Neurosonography in the second half of fetal life: a neonatologist's point of view

This article reviews the interpretation of the fetal motor repertoire in the light of neurophysiology and clinical neurology. The continuity of the maturative process from the fetus to the neonate allows us to speculate on the predictive value of optimal and non-optimal neurological function as observed in the fetus and their morphological consequences. Neonatologists know that early prediction concerning outcome is reliable only at the two ends of the spectrum, e.g., optimal and very abnormal situations. However, in intermediate situations the quality of observations achieved by 3D-4D ultrasonography already allows to demonstrate the prenatal onset of brain damage, based on morphologic and functional signs. Their identification during the second half of pregnancy may serve as a retrospective marker of a prenatal insult.

Intraoperative neurophysiological monitoring technology: recent advances and evolving uses

Intraoperative neurophysiological monitoring has evolved over the last 25 years to become an important component of many types of orthopedic and neurosurgical procedures. From its foundations in VIII cranial nerve surgeries and scoliosis corrections surgeries, intraoperative neurophysiological monitoring has expanded to incorporate nearly all spine procedures and many involving the brain and brainstem. Fundamental to this growth in the use of intraoperative neurophysiological monitoring has been the development of the technology used to perform the neurophysiological tests. Advancements in electronics and computer technology have resulted in significant improvements in the capacity, ease of use, quality and reliability of the equipment as well as the quality of and control over the acquired data. These technological advancements have resulted in remarkable improvements in not only the quality and availability of intraoperative neurophysiological monitoring, but also, as a consequence, patient care, and have arguably propelled the expansion of the use that intraoperative neurophysiological monitoring has seen over the last 10 years.

A method to reversibly degrade proprioceptive feedback in research on human motor control

In research on human motor skills, it is often desirable to manipulate proprioceptive feedback in order to determine its contribution towards subjects' performance. Here we evaluate an easy-to-use, non-invasive method to temporarily reduce proprioceptive responsiveness. Two physiotherapy vibrators contacted the distal end of the subjects' forearm on the flexor and extensor side; they were either turned off, or they vibrated at 80 Hz with an amplitude of 1mm. We found that vibration substantially impaired subjects' ability to use their hand in an angle matching, a force production and a haptic shape perception task. We also found that vibration strongly attenuated the H-reflex of the ipsilateral M. flexor carpi radialis. These results suggest that agonist-antagonist vibration is a useful method to degrade proprioceptive responsiveness for research on higher motor functions.

Prediction of treatment response in major depression: integration of concepts

BACKGROUND

Two promising approaches have been introduced for the prediction of treatment response in major depression: one concept is based on the activity in the rostral anterior cingulate cortex (rACC). Subjects with higher metabolic rates respond better to sleep deprivation or antidepressive medication. Another approach is the investigation of the loudness dependence of the auditory evoked potential (LDAEP). Here, a high LDAEP is supposed to reflect low central serotonergic activity. We present the first study comparing both approaches in the same group of patients.

METHODS

Patients with major depression (n=20) were investigated using both resting EEG and LDAEP before treatment with either citalopram or reboxetine.

RESULTS

We found significant differences between responders and non-responders in the rACC in the theta-frequency range (6.5-8 Hz, p<0.05). In the subgroup of patients, treated with citalopram we found higher LDAEP-values in responders versus non-responders (p<0.05) and a significant correlation between pre-treatment-LDAEP and improvement in the Hamilton score after treatment (r=0.71, p<0.05).

CONCLUSIONS

In combining both methods a prediction whether a patient with major depression might be at risk for non-response to a standard therapy as well as a suggestion for a pharmacological approach of choice seems to be possible.

