Primary Spinal Intradural Extraosseous Ewing Sarcoma in a Pediatric Patient: Case Report and Review of the Literature.

Ewing sarcoma (ES) is an aggressive, primary bone malignancy with occasional soft tissue extension. Purely extra-osseous ES is rare. A primary intraspinal, intradural ES without bone involvement is exceedingly rare. ES may be differentiated from other primitive neuroectodermal tumors by molecular analysis. The authors report the case of a 14-year-old female who suffered an acute neurologic decline from a hemorrhagic, intraspinal, intradural ES. The patient has been tumor free for 2 years after the initial emergency surgery. Our management of the patient and a review of the literature are provided. Considering only those cases with molecular or genetic confirmation of ES, our patient is the fifth pediatric case reported in the English literature.

When "altering brain function" becomes "mind control".

Functional neurosurgery has seen a resurgence of interest in surgical treatments for psychiatric illness. Deep brain stimulation (DBS) technology is the preferred tool in the current wave of clinical experiments because it allows clinicians to directly alter the functions of targeted brain regions, in a reversible manner, with the intent of correcting diseases of the mind, such as depression, addiction, anorexia nervosa, dementia, and obsessive compulsive disorder. These promising treatments raise a critical philosophical and humanitarian question. "Under what conditions does 'altering brain function' qualify as 'mind control'?" In order to answer this question one needs a definition of mind control. To this end, we reviewed the relevant philosophical, ethical, and neurosurgical literature in order to create a set of criteria for what constitutes mind control in the context of DBS. We also outline clinical implications of these criteria. Finally, we demonstrate the relevance of the proposed criteria by focusing especially on serendipitous treatments involving DBS, i.e., cases in which an unintended therapeutic benefit occurred. These cases highlight the importance of gaining the consent of the subject for the new therapy in order to avoid committing an act of mind control.

Constant RMS versus constant peak modulation for the perceptual equivalence of sinusoidal amplitude modulated signals.

Neuroprosthetics using intracortical microstimulation can potentially alleviate sensory deprivation due to injury or disease. However the information bandwidth of a single microstimulation channel remains largely unanswered. This paper presents three experiments that examine the importance of Peak Power/Charge and RMS Power/Charge for detection of acoustic and electrical Sinusoidal Amplitude Modulated stimuli by the auditory system. While the peripheral auditory system is sensitive to RMS power cues for the detection of acoustic stimuli, here we provide results that suggest that the auditory cortex is sensitive to peak charge cues for electrical stimuli. Varying the modulation frequency and depth do not change this effect for detection of modulated electrical stimuli.

The depth, waveform and pulse rate for electrical microstimulation of the auditory cortex.

Intracortical microstimulation of primary sensory regions of the brain offers a compelling platform for the development of sensory prostheses. However, fundamental questions remain regarding the optimal stimulation parameters. The purpose of this paper is to summarize a series of experiments which were designed to answer the following three questions. 1) What is the best electrode implantation depth? 2) What is the optimal stimulation waveform? 3) What is the maximal useful stimulus pulse rate? The present results suggest the following answers: 1) cortical layers V&IV, 2) biphasic, charge balanced, symmetric, cathode leading pulses with of duration of ∼ 100 microseconds per phase, and 3) 80 pulses-per-second.

Asymmetric versus symmetric pulses for cortical microstimulation.

Intracortical microstimulation (ICMS), which has shown promise in the visual, auditory and somatosensory systems as a platform for sensory prostheses, typically relies on charged balanced, symmetric, biphasic stimulation. However, neural stimulation models as well as experiments conducted in cochlear implant users have suggested that charge balanced asymmetric pulses could generate lower detection thresholds for stimulation in terms of charge per phase. For this study, rats were chronically implanted with microelectrode arrays unilaterally in their right auditory cortex and then trained to detect ICMS delivered through a single electrode site in order to determine their behavioral threshold. This model was used in two experiments. The first experiment addressed the effect of lead phase direction, asymmetry, and phase duration on detection threshold. The second experiment fixed the cathode phase duration at 123 µs and varied only the phase asymmetry and lead phase direction. Taken together, the results of these experiments suggest that, for ICMS, the primary determinant of threshold level is cathode phase duration, and that asymmetry provides no significant advantage when compared to symmetric, cathode leading pulses. However, symmetric anode leading pulses of less than or equal to 205 µs per phase consistently showed higher thresholds when compared to all other pulses of equal cathode phase duration.

