA. Akhtarim@ucla.edu

ABSTRACT
Source localization models assume brain electrical conductivities are isotropic at about 0.33 S/m. These assumptions have not been confirmed ex vivo in humans. This study determined bidirectional electrical conductivities from pediatric epilepsy surgery patients. Electrical conductivities perpendicular and parallel to the pial surface of neocortex and subcortical white matter (n = 15) were measured using the 4-electrode technique and compared with clinical variables. Mean (+/-SD) electrical conductivities were 0.10 +/- 0.01 S/m, and varied by 243% from patient to patient. Perpendicular and parallel conductivities differed by 45%, and the larger values were perpendicular to the pial surface in 47% and parallel in 40% of patients. A perpendicular principal axis was associated with normal, while isotropy and parallel principal axes were linked with epileptogenic lesions by MRI. Electrical conductivities were decreased in patients with cortical dysplasia compared with non-dysplasia etiologies. The electrical conductivity values of freshly excised human brain tissues were approximately 30% of assumed values, varied by over 200% from patient to patient, and had erratic anisotropic and isotropic shapes if the MRI showed a lesion. Understanding brain electrical conductivity and ways to non-invasively measure them are probably necessary to enhance the ability to localize EEG sources from epilepsy surgery patients.

Show MeSH
Related in: MedlinePlus