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W W Sutherling

Publications and source records attributed to W W Sutherling.

At least 19 recordsLinked to original sources
PubMed2003

A model for frequency dependence of conductivities of the live human skull.

A mathematical model (sigma(omega) approximately equal to A omega alpha, where, sigma is identical with conductivity, omega = 2 pi f is identical with applied frequency (Hz), A (amplitude) and alpha (unit less) is identical with search parameters) was used to fit the frequency dependence of electrical conductivities of compact, spongiosum, and bulk layers of the live and, subsequently, dead human skull samples. The results indicate that the fit of this model to the experimental data is excellent. The ranges of values of A and alpha were, spongiform (12.0-36.5, 0.0083-0.0549), the top compact (5.02-7.76, -0.137-0.0144), the lower compact (2.31-10.6, 0.0267-0.0452), and the bulk (7.46-10.6, 0.0133-0.0239). The respective values A and alpha for the respective layers of the dead skull samples were (40.1-89.7, -0.0017-0.0287), (5.53-14.5, -0.0296 - -0.0061), (4.58-15.9, -0.0226-0.0268), and (12.7-25.3, -0.0158-0.0132).

Algorithms↗
PubMed2002

Conductivities of three-layer live human skull.

Electrical conductivities of compact, spongiosum, and bulk layers of the live human skull were determined at varying frequencies and electric fields at room temperature using the four-electrode method. Current, at higher densities that occur in human cranium, was applied and withdrawn over the top and bottom surfaces of each sample and potential drop across different layers was measured. We used a model that considers variations in skull thicknesses to determine the conductivity of the tri-layer skull and its individual anatomical structures. The results indicate that the conductivities of the spongiform (16.2-41.1 milliS/m), the top compact (5.4-7.2 milliS/m) and lower compact (2.8-10.2 milliS/m) layers of the skull have significantly different and inhomogeneous conductivities. The conductivities of the skull layers are frequency dependent in the 10-90 Hz region and are non-ohmic in the 0.45-2.07 A/m2 region. These current densities are much higher than those occurring in human brain.

Adolescent↗
PubMed2001

Dipole localization of human induced focal afterdischarge seizure in simultaneous magnetoencephalography and electrocorticography.

Localizations were compared for the same human seizure between simultaneously measured MEG and iEEG, which were both co-registered to MRI. The whole-cortex neuromagnetometer localized a dipole in a sphere phantom, co-registered to the MEG sensor array, with an error of 1.4 mm. A focal afterdischarge seizure was induced in a patient with partial epilepsy, by stimulation at a subdural electrocorticography (ECoG) electrode with a known location, which was co-registered to the MRI and to the MEG sensor array. The simultaneous MEG and ECoG during the 30-second seizure was measured and analyzed using the single, moving dipole model, which is the localization model used clinically. The dipole localizations from simultaneous whole cortex 68-channel MEG and 64-channel ECoG were then compared for the repetitive spiking at six different times during the seizure. There were two main regions of MEG and ECoG activity. The locations of these regions were confirmed by determining the location clusters of 8,000 dipoles on ECoG at consecutive time points during the seizure. The mean distances between the stimulated electrode location versus the dipole location of the MEG and versus the dipole location of the ECoG were each about one (1) centimeter. The mean distance between the dipole locations of the MEG versus the dipole locations of the ECoG was about 2 cm. These errors were compared to errors of MEG and ECoG reported previously for phantoms and for somatosensory evoked responses (SER) in patients. Comparing the findings from the present study to those from prior studies, there appeared to be the expected stepwise increase in mean localization error progressing from the phantom, to the SER, to the seizure.

Adolescent↗
PubMed2000

Conductivities of three-layer human skull.

In this study, electrical conductivities of compact, spongiosum, and bulk layers of cadaver skull were determined at varying electric fields at room temperature. Current was applied and withdrawn over the top and bottom surfaces of each sample and potential drop across different layers was measured using the four-electrode method. We developed a model, which considers of variations in skull thicknesses, to determine the conductivity of the tri-layer skull and its individual anatomical structures. The results indicate that the spongiform and the two compact layers of the skull have significantly different and inhomogeneous conductivities ranging from 0.76 +/- .14 to 11.5 +/- 1.8 milliS/m.

