Dennis D Spencer

Dennis D Spencer
Yale University | YU · Department of Neurosurgery

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222
Publications
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Publications

Publications (222)
Article
Objectives Our study aimed to compare signal characteristics of subdural electrodes (SDE) and depth stereo EEG placed within a 5-mm vicinity in patients with drug-resistant epilepsy. We report how electrode design and placement collectively affect signal content from a shared source between these electrode types. Methods In subjects undergoing inv...
Preprint
Impaired consciousness is a serious clinical manifestation of epilepsy with negative consequences on quality of life. Little work has investigated impaired consciousness in frontal lobe seizures, a common form of focal epilepsy. In temporal lobe seizures, previous studies showed widespread cortical slow waves associated with depressed subcortical a...
Article
Full-text available
Epilepsy is a common neurological disorder, affecting over 65 million people worldwide. Unfortunately, despite resective surgery, over 30 % of patients with drug-resistant epilepsy continue to experience seizures. Retrospective studies considering connectivity using intracranial electrocorticography (ECoG) obtained during neuromonitoring have shown...
Article
Full-text available
It is increasingly understood that the epilepsies are characterized by network pathology that can span multiple spatial and temporal scales. Recent work indicates that infraslow (<0.2 Hz) envelope correlations may form a basis for distant spatial coupling in the brain. We speculated that infraslow correlation structure may be preserved even with so...
Article
Full-text available
Functional coactivation between human brain regions is partly explained by white matter connections; however, how the structure-function relationship varies by function remains unclear. Here, we reference large data repositories to compute maps of structure-function correspondence across hundreds of specific functions and brain regions. We use natu...
Article
OBJECTIVE Medically refractory epilepsy (MRE) often requires resection of the seizure onset zone (SOZ) for effective treatment. However, when the SOZ is in functional cortex (FC), achieving complete and safe resection becomes difficult, due to the seizure network overlap with function. The authors aimed to assess the safety and outcomes of a combin...
Article
Using 6‐minute free‐running intracranial‐electroencephalogram (icEEG) during sleep, an optimized multilayer perceptron (MLP) neural network accurately maps the sensorimotor cortex (SM) and identifies the anterior lip of the central sulcus (CS) in intractable epilepsy patients. We calculated 6 performance metrics to evaluate the MLP's efficacy: accu...
Article
Occipital lobe epilepsy is a debilitating condition, and surgical resection has been effective, though challenges arise because of the cortex's function. ¹⁻⁷ Approximately 57% of patients with normal vision experience new visual field deficits postoperatively. ⁸ A combined approach of resection and responsive neurostimulation (RNS) could aid in dec...
Article
Background The cingulate gyrus (CG), a brain structure above the corpus callosum, is recognised as part of the limbic system and plays numerous vital roles. However, its full functional capacity is yet to be understood. In recent years, emerging evidence from imaging modalities, supported by electrical cortical stimulation (ECS) findings, has impro...
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Objective: To compare the performance of popular machine learning algorithms (ML) in mapping the sensorimotor cortex (SM) and identifying the anterior lip of the central sulcus (CS). Methods: We evaluated support vector machines (SVMs), random forest (RF), decision trees (DT), single layer perceptron (SLP), and multilayer perceptron (MLP) against s...
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Importance: Mesial temporal lobe epilepsy (MTLE) is the most common focal epilepsy subtype and is often refractory to antiseizure medications. While most patients with MTLE do not have pathogenic germline genetic variants, the contribution of postzygotic (ie, somatic) variants in the brain is unknown. Objective: To test the association between p...
Article
Purpose: Purpose Technological innovations in the preoperative evaluation, surgical techniques and outcome prediction in epilepsy surgery have grown exponentially over the last decade. This review highlights and emphasizes relevant updates in techniques and diagnostic tools, discussing their context within standard practice at comprehensive epilep...
