Collision Technique Research Articles

Digital subtraction technique for F wave analysis: A comparison with collision technique

Digital subtraction technique for F wave analysis: A comparison with collision technique

Ion Formation and Fragmentation in Gas-Phase Fast-Atom Bombardment Mass Spectrometry of C60

Abstract The observation of multiply-charged ions C60 Z+ (z=1-4) and fragment ions (C60 - C2n)z+ (z=1-4, n=1-12) has been reported using a new ionization/ collision technique, called gas-phase fast-atom bombardment with a high-energy (8 keV) helium beam.

Central motor delay in the motor neuron diseases

Objective: To quantitatively estimate upper motor neuron (UMN) loss in ALS.Methods: We used the recently developed triple stimulation technique (TST) to study corticospinal conduction to 86 abductor digiti minimi muscles of 48 ALS patients. This method employs a collision technique to estimate the proportion of motor units activated by a transcranial magnetic stimulus. At the same time, it yields an estimate of lower motor neuron (LMN) integrity.Results: The TST disclosed and quantified central conduction failures attributable to UMN loss in 38 sides of 24 patients (subclinical in 15 sides), whereas conventional motor evoked potentials detected abnormalities in only 18 sides of 12 patients (subclinical in two sides). The increased sensitivity of the TST to detect UMN dysfunction was particularly observed in early cases. Increased central motor conduction times (CMCT) occurred exclusively in sides with conduction failure. In sides with clinical UMN syndromes, the TST response size (but not the CMCT) correlated with the muscle weakness. In sides with clinical LMN syndromes, the size of the peripherally evoked compound muscle action potentials correlated with the muscle weakness.Conclusion: The TST is a sensitive method to detect UMN dysfunction in ALS. It allows a quantitative estimate of the UMN loss, which is related to the functional deficit. Therefore, the TST has a considerable impact on diagnostic certainty in many patients. It will be suited to follow the disease progression and therapeutic trials.

Facilitation of responses to motor cortex stimulation: Effects of isometric voluntary contraction

In 7 normal subjects we compared the facilitatory effect of isometric contraction of the tibialis anterior on the size of electromyographic responses evoked in this muscle by electric stimuli applied over the cervical column and by electric and magnetic percutaneous stimulation of the motor cortex. No significant difference was found between the degrees of facilitation of the responses to any of the stimuli. Using collision techniques, we also showed that the pyramidal fibers activated by spinal and cortical stimuli are the same. Facilitation induced by isometric contraction (20% maximum) was of similar or greater magnitude than that found with constant vibration of the tendon of the target muscle. In cases where vibration and contraction had equal facilitatory effects, there was no further facilitation of the responses when both conditions were applied together. These findings indicate that the facilitatory effect of isometric contraction of the target muscle essentially originates at a spinal level rather than in the motor cortex.

Improvements in the response calculation of the dual thin scintillator neutron detector

Abstract The present work describes the new features introduced in the Monte Carlo code - developed for efficiency and proton recoil spectra calculations of the dual thin scintillator (DTS) neutron detector - in order to achieve better accuracy and shorter processing time. The improvements include: relativistic kinematics, anisotropy in the angular distributions and application of the forced collision technique. The new calculated values are compared with experimental results at two neutron energies, namely: 2.446 and 14.04 MeV, obtained by means of the time correlated associated particle technique.

Monte Carlo simulation of electron motion in mercury vapour

The motion of electrons in mercury vapour is traced using the Monte Carlo simulation for 10<or=E/N<or=2000 Td (1 Td=10-17 V cm2) by adopting a null collision technique. The momentum transfer cross sections for electron energy 0.05<or= epsilon <or=50 eV obtained from the literature, and the excitation cross sections are derived as a function of electron energy to produce good agreement between the measured and calculated values of Townsend's first ionization coefficient. Electron swarm parameters, namely the drift velocity, ionization coefficient and mean energy have been calculated, and good agreement is obtained with published results over a wide range of E/N.