Electric Conductivity↗
PubMed1996

Multiple source localization using genetic algorithms.

We present a new procedure for localizing simultaneously active multiple brain sources that overlap in both space and time on EEG recordings. The source localization technique was based on a spatio-temporal model and a genetic algorithm search routine. The method was successfully applied to the localization of two dipole sources from several sets of simulated potentials with various signal-to-noise ratios (SNR). The different SNR values resembled evoked responses and epileptic spikes as commonly seen in the laboratory. Results of the simulation studies yielded localization accuracy ranging from 0.01 to 0.07 cm with an SNR of 10; from 0.02 to 0.26 cm with an SNR of 5; and from 0.06 to 0.73 cm when the SNR was equal to 2. Additionally, two sets of simulations were based on the dipole arrangements and time activities of data obtained during electrical stimulation of the median nerve in human subjects. These studies yielded localization accuracy within 0.1 cm. We also studied the localization accuracy of the algorithm using a physical model incorporating potential measurements of two current dipoles embedded in a sphere. In this situation the algorithm was successful in localizing the two simultaneously active sources to within 0.07-0.15 cm.

Algorithms↗
PubMed1995

MEG and ECoG localization accuracy test.

We tested the localization accuracy of magnetoencephalography (MEG) and electrocorticography (ECoG) for a current dipole in a saline filled sphere at depths ranging from 1 to 6 cm at 1 cm intervals. We used standard neuromagnetometer placements and subdural electrode grids, previously employed for patient studies, with precise measurements of sensor and electrode locations with a 3-dimensional spatial digitizer. MEG and ECoG had comparable accuracy with mean errors of 1.5 and 1.8 mm, respectively. It appears that use of the spatial digitizer increases accuracy for both MEG and EGoG localizations. The larger errors in the ECoG with increasing depths could be attributed to under-sampling of the spatial pattern of the field which spreads out with deeper sources. It should be noted that in clinical applications a grid of the dimensions used here would most typically be used for superficial sources on the cortex with depth recordings being preferred for investigations of deep epileptogenic activity. Results are encouraging for continued development of non-invasive MEG methods for further definition of epileptogenic zones in the brain.

Cerebral Cortex↗
PubMed1994

Comparisons of MEG, EEG, and ECoG source localization in neocortical partial epilepsy in humans.

In order to delineate the characteristics of epileptic spikes, 1946 different spikes were studied in 6 patients with complex partial epilepsy. Non-invasive MEG and EEG source analysis of interictal spikes were contrasted to ECoG localization, surgical outcome and presence of lesions on MRI. Results indicated that: (1) using the most frequent occurring spike topography patterns from a large sample of spikes improved goodness-of-fit values for both MEG and EEG localization, (2) when spike patterns could be appropriately matched on several successive MEG measurements to provide an adequate matrix (3 of 6 subjects), there was excellent agreement between MEG dipole sources and ECoG sources as well as surgical outcome and presence of MRI lesions, (3) EEG source analyses also gave good results but not as consistently as MEG.

Adult↗
PubMed1994

Somatosensory evoked fields and potentials following tibial nerve stimulation.

We studied evoked magnetic fields and electrical potentials following stimulation of the tibial nerve in a group of 24 normal subjects. Both magnetic and electrical recordings demonstrated a series of oscillatory patterns consisting of four peaks (two positive and two negative) occurring between 40 and 100 msec. Magnetic field source localization of all four peaks using a dipole-in-a-sphere model indicated that all four peaks emanated from the same cortical surface located within the longitudinal fissure, an area typically associated with somatosensory function.

Adult↗
PubMed1993

Surgical treatment of partial epilepsy arising from the insular cortex. Report of two cases.

