Developing a hippocampal neural prosthetic to facilitate human memory encoding and recall of stimulus features and categories

Objective

Here, we demonstrate the first successful use of static neural stimulation patterns for specific information content. These static patterns were derived by a model that was applied to a subject's own hippocampal spatiotemporal neural codes for memory.

Approach

We constructed a new model of processes by which the hippocampus encodes specific memory items via spatiotemporal firing of neural ensembles that underlie the successful encoding of targeted content into short-term memory. A memory decoding model (MDM) of hippocampal CA3 and CA1 neural firing was computed which derives a stimulation pattern for CA1 and CA3 neurons to be applied during the encoding (sample) phase of a delayed match-to-sample (DMS) human short-term memory task.

Main results

MDM electrical stimulation delivered to the CA1 and CA3 locations in the hippocampus during the sample phase of DMS trials facilitated memory of images from the DMS task during a delayed recognition (DR) task that also included control images that were not from the DMS task. Across all subjects, the stimulated trials exhibited significant changes in performance in 22.4% of patient and category combinations. Changes in performance were a combination of both increased memory performance and decreased memory performance, with increases in performance occurring at almost 2 to 1 relative to decreases in performance. Across patients with impaired memory that received bilateral stimulation, significant changes in over 37.9% of patient and category combinations was seen with the changes in memory performance show a ratio of increased to decreased performance of over 4 to 1. Modification of memory performance was dependent on whether memory function was intact or impaired, and if stimulation was applied bilaterally or unilaterally, with nearly all increase in performance seen in subjects with impaired memory receiving bilateral stimulation.

Significance

These results demonstrate that memory encoding in patients with impaired memory function can be facilitated for specific memory content, which offers a stimulation method for a future implantable neural prosthetic to improve human memory.

Noradrenaline tracks emotional modulation of attention in human amygdala

The noradrenaline (NA) system is one of the brain's major neuromodulatory systems; it originates in a small midbrain nucleus, the locus coeruleus (LC), and projects widely throughout the brain.1,2 The LC-NA system is believed to regulate arousal and attention3,4 and is a pharmacological target in multiple clinical conditions.5,6,7 Yet our understanding of its role in health and disease has been impeded by a lack of direct recordings in humans. Here, we address this problem by showing that electrochemical estimates of sub-second NA dynamics can be obtained using clinical depth electrodes implanted for epilepsy monitoring. We made these recordings in the amygdala, an evolutionarily ancient structure that supports emotional processing8,9 and receives dense LC-NA projections,10 while patients (n = 3) performed a visual affective oddball task. The task was designed to induce different cognitive states, with the oddball stimuli involving emotionally evocative images,11 which varied in terms of arousal (low versus high) and valence (negative versus positive). Consistent with theory, the NA estimates tracked the emotional modulation of attention, with a stronger oddball response in a high-arousal state. Parallel estimates of pupil dilation, a common behavioral proxy for LC-NA activity,12 supported a hypothesis that pupil-NA coupling changes with cognitive state,13,14 with the pupil and NA estimates being positively correlated for oddball stimuli in a high-arousal but not a low-arousal state. Our study provides proof of concept that neuromodulator monitoring is now possible using depth electrodes in standard clinical use.

Co-occurrence of dural arteriovenous fistula and meningioma: A rare case and systematic review

Background

The coexistence of meningioma and dural arteriovenous fistula (dAVF) is a rare, but highly complex condition. Various pathophysiological mechanisms underlie intracranial meningiomas with continuous or distant dAVFs. We describe a case of coexisting meningioma and dAVF with a systematic review of the literature.

Result

Including the present case, there are 21 reported cases of coexisting intracranial dAVF and meningioma. The patients' ages ranged from 23 to 76 years, with a mean age of 61 years. The most common presenting symptom was headache. The dAVFs were commonly located at the transverse-sigmoid sinus (43%) and superior sagittal sinus (24%). The most common meningioma locations were the tentorium and parietal convexity. In 76% of the cases, the meningioma occluded the sinus. The most common dAVF treatment was transcatheter arterial embolization, followed by tumor resection (52%). Among the 20 cases with available outcome data, 90% reported favorable outcomes.

