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Ghulaxe Y, Joshi A, Chavada J, Huse S, Kalbande B, Sarda PP. Understanding Focal Seizures in Adults: A Comprehensive Review. Cureus 2023; 15:e48173. [PMID: 38046728 PMCID: PMC10693312 DOI: 10.7759/cureus.48173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2023] [Accepted: 11/02/2023] [Indexed: 12/05/2023] Open
Abstract
Focal or partial seizures are a common neurological disorder affecting adults. This review aims to provide an in-depth understanding of focal seizures in adults, including their classification, clinical presentation, etiology, diagnosis, and management. This article seeks to enhance awareness and knowledge among medical professionals and the general public by exploring the latest research and clinical insights. Standard electroencephalography (EEG) and recordings in presurgical electrode depth in humans provide a clear definition of patterns similar to focal seizures. Models of animals with partial seizures and epilepsy mimic seizure patterns with comparable characteristics. However, the network factors supporting interictal spikes, as well as the start, development, and end of seizures remain obscure. According to recent research, inhibitory networks are heavily implicated at the beginning of seizures, and extracellular potassium alterations help start and maintain seizure continuation. An increase in network synchronization, which may be caused by both excitatory and inhibitory pathways, is correlated with the cessation of a partial seizure. Recent research on temporal lobe focal seizures in human and animal models leads to the hypothesis that the active blocking of subcortical arousal processes brings on unconsciousness. Brainstem, basal forebrain, and thalamic arousal networks' neuronal firing is diminished during focal limbic seizures, and cortical arousal can be recovered when subcortical arousal circuits are engaged. These results suggest that thalamic neurostimulation may be therapeutic to restore arousal and consciousness during and after seizures. Targeted subcortical stimulation may increase arousal and consciousness when current treatments cannot halt seizures, enhancing safety and psychosocial function for epileptic patients. We embark on an investigation into adult focal seizures in this thorough review that goes beyond a cursory knowledge of their clinical symptoms.
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Affiliation(s)
- Yash Ghulaxe
- Department of Community Medicine, Jawaharlal Nehru Medical College, Datta Meghe Institute of Higher Education and Research, Wardha, IND
| | - Abhishek Joshi
- Department of Community Medicine, Jawaharlal Nehru Medical College, Datta Meghe Institute of Higher Education and Research, Wardha, IND
| | - Jay Chavada
- Department of Community Medicine, Jawaharlal Nehru Medical College, Datta Meghe Institute of Higher Education and Research, Wardha, IND
| | - Shreyash Huse
- Department of Community Medicine, Jawaharlal Nehru Medical College, Datta Meghe Institute of Higher Education and Research, Wardha, IND
| | - Bhakti Kalbande
- Department of Dentistry, Sharad Pawar Dental College, Datta Meghe Institute of Higher Education and Research, Wardha, IND
| | - Prayas P Sarda
- Department of Community Medicine, Jawaharlal Nehru Medical College, Datta Meghe Institute of Higher Education and Research, Wardha, IND
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Deterministic and Stochastic Components of Cortical Down States: Dynamics and Modulation. J Neurosci 2022; 42:9387-9400. [PMID: 36344267 PMCID: PMC9794366 DOI: 10.1523/jneurosci.0914-22.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Revised: 10/21/2022] [Accepted: 10/25/2022] [Indexed: 11/09/2022] Open
Abstract
Slow oscillations are an emergent activity of the cerebral cortex network consisting of alternating periods of activity (Up states) and silence (Down states). Up states are periods of persistent cortical activity that share properties with that of underlying wakefulness. However, the occurrence of Down states is almost invariably associated with unconsciousness, both in animal models and clinical studies. Down states have been attributed relevant functions, such as being a resetting mechanism or breaking causal interactions between cortical areas. But what do Down states consist of? Here, we explored in detail the network dynamics (e.g., synchronization and phase) during these silent periods in vivo (male mice), in vitro (ferrets, either sex), and in silico, investigating various experimental conditions that modulate them: anesthesia levels, excitability (electric fields), and excitation/inhibition balance. We identified metastability as two complementary phases composing such quiescence states: a highly synchronized "deterministic" period followed by a low-synchronization "stochastic" period. The balance between these two phases determines the dynamical properties of the resulting rhythm, as well as the responsiveness to incoming inputs or refractoriness. We propose detailed Up and Down state cycle dynamics that bridge cortical properties emerging at the mesoscale with their underlying mechanisms at the microscale, providing a key to understanding unconscious states.SIGNIFICANCE STATEMENT The cerebral cortex expresses slow oscillations consisting of Up (active) and Down (silent) states. Such activity emerges not only in slow wave sleep, but also under anesthesia and in brain lesions. Down states functionally disconnect the network, and are associated with unconsciousness. Based on a large collection of data, novel data analysis approaches and computational modeling, we thoroughly investigate the nature of Down states. We identify two phases: a highly synchronized "deterministic" period, followed by a low-synchronization "stochastic" period. The balance between these two phases determines the dynamic properties of the resulting rhythm and responsiveness to incoming inputs. This finding reconciles different theories of slow rhythm generation and provides clues about how the brain switches from conscious to unconscious brain states.