Despite its documented connections with many limbic structures, the role of the insula in the etiology of partial seizures is poorly understood. Two patients are described in whom lesions of the insula were associated with intractable partial seizures. In the first patient, the seizures involved visceral sensory hallucinations followed by motor automatism. Seizures in the second patient began with somatic sensory hallucinations and then produced visceral motor effects. Both patients were found to have low-grade astrocytomas of the insula. In both instances, resection of the lesion and adjacent insular cortex resulted in a cure of the seizures. These cases are placed within the context of the existing literature on the subject.

Adolescent↗
PubMed1992

Surgery of central sensory motor and dorsolateral frontal lobe seizures.

Ten patients who presented with dorsolateral or frontocentral seizures were studied with chronic subdural grid electrodes. Cortical mapping, sensory-evoked potentials and chronic electrocorticography were obtained for each patient. Seizures were classified as focal, regional or dipolar. At the time of explanation, a selective functional corticectomy was performed. Surgical outcome is presented at a mean follow-up of 36 months. Two patients are seizure-free and 7 patients had a significant reduction in seizure frequency. One patient had no change in seizure pattern. Dorsolateral frontal lobe seizures have a focal functional anatomy and can be surgically treated by selective cortectomy.

Adult↗
PubMed1992

Cortical sensory representation of the human hand: size of finger regions and nonoverlapping digit somatotopy.

Findings differ on cortical representation of fingers between human and animal studies, and on digit somatotopy among human studies. To resolve these differences, we mapped cortical sensory representation of each of the five digits and of median and ulnar nerves in three patients, using focal peripheral electrical shock stimuli. We compared locations and sizes of cortical regions among digits and nerves, using the model of a current dipole in a sphere applied to electrocorticography from subdural grids. Cortical representation was larger for the index finger than for the little finger and for the middle finger than for the ring finger, which are similar to findings in the monkey but different from Penfield's classic sensory homunculus. The thumb was larger than the middle finger, as in the homunculus. There was nonoverlapping somatotopy of all digits in each patient. These findings demonstrate a previously unrecognized similarity of cortical sensory organization of the fingers between humans and other primates.

Brain Mapping↗
PubMed1991

Human somatosensory cortical finger representation as studied by combined neuromagnetic and neuroelectric measurements.

We studied somatotopy of human hand somatosensory cortex using evoked responses recorded on magnetoencephalogram (MEG) and scalp-electroencephalogram (EEG) in conjunction with dipole modeling. We found a somatotopic arrangement of cortical digit representations with a sensory sequence from lateral inferior to medial superior in the anatomical order thumb, index finger, middle finger, ring finger, and little finger. MEG alone was able to reproduce this sensory sequence more accurately than scalp-EEG alone. However, the combined information provided by both techniques improved localization accuracy even further. As MEG and scalp-EEG are complementary and confirmatory techniques, this combined approach was useful to get more complete information on the functional organization of human hand somatosensory cortex.

Brain Mapping↗
PubMed1991

Neuromagnetic investigation of somatotopy of human hand somatosensory cortex.

In order to investigate functional topography of human hand somatosensory cortex we recorded somatosensory evoked fields (SEFs) on MEG during the first 40 ms after stimulation of median nerve, ulnar nerve, and the 5 digits. We applied dipole modeling to determine the three-dimensional cortical representations of different peripheral receptive fields. Median nerve and ulnar nerve SEFs exhibited the previously described N20 and P30 components with a magnetic field pattern emerging from the head superior and re-entering the head inferior for the N20 component; the magnetic field pattern of the P30 component was of reversed orientation. Reversals of field direction were oriented along the anterior-posterior axis. SEFs during digit stimulation showed analogous N22 and P32 components and similar magnetic field patterns. Reversals of field direction showed a shift from lateral inferior to medial superior for thumb to little finger. Dipole modeling yielded good fits at these peak latencies accounting for an average of 83% of the data variance. The cortical digit representations were arranged in an orderly somatotopic way from lateral inferior to medial superior in the sequence thumb, index finger, middle finger, ring finger, and little finger. Median nerve cortical representation was lateral inferior to that of ulnar nerve. Isofield maps and dipole locations for these components are consistent with neuronal activity in the posterior bank of central fissure corresponding to area 3b. We conclude that SEFs recorded on MEG in conjunction with source localization techniques are useful to investigate functional topography of human hand somatosensory cortex non-invasively.