Conclusion

This report highlights some of the features of coexisting dAVF and meningioma and presents a systematic review of other reports on this phenomenon. Through an in-depth analysis of the literature, we highlight some of the leading theories regarding the causes of concomitant dAVF and meningiomas. Our report supports one of the leading theories that impaired venous return, whether through the occlusion of sinuses or sinus manipulation during surgery, plays a role in the development of dAVF. Further understanding may help guide future clinical decision-making and surgical planning.

Spinal Intradural Arachnoid Cysts in Adults: An Institutional Experience and Literature Review

BACKGROUND

Adult spinal intradural arachnoid cysts are rare pathologic entities with an unclear etiopathogenesis. These lesions can be dichotomized into primary (idiopathic) or secondary (related to inflammation, intradural surgery, or trauma) etiologies. Limited series have depicted optimal management strategies and clinical outcomes.

OBJECTIVE

To illustrate our experience with spinal intradural arachnoid cysts and to present a literature review of surgically treated cysts to elucidate the clinical and anatomic differences between etiologies.

METHODS

Institutional review revealed 29 patients. Various data were extracted from the medical record. Initial and follow-up symptomatologies of the surgical cohort were compared. The literature review included case series describing cysts managed surgically.

RESULTS

From patients treated surgically at our institution (22), there was a significant reduction in thoracic back pain postoperatively ( P = .034). A literature review yielded 271 additional cases. Overall, primary and secondary lesions accounted for 254 and 39 cases, respectively. Cysts of secondary origin were more likely localized ventral to the spinal cord ( P = .013). The rate of symptomatic improvement after surgical intervention for primary cysts was more than double than that of secondary cysts ( P < .001). Compared with primary etiologies, the rates of radiographic progression ( P = .032) and repeat surgery ( P = .041) were each more than double for secondary cysts.

CONCLUSION

Surgical intervention for spinal intradural arachnoid cysts improves thoracic back pain. The literature supports surgical intervention for symptomatic primary spinal intradural arachnoid cysts with improved clinical outcomes. Surgery should be cautiously considered for secondary cysts given worse outcomes.

Supratentorial cortical ependymoma: A systematic literature review and case illustration

Cortical ependymomas are currently not considered a subgroup of supratentorial ependymomas; however, there is a growing body of literature investigating the natural history of these lesions compared to supratentorial ependymomas. We performed a systematic literature review of cortical ependymomas with a focus on the natural history, clinical characteristics, and clinical outcomes of these lesions as compared to supratentorial ependymomas. Our search revealed 153 unique cases of cortical ependymomas. The mean age on presentation was 21.2 years. Males and females comprised 58.8% (90/153) and 41.2% (63/153) of cases, respectively. The most common presenting symptom was seizure activity occurring in 44.4% of the cohort (68/153). The recently recognized C11orf95-RELA fusion was identified in 13.7% of the cohort (21/153) and 95.5% of cases (21/22) reporting molecular characterization. World Health Organization grades 2 and 3 were reported in 52.3% (79/151) and 47.7% (72/151) of cases, respectively. The frontal lobe was involved in the majority of cases (54.9%, 84/153). Gross total resection was achieved in 80.4% of cases (123/153). Tumor recurrence was identified in 27.7% of cases (39/141). Mean clinical follow-up was 41.3 months. Mean overall survival of patients who expired was 27.4 months whereas mean progression-free survival was 15.0 months. Comparatively, cortical ependymomas with C11orf95-RELA fusions and supratentorial ependymomas with C11orf95 RELA fusions exhibited differing clinical outcomes. Further studies with larger sample sizes are necessary to investigate the significance of RELA fusions on survival in cortical ependymomas and to determine whether cortical ependymomas with C11orf95-RELA fusions should be classified as a distinct entity.