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Abstract
Impaired consciousness during seizures severely affects quality of life for people with
epilepsy but the mechanisms are just beginning to be understood. Consciousness is thought
to involve large-scale brain networks, so it is puzzling that focal seizures often impair
consciousness. Recent work investigating focal temporal lobe or limbic seizures in human
patients and experimental animal models suggests that impaired consciousness is caused by
active inhibition of subcortical arousal mechanisms. Focal limbic seizures exhibit
decreased neuronal firing in brainstem, basal forebrain, and thalamic arousal networks,
and cortical arousal can be restored when subcortical arousal circuits are stimulated
during seizures. These findings open the possibility of restoring arousal and
consciousness therapeutically during and following seizures by thalamic neurostimulation.
When seizures cannot be stopped by existing treatments, targeted subcortical stimulation
may improve arousal and consciousness, leading to improved safety and better psychosocial
function for people with epilepsy.
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Affiliation(s)
- Hal Blumenfeld
- Departments of Neurology, Neuroscience, Neurosurgery, Yale University School of Medicine, New Haven, CT, USA
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Gummadavelli A, Martin R, Goshay D, Sieu LA, Xu J, Gruenbaum BF, McCafferty C, Gerrard JL, Blumenfeld H. Cortical low-frequency power correlates with behavioral impairment in animal model of focal limbic seizures. Epilepsia 2021; 62:1960-1970. [PMID: 34240747 PMCID: PMC8349876 DOI: 10.1111/epi.16964] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 05/29/2021] [Accepted: 06/01/2021] [Indexed: 11/29/2022]
Abstract
OBJECTIVE Impairment in consciousness is a debilitating symptom during and after seizures; however, its mechanism remains unclear. Limbic seizures have been shown to spread to arousal circuitry to result in a "network inhibition" phenomenon. However, prior animal model studies did not relate physiological network changes to behavioral responses during or following seizures. METHODS Focal onset limbic seizures were induced while rats were performing an operant conditioned behavioral task requiring response to an auditory stimulus to quantify how and when impairment of behavioral response occurs. Correct responses were rewarded with sucrose. Cortical and hippocampal electrophysiology measured by local field potential recordings was analyzed for changes in low- and high-frequency power in relation to behavioral responsiveness during seizures. RESULTS As seen in patients with seizures, ictal (p < .0001) and postictal (p = .0015) responsiveness was variably impaired. Analysis of cortical and hippocampal electrophysiology revealed that ictal (p = .002) and postictal (p = .009) frontal cortical low-frequency 3-6-Hz power was associated with poor behavioral performance. In contrast, the hippocampus showed increased power over a wide frequency range during seizures, and suppression postictally, neither of which were related to behavioral impairment. SIGNIFICANCE These findings support prior human studies of temporal lobe epilepsy as well as anesthetized animal models suggesting that focal limbic seizures depress consciousness through remote network effects on the cortex, rather than through local hippocampal involvement. By identifying the cortical physiological changes associated with impaired arousal and responsiveness in focal seizures, these results may help guide future therapies to restore ictal and postictal consciousness, improving quality of life for people with epilepsy.
