Improving the magnetoelectric performance of Metglas/PZT laminates by annealing in a magnetic field.

A comprehensive investigation of magnetostriction optimization in Metglas 2605SA1 ribbons is performed to enhance magnetoelectric performance. We explore a range of annealing conditions to relieve remnant stress and align the magnetic domains in the Metglas, while minimizing unwanted crystallization. The magnetostriction coefficient, magnetoelectric coefficient, and magnetic domain alignment are correlated to optimize magnetoelectric performance. We report on direct magnetostriction observed by in-plane Doppler vibrometer and domain imagining using scanning electron microscopy with polarization analysis for a range of annealing conditions. We find that annealing in an oxygen-free environment at 400 °C for 30 min yields an optimal magnetoelectric coefficient, magnetostriction and magnetostriction coefficient. The optimized ribbons had a magnetostriction of 50.6 ± 0.2 µm m-1 and magnetoelectric coefficient of 79.3 ± 1.5 µm m-1 mT-1. The optimized Metglas 2605SA1 ribbons and PZT-5A (d31 mode) sensor achieves a magnetic noise floor of approximately 600 pT Hz-1/2 at 100 Hz and a magnetoelectric coefficient of 6.1 ± 0.03 MV m-1 T-1.

Performance predictors of brain-computer interfaces in patients with amyotrophic lateral sclerosis.

OBJECTIVE: Patients with amyotrophic lateral sclerosis (ALS) may benefit from brain-computer interfaces (BCI), but the utility of such devices likely will have to account for the functional, cognitive, and behavioral heterogeneity of this neurodegenerative disorder. APPROACH: In this study, a heterogeneous group of patients with ALS participated in a study on BCI based on the P300 event related potential and motor-imagery. RESULTS: The presence of cognitive impairment in these patients significantly reduced the quality of the control signals required to use these communication systems, subsequently impairing performance, regardless of progression of physical symptoms. Loss in performance among the cognitively impaired was accompanied by a decrease in the signal-to-noise ratio of task-relevant EEG band power. There was also evidence that behavioral dysfunction negatively affects P300 speller performance. Finally, older participants achieved better performance on the P300 system than the motor-imagery system, indicating a preference of BCI paradigm with age. SIGNIFICANCE: These findings highlight the importance of considering the heterogeneity of disease when designing BCI augmentative and alternative communication devices for clinical applications.

Adaptive electric field control of epileptic seizures.

We describe a novel method of adaptively controlling epileptic seizure-like events in hippocampal brain slices using electric fields. Extracellular neuronal activity is continuously recorded during field application through differential extracellular recording techniques, and the applied electric field strength is continuously updated using a computer-controlled proportional feedback algorithm. This approach appears capable of sustained amelioration of seizure events in this preparation when used with negative feedback. Seizures can be induced or enhanced by using fields of opposite polarity through positive feedback. In negative feedback mode, such findings may offer a novel technology for seizure control. In positive feedback mode, adaptively applied electric fields may offer a more physiological means of neural modulation for prosthetic purposes than previously possible.

Noninvasive assessment of language dominance in children and adolescents with functional MRI: a preliminary study.

BACKGROUND: Assessment of language organization is crucial in patients considered for epilepsy surgery. In children, the current techniques, intra-carotid amobarbital test (IAT) for language dominance, and cortical electrostimulation mapping (ESM), are invasive and risky. Functional magnetic resonance imaging (fMRI) is an alternative method for noninvasive functional mapping, through the detection of the hemodynamic changes associated with neuronal activation. We used fMRI, to assess language dominance in children with partial epilepsy. METHODS: Eleven right handed children and adolescents performed a word generation task during fMRI acquisition focused on the frontal lobes. Areas where the signal time course correlated with the test paradigm (r = 0.7) were considered activated. Extent and magnitude of signal changes were used to calculate asymmetry indices. Seven patients had IAT, ESM, or surgery outcome available for comparison. RESULTS: fMRI language dominance always agreed with IAT (6 cases) and ESM (1 case), showing left dominance in six and bilateral language in one. fMRI demonstrated left dominance in three additional children, and right dominance in one with early onset of left temporal epilepsy. Four children whose initial studies were equivocal due to noncompliance or motion artifacts were restudied successfully. CONCLUSIONS: fMRI can be used to assess language lateralization noninvasively in children. It has the potential to replace current functional mapping techniques in patients, and to provide important data on brain development.

