Rodent Behavioral Testing to Assess Functional Deficits Caused by Microelectrode Implantation in the Rat Motor Cortex.

Medical devices implanted in the brain hold tremendous potential. As part of a Brain Machine Interface (BMI) system, intracortical microelectrodes demonstrate the ability to record action potentials from individual or small groups of neurons. Such recorded signals have successfully been used to allow patients to interface with or control computers, robotic limbs, and their own limbs. However, previous animal studies have shown that a microelectrode implantation in the brain not only damages the surrounding tissue but can also result in functional deficits. Here, we discuss a series of behavioral tests to quantify potential motor impairments following the implantation of intracortical microelectrodes into the motor cortex of a rat. The methods for open field grid, ladder crossing, and grip strength testing provide valuable information regarding the potential complications resulting from a microelectrode implantation. The results of the behavioral testing are correlated with endpoint histology, providing additional information on the pathological outcomes and impacts of this procedure on the adjacent tissue.

Recording and Modulation of Epileptiform Activity in Rodent Brain Slices Coupled to Microelectrode Arrays.

Temporal lobe epilepsy (TLE) is the most common partial complex epileptic syndrome and the least responsive to medications. Deep brain stimulation (DBS) is a promising approach when pharmacological treatment fails or neurosurgery is not recommended. Acute brain slices coupled to microelectrode arrays (MEAs) represent a valuable tool to study neuronal network interactions and their modulation by electrical stimulation. As compared to conventional extracellular recording techniques, they provide the added advantages of a greater number of observation points and a known inter-electrode distance, which allow studying the propagation path and speed of electrophysiological signals. However, tissue oxygenation may be greatly impaired during MEA recording, requiring a high perfusion rate, which comes at the cost of decreased signal-to-noise ratio and higher oscillations in the experimental temperature. Electrical stimulation further stresses the brain tissue, making it difficult to pursue prolonged recording/stimulation epochs. Moreover, electrical modulation of brain slice activity needs to target specific structures/pathways within the brain slice, requiring that electrode mapping be easily and quickly performed live during the experiment. Here, we illustrate how to perform the recording and electrical modulation of 4-aminopyridine (4AP)-induced epileptiform activity in rodent brain slices using planar MEAs. We show that the brain tissue obtained from mice outperforms rat brain tissue and is thus better suited for MEA experiments. This protocol guarantees the generation and maintenance of a stable epileptiform pattern that faithfully reproduces the electrophysiological features observed with conventional field potential recording, persists for several hours, and outlasts sustained electrical stimulation for prolonged epochs. Tissue viability throughout the experiment is achieved thanks to the use of a small-volume custom recording chamber allowing for laminar flow and quick solution exchange even at low (1 mL/min) perfusion rates. Quick MEA mapping for real-time monitoring and selection of stimulating electrodes is performed by a custom graphic user interface (GUI).

Effect of Acute Ethanol Administration on the Hippocampal Region Neural Activity Using a Microelectrode Array.

BACKGROUND: Because acute ethanol (EtOH) administration is known to influence cognitive processes by impairing hippocampal function, electrophysiological responses of the hippocampus following EtOH exposure warrant investigation. To mimic in vivo conditions, we recorded and analyzed critical firing characteristics of the neuronal population dynamically, particularly in the hippocampal region, before and after acute EtOH administration. METHODS: Microelectrodes were inserted in the hippocampus CA1 region of 21 Institute of Cancer Research mice. The mice were divided into 3 groups, including an EtOH injection group (1.5 g/kg), a saline injection group (1.5 g/kg), and a negative control group that received no injection. A data acquisition system was employed to detect the local field potentials (LFPs) and spike potentials following acute EtOH administration. Various multichannel electrophysiological signals were collected in vivo in each group at 60 minutes, from which the firing rate and wavelet entropy (WE) were analyzed further. RESULTS: Firing rates began to decline at 20 minutes postinjection and then gradually recovered from 40 to 60 minutes. In contrast, 20 minutes post-injection, WE increased maximally and then returned to normal from 40 to 60 minutes (p < 0.05). Pronounced changes in the relative energy of theta and alpha oscillations were also observed after 20 minutes of alcohol exposure and recovery occurred by 60 minutes (p < 0.05). CONCLUSIONS: A major mechanism of EtOH's action on the hippocampus is neurotransmitter blocking in the form of excitatory neuron inhibition in vivo. Changes in hippocampal spikes coincided with changes in LFPs during the entire time course of acute EtOH administration. The correlation between spikes and LFPs suggests that they jointly affect encoding in hippocampus.