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Affiliation(s)
- Abhijeet Gummadavelli
- Department of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520, USA
- Department of Neurosurgery, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520, USA
| | - Reese Martin
- Department of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520, USA
| | - Derek Goshay
- Department of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520, USA
| | - Lim-Anna Sieu
- Department of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520, USA
| | - Jingwen Xu
- Department of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520, USA
| | - Benjamin F. Gruenbaum
- Department of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520, USA
| | - Cian McCafferty
- Department of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520, USA
| | - Jason L. Gerrard
- Department of Neurosurgery, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520, USA
| | - Hal Blumenfeld
- Department of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520, USA
- Department of Neurosurgery, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520, USA
- Department of Neuroscience, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520, USA
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Gruenbaum BF. Comparison of anaesthetic- and seizure-induced states of unconsciousness: a narrative review. Br J Anaesth 2021; 126:219-229. [PMID: 32951841 PMCID: PMC7844374 DOI: 10.1016/j.bja.2020.07.056] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Revised: 06/23/2020] [Accepted: 07/20/2020] [Indexed: 10/23/2022] Open
Abstract
In order to understand general anaesthesia and certain seizures, a fundamental understanding of the neurobiology of unconsciousness is needed. This review article explores similarities in neuronal and network changes during general anaesthesia and seizure-induced unconsciousness. Both seizures and anaesthetics cause disruption in similar anatomical structures that presumably lead to impaired consciousness. Despite differences in behaviour and mechanisms, both of these conditions are associated with disruption of the functionality of subcortical structures that mediate neuronal activity in the frontoparietal cortex. These areas are all likely to be involved in maintaining normal consciousness. An assessment of the similarities in the brain network disruptions with certain seizures and general anaesthesia might provide fresh insights into the mechanisms of the alterations of consciousness seen in these particular unconscious states, allowing for innovative therapies for seizures and the development of anaesthetic approaches targeting specific networks.
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Re CJ, Batterman AI, Gerstner JR, Buono RJ, Ferraro TN. The Molecular Genetic Interaction Between Circadian Rhythms and Susceptibility to Seizures and Epilepsy. Front Neurol 2020; 11:520. [PMID: 32714261 PMCID: PMC7344275 DOI: 10.3389/fneur.2020.00520] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Accepted: 05/12/2020] [Indexed: 12/19/2022] Open
Abstract
Seizure patterns observed in patients with epilepsy suggest that circadian rhythms and sleep/wake mechanisms play some role in the disease. This review addresses key topics in the relationship between circadian rhythms and seizures in epilepsy. We present basic information on circadian biology, but focus on research studying the influence of both the time of day and the sleep/wake cycle as independent but related factors on the expression of seizures in epilepsy. We review studies investigating how seizures and epilepsy disrupt expression of core clock genes, and how disruption of clock mechanisms impacts seizures and the development of epilepsy. We focus on the overlap between mechanisms of circadian-associated changes in SCN neuronal excitability and mechanisms of epileptogenesis as a means of identifying key pathways and molecules that could represent new targets or strategies for epilepsy therapy. Finally, we review the concept of chronotherapy and provide a perspective regarding its application to patients with epilepsy based on their individual characteristics (i.e., being a “morning person” or a “night owl”). We conclude that better understanding of the relationship between circadian rhythms, neuronal excitability, and seizures will allow both the identification of new therapeutic targets for treating epilepsy as well as more effective treatment regimens using currently available pharmacological and non-pharmacological strategies.
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Affiliation(s)
- Christopher J Re
- Department of Biomedical Sciences, Cooper Medical School of Rowan University, Camden, NJ, United States
| | - Alexander I Batterman
- Department of Biomedical Sciences, Cooper Medical School of Rowan University, Camden, NJ, United States
| | - Jason R Gerstner
- Department of Biomedical Sciences, Elson S. Floyd College of Medicine, Washington State University, Spokane, WA, United States
| | - Russell J Buono
- Department of Biomedical Sciences, Cooper Medical School of Rowan University, Camden, NJ, United States
| | - Thomas N Ferraro
- Department of Biomedical Sciences, Cooper Medical School of Rowan University, Camden, NJ, United States
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