Monocyte Count on Admission Is Predictive of Shunt-Dependent Hydrocephalus After Aneurysmal Subarachnoid Hemorrhage

The authors sought to evaluate whether immunologic counts on admission were associated with shunt-dependent hydrocephalus following aneurysmal subarachnoid hemorrhage. A retrospective analysis of 143 consecutive patients with aneurysmal subarachnoid hemorrhage over a 9-year period was performed. A stepwise algorithm was followed for external ventricular drain weaning and determining the necessity of shunt placement. Data were compared between patients with and without shunt-dependent hydrocephalus. Overall, 11.19% of the cohort developed shunt-dependent hydrocephalus. On multivariate logistic regression analysis, acute hydrocephalus (OR: 61.027, 95% CI: 3.890–957.327; p = 0.003) and monocyte count on admission (OR: 3.362, 95% CI: 1.024–11.037; p = 0.046) were found to be independent predictors for shunt dependence. Receiver operating characteristic curve analysis for the prediction of shunt-dependent hydrocephalus confirmed that monocyte count exhibited an acceptable area under the curve (AUC = 0.737, 95% CI: 0.601–0.872; p < 0.001). The best predictive cutoff value to discriminate between successful external ventricular drain weaning and shunt-dependent hydrocephalus was identified as a monocyte count ≥0.80 × 10³/uL at initial presentation. These preliminary data demonstrate that a monocyte count ≥0.80 × 10³/uL at admission predicts shunt-dependent hydrocephalus in patients with aneurysmal subarachnoid hemorrhage; however, further large-scale prospective trials and validation are necessary to confirm these findings.

Neutrophil Count on Admission Predicts Acute Symptomatic Hydrocephalus After Aneurysmal Subarachnoid Hemorrhage

OBJECTIVE

To investigate the association between immunologic counts on admission and acute symptomatic hydrocephalus after aneurysmal subarachnoid hemorrhage (aSAH).

METHODS

We conducted a retrospective analysis of 143 consecutive patients with aSAH. Patient demographics, clinical parameters, laboratory values, and radiographic imaging were obtained. Univariate and multivariate logistic regression analyses were performed to investigate parameters independently associated with acute symptomatic hydrocephalus. Receiver operating characteristic (ROC) curve analysis determined the best threshold value of neutrophil count to differentiate patients with and without hydrocephalus.

RESULTS

Overall, acute symptomatic hydrocephalus developed in 39.16% of patients. In an adjusted multivariate logistic regression model, Hunt and Hess grade 4-5 (odds ratio [OR]: 16.052, 95% confidence interval [CI]: 1.188-216.983; P = 0.037), modified Fisher score 3-4 (OR: 10.107, 95% CI: 1.715-59.572; P = 0.011), intraventricular hemorrhage (OR: 4.578, 95% CI: 1.417-14.788; P = 0.011), neutrophil count (OR: 1.183, 95% CI: 1.033-1.354; P = 0.015), and prior ischemic stroke (OR: 7.003, 95% CI: 1.293-37.929; P = 0.024) were significantly associated with hydrocephalus. ROC analysis for neutrophil count confirmed an acceptable area under the curve (AUC 0.780, 95% CI: 0.701-0.859; P < 0.001). The best threshold value of neutrophil count to predict hydrocephalus was ≥9.80 × 10³/mL. Overall, 81.25% of patients who developed shunt dependence had a neutrophil count ≥9.80 × 10³/mL on admission (P = 0.003).

CONCLUSIONS

Neutrophil count ≥9.80 × 10³/mL on admission predicts acute symptomatic hydrocephalus after aSAH in an adjusted multivariate logistic regression model. Moreover, shunt dependence was associated with higher neutrophil counts.

Idiopathic fourth ventricular outlet obstruction misdiagnosed as normal pressure hydrocephalus: A cautionary case

Background:

Fourth ventricular outlet obstruction is an infrequent but well-established cause of tetraventricular hydrocephalus characterized by marked dilatation of the ventricular system with ballooning of the foramina of Monro, Magendie, and Luschka. Multiple processes including inflammation, infection, hemorrhage, neoplasms, or congenital malformations are known to cause this pathological obstruction. However, true idiopathic fourth ventricular outlet obstruction is a rare phenomenon with only a limited number of cases reported in the literature.