Looking for chaos in brain slices.

Many signals measured from the nervous system exhibit apparently random variability that is usually considered to be noise. The development of chaos theory has revealed that such random appearing variability may not, in fact, be random, but rather may be deterministic behavior that can reveal important information about the system's underlying mechanisms. We present some new methods for distinguishing determinism from randomness in experimental data, and we apply these methods to population neural responses recorded from hippocampal tissue slices.

The effects of temperature on synaptic transmission in hippocampal tissue slices.

Fully submerged rat hippocampal tissue slices were exposed to temperature changes, and the effects on CA1 pyramidal cell electrophysiology studied. Raising the temperature from 29 to 33 or 37 degrees C simultaneously increased the focal-excitatory postsynaptic potentials and decreased the population spikes. These changes were largely reversible for slices warmed to 33 degrees C, but not for slices warmed to 37 degrees C. During warming transiently increased excitatory transmission was observed; the degree of increased transmission was related to the rate of temperature rise. It is postulated that neuronal membrane hyperpolarization with warming is responsible for several of the effects seen.

Hyperexcitability following moderate hypoxia in hippocampal tissue slices.

The effects of moderate hypoxia on CA1 pyramidal cells were studied in submerged rat hippocampal tissue slices. Hyperexcitability developed during re-oxygenation following 30-45 min of hypoxia at 29 degrees C. During hypoxia a sustained increase in extracellular potassium was observed. The post-hypoxic hyperexcitability of CA1 neurons may be the result of their inability to fully recover intracellular potassium lost during oxygen deprivation.

Overshoot of oxygen pressure in post-hypoxic brain tissue: a re-evaluation.

Tissue oxygen pressure (ptO2) was measured with noble metal microelectrodes in hippocampal slices in vitro. During hypoxia, the ptO2 at 100 micron depth fell rapidly to less than 20 mm Hg. During reoxygenation, large transient ptO2 increases above normoxic values were observed. These data demonstrate that ptO2 'overshoots' occur independently of in situ posthypoxic hyperemia and may reflect pathologic chemical reactions in brain tissue during reoxygenation.

Brain chirps: spectrographic signatures of epileptic seizures.

OBJECTIVE: A chirp is a brief signal within which the frequency content changes rapidly. Spectrographic chirps are found in signals produced from many biological and physical phenomena. In radar and sonar engineering, signals with chirps are used to localize direction and range to the signal source. Although characteristic frequency changes during epileptic seizures have long been observed, the correlation with chirps and chirp technology seems never to have been made. METHODS: We analyzed 19404 s (1870 s of which were from 43 seizures) of intracranially (subdural and depth electrode) recorded digital EEG from 6 patients for the presence of spectral chirps. Matched filters were constructed from methods in routine use in non-medical signal processing applications. RESULTS: We found that chirps are very sensitive detectors of seizures (83%), and highly specific as markers (no false positive detections). The feasibility of using spectral chirps as matched filters was demonstrated. CONCLUSIONS: Chirps are highly specific and sensitive spectrographic signatures of epileptic seizure activity. In addition, chirps may serve as templates for matched filter design to detect seizures, and as such, can demonstrate localization and propagation of seizures from an epileptic focus.

Selective neuronal vulnerability to hypoxia in vitro.

