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J D Lewine

Publications and source records attributed to J D Lewine.

At least 19 recordsLinked to original sources
PubMed1999

Integration of preoperative and intraoperative functional brain mapping in a frameless stereotactic environment for lesions near eloquent cortex. Technical note.

The authors present a method of incorporating preoperative noninvasive functional brain mapping data into the frameless stereotactic magnetic resonance (MR) imaging dataset used for image-guided resection of brain lesions located near eloquent cortex. They report the use of functional (f)MR imaging and magnetic source (MS) imaging for preoperative mapping of eloquent cortex in difficult cases of brain tumor resection such as those in which there are large expansive masses or in which reoperations are required and the anatomy is distorted from prior treatments. To correlate methods of preoperative and intraoperative mapping localization directly, the authors have developed techniques of importing preoperative MS and fMR imaging data into an image-guided frameless stereotactic computer workstation. The data appear as a seamless overlay on the same preoperative volumetric MR imaging dataset used for stereotactic guidance during the operation. Intraoperatively identified functional locations mapped by cortical stimulation are recorded as digitally registered points. This approach should prove useful in assessing the accuracy and reliability of various preoperative functional brain mapping techniques.

Adult↗
PubMed1998

A study of dipole localization accuracy for MEG and EEG using a human skull phantom.

OBJECTIVE: To investigate the accuracy of forward and inverse techniques for EEG and MEG dipole localization. DESIGN AND METHODS: A human skull phantom was constructed with brain, skull and scalp layers and realistic relative conductivities. Thirty two independent current dipoles were distributed within the 'brain' region and EEG and MEG data collected separately for each dipole. The true dipole locations and orientations and the morphology of the brain, skull and scalp layers were extracted from X-ray CT data. The location of each dipole was estimated from the EEG and MEG data using the R-MUSIC inverse method and forward models based on spherical and realistic head geometries. Additional computer simulations were performed to investigate the factors affecting localization accuracy. RESULTS: Localization errors using the relatively simpler locally fitted sphere approach are only slightly greater than those using a BEM approach. The average localization error over the 32 dipoles was 7-8 mm for EEG and 3 mm for MEG. CONCLUSION: The superior performance of MEG over EEG appears to be because the latter is more sensitive to errors in the forward model arising from simplifying assumptions concerning the conductivity of the skull, scalp and brain.

Computer Simulation↗
PubMed1998

Spontaneous brain magnetic activity in schizophrenia patients treated with aripiprazole.

This magnetoencaphalographic (MEG) study was conducted as part of a multicenter clinical trial to study the efficacy of aripiprazole. Participants included 5 DSM-IV schizophrenia subjects and 10 age-matched normal controls. The schizophrenia subjects underwent a second MEG recording after 8 weeks of open-label treatment with aripiprazole. Overall, control subjects showed no abnormal spontaneous magnetic brain activity. At washout, 3 patients showed increased delta and theta activity along with paraxosymal bitemporal slow waves. In 2 of these patients, the slow waves were generated in the superior temporal plane, as determined by dipole modeling. In the third patient, the slow waves appeared to have been generated at multiple regions throughout the temporal and inferior parietal lobes. As a group, schizophrenia patients, when compared with normal controls, demonstrated significant decreases in alpha peak frequency and power. Following treatment, aripiprazole had a significant normalizing effect on delta and theta activity. Patients on aripiprazole continued to demonstrate significant abnormalities in alpha frequency and power.

Adult↗
PubMed1996

Magnetoencephalographic assessment of spontaneous brain activity in schizophrenia.

Magnetoencephalography (MEG) offers an attractive alternative to electroencephalography (EEG) in the assessment of psychiatric patients. In this study, a whole-head biomagnetometer equipped with 122 super-cooled sensors was used to assess spontaneous neuromagnetic activity in 11 unmedicated schizophrenic patients and 8 schizophrenic patients medicated for more than 8 weeks with novel antipsychotics (5 of whom were initially studied as part of the unmedicated group). Ten normal (nonpsychiatric) controls were also examined. For each subject, 5 minutes of data were collected in an eyes-closed state. Data were visually inspected for gross MEG abnormalities, and average power spectra were calculated for the data at each sensor. No gross abnormalities were identified for control subjects. One unmedicated schizophrenic patient showed epileptiform sharp waves, and 4 showed abnormal slow waves. No gross MEG abnormalities were found for the medicated schizophrenic group (which included 3 patients who had previously shown slow waves in the unmedicated state). Spectral analyses showed that the schizophrenia patients demonstrated lower alpha power and peak frequency than controls. The data are interpreted within the context of previously reported magnetic resonance abnormalities of the thalamus.