Case Description:

A 61-year-old female presented with several months of unsteady gait, intermittent headaches, confusion, and episodes of urinary incontinence. Conventional magnetic resonance imaging demonstrated tetraventricular hydrocephalus without transependymal flow, but with ventral displacement of the brainstem and dorsal displacement of the cerebellum without an obvious obstructive lesion on pre- or post-contrast imaging prompting a diagnosis of normal pressure hydrocephalus. However, constructive interference in steady state (CISS) and half-Fourier acquisition single-shot turbo spin echo (HASTE) sequences followed by fluoroscopic dynamic cisternography suggested encystment of the fourth ventricle with thin margins of arachnoid membrane extending through the foramina of Luschka bilaterally into the pontocerebellar cistern. Operative intervention was pursued with resection of an identified arachnoid web. Postoperative imaging demonstrated marked reduction in the size of ventricular system, especially of the fourth ventricle. The patient’s symptomatology resolved a few days after the procedure.

Conclusion:

Here, we describe an idiopathic case initially misdiagnosed as normal pressure hydrocephalus. The present case emphasizes the necessity of CISS sequences and fluoroscopic dynamic cisternography for suspected cases of fourth ventricular outlet obstruction as these diagnostic tests may guide surgical management and lead to superior patient outcomes.

Pineal Gland Metastasis From Poorly Differentiated Carcinoma of Unknown Primary Origin

Pineal metastasis is an exceedingly rare finding in patients with systemic malignancies. Such lesions are typically the manifestation of a primary lung cancer; nonetheless, a variety of malignancies have been reported to disseminate to the pineal gland including gastrointestinal, endocrine, and skin cancers, among others. However, to our knowledge, pineal gland metastasis without a primary origin has yet to be described. Carcinoma of unknown primary origin is a heterogeneous group of cancers characterized by the presence of metastatic disease without an identifiable primary tumor on metastatic workup. Here, we present a case of a 65-year-old male found to have a heterogeneously enhancing lesion of the pineal gland as well as an enhancing lesion of the left cerebellar hemisphere. Comprehensive metastatic workup demonstrated multifocal metastatic adenopathy without an identifiable primary lesion. Stereotactic biopsy of the pineal lesion revealed poorly differentiated carcinoma with an immunophenotype most consistent with gastrointestinal origin. To our knowledge, this is the first case to describe a pineal gland metastasis without a primary origin. We discuss the relevant literature on pineal gland metastases as well as carcinoma of unknown primary origin.

Hippocampal CA1 and CA3 neural recording in the human brain: validation of depth electrode placement through high-resolution imaging and electrophysiology

OBJECTIVE

Intracranial human brain recordings typically utilize recording systems that do not distinguish individual neuron action potentials. In such cases, individual neurons are not identified by location within functional circuits. In this paper, verified localization of singly recorded hippocampal neurons within the CA3 and CA1 cell fields is demonstrated.

METHODS

Macro-micro depth electrodes were implanted in 23 human patients undergoing invasive monitoring for identification of epileptic seizure foci. Individual neurons were isolated and identified via extracellular action potential waveforms recorded via macro-micro depth electrodes localized within the hippocampus. A morphometric survey was performed using 3T MRI scans of hippocampi from the 23 implanted patients, as well as 46 normal (i.e., nonepileptic) patients and 26 patients with a history of epilepsy but no history of depth electrode placement, which provided average dimensions of the hippocampus along typical implantation tracks. Localization within CA3 and CA1 cell fields was tentatively assigned on the basis of recording electrode site, stereotactic positioning of the depth electrode in comparison with the morphometric survey, and postsurgical MRI. Cells were selected as candidate CA3 and CA1 principal neurons on the basis of waveform and firing rate characteristics and confirmed within the CA3-to-CA1 neural projection pathways via measures of functional connectivity.