Hippocampal slices were subjected to a sequence of hypoxic periods of progressively increasing duration. In all slices, synaptic transmission returned during reoxygenation in the fascia dentata, but not in CA1. Thus, the relative vulnerability of CA1 and the fascia dentata to ischemia in situ can be replicated by a purely hypoxic insult in vitro.

Quinolinic acid in tumors, hemorrhage and bacterial infections of the central nervous system in children.

A potential mechanism that may contribute to neurological deficits following central nervous system infection in children was investigated. Quinolinic acid (QUIN) is a neurotoxic metabolite of the kynurenine pathway that accumulates within the central nervous system following immune activation. The present study determined whether the levels of QUIN are increased in the cerebrospinal fluid of children with infections of the CNS, hydrocephalus, tumors or hemorrhage. Extremely high QUIN concentrations were found in patients with bacterial infections or the CNS, despite treatment with antimicrobial agents. CSF QUIN levels were also elevated to a lesser degree in patients with hydrocephalus or tumors. CSF L-kynurenine levels increased in parallel to the accumulations in QUIN, which is consistent with increased activity of the first enzyme of the kynurenine pathway, indoleamine-2,3-dioxygenase. The CSF levels of neopterin, a marker of immune and macrophage activation, were also increase in patients with infections. The cytokines tumor necrosis factor-alpha and interleukin-6 were also detected in some patients' samples, and were highest in patients with infection. These results suggest that QUIN is a sensitive marker of the presence of immune activation within the CNS. Further studies of QUIN as a potential contributor to neurologic dysfunction and neurodegeneration in children with CNS inflammation are warranted.

High dose barbiturate therapy in neurosurgery and intensive care.

To assess the uses of high dose barbiturate therapy in neurosurgery and intensive care, the authors have undertaken a concise survey of relevant experimental investigations and a comprehensive review of published clinical experiences.

Randomized trial of cerebrospinal fluid shunt valve design in pediatric hydrocephalus.

OBJECTIVE: Forty percent of standard cerebrospinal fluid shunts implanted for the treatment of pediatric hydrocephalus fail within the first year. Two new shunt valves designed to limit excess flow, particularly in upright positions, were studied to compare treatment failure rates with those for standard differential-pressure valves. METHODS: Three hundred-forty-four hydrocephalic children (age, birth to 18 yr) undergoing their first cerebrospinal fluid shunt insertion were randomized at 12 North American or European pediatric neurosurgical centers. Patients received one of three valves, i.e., a standard differential-pressure valve; a Delta valve (Medtronic PS Medical, Goleta, CA), which contains a siphon-control component designed to reduce siphoning in upright positions; or an Orbis-Sigma valve (Cordis, Miami, FL), with a variable-resistance, flow-limiting component. Patients were monitored for a minimum of 1 year. Endpoints were defined as shunt failure resulting from shunt obstruction, overdrainage, loculations of the cerebral ventricles, or infection. Outcome events were assessed by blinded independent case review. RESULTS: One hundred-fifty patients reached an endpoint; shunt obstruction occurred in 108 (31.4%), overdrainage in 12 (3.5%), loculated ventricles in 2 (0.6%), and infection in 28 (8.1%). Sixty-one percent were shunt failure-free at 1 year and 47% at 2 years, with a median shunt failure-free duration of 656 days. There was no difference in shunt failure-free duration among the three valves (P = 0.24). CONCLUSION: Cerebrospinal fluid shunt failure, predominantly from shunt obstruction and infection, remains a persistent problem in pediatric hydrocephalus. Two new valve designs did not significantly affect shunt failure rates.

Early seizure detection.