Adult↗
PubMed1995

Comparison of functional magnetic resonance imaging with positron emission tomography and magnetoencephalography to identify the motor cortex in a patient with an arteriovenous malformation.

Alterations in gyral contour made it difficult to identify the motor cortex thought to be near an arteriovenous malformation (AVM) in a 24-year-old man considered for stereotactic radiosurgery. Functional imaging in three modalities was performed preoperatively to compare the reliability of localization using functional magnetic resonance imaging (fMRI) on a conventional scanner with positron emission tomography (PET) and magnetoencephalography (MEG). Similar tasks were used for each imaging modality in an attempt to activate and identify the sensory and motor cortex. Data from all three modalities converged for the sensory task, and fMRI and PET data converged for the motor task. The right hemisphere motor strip was localized adjacent and anterior to the AVM. These data were used in planning the radiosurgery isodose configuration to the AVM in order to reduce the irradiation of motor cortex parenchyma. A postoperative fMRI study was also performed using newer techniques to reduce head motion artifact and to improve signal-to-noise ratio. The data confirmed the conclusions derived from the preoperative evaluations. This study demonstrates how conventional MRI scanners can be used for functional studies of use in surgical planning.

Adult↗
PubMed1995

Mapping function in the human brain with magnetoencephalography, anatomical magnetic resonance imaging, and functional magnetic resonance imaging.

Integrated analyses of human anatomical and functional measurements offer a powerful paradigm for human brain mapping. Magnetoencephalography (MEG) and EEG provide excellent temporal resolution of neural population dynamics as well as capabilities for source localization. Anatomical magnetic resonance imaging (MRI) provides excellent spatial resolution of head and brain anatomy, whereas functional MRI (fMRI) techniques provide an alternative measure of neural activation based on associated hemodynamic changes. These methodologies constrain and complement each other and can thereby improve our interpretation of functional neural organization. We have developed a number of computational tools and techniques for the visualization, comparison, and integrated analysis of multiple neuroimaging techniques. Construction of geometric anatomical models from volumetric MRI data allows improved models of the head volume conductor and can provide powerful constraints for neural electromagnetic source modeling. These approaches, coupled to enhanced algorithmic strategies for the inverse problem, can significantly enhance the accuracy of source-localization procedures. We have begun to apply these techniques for studies of the functional organization of the human visual system. Such studies have demonstrated multiple, functionally distinct visual areas that can be resolved on the basis of their locations, temporal dynamics, and differential sensitivity to stimulus parameters. Our studies have also produced evidence of internal retinotopic organization in both striate and extrastriate visual areas but have disclosed organizational departures from classical models. Comparative studies of MEG and fMRI suggest a reasonable but imperfect correlation between electrophysiological and hemodynamic responses. We have demonstrated a method for the integrated analysis of fMRI and MEG, and we outline strategies for improvement of these methods. By combining multiple measurement techniques, we can exploit the complementary strengths and transcend the limitations of the individual neuro-imaging methods.

Brain↗
PubMed1995

Pediatric magnetic source imaging.

Magnetic source imaging has changed the perspective of managing pediatric patients with epilepsy since its introduction into clinical imaging in the pediatric population. Magnetic source imaging can be important in understanding pediatric functional neuroanatomy and for epileptic surgery in children with intractable seizures. The use and efficacy of magnetic source imaging for surgical planning and patient management is demonstrated by case reports presented in this article.

Brain Mapping↗
PubMed1995

Spike and slow wave localization by magnetoencephalography.

At institutions where MEG is available, it is now considered a standard part of the diagnostic workup of most patients with epilepsy. Available data indicate that interictal MEG can be an effective tool for localization of the epileptic irritative zone, and in some cases it can even indicate the seizure onset site. Both spike and ALFMA examinations are clinically viable because of the availability of large-array systems. The current cost of acquiring MEG technology is high (greater than 2 million dollars), but recent technical developments should soon yield more cost-effective systems. It is anticipated that the increasing applicability of this technology to conditions beyond epilepsy (e.g., head trauma, ischemic disease, dementia, and psychiatric dysfunction) will soon render MEG a critical element in the general armamentarium of diagnostic procedures available to epileptologists, radiologists, neurologists, neurosurgeons, and psychiatrists.

Brain↗
PubMed1994

Interhemispheric sharing of visual memory in macaques.