Preprint
Although recent work has made significant headway in understanding the temporal and spatial dynamics of the neural mechanisms of conscious perception, much of that work has focused on visual paradigms. To determine whether there are shared mechanisms for perceptual consciousness across sensory modalities, here we developed a task to test within the...
Article
Background and importance: Stereotactic laser amygdalohippocampotomy (SLAH) using laser interstitial thermal therapy is a minimally invasive surgery used to treat mesial temporal lobe epilepsy. It uses laser probes inserted through occipital and temporo-occipital trajectories to ablate the hippocampus and amygdala. However, these trajectories are...
Chapter
Epilepsy surgery has provided a unique “window into the brain” for the investigation of many disease processes, including the link between febrile seizures and temporal lobe epilepsy. The comprehensive preoperative evaluation and the diagnostic and treatment modalities available through surgery have allowed for in-depth analysis of imaging, electro...
Preprint
Importance: Mesial temporal lobe epilepsy (MTLE) is the most common focal epilepsy subtype and is often refractory to anti-seizure medications. While most MTLE patients do not have pathogenic germline genetic variants, the contribution of post-zygotic (i.e., somatic) variants in the brain is unknown. Objective: To test the association between patho...
Article
Full-text available
Background and objectives The cingulate gyrus (CG) is a frequently studied yet not wholly understood area of the human cerebrum. Previous studies have implicated CG in different adaptive cognitive–emotional functions and fascinating or debilitating symptoms. We describe an unusual loss of gravity perception/floating sensation in consecutive persons...
Article
Full-text available
Precise cortical brain localization presents an important challenge in the literature. Brain atlases provide data-guided parcellation based on functional and structural brain metrics, and each atlas has its own unique benefits for localization. We offer a parcellation guided by intracranial electroencephalography, a technique which has historically...
Article
Full-text available
Dramatic changes have occurred recently in the field of epilepsy, including a fundamental shift in the etiology of epileptogenic substrates found at surgery. Hippocampal sclerosis is no longer the most common etiology found at epilepsy surgery and this decrease has been associated with an increase in the incidence of focal cortical dysplasia and en...
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Objective Temporal lobe epilepsy (TLE) and depression are common comorbid disorders whose underlying shared neural network has yet to be determined. Although animal studies demonstrate a role for the dorsal bed nucleus of the stria terminalis (dBNST) in both seizures and depression, and human clinical studies demonstrate a therapeutic effect of sti...
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This is the first known case report of a profound illusionary time dilation produced by direct electrical cortical stimulation. The patient with drug‐resistant epilepsy was undergoing invasive EEG evaluation for the localization of the focus prior to resection. Stimulation of the non‐dominant claustrum/insula and inferior right frontal gyrus correl...
Article
Objective Identify predictors of a resective surgery and subsequent seizure freedom following intracranial EEG (ICEEG) for seizure onset localization. Methods Retrospective chart review of 178 consecutive patients with medically refractory epilepsy who underwent ICEEG monitoring from 2002 to 2015. Univariable and multivariable regression analysis...
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Full-text available
Objective To evaluate the role of intracranial electroencephalography monitoring in diagnosing and directing the appropriate therapy for MRI‐negative epilepsy and to present the surgical outcomes of patients following treatment. Methods Retrospective chart review between 2015‐2021 at a single institution identified 48 patients with no lesion on MR...
Chapter
• Anteromedial resection is a safe and effective approach for medial temporal lobe epilepsy (MTLE). • Preoperative work-up guides the resection. • Anatomic landmarks are the foundation of a successful operation. • Patient positioning is important. • Knowledge of postoperative deficits is important to address during the discussion preceding consent.
Article
We test the performance of a novel operator-independent EEG-based method for passive identification of the central sulcus (CS) and sensorimotor (SM) cortex. We studied seven patients with intractable epilepsy undergoing intracranial EEG (icEEG) monitoring, in whom CS localization was accomplished by standard methods. Our innovative approach takes a...