Methods for building an olfactometer with known concentration outcomes

We provide detailed instructions and part selections for construction of a five-channel air dilution olfactometer capable of generating neat odorants and binary mixtures at a range of known concentrations. At the heart of the olfactometer is an odorant canister that is (1) cheap and readily available, (2) safe and durable, (3) has minimal odor adherence, (4) is easily incorporated into any olfactometer, and critically (5) produces a highly consistent stimulus. By flowing a given carrier gas at a given flowrate through a given odorant in this canister, the same end-vapor is achieved. Flow/concentration outcomes are provided for several odorants routinely used in olfactometry. This tool will enable researchers to generate known concentrations without expensive analytical machinery.

An ethics perspective on transcranial magnetic stimulation (TMS) and human neuromodulation

This paper concerns the ethics of human neuromodulation using transcranial magnetic stimulation (TMS). We examine the challenges of modulating the brain with TMS through the research ethics lens and in clinical medicine for treating frank pathology, primarily in psychiatric diseases. We also consider contemporary issues raised in the neuroethics literature about managing unexpected findings, and relate these to TMS and to other frontier neurotechnology that is becoming openly available in the public domain. We argue that safety and informed consent are of paramount importance for TMS, but that personal values and sociocultural factors must also be considered when examining the promise of this technology and applications that ought to be highlighted for extra precautions.

Recommendations Regarding the Requirements and Applications for Long-term Recordings in Epilepsy

The purpose of this paper is to update the state of knowledge with respect to long-term monitoring (LTM) in epilepsy and to formulate recommendations regarding the application of LTM in clinical practice. LTM is an established technique in use both in a hospital setting and, increasingly, in an ambulatory and more recently in a community-based setting. There has been sufficient evidence to substantiate the claim that LTM is of crucial importance in documenting electroclinical correlations both in epilepsy and in paroxysmally occurring behavioral changes often mistaken for epilepsy. Internationally recognized neurophysiological equipment standards, data acquisition and data transfer protocols and widely accepted safety standards have made widespread access to LTM facilities in epilepsy possible. Recommendations on efficient and effective use of resources as well as regarding training and competencies for personnel involved in LTM in epilepsy have been formulated. The DMC Neurophysiology Subcommittee of the ILAE recommends use of hospital-based LTM in the documentation of seizures including its application for assessing seizure type and frequency, in the evaluation of status epilepticus, in noninvasive and invasive video/EEG investigations for epilepsy surgery and for the differential diagnosis between epilepsy and paroxysmally occurring nonepileptic conditions, in children and in adults. Ambulatory outpatient and community-based LTM may be used as a substitute for inpatient LTM in cases where the latter is not cost-effective or feasible or when activation procedures aimed at increasing seizure yield are not indicated. However, outpatient ambulatory monitoring may be less informative than is inpatient monitoring in some cases because: (1) reduction of medication to provoke seizures may not be safe as an outpatient; (2) faulty electrode contacts cannot quickly be noticed and repaired; (3) the patient may move out of video surveillance; and (4) duration of ambulatory monitoring can be limited by technical constraints.

A new multi-electrode array design for chronic neural recording, with independent and automatic hydraulic positioning

We report on a new microdrive design, which enables the construction of multi-electrode arrays capable of chronically recording the multi-unit neural activity of waking animals. Our principal motivation for inventing this device was to simplify the task of positioning electrodes, which consumes a considerable amount of time and requires a high level of skill. With the new microdrives, each electrode is independently and automatically driven into place. A hydraulic drive system is adopted to reduce the size, weight, and cost of the structure. The hydraulic fluid is also used as a part of the electrical circuit, and facilitates the wiring of the electrodes. A routing system has been attached to reduce the number of tube connections. The microdrive is cylindrical, has a diameter of 23.5 mm, a height of 37 mm, and a weight of 15 g. It allows for up to 22 electrodes, which are arranged on a 0.35 mm grid. Each electrode can be positioned at any depth up to approximately 4mm. The microdrive was evaluated under acute and chronic recording experiments, and is shown to be capable of automatically positioning each electrode and successfully recording the neural signals of waking rats.