RESULTS

Cross-correlation analysis confirmed that nearly 80% of putative CA3-to-CA1 cell pairs exhibited positive correlations compatible with feed-forward connection between the cells, while only 2.6% exhibited feedback (inverse) connectivity. Even though synchronous and long-latency correlations were excluded, feed-forward correlation between CA3-CA1 pairs was identified in 1071 (26%) of 4070 total pairs, which favorably compares to reports of 20%-25% feed-forward CA3-CA1 correlation noted in published animal studies.

CONCLUSIONS

This study demonstrates the ability to record neurons in vivo from specified regions and subfields of the human brain. As brain-machine interface and neural prosthetic research continues to expand, it is necessary to be able to identify recording and stimulation sites within neural circuits of interest.

Factors affecting R01 grant funding among academic neurosurgeons over the last decade

Background

Recent studies have reported a gender and medical degree disparity for those receiving Research Project Grants in surgical specialties. The aim of the present study is to analyze factors among academics neurosurgeons that correlate to higher amounts of R01 grant monies awarded.

Materials and methods

The National Institutes of Health Research Portfolio Online Reporting Tools Expenditures and Results database was queried for neurosurgery funding between 2008 and 2018. Grant recipients were categorized among type of degree, secondary degree(s), professorship, gender, and h - index. Statistical analysis was performed.

Results

The National Institutes of Health awarded 480 R01 grants totaling $182,482,644 to 81 allopathic neurosurgeons between 2008 and 2018. No osteopathic neurosurgeons were awarded an R01 grant during this timeframe. There was a significant difference for type of professorship on the total awarded amount at the p < 0.05 level for the three types of professorship [F (2,78) = 4.85, p < 0.01)]. There was a significant difference for magnitude of h - index on total R01 monies (p < 0.00001). Males accounted for the majority of R01 monies (93.99%); however, no significant difference between average amount awarded and gender was identified (p = 0.86). A secondary degree was without significant difference for R01 amount awarded (p = 0.75).

Conclusions

The present study establishes a medical degree disparity for academic neurosurgeons who receive an R01 grant. Statistically significant factors found to affect amount of R01 grant monies awarded were limited to type of professorship and magnitude of h - index.

N-butyl cyanoacrylate embolization of a traumatic pseudoaneurysm and arteriovenous fistula of the middle meningeal artery

We report a case of combined traumatic pseudoaneurysm and arteriovenous fistula of the middle meningeal artery, which presented clinically 1 year after initial head trauma. A 39-year-old male presented with seizure activity after a closed head injury from a fall. He was hospitalized for multiple intraparenchymal hemorrhages and ultimately discharged 2 weeks later without neurologic deficits. One year later, he presented with a new right anterior temporal intraparenchymal hemorrhage after a syncopal event. Selective angiography of the right external carotid artery demonstrated a chronic appearing traumatic laceration of the proximal middle meningeal artery with a 6 × 10 mm pseudoaneurysm and a single fistula with venous varix draining into the lateral pterygoid veins. The pseudoaneurysm and arteriovenous fistula were successfully embolized with n-butyl cyanoacrylate.

A Novel Approach for Responsive Neural Stimulator Implantation With Infraclavicular Placement of the Internal Pulse Generator

INTRODUCTION

The Responsive Neurostimulation System (RNS, Neuropace, Mountain View, California) has been proven to be effective at reducing seizures in patients with partial-onset epilepsy. The system incorporates a skull-mounted neurostimulator that requires a cranial incision for replacement. Although integral to the functioning of the system, in some circumstances, such as in the setting of infection, this can be disadvantageous. At present, there are no alternatives to cranial implantation of the RNS System.

METHODS

We describe a novel procedure enabling implantation of the neurostimulator within the chest wall, using components from a peripheral nerve stimulator. In a patient who achieved complete seizure freedom with the use of the RNS System, distant site implantation provided a viable means of continuing therapy in a setting where device explantation would have otherwise been inevitable as a result of cranial infection. We present continuous electrocorticographic data recorded from the device documenting the performance of the system with the subclavicular neurostimulator.