Multimodal, longitudinal assessment of intracortical microstimulation.

The fundamental obstacle to neuroprostheses based on penetrating microstimulation is the tissue's response to the device insertion and to the application of the electrical stimulation. Our long-term goal is to develop multichannel microstimulation of central nervous tissue for clinical therapy. The overall objective of this research is to identify the optimal parameters for a chronically implanted microstimulation device. In particular, the work presented here focuses on the effects of repeated stimulation and the reactive tissue response on the efficacy of stimulation-driven behavior. To this end, psychophysical experiments were performed using multichannel cortical implants in the auditory cortex of rats. Further, we investigated the effect of the device-tissue interfacial quality on the psychophysical threshold. Here, we report the effects of cortical depth, days postimplant on the psychophysical threshold of auditory cortical microstimulation, along with correlated impedance spectral changes and post vivo histology. We expect that these data will further enable neuroprosthetic development.

Rat behavioral model for high-throughput parametric studies of intracortical microstimulation.

In the development of sensory prosthetic devices based on intracortical microstimulation (ICMS) an important objective is to optimize the stimulus waveform. However, because of the large design space such optimization is an imposing challenge. This study highlights the ability of individual rats, trained using a conditioned avoidance paradigm and performing an adaptive task, to generate highly consistent and significant data. Three experiments on the effects of phase delay, stimulus pulse rate, and waveform asymmetry were completed and revealed detailed and significant results. These results, consisting of 244 individual thresholds, were generated by one rat in 19 days.

Evaluation of micro-electrocorticographic electrodes for electrostimulation.

Chronic neural recording and stimulation on the surface of the cortex with macroelectrodes has been shown to be promising for treating a wide range of neurological deficits. To enhance the specificity of these devices, dense arrangements of small area electrodes have been microfabricated for precise recording and control of neural populations. In this study micro-electrocorticographic (microECoG) electrodes were evaluated for electrostimulation. Surface modification with electrodeposited iridium oxide (EIrOx) resulted in lower impedance, higher charge carrying capacity, and lower, more linear voltage excursions during current controlled stimulation.

Raloxifene enhances material-level mechanical properties of femoral cortical and trabecular bone.

We have previously documented that raloxifene enhances the mechanical properties of dog vertebrae independent of changes in bone mass, suggesting a positive effect of raloxifene on material-level mechanical properties. The goal of this study was to determine the separate effects of raloxifene on the material-level mechanical properties of trabecular and cortical bone from the femur of beagle dogs. Skeletally mature female beagles (n = 12 per group) were treated daily for 1 yr with oral doses of vehicle or raloxifene (0.50 mg/kg d). Trabecular bone mechanical properties were measured at the femoral neck using reduced platen compression, a method that allows the trabecular bone to be tested without coring specimens. Cortical bone properties were assessed on prismatic beam specimens machined from the femoral diaphysis using both monotonic and dynamic (cyclic relaxation) four-point bending tests. Trabecular bone from raloxifene-treated animals had significantly higher ultimate stress (+130%), modulus (+89%), and toughness (+152%) compared with vehicle-treated animals. Cortical bone from raloxifene-treated animals had significantly greater toughness (+62%) compared with vehicle, primarily as a function of increased postyield displacement (+100%). There was no significant difference between groups in the percentage of stiffness loss during cortical bone cyclic relaxation tests. These results are consistent with previous data from the vertebrae of these same animals, showing raloxifene has positive effects on biomechanical properties independent of changes in bone volume/density. This may help explain how raloxifene reduces osteoporotic fractures despite modest changes in bone mass.