(1) In macaques with the optic chiasm transected, and forebrain commissural communication limited to the anterior commissure or the posterior 5 mm of the splenium of the corpus callosum, visual patterns viewed initially by only one eye (hemisphere) are subsequently recognized by the other with normal accuracy. (2) The efficiency of these commissural paths is further indicated by the fact that even when as many as six "target" images are presented for memorization to only one hemisphere, it makes essentially no difference as to accuracy or latency of performance which hemisphere is then required to distinguish "target" from "non-target" images. (3) By electrically tetanizing structures in one or the other temporal lobe at various times in relation to visual input and/or mnemonic testing it could be shown: (a) that a memory trace restricted in its formation to a single hemisphere was available to the other via either forebrain commissure, and (b) that the memory is formed bilaterally despite unilateral input. (4) When the chiasm is split but the commissures are intact, simultaneous presentation of disparate images to each hemisphere severely perturbs performance, suggesting that the callosal system operates continuously to unify visual percepts; but when only the anterior commissure is intact, the two hemispheres accept incongruent images without perturbation. (5) In the fully "split-brain" condition, when one hemisphere cannot access memories held in the other, the accuracy of performance by each hemisphere is nevertheless burdened by the memory load of its neocortically disconnected partner. It can thus be inferred that the brainstem plays a critical, unifying role in this mnemonic process.

Animals↗
PubMed1994

Cortical organization in adulthood is modified by neonatal infarct: a case study.

PURPOSE: To assess anomalous cortical organization of somatosensory function in a 23-year-old man who had had a neonatal infarct involving the left middle cerebral artery. MATERIALS AND METHODS: The infarct destroyed the primary and secondary somatosensory areas of the subject's left hemisphere but caused only mild perturbation of somatosensation on the right side of his body. With magnetic source imaging, the authors integrated magnetoencephalographic data with magnetic resonance imaging data to create magnetic source localization images that showed the mapping between brain function and structure. RESULTS: Electrical stimulation of the right median nerve evoked activity in two nontraditional areas: (a) an intact region of the left inferior temporal gyrus and (b) the ipsilateral right medial parietal cortex. CONCLUSION: These data suggest that bilateral neural reorganization can be induced by unilateral neonatal damage.

Adult↗
PubMed1994

Neonatal hypoglycemia: CT and MR findings.

A case of neonatal hypoglycemia with extensive occipital cortical loss is presented. Imaging studies revealed a predominance of brain parenchymal loss in the occipital lobes bilaterally with nearly complete absence of cortex in the posterior parietal and occipital regions and generalized thinning of the cortex throughout the brain.

Blood Glucose↗
PubMed1994

Role of the forebrain commissures in bihemispheric mnemonic integration in macaques.

A serial probe recognition task was used to examine the interhemispheric exchange of visual data in macaques. Each block of trials began with the memorization of one to six visual target images. The monkeys then had to determine, in tests that followed immediately, whether probe images were or were not members of the learned target set. Previous work with both humans and macaques has shown that the time required for the evaluation of probes generally increases, while response accuracy decreases, as a function of the number of targets, the "memory load". By testing animals with bisected optic chiasm, it was possible to direct visual information to only one hemisphere at a time, simply by occluding the opposite eye. In this fashion, the quality of intrahemispheric evaluations (in which a monocular probe was a match for a target previously viewed through the same eye) was compared with that of interhemispheric evaluations (in which a probe was a match for a target previously designated through the opposite eye). A key question was whether division of the target list between the hemispheres modified the relationships between reaction time, response accuracy, and memory load. Provided that either the anterior commissure or the splenium of the corpus callosum was intact, interhemispheric processing was only subtly less efficient than intrahemispheric processing. The ability to perform interhemispheric evaluations was selectively and completely disrupted if all forebrain commissural fibers were transected. In this latter split-brain condition, the time required for probe evaluations was, as expected, determined solely by the number of target items memorized by the probed hemisphere. Accuracy, however, was always a function of the total memory load, regardless of the distribution of targets between the hemispheres. This implies, first, that accuracy and latency do not reflect identical mnemonic factors, as frequently held, and second, that in mnemonic processing, the two hemispheres draw upon a unified, shared resource, probably allocated by the intact brainstem.

Animals↗
PubMed1993

Neuromagnetic mapping of brain function.

Magnetic source imaging, a technique that combines magnetoencephalography (MEG) and magnetic resonance (MR) imaging, was used to localize the somatosensory and auditory cortex in seven healthy subjects. Functional neuromagnetic data were obtained with a 37-channel biomagnetometer. Structural MR imaging data were obtained with a 1.5-T superconducting imager. Coordinates used in defining MEG and MR imaging space were reconciled to produce magnetic source images that displayed the putative locations of somatosensory and auditory activity in relation to brain anatomy. Sources of somatosensory activity were typically localized to the postcentral gyrus; sources of auditory activity were localized to the superior temporal plane. Extension of these results to patients with tumors (or other disorders) that distort normal brain anatomy has the potential to make noninvasive magnetic source imaging examinations clinically useful in guiding neurosurgical interventional procedures.

Adult↗