Wireless Cortical Brain-Machine Interface for Whole-Body Navigation in Primates.

Several groups have developed brain-machine-interfaces (BMIs) that allow primates to use cortical activity to control artificial limbs. Yet, it remains unknown whether cortical ensembles could represent the kinematics of whole-body navigation and be used to operate a BMI that moves a wheelchair continuously in space. Here we show that rhesus monkeys can learn to navigate a robotic wheelchair, using their cortical activity as the main control signal. Two monkeys were chronically implanted with multichannel microelectrode arrays that allowed wireless recordings from ensembles of premotor and sensorimotor cortical neurons. Initially, while monkeys remained seated in the robotic wheelchair, passive navigation was employed to train a linear decoder to extract 2D wheelchair kinematics from cortical activity. Next, monkeys employed the wireless BMI to translate their cortical activity into the robotic wheelchair's translational and rotational velocities. Over time, monkeys improved their ability to navigate the wheelchair toward the location of a grape reward. The navigation was enacted by populations of cortical neurons tuned to whole-body displacement. During practice with the apparatus, we also noticed the presence of a cortical representation of the distance to reward location. These results demonstrate that intracranial BMIs could restore whole-body mobility to severely paralyzed patients in the future.

Differences in globus pallidus neuronal firing rates and patterns relate to different disease biology in children with dystonia.

BACKGROUND: The pathophysiology underlying different types of dystonia is not yet understood. We report microelectrode data from the globus pallidus interna (GPi) and globus pallidus externa (GPe) in children undergoing deep brain stimulation (DBS) for dystonia and investigate whether GPi and GPe firing rates differ between dystonia types. METHODS: Single pass microelectrode data were obtained to guide electrode position in 44 children (3.3-18.1 years, median 10.7) with the following dystonia types: 14 primary, 22 secondary Static and 8 progressive secondary to neuronal brain iron accumulation (NBIA). Preoperative stereotactic MRI determined coordinates for the GPi target. Digitised spike trains were analysed offline, blind to clinical data. Electrode placement was confirmed by a postoperative stereotactic CT scan. FINDINGS: We identified 263 GPi and 87 GPe cells. Both GPi and GPe firing frequencies differed significantly with dystonia aetiology. The median GPi firing frequency was higher in the primary group than in the secondary static group (13.5 Hz vs 9.6 Hz; p=0.002) and higher in the NBIA group than in either the primary (25 Hz vs 13.5 Hz; p=0.006) or the secondary static group (25 Hz vs 9.6 Hz; p=0.00004). The median GPe firing frequency was higher in the NBIA group than in the secondary static group (15.9 Hz vs 7 Hz; p=0.013). The NBIA group also showed a higher proportion of regularly firing GPi cells compared with the other groups (p<0.001). A higher proportion of regular GPi cells was also seen in patients with fixed/tonic dystonia compared with a phasic/dynamic dystonia phenotype (p<0.001). The GPi firing frequency showed a positive correlation with 1-year outcome from DBS measured by improvement in the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS-m) score (p=0.030). This association was stronger for the non-progressive patients (p=0.006). INTERPRETATION: Pallidal firing rates and patterns differ significantly with dystonia aetiology and phenotype. Identification of specific firing patterns may help determine targets and patient-specific protocols for neuromodulation therapy. FUNDING: National Institute of Health Research, Guy's and St. Thomas' Charity, Dystonia Society UK, Action Medical Research, German National Academic Foundation.

Development of the Mayo Investigational Neuromodulation Control System: toward a closed-loop electrochemical feedback system for deep brain stimulation.