A new method to measure the distribution of motor conducgtion velocity in man

A new method of measuring the distribution of conduction velocities in human motor fibers is described. In this method, a modification of Kimura's collision technique is combined with Hopf's technique. This enabled us to determine the collision end-point in Hopf's technique, from which the minimum velocity is derived. The size of the distorted compound muscle action potential (CMAP) measured with Hopf's technique is corrected using the CMAP size with the modified Kimura technique. This revolves the problem of CMAP distortion due to transient change in muscle conduction in Hopf's technique. In addition, a new equation to correct for the refractory period was developed. This can be applied even if there is stimulus spread. Using our method, one can clearly determine the maximum and minimum velocities. The former corresponds to the motor conduction velocity as measured by the conventional method.

Somatosensory response properties of contralaterally projecting spinothalamic and nonspinothalamic neurons in the second cervical segment of the cat

1. The upper cervical spinal cord contains over one-third of the cells of the spinothalamic tract (STT). This study investigated response properties of contralaterally projecting STT neurons in C2 of the cat by the use of single-unit, microelectrode recordings. Standard antidromic stimulation and collision techniques were used to identify STT units projecting to the contralateral thalamus. Once an STT unit was found, its receptive field (RF) and responses to cutaneous stimuli such as touch, pressure, deep muscle squeeze, tap, noxious pinch, and heat were characterized. C2 units that were not activated from the contralateral thalamus (non-STT units) were also characterized. The locations of thalamic stimulation electrodes and spinal recording sites were reconstructed from electrolytic lesions. 2. A total of 48 STT and 68 non-STT units were well characterized. RF sizes were classified as small, intermediate, large, or whole body. Each unit was also classified as having one of two possible response types: simple units were those with homogeneous responses within the RF and were classified as low threshold (LT), high threshold (HT), wide dynamic range (WDR), deep, or tap. Complex units were those that responded differently in different regions of the RF. 3. The average depth of non-STT units subdivided by RF size was 2.1 +/- 0.6 (SD) mm for cells with small RFs, 2.4 +/- 0.8 mm for cells with intermediate RFs, 2.8 +/- 0.3 mm for cells with large RFs, and 2.7 +/- 0.5 mm for cells with whole-body RFs. The average depth of non-STT units based on response type was 2.0 +/- 0.5 mm for LT, 2.3 +/- 0.7 mm for HT, 2.1 +/- 0.7 mm for WDR, 2.6 +/- 0.9 mm for deep, 2.6 +/- 0.5 mm for tap, and 2.4 +/- 0.2 mm for complex. 4. A somatotopic organization along the rostrocaudal length of C2 and upper C3 was observed for non-STT units with small- and intermediate-size RFs. The average distance of the recording sites from the rostralmost dorsal rootlet of C2 was 3.8 +/- 2.1 mm for units with RFs on the face, 7.1 +/- 4.3 mm for units with RFs on the neck, and 11.9 +/- 5.1 mm for units with RFs on the forelimb. 5. The average threshold for antidromic activation of STT units was 175 +/- 120 microA. Most C2 STT units were activated from the ventroposterior region of the thalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

Optimization of Monte Carlo codes using null collision techniques for experimental simulation at low E/N

The use of the null collision method in Monte Carlo simulations of electron and ion motion in gases is briefly reviewed, with particular reference to conditions where only a handful of collision cross sections are required to describe the electron/ion-molecule interaction. An efficient algorithm is proposed for use in such conditions as an alternative to S.L. Lin and J.N. Bardsley's (1977) implementation of H.R. Skullerud's (1973) original null collision algorithm. The alternative implementation is described, and some examples of the advantages of the new algorithm are given for electron scattering from argon, helium, and the Reid ramp model gas.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Light and electron microscopic analyses of intraspinal axon collaterals of sympathetic preganglionic neurons