Efficient measurement of endogenous neurotransmitters in small localized regions of central nervous systems in vitro with HPLC

High performance liquid chromatography (HPLC) is widely used to determine neurotransmitter concentrations in the central nervous system (CNS). Finding the optimal methods to sample from CNS tissue poses a challenge for neuroscientists. Here, we describe a method that allows assay of neurotransmitters (or other chemicals) in small regions (down to 180mum in diameter) in in vitro preparations concurrently with electrophysiological recordings. The efficiency for measuring small amounts of chemicals is enhanced by a sample collecting pipette with filter paper at the tip that makes close contact with the target region in CNS tissue. With a wire plunger in the calibrated pipette controlled by a microsyringe pump, there is virtually no dead volume. Samples in a volume of 10muL (taken, e.g., at 2muL/min over 5min) can be injected into a HPLC machine with microbore columns. We demonstrate the effectiveness of this method by measuring acetylcholine (ACh) in the ventral horn and its surrounding areas of the spinal cord in en bloc brainstem-spinal cord preparations. In control conditions, endogenous ACh levels in these regions were detectable. Application of neostigmine (an inhibitor of acetylcholinesterases (AChEs)) increased ACh concentrations, and at the same time, induced tonic/seizure-like activity in efferent motor output recorded from cervical ventral nerve roots. Higher ACh concentrations in the ventral horn were differentiated from nearby regions: the lateral and midline aspects of the ventral spinal cord. In addition, ACh in the preBötzinger Complex (preBötC) and the hypoglossal nucleus in medullary slice preparations can also be measured. Our results indicate that the method proposed in this study can be used to measure neurotransmitters in small and localized CNS regions. Correlation between changes in neurotransmitters in target regions and the neuronal activities can be revealed in vitro. Our data also suggest that there is endogenous ACh release in spinal ventral motor columns at fourth cervical (C4) level that regulates the respiratory-related motor activity.

Spatiotemporal pH dynamics following insertion of neural microelectrode arrays

Insertion trauma is a critical issue when assessing intracortical electrophysiological and neurochemical recordings. Previous reports document a wide variety of insertion techniques with speeds ranging from 10 microm/s to 10 m/s. We hypothesize that insertion speed has an effect on tissue trauma induced by implantation of a neural probe. In order to monitor the neural interface during and after probe insertion, we have developed a silicon-substrate array with hydrous iridium oxide microelectrodes for potentiometric recording of extracellular pH (pH(e)), a measure of brain homeostasis. Microelectrode sites were sensitive to pH in the super-Nernstian range (-85.9 mV/pH unit) and selective over other analytes including ascorbic acid, Na(+), K(+), Ca(2+), and Mg(2+). Following insertion, arrays recorded either triphasic or biphasic pH(e) responses, with a greater degree of prolonged acidosis for insertions at 50 microm/s than at 0.5 mm/s or 1.0 mm/s (p<0.05). Spatiotemporal analysis of the recordings also revealed micro-scale variability in the pH(e) response along the array, even when using the same insertion technique. Implants with more intense acidosis were often associated histologically with blood along the probe tract. The potentiometric microsensor array has implications not only as a useful tool to measure extracellular pH, but also as a feedback tool for delivery of pharmacological agents to treat surgical brain trauma.

Low-density neuronal networks cultured using patterned poly-l-lysine on microelectrode arrays

Synaptic activity recorded from low-density networks of cultured rat hippocampal neurons was monitored using microelectrode arrays (MEAs). Neuronal networks were patterned with poly-l-lysine (PLL) using microcontact printing (microCP). Polydimethysiloxane (PDMS) stamps were fabricated with relief structures resulting in patterns of 2 microm-wide lines for directing process growth and 20 microm-diameter circles for cell soma attachment. These circles were aligned to electrode sites. Different densities of neurons were plated in order to assess the minimal neuron density required for development of an active network. Spontaneous activity was observed at 10-14 days in networks using neuron densities as low as 200 cells/mm(2). Immunocytochemistry demonstrated the distribution of dendrites along the lines and the location of foci of the presynaptic protein, synaptophysin, on neuron somas and dendrites. Scanning electron microscopy demonstrated that single fluorescent tracks contained multiple processes. Evoked responses of selected portions of the networks were produced by stimulation of specific electrode sites. In addition, the neuronal excitability of the network was increased by the bath application of high K(+) (10-12 mM). Application of DNQX, an AMPA antagonist, blocked all spontaneous activity, suggesting that the activity is excitatory and mediated through glutamate receptors.