OBJECT: Conventional deep brain stimulation (DBS) devices continue to rely on an open-loop system in which stimulation is independent of functional neural feedback. The authors previously proposed that as the foundation of a DBS "smart" device, a closed-loop system based on neurochemical feedback, may have the potential to improve therapeutic outcomes. Alterations in neurochemical release are thought to be linked to the clinical benefit of DBS, and fast-scan cyclic voltammetry (FSCV) has been shown to be effective for recording these evoked neurochemical changes. However, the combination of FSCV with conventional DBS devices interferes with the recording and identification of the evoked analytes. To integrate neurochemical recording with neurostimulation, the authors developed the Mayo Investigational Neuromodulation Control System (MINCS), a novel, wirelessly controlled stimulation device designed to interface with FSCV performed by their previously described Wireless Instantaneous Neurochemical Concentration Sensing System (WINCS). METHODS: To test the functionality of these integrated devices, various frequencies of electrical stimulation were applied by MINCS to the medial forebrain bundle of the anesthetized rat, and striatal dopamine release was recorded by WINCS. The parameters for FSCV in the present study consisted of a pyramidal voltage waveform applied to the carbon-fiber microelectrode every 100 msec, ramping between -0.4 V and +1.5 V with respect to an Ag/AgCl reference electrode at a scan rate of either 400 V/sec or 1000 V/sec. The carbon-fiber microelectrode was held at the baseline potential of -0.4 V between scans. RESULTS: By using MINCS in conjunction with WINCS coordinated through an optic fiber, the authors interleaved intervals of electrical stimulation with FSCV scans and thus obtained artifact-free wireless FSCV recordings. Electrical stimulation of the medial forebrain bundle in the anesthetized rat by MINCS elicited striatal dopamine release that was time-locked to stimulation and increased progressively with stimulation frequency. CONCLUSIONS: Here, the authors report a series of proof-of-principle tests in the rat brain demonstrating MINCS to be a reliable and flexible stimulation device that, when used in conjunction with WINCS, performs wirelessly controlled stimulation concurrent with artifact-free neurochemical recording. These findings suggest that the integration of neurochemical recording with neurostimulation may be a useful first step toward the development of a closed-loop DBS system for human application.

Phase synchronization of neuronal noise in mouse hippocampal epileptiform dynamics.

Organized brain activity is the result of dynamical, segregated neuronal signals that may be used to investigate synchronization effects using sophisticated neuroengineering techniques. Phase synchrony analysis, in particular, has emerged as a promising methodology to study transient and frequency-specific coupling effects across multi-site signals. In this study, we investigated phase synchronization in intracellular recordings of interictal and ictal epileptiform events recorded from pairs of cells in the whole (intact) mouse hippocampus. In particular, we focused our analysis on the background noise-like activity (NLA), previously reported to exhibit complex neurodynamical properties. Our results show evidence for increased linear and nonlinear phase coupling in NLA across three frequency bands [theta (4-10 Hz), beta (12-30 Hz) and gamma (30-80 Hz)] in the ictal compared to interictal state dynamics. We also present qualitative and statistical evidence for increased phase synchronization in the theta, beta and gamma frequency bands from paired recordings of ictal NLA. Overall, our results validate the use of background NLA in the neurodynamical study of epileptiform transitions and suggest that what is considered "neuronal noise" is amenable to synchronization effects in the spatiotemporal domain.

The use of macroelectrodes in recording cellular spiking activity.

Microelectrode recording (MER) is an important navigational and investigational tool, specifically with regard to deep brain stimulation (DBS) surgery. MER is often utilized when targeting the subthalamic nucleus (STN) and other deep brain nuclei in the management of Parkinson's disease (PD), tremor, dystonia and other emerging applications. Microelectrodes are used to detect and measure cellular spiking activity while macroelectrodes are considered more suitable for measuring the collective sum of slow potentials from multiple cells near the electrode, the local field potential (LFP). Precisely how the characteristics of an electrode affect the data recorded is still unclear. Technical idiosyncrasies of some surgical cases allowed serendipitous data collection from a 250 to 6000 Hz bandpassed macroelectrode recording during DBS implantation for PD. Simultaneous recording from both a microelectrode and macroelectrode were compared along the same surgical trajectory. Audio, normalized root mean square of the recorded signal, and power spectrograms were used to analyze the data. The analyses demonstrate similar results in detecting cellular spiking activity when recording with macroelectrodes compared with microelectrodes. This has important implications for the standardization of recording electrophysiological data as well as for the development of next generation closed-loop deep brain stimulation systems.

Towards a noise prediction model for in vivo neural recording.

