6 results
The effects of luminance and chromatic background flicker on the human visual evoked potential
- Mitchell Brigell, Antonio Strafella, Lucio Parmeggiani, Paul J. Demarco, Jr, Gastone G. Celesia
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- Journal:
- Visual Neuroscience / Volume 13 / Issue 2 / March 1996
- Published online by Cambridge University Press:
- 02 June 2009, pp. 265-275
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Previous studies report that background luminance flicker, which is asynchronous with signal averaging, reduces the amplitude and increases the latency of the pattern-onset visual evoked potential (VEP). This effect has been attributed to saturation of the magnocellular (m-) pathway by the flicker stimulus. In the current study, we evaluate this hypothesis and further characterize this effect. We found that flicker had similar effects on the pattern-onset and pattern-reversal VEP, suggesting that the reversal and onset responses have similar generators. Chromatic flicker decreased latency of the chromatic VEP whereas luminance flicker increased peak latency to luminance targets. This result indicates that luminance flicker saturates a rapidly conducting m-pathway whereas chromatic flicker saturates a more slowly conducting parvocellular (p-) pathway. Finally, evoked potentials to chromatic and luminance stimuli were recorded from 34 electrodes over the scalp in the presence of static and asynchronously modulated backgrounds. An equivalent dipole model was used to assess occipital, parietal, and temporal lobe components of the surface response topography. Results showed that chromatic flicker reduced activity to a greater extent in the ventral visual pathway whereas luminance flicker reduced activity to a greater extent in the dorsal visual pathway to parietal lobe. We conclude that the VEP to isoluminant color and luminance stimuli contains both m- and p-pathway components. Asynchronous flicker can be used to selectively reduce the contribution of these pathways to the surface recorded VEP. Our results provide evidence of parallel pathways in the human visual system, with a dorsal luminance channel projecting predominantly to the posterior parietal lobe and a ventral color channel projecting predominantly to inferior temporal lobe.
Pallister–Killian syndrome: an unusual cause of epileptic spasms
- Rocio Sánchez-Carpintero, Ailsa McLellan, Lucio Parmeggiani, Annette E Cockwell, Richard J Ellis, J Helen Cross, Susan Eckhardt, Renzo Guerrini
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- Journal:
- Developmental Medicine and Child Neurology / Volume 47 / Issue 11 / November 2005
- Published online by Cambridge University Press:
- 17 October 2005, pp. 776-779
- Print publication:
- November 2005
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Pallister–Killian syndrome (PKS) is a rare, sporadic, genetic disorder characterized by dysmorphic features, learning disability, and epilepsy. It is caused by a mosaic supernumerary isochromosome 12p (i[12p]). The i(12p) is rarely found in peripheral blood but it is present in skin fibroblasts. Recognition is essential for cytogenetic diagnosis. We describe a male aged 2 years 6 months and a female aged 11 years with PKS and epileptic spasms (ES). This type of seizure is not unusual in patients with brain malformations and with severe developmental delay, but it is sometimes difficult to recognize without video–electroencephalogram studies and could be mistaken for other types of seizure or behavioural manifestations. In these two patients with PKS, spasms had late onset, persisted beyond infancy, and were drug resistant. Clinicians should be aware of this possibility in PKS, which appears to be a rare cause of ES.
74 - The clinical spectrum of epilepsy
- from PART IX - EPILEPSY
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- By Renzo Guerrini, Institute of Child Health and Great Ormond Street Hospital, University College, London, UK, Lucio Parmeggiani, Institute of Child Health and Great Ormond Street Hospital, University College, London, UK, Pierre Thomas, Service de Neurologie et Consultation d'Epileptologie, CHU de Nice, France
- Edited by Arthur K. Asbury, University of Pennsylvania School of Medicine, Guy M. McKhann, The Johns Hopkins University School of Medicine, W. Ian McDonald, University College London, Peter J. Goadsby, University College London, Justin C. McArthur, The Johns Hopkins University School of Medicine
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- Book:
- Diseases of the Nervous System
- Published online:
- 05 August 2016
- Print publication:
- 11 November 2002, pp 1248-1270
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Summary
Historical note
An epileptic seizure is a paroxysmal event due to an excessive, usually self-limited, abnormal activity in the cerebral cortex. Epilepsy is defined by the recurrence of seizures and derives its name from the Greek verb which means ‘to be seized’. In the past it has been alternatively known as the falling sickness as falling down is a common symptom during a seizure, or the sacred disease because seizures were interpreted as an indication of demonic possession.