Experiments were performed in pigeons ( Columba livia). Sympathetic preganglionic neurons (SPNs) in the first thoracic spinal cord segment (T 1) were identified electrophysiologically using antidromic activation and collision techniques and then intracellularly labeled with horseradish peroxidase (HRP). In 6 of 10 HRP-labeled SPNs, the site of axon origin and intraspinal axonal trajectory could be specified. In 2 of the 6 HRP-labeled axons, the peripherally projecting process branched intraspinally. The presence or absence of SPN intraspinal axonal collateralization did not correlate with parent perikaryal subnuclear location or dendritic alignment. None of the collaterals were recurrent onto the SPN of origin. Light microscopically, the collateral branches appeared to end with punctate, bulbous swellings. The spinal regions of the terminal end swellings for the two axons did not overlap one another. In one instance the entire terminal field was confined within the principal preganglionic cell column (column of Terni). The other axon had collateral branches which terminated in the lateral white matter and in a ventrolateral region of lamina VII. A serial section, electron microscopic reconstructive analysis of the entire intraspinal collateral terminal field within the column of Terni revealed that: (a) the primary collateral process was unmyelinated and arose at a node of Ranvier; (b) after issuance of the collateral branch, the myelinated parent axon continued to increase its myelin wrapping throughout the spinal gray; (c) the bulbous swellings observed light microscopically corresponded to axon terminal boutons and regions of synaptic contact; (d) the axon collateral terminals were exclusively presynaptic to small caliber dendrites and formed only asymmetric specializations; and (e) the collateral terminals contained numerous mitochondria, and densely packed, electron-lucent, spherical vesicles.

Dissociative attachment of electrons with Si 2H 6

Cross-sections for the production of negative ion fragments by electron attachment to Si 2H 6 and ion pair formation from it have been measured by utilizing the crossed electron beam-molecular beam collision technique. The negative ions are mass analyzed by employing a quadrupole mass spectrometer. There are serious disagreements between the present and two previously published results. In the present paper cross-section values, appearance potentials, and the various channels of dissociation for the formation of negative monosilane fragments are presented.

Physiological properties and patterns of projection in the cortico-cortical connections from the second somatosensory cortex to the motor cortex, area 4γ, in the cat

The physiological properties of neurons in the second somatosensory cortex (SII), and the pattern of projection of these neurons to area 4γ of the motor cortex in cat were studied by using single unit recording and collision techniques. Antidromically activated neurons were recorded along the anterior and posterior regions of the lateral bank of the anterior suprasylvian sulcus (ASSS) and from the middle part of the anterior ectosylvian gyrus (AESG) following weak intracortical microstimulation (ICMS) to area 4γ. Stimulation of the region around the activated neurons failed to produce muscle contraction or movement with currents of 30 μA or less. The majority of antidromically identified neurons received somatotopically organized afferent inputs from the skin on the contralateral side of the body. A small number of SII neurons received bilateral input. In 91% of the cases receptive field information was available for both the antidromically activated SII neuron and for neurons around the stimulating electrode in area 4γ. In 71% of these cases, both cortical sites were activated by sensory input from the same or adjacent peripheral area of the body. Neurons in the rostrocaudal region of the lateral bank of ASSS and the upper part of AESG (forelimb area) projected to the lateral cruciate gyrus of the motor cortex (forelimb area), while neurons in the ventrocaudal region of the medial part of AESG (hindlimb area) projected to the medial part of the postcruciate subregion of the motor cortex (hindlimb area. Antidromically activated SII neurons were typically found in layer III. These results suggest a topographically organized pattern of projection to the motor cortex from SII.

Does stimulation of sympathetic axons elicit an increase in cat spindle afferent discharge detectable by the antidromic collision technique?

Averaged antidromic action potentials of Group I and Group II fibres elicited in cats by stimulation of L7 and S1 dorsal roots were recorded from intact tibial nerves (near the ankle) either in absence of or during repetitive stimulation of the ipsilateral lumbar sympathetic chain. This was done to test the suggestion that stimulation of noradrenergic sympathetic axons may elicit, in spindles of foot muscles, a substantial increase in the firing rate of secondary endings, capable of reducing the size of afferent antidromic volleys by collision with orthodromic impulses. We found that potentials recorded during sympathetic stimulation were identical to those recorded in absence of stimulation. The reduction in size of a component of the compound action potentials led from the intact tibial nerve during stimulation at 10–20 Hz of the sciatic nerve with C strength pulses, as described by Grassi, Filippi and Passatore ( Brain Research, 435 (1987) 15–23), was observed in certain conditions of stimulation. However this reduction cannot be ascribed to antidromic collision, because it is still observed after severing the tibial nerve distal to the recording electrode.

