Book contents
- Frontmatter
- Contents
- List of contributors
- Preface and overview
- 1 Epilepsies as channelopathies
- 2 Epilepsy and movement disorders in the GABAA receptor β3 subunit knockout mouse: model of Angelman syndrome
- 3 Genetic reflex epilepsy from chicken to man: relations between genetic reflex epilepsy and movement disorders
- 4 Functional MRI of the motor cortex
- 5 Neuromagnetic methods and transcranial magnetic stimulation for testing sensorimotor cortex excitability
- 6 Motor dysfunction resulting from epileptic activity involving the sensorimotor cortex
- 7 Nocturnal frontal lobe epilepsy
- 8 Motor cortex hyperexcitability in dystonia
- 9 The paroxysmal dyskinesias
- 10 Normal startle and startle-induced epileptic seizures
- 11 Hyperekplexia: genetics and culture-bound stimulus-induced disorders
- 12 Myoclonus and epilepsy
- 13 The spectrum of epilepsy and movement disorders in EPC
- 14 Seizures, myoclonus and cerebellar dysfunction in progressive myoclonus epilepsies
- 15 Opercular epilepsies with oromotor dysfunction
- 16 Facial seizures associated with brainstem and cerebellar lesions
- 17 Neonatal movement disorders: epileptic or non-epileptic
- 18 Epileptic and non-epileptic periodic motor phenomena in children with encephalopathy
- 19 Epileptic stereotypies in children
- 20 Non-epileptic paroxysmal eye movements
- 21 Shuddering and benign myoclonus of early infancy
- 22 Epilepsy and cerebral palsy
- 23 Sydenham chorea
- 24 Alternating hemiplegia of childhood
- 25 Motor attacks in Sturge–Weber syndrome
- 26 Syndromes with epilepsy and paroxysmal dyskinesia
- 27 Epilepsy genes: the search grows longer
- 28 Genetics of the overlap between epilepsy and movement disorders
- 29 Seizures and movement disorders precipitated by drugs
- 30 Steroid responsive motor disorders associated with epilepsy
- 31 Drugs for epilepsy and movement disorders
- Index
- Plate section
5 - Neuromagnetic methods and transcranial magnetic stimulation for testing sensorimotor cortex excitability
Published online by Cambridge University Press: 03 May 2010
- Frontmatter
- Contents
- List of contributors
- Preface and overview
- 1 Epilepsies as channelopathies
- 2 Epilepsy and movement disorders in the GABAA receptor β3 subunit knockout mouse: model of Angelman syndrome
- 3 Genetic reflex epilepsy from chicken to man: relations between genetic reflex epilepsy and movement disorders
- 4 Functional MRI of the motor cortex
- 5 Neuromagnetic methods and transcranial magnetic stimulation for testing sensorimotor cortex excitability
- 6 Motor dysfunction resulting from epileptic activity involving the sensorimotor cortex
- 7 Nocturnal frontal lobe epilepsy
- 8 Motor cortex hyperexcitability in dystonia
- 9 The paroxysmal dyskinesias
- 10 Normal startle and startle-induced epileptic seizures
- 11 Hyperekplexia: genetics and culture-bound stimulus-induced disorders
- 12 Myoclonus and epilepsy
- 13 The spectrum of epilepsy and movement disorders in EPC
- 14 Seizures, myoclonus and cerebellar dysfunction in progressive myoclonus epilepsies
- 15 Opercular epilepsies with oromotor dysfunction
- 16 Facial seizures associated with brainstem and cerebellar lesions
- 17 Neonatal movement disorders: epileptic or non-epileptic
- 18 Epileptic and non-epileptic periodic motor phenomena in children with encephalopathy
- 19 Epileptic stereotypies in children
- 20 Non-epileptic paroxysmal eye movements
- 21 Shuddering and benign myoclonus of early infancy
- 22 Epilepsy and cerebral palsy
- 23 Sydenham chorea
- 24 Alternating hemiplegia of childhood
- 25 Motor attacks in Sturge–Weber syndrome
- 26 Syndromes with epilepsy and paroxysmal dyskinesia
- 27 Epilepsy genes: the search grows longer
- 28 Genetics of the overlap between epilepsy and movement disorders
- 29 Seizures and movement disorders precipitated by drugs
- 30 Steroid responsive motor disorders associated with epilepsy
- 31 Drugs for epilepsy and movement disorders
- Index
- Plate section
Summary
Magnetoencephalography (MEG): physiological background
Magnetoencephalography (MEG) is a non-invasive technique able to spatially identify the synchronous firing neurons in restricted cortical areas, either for spontaneous cerebral activity or in response to an external stimulus. MEG is unaffected by scalp and skull, and preferentially reflects the tangential component of dipoles in the depth of gyri and sulci.
The neuromagnetic technique consists of measurement of the magnetic field over the scalp, as generated by the bioelectrical currents in the brain. In order to achieve the sensitivity needed to measure these very weak magnetic fields (about 10 as compared to the earth magnetic field), the use of new superconducting magnetometers (superconducting quantum interferences devices or SQUID) and of devoted shielding is mandatory. Under the symmetry conditions, well approximated in the case of the head, it can be shown that the component of the magnetic field perpendicular to the skull is mostly sensitive to the tangential component of the primary current source, and negligibly to the field generated by the volume currents and to the distortions, smearing effects and filtering of frequency components, mainly in the faster rhythms caused by the intervening tissues (Romani & Rossini, 1988; Okada et al., 1999). This represents an advantage in respect to the purely electric measurement of neural activity, especially for the postsynaptic component at the level of the cortical mantle. The magnetic field is simultaneously measured over many scalp sites, with a rapid sampling in the time domain, and from these data the isofield contour maps are calculated and studied.
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- Information
- Epilepsy and Movement Disorders , pp. 59 - 76Publisher: Cambridge University PressPrint publication year: 2001