The signal-to-noise ratio of in vivo extracellular neural recordings with microelectrodes is influenced by many factors including the impedance of the electrode-tissue interface, the noise of the recording equipment and biological background noise from distant neurons. In this work we study the different noise sources affecting the quality of neural signals. We propose a simplified noise model as an analytical tool to predict the noise of an electrode given its geometrical dimensions and impedance characteristics. With this tool we are able to quantify different noise sources, which is important to determine realistic noise specifications for the design of electronic neural recording interfaces.

Measuring the electric field of bioelectrodes in saline during stimulation.

In order to provide effective vision in a retinal prosthesis, it is necessary to provide sufficient phosphene quantities ideally by parallel stimulation of multiple electrodes. A common, limiting factor in parallel stimulation is the occurrence of cross talk, which can cause undesired tissue stimulation leading to inconsistent percepts. In this paper we present a system developed for measuring the electric field in an in vitro environment by stimulation of bioelectrodes immersed in an electrolyte. The results from this study provides a better understanding of the electric field generated by stimulating electrodes. Calculation of activation area can provide useful information in regards to electrode separation to eliminate cross talk during parallel stimulation.

High dose ascorbic acid does not reverse central sympathetic overactivity in chronic heart failure.

WHAT IS KNOWN AND OBJECTIVE: The increased central sympathetic activity typically associated with chronic heart failure (CHF) is probably mediated by formation of reactive oxygen species (ROS) in the brain. Our objective was to undertake a trial to test our hypothesis that administration of the well-known antioxidant and ROS scavenger ascorbic acid, would reverse or reduce the sympathetic overactivity in CHF patients. METHODS: In a prospective, randomized, placebo-controlled, double-blind, cross-over trial, 11 CHF patients were treated with ascorbic acid 2 g/day or placebo for 3 days. At the end of each treatment period, sympathetic nervous system activity was measured by microneurography for direct muscle sympathetic nerve activity (MSNA) recording, analysis of heart rate variability (HRV) and measurement of plasma norepinephrine concentrations. RESULTS: During ascorbic acid administration, plasma vitamin C levels were higher than during placebo (74·9 ± 6·0 µmol/L vs. 54·8 ± 4·6 µmol/L, P = 0·03). Ascorbic acid had no effect on sympathetic activity: MSNA (ascorbic acid: 66·8 ± 3·3 vs. placebo 66·9 ± 3·2 bursts/100 beats, P = 0·98). In addition, HRV and plasma norepinephrine levels did not differ. WHAT IS NEW AND CONCLUSION: Short-term administration of the antioxidant ascorbic acid in CHF patients does not reverse the increased sympathetic activity as measured by microneurography, HRV and plasma norepinephrine levels. The use of higher oral dosages seems not feasible due to accompanying side effects.

Maximal subthalamic beta hypersynchrony of the local field potential in Parkinson's disease is located in the central region of the nucleus.

A pathological marker of Parkinson's disease is the existence of abnormal synchrony of neuronal activity within the beta frequency range (13-35 Hz) in the subthalamic nucleus (STN). Recent studies examining the topography of this rhythm have located beta hypersynchrony in the most dorsal part of the STN. In contrast, this study of the topography of the local field potential beta oscillations in 18 STNs with a 1 mm spatial resolution revealed that the point of maximal beta hypersynchrony was located at 53 ± 24% of the trajectory span from the dorsal to the ventral borders of the STN (corresponding to a 3.0 ± 1.6 mm depth for a 5.9 ± 0.75 mm STN span). This suggests that maximal beta hypersynchrony is located in the central region of the nucleus and that further investigation should be done before using STN spectral profiles as an indicator for guiding placement of deep brain stimulation leads.

Microscale recording from human motor cortex: implications for minimally invasive electrocorticographic brain-computer interfaces.