Brain Mapping↗
PubMed1991

Functional anatomy of human hand sensorimotor cortex from spatiotemporal analysis of electrocorticography.

We measured chronic electrocorticography (ECoG) of sensorimotor cortex during contralateral median nerve stimulation in 6 patients with partial seizures evaluated for surgery. We analyzed the spatiotemporal structure of the somatosensory evoked response (SER) using multiple source modeling to investigate functional anatomy of its neuronal sources. Two dipole sources in postcentral gyrus explained the large majority of the first 60 msec of the SER, indicating a subregion of hand somatosensory cortex generating this activity. The source locations agreed with normal functional anatomy from cortical stimulations, intraoperative photographs, and postoperative neurological examinations after focal excisions. The time patterns of both sources were biphasic like the previously described N20-P30 and P25-N35 peaks. The spatiotemporal patterns of both sources overlapped. Spatiotemporal analysis with multiple dipole sources appears useful to determine the number, locations, and spatiotemporal field patterns of cortical regions active during peripheral somatosensory stimulation and reveals simplicity in the macroscopic functional anatomy of dynamic human sensorimotor cortex.

Adolescent↗
PubMed1991

Spatiotemporal modeling of cerebral evoked magnetic fields to median nerve stimulation.

We measured somatosensory evoked magnetic fields during median nerve stimulation in 6 normal subjects. We applied multiple dipole models to study the spatiotemporal structure of early somatosensory evoked magnetic fields (SEFs), as well as the number, 3-dimensional location and time activity of their underlying neuronal sources. Two dipole sources were necessary to model the first 40 msec of SEFs explaining 85% of the data variance. Source 1 was located deeper than source 2, showed primarily a tangential orientation, and accounted for a larger part of the variance; source 2 showed no consistent orientation across subjects. Both sources showed biphasic time activities corresponding to the previously described N20-P30 and P25-N35 components. Spatiotemporal modeling could identify sources which could not be modeled consistently above noise by single moving dipoles (P25 component), revealed small latency differences of the two sources in some subjects suggesting parallel activation of these sources, and allowed separation of sources overlapping considerably both in space and time. We conclude that spatiotemporal modeling of SEFs may be useful to study functional anatomy of human sensorimotor cortex non-invasively.

Electric Stimulation↗
PubMed1991

Localization of partial epilepsy using magnetic and electric measurements.

Dipole methods applied to brain electric and magnetic fields have made several significant advances in investigation of epilepsy and sensorimotor cortex. The magnetoencephalogram (MEG) and the MEG-electroencephalogram (EEG) combination have contributed substantially. The MEG-EEG combination has shown a mean accuracy of somatosensory evoked response (SER) localization of the central fissure similar to electrocorticography (ECoG), resolution of ambiguity in ECoG of alternative configurations of hand sensorimotor cortex, and resolution of ambiguity of the causes of the difference between EEG and ECoG map patterns. MEG has shown simple dipolar maps of the temporal lobe interictal spike, localization estimates with about 6 mm error, and spatial separation of propagating multiple sources. MEG and EEG have shown a new neocortical propagation pathway in the temporal lobe, noninvasive estimates of the area of the spike focus, and complementary detection sensitivity. Application of spatiotemporal multiple dipole modeling in the simplest field using MEG has given a realistic quantification of spike zones. MEG and EEG have shown simple dipolar patterns for seizure origin, suggesting focality of some frontal seizures, and appears to increase EEG utility. Improved accuracy may result from a combined methodology including MEG and EEG. Dipole methods have potential utility as a noninvasive diagnostic procedure in epilepsy.

Brain Mapping↗