Chronically mountable goggles for persistent exposure to single orientation

To examine the effect of experience on the developmental plasticity of functional maps in the visual cortex, we need to establish a method for a stable visual experience manipulation under the freely moving condition. For this purpose, we fabricated goggles that are chronically mounted stably on the animal's head, but easy to replace according to the animal's growth. Here we report the design of the goggles and the method of mounting them on the head of animals. By this method, combined with the intrinsic signal optical imaging technique, we were able to observe a rapid and robust reorganization of orientation maps.

A method for recording single unit activity in lumbar spinal cord in rats anesthetized with nitrous oxide in a hyperbaric chamber

The limited potency of nitrous oxide mandates the use of a hyperbaric chamber to produce anesthesia. Use of a hyperbaric chamber complicates anesthetic delivery, ventilation, and electrophysiological recording. We constructed a hyperbaric acrylic-aluminum chamber allowing recording of single unit activity in spinal cord of rats anesthetized only with N(2)O. Large aluminum plates secured to each other by rods that span the length of the chamber close each end of the chamber. The 122 cm long, 33 cm wide chamber housed ventilator, intravenous infusion pumps, recording headstage, including hydraulic microdrive and stepper motors (controlled by external computers). Electrical pass-throughs in the plates permitted electrical current or signals to enter or leave the chamber. In rats anesthetized only with N(2)O we recorded extracellular action potentials with a high signal-to-noise ratio. We also recorded electroencephalographic activity. This technique is well-suited to study actions of weak anesthetics such as N(2)O and Xe at working pressures of 4-5 atm or greater. The safety of such pressures depends on the wall thickness and chamber diameter.

Neurophysiologic and long-term effects of clinical hypnosis in oral and maxillofacial treatment--a comparative interdisciplinary clinical study

This prospective comparative clinical study evaluated the effectiveness of clinical hypnosis and its long-term effect in oral and maxillofacial treatment. A total of 45 highly anxious and nonanxious subjects were evaluated by subjective experience and objective parameters. Parameters were EEG, ECG, heart rate, blood pressure, blood oxygen saturation, respiration rate, salivary cortisol concentration, and body temperature. During and subsequent to the operative treatment, hypnosis led to a significant reduction of systolic blood pressure, and respiration rate and to significant changes in the EEG. The subjective values of the parameters evaluated existing anxiety mechanisms and patterns and possible strategies to control them, whereas the objective parameters proved the effectiveness of hypnosis and its long-term effect.

A method for quantifying directional strength and motor control of the trunk

We describe a new apparatus for studying trunk motor control. Quasi-isometric trunk forces are exerted in any horizontal direction while seated, with or without the pelvis stabilised. Trunk force magnitude and direction are measured using a novel transducing system. In addition, reaction forces between the buttocks and the seat and between each foot and the ground are measured with three force plates. Twenty-four healthy subjects exerted maximal forces in eight directions, with and without pelvis fixation. Accuracy of trunk force measurements was assessed by comparing them with reaction force measurements. The agreement analysis showed a small mean bias of the new system of -3.0 N for force magnitude and 0.72 degrees for force direction. The trunk force measurement system was sensitive enough to detect effects of movement direction and pelvis fixation on maximum force magnitude. When subjects repeated the test at a later date there were no significant differences between the two sessions. In conclusion, the new device allows measurement of static and dynamic aspects of voluntary trunk activation in multiple directions while seated and provides reproducible measurements for application to longitudinal studies. The method should prove useful for quantifying deficits and recovery of trunk motor control following neurological damage.