Identification of afferents in a fine nerve strand by selective elimination of signals from C-fibers by electric current pulses

Fine nerve strands teased mechanically from saphenous nerve in anesthetized cats contained 2–5 intact myelinated (A) and up to 15 unmyelinated (C) fibers. An electric current pulse of 3 μA applied through a platinum wire electrode to such a strand during 10 s irreversibly eliminated spikes from C-fibers, yet did not disturb spikes of 80% of A-fibers and decreased the amplitude of the spikes of other A-fibers by not more than 3-fold. When this decrease took place the spike wave form was not distorted and could still be recognized. To diminish the influence of electric current upon signals of some A-fibers current pulses of gradual increasing amplitude in the range of 1–3 μA were applied repetitively until the C-wave in the compound action potential was suppressed. The selective elimination of the signals of C-fibers in fine nerve strands may be used as a method to assist the identification of individual fiber type (A or C). This method is particularly useful in experiments with chemo- and thermo-receptive afferents where the standard collision technique is difficult to apply.

A common somaesthetic pathway to red nucleus and motor cortex

Comparable short latency somaesthetic responses have been observed in the red nucleus and the motor cortex. Since previous experiments showed that a ventral spinal ascending pathway could account for red nucleus responses, the present experiments were designed to establish whether the same pathway could also transmit the short latency peripheral inputs to motor cortex. Two experimental data argue in favour of a such organization: (1) Using the collision technique, it was demonstrated that somaesthetic responses recorded in red nucleus cells are transmitted by collaterals of ascending fibres ending in the ventrobasal thalamus. (2) Intracellular recordings from identified corticospinal cells were performed on cats acutely prepared on section of the brachium conjunctivum and the dorsal columns of the spinal cord. Cortico-cortical connections to motor cortex were also eliminated by lesions of the ipsilateral sensory cortex and contralateral motor cortex. With this preparation it is still possible to record postsynaptic potentials after stimulation of primary afferent fibres in the dorsal columns, caudally to their section. The existence of these somaesthetic parallel inputs to rubro- and corticospinal cells suggests that the ongoing movement might be corrected on-line by these two pathways.

Comparisons of connectivity and conduction velocities for medial forebrain bundle fibers subserving stimulation-induced feeding and brain stimulation reward

A behavioral adaptation of the paired-pulse collision technique was used to determine whether the same medial forebrain bundle (MFB) fibers of passage mediate brain stimulation reward (BSR) and stimulation-induced feeding (SIF) induced by lateral hypothalamic and ventral tegmental electrical stimulation. Step-functions relating second-pulse effectiveness to interpulse interval suggested connectivity between the directly activated SIF fibers at these two stimulation sites were seen in 4 animals; these data indicate that SIF, like BSR, is mediated, at least in part, by long-axon MFB fibers. In the two animals that could be tested in both paradigms, similar effects were seen in BSR tests; this suggests that either the same fibers or fibers with remarkably similar conduction velocities and medial-lateral and dorsal-ventral alignment contribute to the two behaviors.

Tension development in lumbrical muscles and concomitant increase of activity in Aα and Aβ afferents during sympathetic stimulation in the cat

In anaesthetized and curarized cats electrical stimulation of the lumbar sympathetic trunk, at frequencies within the physiological range, induces the development of a small tension in superficial lumbrical muscles (50–100 mg in different preparations). This effect can be reproduced in anaesthetized and curarized cats by stimulating the peripheral stump of the tibial nerve with parameters adequate to activate the entire C-fibre group, and therefore postganglionic sympathetic fibers. The collision technique was used to evaluate in the tibial nerve possible changes in afferent activity from the skinned foot. It was found that an increase of non-cutaneous activity consistently occurs in Aβ and, occasionally, in Aα fibre groups. Secondary and primary spindle afferents, respectively, belong to these fibre groups. It was also found that: (1) the tension development in lumbrical muscles and the increase of the afferent activity of non-cutaneous origin exhibit similar time course; (2) the two events are affected in parallel by the same stimulus parameters; (3) both events are abolished by α-adrenoceptor antagonists. Therefore the possibility of a sympathetic fusimotor action affecting mainly secondary afferents is suggested and discussed.

Electron-transfer collisions of low-energy multicharged nitrogen ions with H2 and N2.