RESULTS

Band pass detection rates increased by 50%, while line length detection rates decreased by 50%. The number of detections decreased from 1046 to 846, with a resultant decrease in stimulations. Although there was some compromise of function due to the elevated noise floor, more than 2 yr following the procedure the patient remains free of seizures and infection.

CONCLUSION

The salvage procedure we describe offered an alternative therapeutic option in a patient with a complicated cranial wound issue, using heterogeneous components with marginal compromises in device functionality and no sacrifice in patient outcome.

Clinical Neuroscience in Practice: An Experiential Learning Course for Undergraduates Offered by Neurosurgeons and Neuroscientists

Many pre-health students pursue extracurricular shadowing opportunities to gain clinical experience. The Virginia Tech School of Neuroscience introduced a formal course that provides a clinical experience superior to that received by many medical students. This course is composed of weekly 75-minute seminars that cover diseases affecting the nervous system, their diagnosis and treatment, complemented by weekly half-day intensive clinical experiences with unprecedented access to a team of neurosurgeons (in hospital operating rooms, Intensive Care Units, emergency room, angiographic suites, and wards). In the operating rooms, students routinely "scrub-in" for complex surgeries. On hospital rounds, students experience direct patient care and receive in-depth exposure to modern nervous system imaging. Students participate in two 24-hour "on-call" experiences with team providers. After call, students participate in cognitive and psychological studies to assess physiological and psychological effects of call-related sleep deprivation. Students prepare weekly essays on challenging socioeconomic and ethical questions, exploring subjects such as the cost of medicine and inequalities in access to health care. Towards the end of the course, students meet with the admission dean of the Virginia Tech Carilion medical school; they prepare a personal statement for medical school/graduate school applications, and attend a half-day block of mock medical school/graduate school interviews delivered by experienced clinicians. In lieu of a final exam, each student presents to the entire neurosurgery department, an in-depth clinical analysis of a case in which they participated. We provide details on implementation, challenges and outcomes based on experiences from three semesters with a total enrollment of approximately 60 students.

The Protective Action Encoding of Serotonin Transients in the Human Brain

The role of serotonin in human brain function remains elusive due, at least in part, to our inability to measure rapidly the local concentration of this neurotransmitter. We used fast-scan cyclic voltammetry to infer serotonergic signaling from the striatum of 14 brains of human patients with Parkinson's disease. Here we report these novel measurements and show that they correlate with outcomes and decisions in a sequential investment game. We find that serotonergic concentrations transiently increase as a whole following negative reward prediction errors, while reversing when counterfactual losses predominate. This provides initial evidence that the serotonergic system acts as an opponent to dopamine signaling, as anticipated by theoretical models. Serotonin transients on one trial were also associated with actions on the next trial in a manner that correlated with decreased exposure to poor outcomes. Thus, the fluctuations observed for serotonin appear to correlate with the inhibition of over-reactions and promote persistence of ongoing strategies in the face of short-term environmental changes. Together these findings elucidate a role for serotonin in the striatum, suggesting it encodes a protective action strategy that mitigates risk and modulates choice selection particularly following negative environmental events.

Developing a hippocampal neural prosthetic to facilitate human memory encoding and recall

OBJECTIVE

We demonstrate here the first successful implementation in humans of a proof-of-concept system for restoring and improving memory function via facilitation of memory encoding using the patient's own hippocampal spatiotemporal neural codes for memory. Memory in humans is subject to disruption by drugs, disease and brain injury, yet previous attempts to restore or rescue memory function in humans typically involved only nonspecific, modulation of brain areas and neural systems related to memory retrieval.

APPROACH

We have constructed a model of processes by which the hippocampus encodes memory items via spatiotemporal firing of neural ensembles that underlie the successful encoding of short-term memory. A nonlinear multi-input, multi-output (MIMO) model of hippocampal CA3 and CA1 neural firing is computed that predicts activation patterns of CA1 neurons during the encoding (sample) phase of a delayed match-to-sample (DMS) human short-term memory task.