Neuroimaging: a story of physicians and basic scientists

Until just a few decades ago, it was very difficult to detect, non invasively, physiological signals from the brain. However, the discoveries in physics, the evolution of information technology, and the invention of non-invasive biomedical technologies in the last decades of the twentieth century transformed this scenario and created numerous opportunities for studying the brain in living subjects. The authors trace the extraordinary evolution of brain imaging techniques (magnetic resonance imaging, emission tomography, and ?functional neuroimaging?) in the second part of the twentieth century. Not only have these methods had a remarkable clinical impact, they have also been outstanding research tools in the field of the neurosciences. In their most recent applications, they are employed in the quest to uncover the neuronal substrate of the human mind.

Dry beveling micropipettes using a computer hard drive

It is sometimes useful in electrophysiological recordings to try various micropipette profiles in order to determine which tip works best in a given experiment. A pipette puller can be used to pull very sharp or blunt pipettes, and to fire polish tips for whole cell patch recordings. Broken tip pipettes can be "bumped" to an acceptable tip diameter under a microscope. However, it may be difficult to rationalize the purchase of a commercial beveling machine simply to test whether beveled pipettes are best for recording intracellularly from the cell types of interest. Presented here are methods that use a surplus computer hard drive to reproducibly dry bevel glass micropipettes. Compared to sharp or broken tip electrodes, pipettes dry beveled with this simple system are superior for making intracellular recordings from cichlid Mauthner neurons. Preliminary data obtained with this inexpensive apparatus may allow investigators to successfully justify the purchase of a commercial beveler.

Validation of a mechanical apparatus for the measurement of avian walking

Recent research has demonstrated that avian species may show an enhanced locomotor response to repeated drug exposure, a phenomenon called sensitization. Further research in this domain is warranted as such results not only establish the generality of previous findings, but may lend to a better understanding of sensitization in general. At present, there are no well-studied measurement devices for automating the measurement of bird movement. The present research evaluated a mechanical device comprised of moveable floor panels to assess its suitability. Evaluations of the device were made over the course of repeated cocaine administration. The results showed that there was high correspondence between the apparatus' responses and human observers' responses to movement by pigeons. The apparatus, furthermore, provided useful data on spatial orientation that revealed individual differences in the response to cocaine beyond those available from a collapsed measure of overall output. In sum, this recording strategy appears a viable instrument for the measurement of avian locomotion.

The use of radiotelemetry to evaluate electrographic seizures in rats with kainate-induced epilepsy

Temporal lobe epilepsy in humans is a chronic condition with a highly variable temporal evolution. Animal models of this disorder have been developed to recapitulate many of the characteristics seen in humans with temporal lobe epilepsy. These animal models generate chronic spontaneous electrographic and motor seizures with a progressive increase in frequency over many months. In order to understand the underlying cellular and molecular mechanisms driving epileptogenesis, a practical means for accurately assessing seizure progression over this extended time period must be devised. In this report, we describe the use of a three-channel radiotelemetry system to record spontaneous electrographic interictal "spikes" and seizure activity from the cortical surface and the two hippocampi. This approach has allowed continuous recording before, during, and several months after kainate-induced status epilepticus. The important advantages of this approach are the potential for long-term continuous electrographic recording with comparatively unrestricted behavior; the disadvantages include increased cost, surgical difficulty and lower frequency-response in the recordings.

Large-scale neural ensemble recording in the brains of freely behaving mice

With the availability of sophisticated genetic techniques, the mouse is a valuable mammalian model to study the molecular and cellular basis of cognitive behaviors. However, the small size of mice makes it difficult for a systematic investigation of activity patterns of neural networks in vivo. Here we report the development and construction of a high-density ensemble recording array with up to 128-recording channels that can be formatted as single electrodes, stereotrodes, or tetrodes. This high-density recording array is capable of recording from hundreds of individual neurons simultaneously in the hippocampus of the freely behaving mice. This large-scale in vivo ensemble recording techniques, once coupled with mouse genetics, should be valuable to the study of complex relationship between the genes, neural network, and cognitive behaviors.

