Optimal parameters of transcranial electrical stimulation for intraoperative monitoring of motor evoked potentials of the tibialis anterior muscle during pediatric scoliosis surgery.

OBJECTIVE: Transcranial electric stimulation elicited muscle motor evoked potentials (TESmMEPs) is one of the best methods for corticospinal tract's function monitoring during spine and spinal cord surgeries. A train of multipulse electric stimulation is required for eliciting TESmMEPs under general anaesthesia. Here, we investigated the best stimulation parameters for eliciting and recording tibialis anterior's TESmMEPs during paediatric scoliosis surgery. PATIENTS AND METHODS: Numbers of pulses (NOP), inter-stimulus intervals (ISI) and current intensities allowing the best size tibialis anterior muscle's TESmMEPs under general anaesthesia, were tested and collected during 77 paediatric scoliosis surgery monitoring procedures in our hospital. Individual pulse duration was kept at 0.5 ms and stimulating electrodes were positioned at C1 and C2 (International 10-20-EEG-System) during all the tests. RESULTS: The NOP used for eliciting the best tibialis anterior TESmMEPs response was 5, 6, and 7 respectively in 21 (27%), 47 (61%) and 9 (12%) out of the 77 patients. The ISI was 2, 3 and 4 ms respectively in 13 (17%), 55 (71%) and 9 (12%) of them. The current intensity used varied from 300 to 700 V (mean: 448±136 V). CONCLUSION: Most patients had 6 as best NOP (61%) and 3 ms as best ISI (71%). These findings support that a NOP of 6 and an ISI of 3 ms should be preferentially used as optimal stimulation settings for intraoperative tibialis anterior muscle's TESmMEPs eliciting and recording during paediatric scoliosis surgery.

Rhythmic movement in Parkinson's disease: effects of visual feedback and medication state.

Previous studies examining discrete movements of Parkinson's disease (PD) patients have found that in addition to performing movements that were slower than those of control participants, they exhibit specific deficits in movement coordination and in sensorimotor integration required to accurately guide movements. With medication, movement speed was normalized, but the coordinative aspects of movement were not. This led to the hypothesis that dopaminergic medication more readily compensates for intensive aspects of movement (such as speed), than for coordinative aspects (such as coordination of different limb segments) (Schettino et al., Exp Brain Res 168:186-202, 2006). We tested this hypothesis on rhythmic, continuous movements of the forearm. In our task, target peak speed and amplitude, availability of visual feedback, and medication state (on/off) were varied. We found, consistent with the discrete-movement results, that peak speed (intensive aspect) was normalized by medication, while accuracy, which required coordination of speed and amplitude modulation (coordinative aspect), was not normalized by dopaminergic treatment. However, our findings that amplitude, an intensive aspect of movement, was also not normalized by medication, suggests that a simple pathway gain increase does not act to remediate all intensive aspects of movement to the same extent. While it normalized movement peak speed, it did not normalize movement amplitude. Furthermore, we found that when visual feedback was not available, all participants (PD and controls) made faster movements. The effects of dopaminergic medication and availability of visual feedback on movement speed were additive. The finding that movement speed uniformly increased both in the PD and the control groups suggests that visual feedback may be necessary for calibration of peak speed, otherwise underestimated by the motor control system.

Modeling parkinsonian circuitry and the DBS electrode. I. Biophysical background and software.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) for Parkinson's disease (PD) has become routine over the past decade, utilizing microelectrode recordings to ensure accurate placement of the stimulating electrodes. The clinical benefits of STN DBS for PD are well documented, but the mechanisms by which DBS achieves these results remain elusive. We have created a closed-form mathematical function of the potential field generated by a typical 4-contact DBS electrode and inserted this function into a computational model designed to simulate individual neurons and neural circuitry of significant portions of the basal ganglia. We present the mathematical function representing the potential field itself and the basis for the neural circuitry modeling in this paper.

Modeling parkinsonian circuitry and the DBS electrode. II. Evaluation of a computer simulation model of the basal ganglia with and without subthalamic nucleus stimulation.

Treatment with deep brain stimulation (DBS) for Parkinson's disease (PD) has become routine over the past decade, particularly using the subthalamic nucleus (STN) as a target and utilizing microelectrode recordings to ensure accurate placement of the stimulating electrodes. The clinical changes seen with DBS in the STN for PD are consistently beneficial, but there continues to be only marginal understanding of the mechanisms by which DBS achieves these results. Using an analytical model of the typical DBS 4-contact electrode and software developed to simulate individual neurons and neural circuitry of the basal ganglia we compare the results of the model to those of data obtained during DBS surgery of the STN. Firing rate, interspike intervals and regularity analyses were performed on the simulated data and compared to results in the literature.

Sixty hertz pallidal deep brain stimulation for primary torsion dystonia.

OBJECTIVE: To evaluate the safety and efficacy of 60 Hz deep brain stimulation (DBS) of the globus pallidus internus (GPi) in 15 consecutive patients with primary dystonia. METHODS: We conducted a retrospective analysis of clinic charts relative to 15 consecutive patients with medically refractory primary dystonia who underwent stereotactic implantation of DBS leads within the GPi. Twelve had the DYT1 gene mutation. Frame-based MRI and intraoperative microelectrode recording were employed for targeting. All patients were treated exclusively with stimulation at 60 Hz from therapy outset. The Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) served as the primary measure of symptom severity at baseline and 1, 3, 6, and 12 months after treatment. RESULTS: All patients tolerated DBS treatment well and showed a progressive median improvement of their BFMDRS motor subscores from 38% at 1 month to 89% at 1 year (p < 0.001, Wilcoxon rank sum test). The disability subscores were similarly improved. The clinical response to DBS allowed seven patients to completely discontinue their medications; six additional patients had reduced their medications by at least 50%. Surgical complications were limited to two superficial infections, which were treated successfully. CONCLUSIONS: Stimulation of the internal globus pallidus at 60 Hz is safe and effective for treating medically refractory primary dystonia.

Intraoperative microelectrode recording equipment: what features are necessary?

Intraoperative neurophysiologic methods for localizing targets deep in the brain require the use of specialized monitoring and recording equipment, including stimulators, neurophysiologic recording devices, and image manipulation tools. When using microelectrode recording devices there are some specifications that are more important than others, such as signal-to-noise ratios and amplifier impedance. As more companies develop tools to be used in the operating room, the end users have more choices. Some of the more important specifications are discussed and a comparison is made of the five major brands on the market today.

Bispectral analysis of visual interactions in humans.

Previous electrophysiological studies have demonstrated interactions between dichoptic visual stimuli presented to the same location in visual space. In this study, we used non-liner spectral analysis, in particular the bispectrum, to study interactions between the electrocerebral activity resulting from stimulation of the left and right visual fields. The stimulus consisted of two squares, one in each visual field, flickering at different frequencies. Bispectra, bichoherence and biphase were calculated for 8 subjects monocularly observing a visual stimulus. Both phase vs. frequency and biphase vs. frequency plots were made to determine weighted time delays from stimulus application to signal appearance in the EEG electrodes. Bispectral analysis reveals non-liner interactions between visual fields occurring with weighted delay times of 410 + / - 58 msec while non-interactive components propagated with weighted time delays of 202 + / - 39 msec. Evaluating these results in light of the predictions of various models, we were able to conclude that this interaction does not occur in the retina. These results illustrate how bispectral analysis can be a powerful tool in analyzing the connectivity of neural networks in complex systems. It allows different neuronal systems to be labeled with stimuli at specific frequencies, whose connections can be traced using frequency analysis of the scalp EEG.