Article
OBJECTIVE Temporal lobe encephaloceles (TLENs) are a significant cause of medically refractory epilepsy, but there is little consensus regarding their workup and treatment. This study characterizes these lesions and their role in seizures and aims to standardize preoperative evaluation and surgical management. METHODS Patients with TLEN who had un...
Article
Full-text available
The objective of this study was to monitor the extracellular brain chemistry dynamics at baseline and in relation to spontaneous seizures in human patients with refractory epilepsy. Thirty patients with drug‐resistant focal epilepsy underwent intracranial electroencephalography and concurrent brain microdialysis for up to 8 continuous days. Extrace...
Article
Intraoperative electrocorticography (ECoG) is a useful technique to guide resections in epilepsy surgery and is mostly performed under general anesthesia. In this systematic literature review, we seek to investigate the effect of anesthetic agents on the quality and reliability of ECoG for localization of the epileptic focus. We conducted a systema...
Article
Objective To test the hypothesis that glutamate and GABA are linked to the formation of epilepsy networks and the triggering of spontaneous seizures, we examined seizure initiation/propagation characteristics and neurotransmitter levels during epileptogenesis in a translationally relevant rodent model of mesial temporal lobe epilepsy. Methods The...
Article
Abstract Background: Glossokinetic artifact (GKA) is a well-known scalp EEG artifact characterized by deflections within the delta to low-theta frequency bands and dynamic polarity typically attributed to the direction of tongue movement. This study aims to investigate intracranial EEG (icEEG) correlations of scalp-GKA. If the tongue is a dipole, p...
Article
Full-text available
Neurosurgery has the potential to cure epilepsy but carries the risk of permanent language impairment. This risk can be estimated and minimized using Electrical Stimulation Mapping (ESM), which uses cognitive tasks and cortical stimulation to identify “eloquent” and “resectable” areas. One such task, counting, is often used to screen and characteri...
Article
The term ‘implantation effect’ is used to describe an immediate and transient improvement in seizure frequency following an intracranial study for seizure onset localization. We conducted a retrospective analysis of 190 consecutive patients undergoing intracranial electroencephalogram (EEG) monitoring, of whom 41 had no subsequent resection/ablatio...
Article
Full-text available
Seizures often exhibit striking circadian-like (~24-h) rhythms. While chronotherapy has shown promise in treating epilepsy, it is not widely used, in part because the patterns of seizure rhythmicity vary considerably among patients and types of epilepsy. A better understanding of the mechanisms underlying rhythmicity in epilepsy could be expected t...
Article
Objective To recount the evolution of Electrical Cortical Stimulation (ECS) in localizing brain functions with an emphasis on epilepsy, and a discussion of related instruments and personnel. Design/methods Literature review through historical archives implementing chain-referral sampling. Results There were important milestones leading to the inc...
Article
OBJECTIVE The aim of this study was to investigate the performance of a metric of functional connectivity to classify and grade the excitability of brain regions based on evoked potentials in response to single-pulse electrical stimulation (SPES). METHODS Patients who underwent 1-Hz frequency stimulation at prospectively selected contacts between...
Preprint
Full-text available
Objective: To investigate the performance of a metric of functional connectivity to classify and grade the excitability of brain regions based on evoked potentials to single pulse electrical stimulation (SPES). Methods: Patients who received 1-Hz frequency stimulation between 2003 and 2014 at Yale at prospectively selected contacts were included. T...
Article
Importance Seizures recur in as many as half of patients who undergo surgery for drug-resistant temporal lobe epilepsy (TLE). Understanding why TLE is resistant to surgery in some patients may reveal insights into epileptogenic networks and direct new therapies to improve outcomes. Objective To characterize features of surgically refractory TLE....
Article
Objective: Localization related epilepsy (LRE) is increasingly accepted as a network disorder. To better understand the network specific characteristics of LRE, we defined individual epilepsy networks and compared them across patients. Methods: The epilepsy network was defined in the slow cortical potential frequency band in 10 patients using in...