A lightweight telemetry system for recording neuronal activity in freely behaving small animals

A miniature lightweight radio telemetric device is described which is shown to be suitable for recording neuronal activity in freely behaving animals. Its size (12 x 5 x 8 mm) and weight (1.0-1.1 g with batteries, 0.4-0.5 g without) make the device particularly suitable for recording neuronal units in small animals such as mice or zebra finches. The device combines a high impedance preamplifier, RC-filters and an FM-transmitter. Using the device we recorded action potentials in field L of freely behaving zebra finches (12-17 g) through chronically implanted tungsten electrodes. In freely behaving birds we observed frequency dependent responses of field L units to auditory stimuli for periods of up to 7 days. We investigated the effect of the device on singing and locomotor activity of the zebra finches. Singing and locomotion were significantly affected on the first day after surgery. Both anesthesia and the presence of the transmitter contributed to the observed effect. After 1 day of recovery, singing activity returned to 99.6% and perch-hopping activity to 55.3% of the baseline levels. It is concluded that the device is well suited for recording spike trains from small animals while they behave freely and naturalistically.

Nyquist interpolation improves neuron yield in multiunit recordings

Multiunit electrodes, in particular tetrodes and polytrodes, are able to isolate action potentials from many neurons simultaneously. However, inaccuracies in the post-acquisition reconstruction of recorded spike waveforms can affect the reliability of spike detection and sorting. Here we show that bandlimited interpolation with sample-and-hold delay correction reduces waveform variability, leading to improved reliability of threshold-based event detection and improved spike sorting accuracy. Interpolation of continuously acquired data is, however, computationally expensive. A cost-benefit analysis was made of varying sampling rates from 12.5 kHz (no interpolation) to 100 kHz (eight times oversampling, with respect to the Nyquist frequency), taking into consideration the final application of the data. For most purposes, including spike sorting, sample rates below 25 kHz with bandlimited interpolation to 50 kHz were ideal, with negligible gains above this rate. A practical benefit, especially for large electrode arrays, is that the bandwidth and storage requirements can be greatly reduced by using data acquisition rates at or slightly above the Nyquist frequency.

MRI compatible electrodes for the induction of amygdala kindling in rats

The rat electrical kindling model has been widely utilized in epilepsy research. This study aimed to identify the optimum "MRI compatible" bipolar stimulating and recording electrodes to enable serial MRI acquisition in this model. Two types of custom-made electrodes (gold and carbon) were compared with commercial platinum-iridium alloy electrodes for suitability based on size, effect on image quality and kindling induction. The custom-made gold electrodes, based on these parameters, were found to be most suitable. These electrodes enable the study of epileptogenesis utilizing MRI in this model of temporal lobe epilepsy (TLE).

Analysis of a gain control model of V1: is the goal redundancy reduction?

In this paper we analyze a popular divisive normalization model of V1 with respect to the relationship between its underlying coding strategy and the extraclassical physiological responses of its constituent modeled neurons. Specifically we are interested in whether the optimization goal of redundancy reduction naturally leads to reasonable neural responses, including reasonable distributions of responses. The model is trained on an ensemble of natural images and tested using sinusoidal drifting gratings, with metrics such as suppression index and contrast dependent receptive field growth compared to the objective function values for a sample of neurons. We find that even though the divisive normalization model can produce "typical" neurons that agree with some neurophysiology data, distributions across samples do not agree with experimental data. Our results suggest that redundancy reduction itself is not necessarily causal of the observed extraclassical receptive field phenomena, and that additional optimization dimensions and/or biological constraints must be considered.