OBJECT: There is a growing interest in the use of recording from the surface of the brain, known as electrocorticography (ECoG), as a practical signal platform for brain-computer interface application. The signal has a combination of high signal quality and long-term stability that may be the ideal intermediate modality for future application. The research paradigm for studying ECoG signals uses patients requiring invasive monitoring for seizure localization. The implanted arrays span cortex areas on the order of centimeters. Currently, it is unknown what level of motor information can be discerned from small regions of human cortex with microscale ECoG recording. METHODS: In this study, a patient requiring invasive monitoring for seizure localization underwent concurrent implantation with a 16-microwire array (1-mm electrode spacing) placed over primary motor cortex. Microscale activity was recorded while the patient performed simple contra- and ipsilateral wrist movements that were monitored in parallel with electromyography. Using various statistical methods, linear and nonlinear relationships between these microcortical changes and recorded electromyography activity were defined. RESULTS: Small regions of primary motor cortex (< 5 mm) carry sufficient information to separate multiple aspects of motor movements (that is, wrist flexion/extension and ipsilateral/contralateral movements). CONCLUSIONS: These findings support the conclusion that small regions of cortex investigated by ECoG recording may provide sufficient information about motor intentions to support brain-computer interface operations in the future. Given the small scale of the cortical region required, the requisite implanted array would be minimally invasive in terms of surgical placement of the electrode array.

Brain penetration effects of microelectrodes and DBS leads in STN or GPi.

OBJECTIVE: To determine how intraoperative microelectrode recordings (MER) and intraoperative lead placement acutely influence tremor, rigidity, and bradykinesia. Secondarily, to evaluate whether the longevity of the MER and lead placement effects were influenced by target location (subthalamic nucleus (STN) or globus pallidus interna (GPi)). BACKGROUND: Currently most groups who perform deep brain stimulation (DBS) for Parkinson disease (PD) use MER, as well as macrostimulation (test stimulation), to refine DBS lead position. Following MER and/or test stimulation, however, there may be a resultant "collision/implantation" or "microlesion" effect, thought to result from disruption of cells and/or fibres within the penetrated region. These effects have not been carefully quantified. METHODS: 47 consecutive patients with PD undergoing unilateral DBS for PD (STN or GPi DBS) were evaluated. Motor function was measured at six time points with a modified motor Unified Parkinson Disease Rating Scale (UPDRS): (1) preoperatively, (2) immediately after MER, (3) immediately after lead implantation/collision, (4) 4 months following surgery-off medications, on DBS (12 h medication washout), (5) 6 months postoperatively-off medication and off DBS (12 h washout) and (6) 6 months-on medication and off DBS (12 h washout). RESULTS: Significant improvements in motor scores (p<0.05) (tremor, rigidity, bradykinesia) were observed as a result of MER and lead placement. The improvements were similar in magnitude to what was observed at 4 and 6 months post-DBS following programming and medication optimisation. When washed out (medications and DBS) for 12 h, UPDRS motor scores were still improved compared with preoperative testing. There was a larger improvement in STN compared with GPi following MER (p<0.05) and a trend for significance following lead placement (p<0.08) but long term outcome was similar. CONCLUSION: This study demonstrated significant acute intraoperative penetration effects resulting from MER and lead placement/collision in PD. Clinicians rating patients in the operating suite should be aware of these effects, and should consider pre- and post-lead placement rating scales prior to activating DBS. The collision/implantation effects were greater intraoperatively with STN compared with GPi, and with greater disease duration there was a larger effect.

Comparison of the use of tympanic and extratympanic electrodes for electrocochleography.

OBJECTIVES: To determine the differences between tympanic and extratympanic electrodes regarding recording technique, comfort and ease of execution of the exam, and quality of auditory potential tracings. STUDY DESIGN: Prospective cross-section investigation. METHODS: Determination of the summation potential/action potential (SP/AP) ratio by electrocochleography (EchoG) using tympanic and extratympanic electrodes and separate analysis of SP and AP regarding the amplitude recorded. RESULTS: Twenty-three subjects (15 men and 8 women; mean age: 33.17 years) with normal tonal threshold audiometry were evaluated. EchoG analysis revealed no significant difference between the two tympanic electrodes. Eleven of the 23 subjects reported discomfort with the insertion of the tympanic electrode even with the use of topical xylocaine, whereas no complaints of discomfort were reported with the use of the extratympanic electrode. CONCLUSIONS: Both electrodes were effective for EchoG evaluation, but the extratympanic one was easier to insert and did not cause discomfort. However, the tympanic electrode produced tracings of greater amplitude and of better reproducibility.

The effects of co-culture of fibroblasts on mast cell exocytotic release characteristics as evaluated by carbon-fiber microelectrode amperometry.

