Neurophysiological Applications Research Articles

Noninvasive Human Brain Stimulation

Noninvasive brain stimulation with transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) is valuable in research and has potential therapeutic applications in cognitive neuroscience, neurophysiology, psychiatry, and neurology. TMS allows neurostimulation and neuromodulation, while tDCS is a purely neuromodulatory application. TMS and tDCS allow diagnostic and interventional neurophysiology applications, and focal neuropharmacology delivery. However, the physics and basic mechanisms of action remain incompletely explored. Following an overview of the history and current applications of noninvasive brain stimulation, we review stimulation device design principles, the electromagnetic and physical foundations of the techniques, and the current knowledge about the electrophysiologic basis of the effects. Finally, we discuss potential biomedical and electrical engineering developments that could lead to more effective stimulation devices, better suited for the specific applications.

Self-consistent analyses for potential conduction block in nerves by an ultrashort high-intensity electric pulse

Simulation studies are presented that probe the possibility of using high-field (> 100 kV/cm) , short-duration ( approximately 50 ns) electrical pulses for nonthermal and reversible cessation of biological electrical signaling pathways. This would have obvious applications in neurophysiology, clinical research, neuromuscular stimulation therapies, and even nonlethal bioweapons development. The concept is based on the creation of a sufficiently high density of pores on the nerve membrane by an electric pulse. This modulates membrane conductance and presents an effective "electrical short" to an incident voltage wave traveling across a nerve. Net blocking of action potential propagation can then result. A continuum approach based on the Smoluchowski equation is used to treat electroporation. This is self-consistently coupled with a distributed circuit representation of the nerve dynamics. Our results indicate that poration at a single neural segment would be sufficient to produce an observable, yet reversible, effect.

Linear and nonlinear causality between signals: methods, examples and neurophysiological applications

In this paper, we will present and review the most usual methods to detect linear and nonlinear causality between signals: linear Granger causality test (Geweke in J Am Stat Assoc 77:304-313, 1982) extended to direct causality in multivariate case (LGC), directed coherence (DCOH, Saito and Harashima in Recent advances in EEG and EMG data processing, Elsevier, Amsterdam, 1981), partial directed coherence (PDC, Sameshima and Baccala 1999) and nonlinear Granger causality test of Baek and Brock (in Working Paper University of Iowa, 1992) extended to direct causality in multivariate case (partial nonlinear Granger causality, PNGC). All these methods are tested and compared on several ARX, Poisson and nonlinear models, and on neurophysiological data (depth EEG). The results show that LGC, DCOH and PDC are not very robust in relation to nonlinear linkages but they seem to correctly find linear linkages if only the autoregressive parts are nonlinear. PNGC is extremely dependent on the choice of parameters. Moreover, LGC and PNGC may give misleading results in the case of causality on a spectral band, which is illustrated by our neurophysiological database.

DELAYED FEEDBACK SUPPRESSION OF COLLECTIVE RHYTHMIC ACTIVITY IN A NEURONAL ENSEMBLE

We analyze the delayed feedback approach to suppression of collective synchrony in a population of globally or randomly coupled neurons. In particular, we consider the main factors of imperfection of the control scheme and their influence on the suppression efficiency. Next, with the help of a realistic model of synaptically coupled population of inhibitory and excitatory neurons we demonstrate the potential of the suppression scheme for neurophysiological applications.

Testing equality of two functions using BARS

This article presents two methods of testing the hypothesis of equality of two functions H(0):f(1)(t)=f(2)(t) for all t, in a generalized non-parametric regression framework using a recently developed generalized non-parametric regression method called Bayesian adaptive regression splines (BARS). Of particular interest is the special case of testing equality of two Poisson process intensity functions lambda(1) (t)=lambda(2) (t), which arises frequently in neurophysiological applications. The first method uses Bayes factors, and the second method uses a modified Hotelling T(2) test. Both methods are applied to the analysis of 347 motor cortical neurons and, for certain choices of test criteria, the two methods lead to the same conclusions for all but 7 neurons. A small simulation study of power indicates that the Bayes factor can be somewhat more powerful in small samples. The T(2)-type test should be useful in screening large number of neurons for condition-related activity, while the Bayes factor will be especially helpful in assessing evidence in favour of H(0).

Localization of the motor and speech zones of the cerebral cortex by functional magnetic resonance tomography.

Functional magnetic resonance tomography provides a non-invasive method for mapping the cerebral cortex. The aim of the present work was to assess the potential and suitability of this method in a series of brain disorders. Studies were performed on 32 volunteers (mean age 37.8 +/- 20.9 years) and 16 patients with tumors of the cerebral cortex (mean age 36.2 +/- 24.2 years). Initial functional images were processed by statistical methods. Computed activation maps were superimposed on anatomical images. In 89% of cases, functional magnetic resonance tomography allowed the motor cortex and Broca's area to be localized; in almost 69%, the method impinged on the therapeutic tactics used in patients with cerebral cortex lesions. Thus, functional magnetic resonance tomography can be used in clinical conditions to obtain information not yielded by other diagnostic methods and which can be used to plan the neurosurgical treatment of patients with supratentorial brain tumors with maximum preservation of cerebral cortex function. Assessments of the state of the motor and speech areas by this tomographic method has potential applications in neurosurgery and neurophysiology.