For centuries the study of epilepsy was mainly identified with the description of seizures. We know now that the clinical spectrum of epilepsy is extremely wide. It ranges from benign, age-related, isolated idiopathic seizures in normal individuals, to malignant symptomatic epileptic encephalopathies with major disability and cognitive impairment. Although for practical clinical purposes, epilepsy may still be a useful diagnostic category, it would be too simplistic to consider it as a single nosologic entity. Epileptic seizures represent a common response of the brain to different etiologic substrates, which can comprise conditions such as age-related ion channel dysfunction and brain tumours.
Epidemiology
Epilepsy is one of the most frequently occurring neurological diseases. However, epidemiological studies have encountered difficulties due to methodological limitations. These are related to clinical and etiological heterogeneity as well as to the criteria used in order to define the disorder (isolated vs. repetitive seizures) and data collection (population-based studies vs. hospital-based studies or national general practice surveys).
Prevalence of active epilepsy in Rochester, Minnesota (Hauser et al., 1991) was estimated at 0.68% when either spontaneous recurring seizures had occurred or an antiepileptic drug treatment had been taken during the last 5 years. Prevalence rates at 0.5–0.8% appeared in other studies in different parts of the world. The incidence of epilepsy has been estimated to range between 17.3 and 136 per 100000 individuals. The incidence curve for epilepsy with respect to age, has a peculiar bimodal distribution (Fig. 74.1; Hauser et al., 1993). Although the incidence of various seizure types has not been clearly determined, focal seizures seem to be the more frequent. (Fig. 74.2) The incidence of the various epilepsy syndromes is still under evaluation (Commission, 1993).
26 - Syndromes with epilepsy and paroxysmal dyskinesia
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- By Renzo Guerrini, Neurosciences Unit, Institute of Child Health, The Wolfson Centre, London, UK, Lucio Parmeggiani, Institute of Child Neurology and Psychiatry, University of Pisa, Italy, Giorgio Casari, Department of Human Molecular Genetics IRCCS San Raffaele Hospital, Milan, Italy
- Edited by Renzo Guerrini, University of London, Jean Aicardi, Hôpital Robert-Debré, Paris, Frederick Andermann, Montreal Neurological Institute & Hospital, Mark Hallett, National Institutes of Health, Baltimore
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- Book:
- Epilepsy and Movement Disorders
- Published online:
- 03 May 2010
- Print publication:
- 13 December 2001, pp 407-420
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Summary
Introduction
Epilepsy and paroxysmal dyskinesia (PD) may sometimes be difficult to differentiate clinically. Although for this reason in the past it has been hypothesized that episodes of PD could represent a form of epilepsy (Lishman et al., 1962; Whitty et al., 1964; Burger et al., 1972), the current understanding is that the two disorders are distinct (Fahn, 1994).
However, there are several recent reports of families in which some individuals presented either or both paroxysmal disorders, with different age-related expression. Co-occurrence makes it likely that a common, genetically determined, pathophysiological abnormality is variably expressed in the cerebral cortex and in basal ganglia.
A rather homogeneous syndrome of autosomal dominant infantile convulsions and paroxysmal (dystonic) choreoathetosis (ICCA) was described in 20 families from France, China, Japan, and the United States (Szepetowski et al., 1997; Lee et al., 1998; Guerrini et al., 1999; Swoboda et al., 2000; Tomita et al., 1999). Linkage analysis allowed the mapping of the disease gene to partially overlapping loci in the pericentromeric region of chromosome 16.
Additional autosomal dominant pedigrees are on record, from Australia and Italy, in which epilepsy was variably associated with paroxysmal kinesigenic or exercise-induced dystonia (Perniola et al., 1998; Singh et al., 1999).
A pedigree in which three members in the same generation were affected by rolandic epilepsy, paroxysmal exercise-induced dystonia (PED) and writer's cramp was reported from Italy (Guerrini et al., 1999).