Chapter
The relationship between neuroimaging and the care of patients with neurosurgical and neurological disorders has long been a close one. The integration of these fields dates back to neuroimaging’s earliest days in the 20th century. However, no single imaging technique has had the enduring impact on clinical medicine that magnetic resonance imaging...
Article
Functional MRI with BOLD (Blood Oxygen Level Dependent) imaging is one of the commonly used modalities for studying brain function in neuroscience. The underlying source of the BOLD fMRI signal is the variation in oxyhemoglobin to deoxyhemoglobin ratio at the site of neuronal activity in the brain. fMRI is mostly used to map out the location and in...
Article
Objective Studies of infraslow amplitude modulations (<0.15 Hz) of band power time series suggest that these envelope correlations may form a basis for distant spatial coupling in the brain. In this study, we sought to determine how infraslow relationships are affected by antiepileptic drug (AED) taper, time of day, and seizure. Methods We studied...
Article
Full-text available
Seizures have traditionally been considered hypersynchronous excitatory events and epilepsy has been separated into focal and generalized epilepsy based largely on the spatial distribution of brain regions involved at seizure onset. Epilepsy, however, is increasingly recognized as a complex network disorder that may be distributed and dynamic. Resp...
Article
Full-text available
Little is known about how language functional MRI (fMRI) is executed in clinical practice in spite of its widespread use. Here we comprehensively documented its execution in surgical planning in epilepsy. A questionnaire focusing on cognitive design, image acquisition, analysis and interpretation, and practical considerations was developed. Individ...
Conference Paper
Full-text available
Objective: To investigate the performance of a metric of functional connectivity to classify and grade the excitability of brain regions based on evoked potentials to single pulse electrical stimulation (SPES). Methods: Patients who received 1-Hz frequency stimulation between 2003 and 2014 at Yale at prospectively selected contacts were included....
Conference Paper
Full-text available
Introduction To investigate the effect of the anesthesia on the quality and reliability of electrocorticography (ECOG) for localization of the epileptic focus based on literature review. Although there is plethora of literature reporting on the utility of intraoperative ECOG for localization of the epileptic focus. Less is known about the effect of...
Article
Introduction Although consciousness is commonly impaired in epileptic seizures, limited literature is available on loss of consciousness induced by electrical cortical stimulation (ECS) in humans undergoing intracranial EEG evaluations for localization of epileptic focus. Methods Case-study and review of literature. Results We report a case of im...
Conference Paper
Full-text available
Introduction: Identifying indispensable eloquent cortex is an integral process of the surgical evaluations. The current accepted ‘gold’ standard of functional mapping of eloquent cortex is electrical cortical stimulation (ECS) suffers from known limitations. In recent years, electrocorticographic (ECOG) recording of task-related high gamma (70–120...
Article
Intracranial electrophysiological recording in patients with refractory focal epilepsy is the gold standard for defining epileptogenic tissue. Although the concordance of intracranial electrophysiology, structural MRI, and pathology can identify brain regions for resection, complete seizure control after surgery is not achieved in all patients with...
Article
Full-text available
The goal of this study was to document current clinical practice and report patient outcomes in presurgical language functional MRI (fMRI) for epilepsy surgery. Epilepsy surgical programs worldwide were surveyed as to the utility, implementation, and efficacy of language fMRI in the clinic; 82 programs responded. Respondents were predominantly US (...
Preprint
Full-text available
Little is known about how language functional MRI (fMRI) is executed in clinical practice in spite of its widespread use. Here we comprehensively documented its execution in surgical planning in epilepsy. A questionnaire focusing on cognitive design, imaging acquisition, analysis and interpretation and practical considerations was developed. Indivi...
Article
Full-text available
Conscious perception occurs within less than 1 s. To study events on this time scale we used direct electrical recordings from the human cerebral cortex during a conscious visual perception task. Faces were presented at individually titrated visual threshold for 9 subjects while measuring broadband 40-115 Hz gamma power in a total of 1621 intracran...