MAIN RESULTS

MIMO model-derived electrical stimulation delivered to the same CA1 locations during the sample phase of DMS trials facilitated short-term/working memory by 37% during the task. Longer term memory retention was also tested in the same human subjects with a delayed recognition (DR) task that utilized images from the DMS task, along with images that were not from the task. Across the subjects, the stimulated trials exhibited significant improvement (35%) in both short-term and long-term retention of visual information.

SIGNIFICANCE

These results demonstrate the facilitation of memory encoding which is an important feature for the construction of an implantable neural prosthetic to improve human memory.

Designing Patient-Specific Optimal Neurostimulation Patterns for Seizure Suppression

Neurostimulation is a promising therapy for abating epileptic seizures. However, it is extremely difficult to identify optimal stimulation patterns experimentally. In this study, human recordings are used to develop a functional 24 neuron network statistical model of hippocampal connectivity and dynamics. Spontaneous seizure-like activity is induced in silico in this reconstructed neuronal network. The network is then used as a testbed to design and validate a wide range of neurostimulation patterns. Commonly used periodic trains were not able to permanently abate seizures at any frequency. A simulated annealing global optimization algorithm was then used to identify an optimal stimulation pattern, which successfully abated 92% of seizures. Finally, in a fully responsive, or closed-loop, neurostimulation paradigm, the optimal stimulation successfully prevented the network from entering the seizure state. We propose that the framework presented here for algorithmically identifying patient-specific neurostimulation patterns can greatly increase the efficacy of neurostimulation devices for seizures.

Astroglial networks and implications for therapeutic neuromodulation of epilepsy

Epilepsy is a common chronic neurologic disorder affecting approximately 1% of the world population. More than one-third of all epilepsy patients have incompletely controlled seizures or debilitating medication side effects in spite of optimal medical management. Medically refractory epilepsy is associated with excess injury and mortality, psychosocial dysfunction, and significant cognitive impairment. Effective treatment options for these patients can be limited. The cellular mechanisms underlying seizure activity are incompletely understood, though we here describe multiple lines of evidence supporting the likely contribution of astroglia to epilepsy, with focus on individual astrocytes and their network functions. Of the emerging therapeutic modalities for epilepsy, one of the most intriguing is the field of neuromodulation. Neuromodulatory treatment, which consists of administering electrical pulses to neural tissue to modulate its activity leading to a beneficial effect, may be an option for these patients. Current modalities consist of vagal nerve stimulation, open and closed-loop stimulation, and transcranial magnetic stimulation. Due to their unique properties, we here present astrocytes as likely important targets for the developing field of neuromodulation in the treatment of epilepsy.

Three-dimensional relationships between perisynaptic astroglia and human hippocampal synapses

Perisynaptic astroglia are critical for normal synaptic development and function. Little is known, however, about perisynaptic astroglia in the human hippocampus. When mesial temporal lobe epilepsy (MTLE) is refractory to medication, surgical removal is required for seizure quiescence. To investigate perisynaptic astroglia in human hippocampus, we recovered slices for several hours in vitro from three surgical specimens and then quickly fixed them to achieve high-quality ultrastructure. Histological samples from each case were found to have mesial temporal sclerosis with Blumcke Type 1a (mild, moderate) or 1b (severe) pathology. Quantitative analysis through serial section transmission electron microscopy in CA1 stratum radiatum revealed more synapses in the mild (10/10 microm(3)) than the moderate (5/10 microm(3)) or severe (1/10 microm(3)) cases. Normal spines occurred in mild and moderate cases, but a few multisynaptic spines were all that remained in the severe case. Like adult rat hippocampus, perisynaptic astroglial processes were preferentially associated with larger synapses in the mild and moderate cases, but rarely penetrated the cluster of axonal boutons surrounding multisynaptic spines. Synapse perimeters were only partially surrounded by astroglial processes such that all synapses had some access to substances in the extracellular space, similar to adult rat hippocampus. Junctions between astroglial processes were observed more frequently in moderate than mild case, but were obscured by densely packed intermediate filaments in astroglial processes of the severe case. These findings suggest that perisynaptic astroglial processes associate with synapses in human hippocampus in a manner similar to model systems and are disrupted by severe MTLE pathology.

