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It has been proposed that the underlying epileptic process is mediated by changes in both excitatory and inhibitory circuits leading to the formation of hyper-excitable seizure networks. In this review we aim to shed light on the many physiological factors that modulate excitability within these networks. These factors have been discussed extensively in many reviews each as a separate entity and cannot be extensively covered in a single manuscript. Thus for the purpose of this work in which we aim to bring those factors together to explain how they interact with epilepsy, we only provide brief descriptions. We present reported evidence supporting the existence of the epileptic brain in several states; interictal, peri-ictal and ictal, each with distinct excitability features. We then provide an overview of how many physiological factors influence the excitatory/inhibitory balance within the interictal state, where the networks are presumed to be functioning normally. We conclude that these changes result in constantly changing states of cortical excitability in patients with epilepsy.
Department of Clinical Neurosciences, St Vincent's Hospital, Fitzroy, Australia; Department of Medicine, The University of Melbourne, Parkville, Australia; Department of Electrical and Electronic Engineering, The University of Melbourne, Parkville, Austra
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Measurable changes in activities in the CEREBRAL CORTEX upon a stimulation. A change in cortical excitability as measured by various techniques (e.g., TRANSCRANIAL MAGNETIC STIMULATION) is associated with brain disorders.
Heterogeneous disorders of cortical malformation characterized by excessive and small fused gyri and shallow sulci of the CORTEX with abnormal cortical lamination. It is considered a malformation secondary to abnormal post-migrational development of the neurons during cerebral cortical development and is associated with EPILEPSY and learning difficulties.
A neurosurgical procedure that removes or disconnects the epileptogenic CEREBRAL CORTEX of a hemisphere. Hemispherectomy is usually performed for patients with intractable unilateral EPILEPSY due to malformations of cortical development or brain lesions. Depending on the epileptogenic area in the hemisphere, cortical removal can be total or partial.
Cortical malformations secondary to abnormal cortical maturation after CELL MIGRATION in NEUROGENESIS. This group includes injury to the cortex during later stages of cortical development such as POLYMICROGYRIA and focal cortical dysplasias.
A disorder characterized by recurrent partial seizures marked by impairment of cognition. During the seizure the individual may experience a wide variety of psychic phenomenon including formed hallucinations, illusions, deja vu, intense emotional feelings, confusion, and spatial disorientation. Focal motor activity, sensory alterations and AUTOMATISM may also occur. Complex partial seizures often originate from foci in one or both temporal lobes. The etiology may be idiopathic (cryptogenic partial complex epilepsy) or occur as a secondary manifestation of a focal cortical lesion (symptomatic partial complex epilepsy). (From Adams et al., Principles of Neurology, 6th ed, pp317-8)
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