Transcranial magnetic stimulation: Neurophysiological applications and safety

TMS is a non-invasive tool for measuring neural conduction and processing time, activation thresholds, facilitation and inhibition in brain cortex, and neural connections in humans. It is used to study motor, visual, somatosensory, and cognitive functions. TMS does not appear to cause long-term adverse neurological, cardiovascular, hormonal, motor, sensory, or cognitive effects in healthy subjects. Single-pulse (<1 Hz) TMS is safe in normal subjects. High frequency, high-intensity repetitive TMS (rTMS) can elicit seizures even in normal subjects. Safety guidelines for using rTMS have been published.

Optimisation of shape kernel and threshold in image-processing motion analysers.

The aim of the work is to optimise the image processing of a motion analyser. This is to improve accuracy, which is crucial for neurophysiological and rehabilitation applications. A new motion analyser, ELITE-S2, for installation on the International Space Station is described, with the focus on image processing. Important improvements are expected in the hardware of ELITE-S2 compared with ELITE and previous versions (ELITE-S and Kinelite). The core algorithm for marker recognition was based on the current ELITE version, using the cross-correlation technique. This technique was based on the matching of the expected marker shape, the so-called kernel, with image features. Optimisation of the kernel parameters was achieved using a genetic algorithm, taking into account noise rejection and accuracy. Optimisation was achieved by performing tests on six highly precise grids (with marker diameters ranging from 1.5 to 4 mm), representing all allowed marker image sizes, and on a noise image. The results of comparing the optimised kernels and the current ELITE version showed a great improvement in marker recognition accuracy, while noise rejection characteristics were preserved. An average increase in marker co-ordinate accuracy of +22% was achieved, corresponding to a mean accuracy of 0.11 pixel in comparison with 0.14 pixel, measured over all grids. An improvement of +37%, corresponding to an improvement from 0.22 pixel to 0.14 pixel, was observed over the grid with the biggest markers.

Virtual reality: a tutorial

Virtual reality (VR) technology is complex and relies on multidisciplinary knowledge. VR applications are attracting an increasing interest among neuroscientists, in particular in the study of the human brain. Here we present a brief tutorial in which we address aspects of VR methodology that are most relevant to neurophysiology applications. After a brief survey of possible applications to neurophysiology, we discuss the following issues in VR: display technology, visual stimulus presentation techniques, visual spatial resolution and accuracy, devices for real-time interaction with the virtual environment and force-feedback.

SIGIF: a digital signal interchange format with application in neurophysiology.

In this paper, the authors describe a biomedical digital-signal interchange format. The format supports both raw and processed data, multiple segments, several signal structures and representations, and an open architecture. Its versatility and adaptability allows the software to take advantage of any particular features of the acquisition hardware. The format has been used and improved in routine work during a five-year period involving the cooperation between two hospitals and one engineering research center. In order to support the format, an object oriented C language library has been developed and is also shortly described.

Where have we been? Where are we going?

The field of human stereotactic and functional neurosurgery is 50 years old. It began with the pioneering work of Spiegel and Wycis, who developed an apparatus to be used in human neurosurgery designed like the Horsley-Clarke apparatus invented for animal experimentation 40 years earlier, but based on targeting by intracerebral landmarks. During the past half century, the field of stereotactic surgery has evolved from a small field involving a handful of scientists to a field dominated by a technology that is permeating all of neurosurgery. A review of the scientific programs and activities of the World Society for Stereotactic and Functional Neurosurgery reflects the changing level of activity in these fields, the waxing and waning of functional neurosurgery that is now vital and active, and the evolution of stereotactic guidance into the field of computer-assisted neurosurgery. Functional neurosurgery involves the application of human neurophysiology to the treatment of various diseases that produce malfunction of the nervous system, and remains the domain of those few neurosurgeons well versed in neurological pathophysiology. Image-based or computerized stereotactic surgery, on the other hand, is used in those procedures common to neurosurgery, and should be available to any operating neurosurgeon.

Quantitative Analysis of Human Movement Synergies: Constructive Pattern Analysis for Gait

To record three-dimensional coordinates of the joints from normal human subjects during locomotion, we used a digital motion analysis system (ELITE). Recordings were obtained under several different conditions, which included normal walking and stepping over obstacles. Principal component analysis was used to analyze coordinate data after conversion of the data to segmental angles. This technique gave a stable summary of the redundancy in gait kinematic data in the form of reduced variables (principal components). By modeling the shapes of the phase plots of reduced variables (distortion analysis) and using a limited number of model parameters, good resolution was obtained between subtly different conditions. Hence, it was possible to accurately resolve small distributed changes in gait patterns within subjects. These methods seem particularly suited to longitudinal studies in which relevant movement features are not known a priori. Assumptions and neurophysiological applications are discussed.