Preprint
Full-text available
The goal of this study was to document current clinical practice and report patient outcomes in presurgical language functional MRI (fMRI) for epilepsy surgery. Epilepsy surgical programs worldwide were surveyed as to the utility, implementation, and efficacy of language fMRI in the clinic; 82 programs responded between July 2015 and January 2016....
Article
Full-text available
We report a case of impairment of consciousness (IOC) induced by electrical cortical stimulation (ECS) of homologous regions within the lateral frontal convexities in a patient with medically intractable epilepsy. The patient had mixed features of idiopathic generalized and focal epilepsy. On intracranial EEG recording, interictal and ictal dischar...
Conference Paper
Full-text available
OBJECTIVES/SPECIFIC AIMS: To investigate the performance of a metric for passive localization of central sulcus. METHODS/STUDY POPULATION: We studied 7 patients with intractable epilepsy undergoing intra-cranial EEG (icEEG) monitoring at Yale, in whom central sulcus (CS) localization was obtained by standard methods. Our method takes advantage of i...
Article
Objective: We examined low-frequency amplitude modulations of band power time-series, i.e. the second spectrum, of the intracranial EEG (icEEG) for evidence of support for spatial relationships between different parts of the brain and within the default mode network (DMN). Methods: We estimated magnitude-squared coherence (MSC) of the running po...
Article
Objective: A considerable decrease in spike rate accompanies antiepileptic drug (AED) taper during intracranial EEG (icEEG) monitoring. Since spike rate during icEEG monitoring can be influenced by surgery to place intracranial electrodes, we studied spike rate during long-term scalp EEG monitoring to further test this observation. Methods: We a...
Article
Objective: Aberrant glutamate and γ-aminobutyric acid (GABA) neurotransmission contribute to seizure generation and the epileptic state. However, whether levels of these neurochemicals are abnormal in epileptic patients is unknown. Here, we report interictal levels of glutamate, glutamine and GABA in epilepsy patients at seizure onset and non-epil...
Article
Objective We evaluated changes to sleep structure during continuous intracranial EEG (icEEG) monitoring of epilepsy patients undergoing localization of the seizure onset area. Methods We studied 28 adult epilepsy patients who underwent icEEG monitoring for a median of 12 nights. We used a metric calculated from relative delta power (RDP) to evalua...
Article
Full-text available
Objective: The effect of electrical stimulation on brain glutamate release in humans is unknown. Glutamate is elevated at baseline in the epileptogenic hippocampus of patients with refractory epilepsy, and increases during spontaneous seizures. We examined the effect of 50 Hz stimulation on glutamate release and its relationship to interictal leve...
Article
Objective: Our study investigated the effects of the intact skull on background EEG rhythms recorded simultaneously by subdural electrocorticography (ECoG) and scalp EEG. Methods: We performed a retrospective analysis of twenty patients undergoing intracranial EEG monitoring. EEG and ECoG were recorded simultaneously from the central and occipit...
Article
Objective Epilepsy surgery is the most effective treatment for select patients with drug-resistant epilepsy. In this article, we aim to provide an accurate understanding of the current epidemiologic characteristics of this intervention, as this knowledge is critical for guiding educational, academic, and resource priorities.Methods We profile the p...
Article
Full-text available
A widely accepted view is that wakefulness is a state where the entire cortical mantle is persistently activated, and therefore desynchronized. Consequently, the EEG is dominated by low amplitude, high frequency fluctuations. This view is currently under revision because the 1-4 Hz-delta-rhythm is often evident during "quiet" wakefulness in rodents...
Article
Full-text available
When drug-resistant epilepsy is poorly localized or surgical resection is contraindicated, current neurostimulation strategies such as deep brain stimulation and vagal nerve stimulation can palliate the frequency or severity of seizures. However, despite medical and neuromodulatory therapy, a significant proportion of patients continue to experienc...