For patients with medically intractable epilepsy, there have been few effective alternatives to resective surgery, a destructive, irreversible treatment. A strategy receiving increased attention is using interictal spike patterns and continuous EEG measurements from epileptic patients to predict and ultimately control seizure activity via chemical or electrical control systems. This work compares results of seven linear and nonlinear methods (analysis of power spectra, cross-correlation, principal components, phase, wavelets, correlation integral, and mutual prediction) in detecting the earliest dynamical changes preceding 12 intracranially-recorded seizures from 4 patients. A method of counting standard deviations was used to compare across methods, and the earliest departures from thresholds determined from non-seizure EEG were compared to a neurologist's judgement. For these data, the nonlinear methods offered no predictive advantage over the linear methods. All the methods described here were successful in detecting changes leading to a seizure between one and two minutes before the first changes noted by the neurologist, although analysis of phase correlation proved the most robust. The success of phase analysis may be due in part to its complete insensitivity to amplitude, which may provide a significant source of error.

A surgeon's risk of AIDS.

A probabilistic model is used to estimate the cumulative risk to surgeons from human immunodeficiency virus (HIV). Recent data suggest that the probability of infection following percutaneous inoculation is about 1 in 250 cases. Several studies suggest that the frequency of percutaneous injury in surgery is at least 1 in 40 cases, for some as high as 1 in 20 cases. Assuming that on the average a surgeon will perform 350 operations per year and will practice for 30 years, the cumulative risk of HIV infection will depend on the prevalence of HIV infection in the surgical population. For HIV prevalences of 1 in 100 to 1 in 10, the cumulative risk per surgeon ranges from 1 in 100 to 1 in 5, respectively. Based on these risk estimates, it is crucial to decrease the frequency of percutaneous injury. The case is made for substantial improvements in barrier protection and modification of surgical technique.

Use of recombinant human erythropoietin to avoid blood transfusion in a Jehovah's Witness requiring hemispherectomy. Case report.

The use of perioperative human recombinant erythropoietin is described in a Jehovah's Witness patient. Despite significant anemia, the child's hematocrit was sufficiently increased by the use of erythropoietin so that a two-stage hemispherectomy could be performed without blood transfusion.

Reflex variability in selective dorsal rhizotomy.

The variability of reflex responses during selective dorsal rhizotomy was studied in eight children between the ages of 3 and 7 years. For a given dorsal root or rootlet, the electrical reflex threshold and response varied considerably when observed over several minutes. Changes in electrode pressure, mechanical dissection of the root, and reflex spatial facilitation were all found to contribute to the variability. Even when electrode pressure was held constant, intrinsic spinal cord reflex variability substantially weakened the predictability of the intraoperative selection method used during this surgery.

Barbiturate protection against hypoxic neuronal damage in vitro.

Hippocampal tissue slices in vitro were exposed to periods of hypoxia of different durations. Addition of pentobarbital to the perfusion medium significantly increased the duration of hypoxia that was survived by CA1 pyramidal cells.

An experimental study of reflex variability in selective dorsal rhizotomy.

Significant problems regarding the measurement technique currently used to choose nerve roots for sectioning in the selective dorsal rhizotomy procedure have recently been reported. To better understand the source of these problems, a series of six experiments was performed in which the selective rhizotomy technique was applied to cats that were either intact, decerebrate, or spinalized. Measurements were made before and after partial rhizotomy. In decerebrate preparations, large, spontaneous changes in reflex threshold were observed over short periods of time, especially after partial rhizotomy was performed, and threshold changes greater than 1000% could be observed over 10-minute periods. Using constant-current stimulation of the dorsal root at threshold, the response of each ipsilateral leg muscle demonstrated frequent changes, and changes coincided with the variability in threshold estimation. In addition, very low thresholds were measured (0.1 to 0.25 mA) in half (3 of 6) of these experiments, these measurements being well below the currents customarily used for intraoperative decision making. Stimulation at twice threshold was found to consistently increase the pathological quality of the responses observed. Although intact animals never displayed contralateral responses when stimulated at threshold, such contralateral responses could readily be elicited at twice threshold. These laboratory results raise further doubts regarding the reliability of the measurement techniques now widely used for selective dorsal rhizotomy.