31 - Drugs for epilepsy and movement disorders
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- By Lucio Parmeggiani, Institute of Child Neurology and Psychiatry, University of Pisa, Italy, Renzo Guerrini, Neurosciences Unit, Institute of Child Health, The Wolfson Centre, London, UK, Brian Meldrum, Institute of Psychiatry, King's College Hospital, London, UK
- Edited by Renzo Guerrini, University of London, Jean Aicardi, Hôpital Robert-Debré, Paris, Frederick Andermann, Montreal Neurological Institute & Hospital, Mark Hallett, National Institutes of Health, Baltimore
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- Book:
- Epilepsy and Movement Disorders
- Published online:
- 03 May 2010
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- 13 December 2001, pp 517-547
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Summary
Introduction
This chapter is intended as an overview of the different antiepileptic drugs (AED) that can also be used to treat movement disorders and of the rationale for their use. There are two main sections: the first reports in alphabetic order AEDs with a well-established use in both fields (epilepsy and movement disorders); the second contains other AEDs that have a less defined use profile in movement disorder treatment, because of their recent introduction or their narrow spectrum of action. The aim is, whenever possible, to highlight the mechanisms of action that can be shared by the drugs in the treatment of both epilepsy and movement disorders.
Acetazolamide
Acetazolamide (AZM) is a sulfonamide that inhibits carbonic anhydrase, an enzyme responsible for conversion of carbon dioxide and water to bicarbonate (Roblin & Clapp, 1950). Its use in epilepsy has a long history but remains limited (Bergstron et al., 1952; Ramsey & De Toledo, 1997). On the contrary, AZM is highly effective in treating episodic ataxias as serendipitously discovered in a patient misdiagnosed with periodic paralysis (Griggs et al., 1978).
Epilepsy
Although several reports have claimed the efficacy of AZM as an AED, most of these studies were performed before the adoption of the International Classification of the Epilepsies (Commission, 1989) and it is therefore difficult to determine clearly what types of epilepsies respond to the drug.
In partial epilepsies, different open studies indicate more than 50% seizure reduction in 25% to 52% of patients, with a minority of them being seizure free.
6 - Motor dysfunction resulting from epileptic activity involving the sensorimotor cortex
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- By Renzo Guerrini, Neurosciences Unit, Institute of Child Health, The Wolfson Centre, London, UK, Lucio Parmeggiani, Institute of Child Neurology and Psychiatry, University of Pisa, Italy, Alan Shewmon, Department of Pediatric Neurology, UCLA Medical Center, Los Angeles, CA, USA, Guido Rubboli, Department of Neurology, Bellaria Hospit al, University of Bologna, Italy, Carlo A. Tassinari, Department of Neurology, Bellaria Hospit al, University of Bologna, Italy
- Edited by Renzo Guerrini, University of London, Jean Aicardi, Hôpital Robert-Debré, Paris, Frederick Andermann, Montreal Neurological Institute & Hospital, Mark Hallett, National Institutes of Health, Baltimore
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- Book:
- Epilepsy and Movement Disorders
- Published online:
- 03 May 2010
- Print publication:
- 13 December 2001, pp 77-96
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Summary
Introduction
Epileptic activity involving the sensorimotor cortex can be associated with a wide spectrum of motor manifestations, such as clonic or tonic phenomena, paresis (Penfield & Jasper, 1954; Fisher, 1978; Globus et al., 1982; Tinuper et al., 1987; Lee & Lerner, 1990; Primavera et al., 1993; So, 1995), epileptic negative myoclonus (Tassinari, 1981; Guerrini et al., 1993; Tassinari et al., 1995; Noachtar et al., 1997), apraxia (Neville & Boyd, 1995; Maquet et al., 1995), ataxia (Bennett et al., 1982; Dalla Bernardina et al., 1989), and motor neglect (Galletti et al., 1992; Guerrini et al., 1993). Neurophysiological investigations and, more recently, functional imaging studies have provided a growing amount of data that have proved extremely useful for diagnostic purposes and for pathophysiological speculations. However, the understanding of the mechanisms underlying the different clinical events associated with paroxysmal activity in the sensorimotor cortex is still incomplete. Excitatory or disinhibitory neuronal mechanisms as well as hypersynchronous inhibitory phenomena may play a role (Engel, 1995), as suggested by the finding that ‘interictal’ spike-and-wave discharges (SW) involving a specific cortical area can disrupt its physiological functions (Shewmon & Erwin, 1988a, b, c; 1989).
In the present chapter, we will focus on those types of motor dysfunction resulting from epileptic activity in the sensorimotor cortex, characterized clinically by an altered execution of a motor task or by the inability to perform it, such as epileptic negative myoclonus (ENM), partial atonic seizures (PAS), and syndromes resulting from frequent paroxysmal activity in the sensorimotor cortex.