Postoperative pain management with tramadol after craniotomy: evaluation and cost analysis

OBJECT

Patients undergoing craniotomies have traditionally received opiates with acetaminophen for the management of their postoperative pain. The use of narcotic pain medications can be costly, decrease rates of early postoperative ambulation, lengthen hospital stays, and alter a patient's neurological examination. The use of alternative pain medications such as tramadol may benefit patients by resolving many of these issues.

METHODS

The authors conducted a randomized, blinded prospective study to evaluate the efficacy of alternative pain management strategies for patients following craniotomies. Fifty patients were randomly assigned either to a control group who received narcotics and acetaminophen alone or an experimental group who received tramadol in addition to narcotic pain medications (25 patients assigned to each group).

RESULTS

The control group was noted to have statistically significant higher visual analog scale pain scores, an increased length of hospital stay, and increased narcotic use compared with the tramadol group. The narcotics and acetaminophen group also had increased hospitalization costs when compared with the tramadol group.

CONCLUSIONS

The use of scheduled atypical analgesics such as tramadol in addition to narcotics with acetaminophen for the management of postoperative pain after craniotomy may provide better pain control, decrease the side effects associated with narcotic pain medications, encourage earlier postoperative ambulation, and reduce total hospitalization costs.

Plasticity of perisynaptic astroglia during synaptogenesis in the mature rat hippocampus

Astroglia are integral components of synapse formation and maturation during development. Less is known about how astroglia might influence synaptogenesis in the mature brain. Preparation of mature hippocampal slices results in synapse loss followed by recuperative synaptogenesis during subsequent maintenance in vitro. Hence, this model system was used to discern whether perisynaptic astroglial processes are similarly plastic, associating more or less with recently formed synapses in mature brain slices. Perisynaptic astroglia was quantified through serial section electron microscopy in perfusion-fixed or sliced hippocampus from adult male Long-Evans rats that were 65-75 days old. Fewer synapses had perisynaptic astroglia in the recovered hippocampal slices (42.4% +/- 3.4%) than in the intact hippocampus (62.2% +/- 2.6%), yet synapses were larger when perisynaptic astroglia was present (0.055 +/- 0.003 microm2) than when it was absent (0.036 +/- 0.004 microm2) in both conditions. Importantly, the length of the synaptic perimeter surrounded by perisynaptic astroglia and the distance between neighboring synapses was not proportional to synapse size. Instead, larger synapses had longer astroglia-free perimeters where substances could escape from or enter into the synaptic clefts. Thus, smaller presumably newer synapses as well as established larger synapses have equal access to extracellular glutamate and secreted astroglial factors, which may facilitate recuperative synaptogenesis. These findings suggest that as synapses enlarge and release more neurotransmitter, they attract astroglial processes to a discrete portion of their perimeters, further enhancing synaptic efficacy without limiting the potential for cross talk with neighboring synapses in the mature rat hippocampus.

Corpus callosotomy for treatment of pediatric epilepsy in the modern era

OBJECTIVE

The purpose of this study was to evaluate seizure outcome in children with intractable secondary generalized epilepsy without a resectable focus who underwent complete corpus callosotomy and compare these results to those of anterior two-third callosotomy.

METHOD

Data were obtained for all patients who underwent a corpus callosotomy from 2000 to 2005. The study involved 37 patients. Eleven patients had anterior two-third corpus callosotomy compared with 28 patients who underwent complete corpus callosotomy. Two of these patients had completion of their callosotomy following initial partial callosotomy. Seizure type, seizure frequency, and family satisfaction were evaluated for all patients pre- and postoperatively.

RESULTS

A reduction of >or=75% in seizures occurred in 75% of the total-callosotomy patients compared to 55% of the partial-callosotomy patients. Family satisfaction for complete and partial callosotomy was 89 and 73%, respectively. No prolonged neurologic deficits were observed in either group.

CONCLUSION

Complete corpus callosotomy is the most effective treatment for secondary generalized intractable seizures not amenable to focal resection in children.