A stored-ion collision technique has been used to study the charge-changing collisions of multicharged nitrogen ions with ${\mathrm{H}}_{2}$ and ${\mathrm{N}}_{2}$ target gases. The ions were produced inside a Penning trap with use of electron-impact ionization. The time constants for exponential ion loss by charge-changing collisions were measured at several target-gas densities, and from these time constants and densities the rate coefficients for electron capture were calculated. For the collision of ${\mathrm{N}}^{3+}$ with ${\mathrm{H}}_{2}$, for which calculations by Gargaud and McCarroll were available, the cross section for electron capture was obtained from the rate coefficient using v\ifmmode\bar\else\textasciimacron\fi{}, where v\ifmmode\bar\else\textasciimacron\fi{} is the rms ion velocity. The relationships of the other measurements to available theory and to ion-beam measurements at higher energies are discussed. Rate coefficients were obtained at mean ion energies near 1.1, 1.65, and 2.3 eV for ${\mathrm{N}}^{\mathrm{q}+}$ charges q of 2, 3, and 4, respectively. The results of the rate coefficient determinations are k(${\mathrm{N}}^{2+}$,${\mathrm{H}}_{2}$)=[7.8(1.2)]\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ ${\mathrm{cm}}^{3}$/s, k(${\mathrm{N}}^{3+}$,${\mathrm{H}}_{2}$)=[5.4(0.8)]\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}11}$ ${\mathrm{cm}}^{3}$/s, k(${\mathrm{N}}^{4+}$,${\mathrm{H}}_{2}$)=[4.2(0.6)]\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ ${\mathrm{cm}}^{3}$/s, k(${\mathrm{N}}^{2+}$,${\mathrm{N}}_{2}$)=[2.6(0.3)]\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}9}$ ${\mathrm{cm}}^{3}$/s, k(${\mathrm{N}}^{3+}$,${\mathrm{N}}_{2}$)=[3.5(0.4)]\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ ${\mathrm{cm}}^{3}$/s, and k(${\mathrm{N}}^{4+}$,${\mathrm{N}}_{2}$)=[2.0(0.3)]\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ ${\mathrm{cm}}^{3}$/s.

Many ventral root afferent fibers in the cat are third branches of dorsal root ganglion cells

The arrangement of the ventral root afferent fibers was investigated in anesthetized and paralyzed cats. Single unit activity was recorded from a fascicle of the distal stump of the cut S 1 dorsal root. Activity was elicited by stimulating the distal stump of the cut S 1 ventral root. Attempts were then made to collide this activity with that elicited by stimulation of the S 1 spinal nerve. Single unit activity elicited by ventral root stimulation was recorded from a total of 33 axons. In 17 of these, the activity collided with that elicited by peripheral stimulation. These results indicate that more than half the sampled population of ventral root afferent fibers are branches of dorsal root ganglion cells that have at least 3 processes: one in the dorsal root, one in the ventral root and one in a peripheral nerve. In 10 of these units, the conduction velocity of each of 3 processes was determined using the collision technique. The conduction velocities differed in the processes of a given ganglion cell, with conduction in the ventral root process generally being the slowest. The change in conduction velocity along the length of the ventral root was examined by comparing latency differences for the unit activity elicited by ventral root stimulation at different sites in the same root separated by known distances. The conduction velocity was found not to be uniform along the course of the ventral root. In many cases, the conduction velocity slowed down as the fiber approached the spinal cord. We conclude from the present study that many ventral root afferent fibers are the third branches of dorsal root ganglion cells that have processes in the dorsal root and in a peripheral nerve. The sizes of each of these 3 processes of the dorsal root ganglion cell may differ; the ventral root process tends to be the smallest and is usually umyelinated. Furthermore, many of the ventra root afferent fibers may taper as they approach tthe spinal cord.

Electrophysiological analysis of efferent neurons of cat associative parietal cortex

We have studied in acute experiments the neurons of the associative parietal cortex in the cat, using the microelectrode take-off technique. We identified the efferent neurons sending axons to the sensomotor cortex, the red nucleus, and the pontine nuclei by antidromic stimulation. We investigated the collateral branching of axons of neurons projected simultaneously into two of the formations mentioned, using the impulse collision technique. We studied the characteristics of the spatial distribution of efferent neurons in the parietal cortex.