In this work, carbon-fiber microelectrode amperometry (CFMA) is employed to probe changes in the biophysical mechanism of exocytosis under varied cell culture conditions. Degranulation and serotonin exocytosis from mouse peritoneal mast cells (MPMCs) were measured both without and with co-cultured Swiss-albino 3t3 fibroblasts using CFMA. After 24 h in culture, there are distinct differences in the exocytotic characteristics of MPMCs cultured with and without fibroblast support cells, as detected by CFMA, including an increased number of secreted serotonin molecules, number of granule fusion events, secretion rate, and granule membrane tension. Beyond 48 h in culture, MPMCs cultured alone cannot be analyzed using CFMA due to decreased viability and membrane tension whereas MPMCs co-cultured with fibroblasts were maintained for up to 28 days in culture. Some secretion characteristics evolved over the long-term co-culture but the total amount of serotonin released per cell remained largely constant. This work quantitatively demonstrates that the MPMC/fibroblast co-culture system presents a promising model system for chronic exposure or disease model studies based on CFMA analysis.

Reversible meiotic abnormalities in azoospermic men with bilateral varicocele after microsurgical correction.

Because of a possible relationship between microenvironmental disturbances and meiotic abnormalities and of a straight relationship between lower-quality semen in patient carrying a varicocele and first meiotic non-disjunction, bilateral bipolar testicular biopsies are realized according the thermic differential gradient described in varicocele. Systematic meiotic studies of multiple testicular biopsies from 65 azoospermic men with bilateral varicocele were done in a multi-centric study on microsurgical correction of bilateral varicocele with microthermic intra-operative evaluation using minimally invasive thermal microsensors (Betatherm 10K3MCD2). In the present study abnormal temperature raising, histomorphometric abnormalities (spermatocyte arrest) and meiotic abnormalities (class IIC) are strongly correlated. In the ten patients submitted to another testicular biopsy procedure six months after surgery for TESE, normal thermal differential is registered and no meiotic abnormalities recurrences are found.

Safety and risk of microelectrode recording in surgery for movement disorders.

There is an ongoing controversy about whether it is necessary to use microelectrode recording (MER) techniques in stereotactic surgery for Parkinson's disease and other movement disorders. This paper consists of a critical review of the published literature in order to analyze the value of MER in providing safe, efficient and accurate functional stereotactic surgery. Review of the literature revealed that MER techniques do not necessarily improve targeting accuracy or clinical results, compared to techniques using impedance monitoring and macrostimulation. In terms of safety for the patients, however, MER techniques are relatively safe, but non-Mer techniques, based on macrostimulation-guided surgery, are at least five times safer.

Localisation of the subthalamic nucleus using Radionics Image Fusion and Stereoplan combined with field potential recording. A technical note.

Subthalamic nucleus stimulation is an effective therapy for alleviating parkinsonian tremor, rigidity and bradykinesia. Although microelectrode recording is said to be essential for accurate targeting, this often prolongs the operation and the multiple recording tracts required may increase the incidence of complications, particularly haemorrhage. We describe a technique for implantation of deep brain electrodes in the subthalamic nucleus using MRI/CT fusion for anatomical localisation followed by bipolar recording of focal field potentials via the implanted stimulating electrode for neurophysiological confirmation of the stimulation site. The technique is effective, safe and requires much less time, and can be used as an alternative method to microelectrode recording.

Magnitude of microelectrode refinement in pallidotomy and thalamotomy.

The relative accuracy of starting point algorithms in microelectrode-guided stereotactic pallidotomy and thalamotomy was evaluated using postoperative magnetic resonance imaging (MRI) data. Multiplanar reformations were performed to align postoperative MRI in anterior-posterior, dorsal-ventral and mediolateral planes. Three-dimensional distance and direction from the pallidal and thalamic stereotactic starting points to the respective radiofrequency lesions were measured. Similar magnitude of microelectrode refinement in pallidotomy and thalamotomy suggested similar accuracy of algorithms used to set the stereotactic starting point. Fewer microelectrode-recording tracts were required to identify optimal lesioning sites in thalamotomy compared to pallidotomy. Lesions were consistently localized anterior and superior to the starting point and a refined starting point algorithm may reduce the number of microelectrode recording tracts.