Neurosurgical applications of topographic mapping

Sophisticated spectral analysis and mapping of the EEG with computer techniques provides objective and reliable diagnostic information, which is superior to that obtained by naked-eye observation, even by experienced clinicians. In our department, a topographic system was introduced as one of major adjuncts to EEG examination in 1980, and we devised our own software (dynamic topography, compound dynamic topography, deviation ratio topography) to facilitate its clinical application. Topographic mapping is applied to assessment of the dominant hemisphere, evaluation after medical and surgical treatment, spatial localization of epileptic foci, and intraoperative monitoring for cerebral hypoperfusion. Besides these surgical applications, topographic analysis has contributed to human neurophysiology, for instance in determining the participation of the dentatethalamic tract in movement-related cortical potentials. Our experience of the neurosurgical and neurophysiological applications of topographic mapping will be presented.

Electrophysiological measures of regional neural interactive coupling. Linear and non-linear dependence relationships among multiple channel electroencephalographic recordings

Linear spectral coherence (Sklat et al., 1973) measures have been used in the neurosciences to test hypotheses which address the question of whether multiple EEG recording sites are independent or whether they are activated by common sources of neurophysiological activity. This measure is appropriate when regional neural sources interact and thereby electrically activate several recording sites through linear transmission pathways which may or may not be different in their linear transformation properties. However, if the transmission media are non-linear, then interactive dependency is not necessarily revealed by a linear coherence test. Therefore, if common sources are activating EEG recording sites through nonlinear media, evaluating the resulting relationships among the signals recorded from these sites requires a test which reveals the presence of such nonlinear relationships. In neurophysiological applications, a polycoherence cross-spectral measure provides such a test for nonlinear dependency (similar to the linear coherence test) among EEG recording sites. The data requirements and statistical properties of these linear and non-linear measures are described and results of a linear coherence analysis are presented in the context of an EEG pilot study of learning diabled children.

Selective interaction within a point process and their applications

We consider, in this article, interaction of two types of events, arriving according to a stationary point process, resulting in a process consisting of response yielding events. The interval density between two consecutive responses are of interest. Certain applications in neurophysiology, and replacement models are indicated

Digitizing graphic data

Using a digitizing pad instead of a ruler and calipers accelerates and increases the accuracy of graphic data analysis. Factors important in choosing and using such a pad are discussed in this article. A program is presented which facilitates use of the Houston Instruments HiPad DT11, a digitizing pad which is particularly well suited to neurophysiological applications.

A 19-channel matrix drive with individually controllable fiber microelectrodes for neurophysiological applications

An electrode matrix manipulator for independent positioning of up to 19 microelectrodes for the recording of electrical activity of a multitude of single units within a neural population is described. It is operated by the combined action of a stepping motor and a system of independently controllable solenoid-operated coupling elements for each electrode. Glass-metal fiber electrodes of 100-μm outside diameter travel in parallel capillary guide tubes, arranged in concentric array with a 220-μm interelectrode distance. Electrode movement is in steps of 2 μm. Simultaneous movement of any combination of electrodes is possible.

Technique for precision beveling of relatively large micropipettes

A technique is described for embedding various sizes of diamond dust in a film of Varathane laid upon an optically flat glass surface. This forms a precise and very durable abrasive surface. When such abrasive surfaces are used with previously described equipment, micropipettes may be beveled rapidly and reliably to tip diameters extending from 0.5 μm to indefinitely large sizes. Beveled tips formed in this manner are extremely sharp, as shown by high resolution SEM photographs. Plugging of the micropipette tip during beveling is prevented by applying pressure to the contained electrolyte. This procedure allows the micropipette's electrical resistance to be monitored accurately and continuously, so that beveling may be stopped at the electrical resistance associated with any predetermined tip diameter. The beveling of such relatively large micropipettes appears to have a variety of applications in neurophysiology, plus additional applications in kidney and capillary micropuncture work.

A spatio-temporal model of cat's retinal cells.

This paper presents a model of the spatiotemporal processes of simple ganglion cells of cat's retina. The model is based on the existence of two anatomical paths in the retina: a direct path, responsible for central excitatory effects, and a transversal path, responsible for peripherical inhibitory effects. Plausible spatial weighting functions and temporal transfer functions for photoreceptors, horizontal, bipolar and ganglion cell are introduced by prudent application of comparative neurophysiology.

Neurophysiological applications of a calcium-selective microelectrode

Neurophysiological applications of a calcium-selective microelectrode