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Epileptic auditory verbal agnosia
s117 The diagnosis of epileptic auditory verbal agnosia was unsuspected until the EEG was performed. The disappearance of the EEG abnormalities and the full remission of the clinical signs after treatment with clonazepam established the diagnosis. It seems clear that the presence of epileptic activity, if prolonged, can alter mechanisms underlying cerebral organization.
A reproducible MEP was present at lower intensities of stimulation only in patients at stage II (early stage) of the IAPS scale. At greater intensities of stimulation reproducible MEPs were obtained in all patients except in those at stage IV (last stage) of the disease. CMCT was delayed, compared to our normal values, in all the cases in which it could be calculated.
AN ERP STUDY OF MENTAL ROTATION.
EVENT-RELATED
E Peronnet and M.J. Farah
G. Pfurischeller
(INSERM,
(University
U280, Lyon, France)
Mental rotation is a process by which a misoriented stimulus can be imagined undergoing a rotation to the upright. In an initial study, we recorded event-related potentials while subjects performed a validated mental rotation task, taken from the cognitive psychology literature. The ERP showed a late posterior negativity relative to the ERP from a baseline condition, in which all of the same cognitive processes were required save for the mental rotation itself. We demonstrated that the amount of this late posterior negativity is directly related to the mental rotation performed by the subject. In a second study, we recorded the topography of this mental rotation process as compared to the process by which, in the same experiment, subjects have to discriminate between normal and mirror-reversed non-rotated stimuli. ERPs associated with these two processes can be discriminated on both a temporal and spatial basis. The mental rotation process began later and culminated on the left temporo-occipital areas.
CENTRAL MOTOR CONDUCIION BY DIFFERENT STIMULATION TECHNIQUES: A STUDY IN FRIEDREICH’S ATAXIA PATIENTS. A. Perretti, G. Caruso, L. Santoro (University
of Naples,
B. Lanzillo,
C. Madonna,
of Technology,
Graz,
Austria)
One of the characteristic features of the spontaneous EEG is the amplitude attenuation or desynchronization of rhythms within the alpha band. Since a great variety of alpha band rhythms exist, each one of them can have its own spatial and temporal pattern of desynchronization. Occipital alpha is affected after visual stimulation, central alpha or mu rhythm is desynchronized during motor behavior. Externally or internally paced events are accompanied by at least two neuronal reactions: the generation of event-related potentials (ERP) and the change in the spontaneous EEG in the form of an event-related desynchronization (ERD). ERP and ERD can be measured by averaging techniques. These phenomena display different topographical patterns and timecourses and therefore do not necessarily reflect the same underlying neuronal process. The ERD can be displayed topographically in the form of maps and as time courses for different electrodes or cortical regions. Data from replicated experiments with visual-verbal stimulation and semantic judgements are reported. It will be shown that the ERD mapping technique makes it possible to study encoding processes in space and time and to differentiate between task-specific and non-task-specific cognitive processes.
A. Filla and FUNCTIONAL PING.
Naples,
EEG DESYNCHRONIZATION.
BRAIN TOPOGRAPHY
AND ERD MAP-
Italy) G. Pfurtscheller and W. Klimesch
Nine patients affected by Friedreich’s ataxia, at different stages of the disease, according to the Inherited Ataxias Progressive Scale (IAPS), were investigated electrophysiologically by transcranial stimulation of the hand motor cortex. In all patients, ‘unifocal’ electrical stimulation of the motor cortex was performed at different intensities to elicit motor-evoked potentials (MEPs) from the contralateral abductor pollicis brevis muscle during moderate contraction. Central motor conduction time (CMCT) was calculated, indirectly, by subtracting F wave latency from MEP latency. Some of these patients also underwent “bifocal” and magnetic cortical motor stimulation of the motor cortex during contraction and relaxation of the target muscle.
(University
of Technology,
Graz,
Austria)
The human brain generates a great variety of alpha band rhythms, some of them closely linked to different cortical fields. When such a cortical field becomes activated, the intrinsic rhythm is desynchronized or blocked. Since such an amplitude attenuation is always connected with an externally or internally paced event, the phenomenon was named “event-related desynchronization” (ERD). Based on multichannel EEG data and the quantification and topographical display of the ERD in the form of maps, the functional topography of the human brain can be studied.
A reproducible MEP was present at lower intensities of stimulation only in patients at stage II (early stage) of the IAPS scale. At greater intensities of stimulation reproducible MEPs were obtained in all patients except in those at stage IV (last stage) of the disease. CMCT was delayed, compared to our normal values, in all the cases in which it could be calculated.
AN ERP STUDY OF MENTAL ROTATION.
EVENT-RELATED
E Peronnet and M.J. Farah
G. Pfurischeller
(INSERM,
(University
U280, Lyon, France)
Mental rotation is a process by which a misoriented stimulus can be imagined undergoing a rotation to the upright. In an initial study, we recorded event-related potentials while subjects performed a validated mental rotation task, taken from the cognitive psychology literature. The ERP showed a late posterior negativity relative to the ERP from a baseline condition, in which all of the same cognitive processes were required save for the mental rotation itself. We demonstrated that the amount of this late posterior negativity is directly related to the mental rotation performed by the subject. In a second study, we recorded the topography of this mental rotation process as compared to the process by which, in the same experiment, subjects have to discriminate between normal and mirror-reversed non-rotated stimuli. ERPs associated with these two processes can be discriminated on both a temporal and spatial basis. The mental rotation process began later and culminated on the left temporo-occipital areas.
CENTRAL MOTOR CONDUCIION BY DIFFERENT STIMULATION TECHNIQUES: A STUDY IN FRIEDREICH’S ATAXIA PATIENTS. A. Perretti, G. Caruso, L. Santoro (University
of Naples,
B. Lanzillo,
C. Madonna,
of Technology,
Graz,
Austria)
One of the characteristic features of the spontaneous EEG is the amplitude attenuation or desynchronization of rhythms within the alpha band. Since a great variety of alpha band rhythms exist, each one of them can have its own spatial and temporal pattern of desynchronization. Occipital alpha is affected after visual stimulation, central alpha or mu rhythm is desynchronized during motor behavior. Externally or internally paced events are accompanied by at least two neuronal reactions: the generation of event-related potentials (ERP) and the change in the spontaneous EEG in the form of an event-related desynchronization (ERD). ERP and ERD can be measured by averaging techniques. These phenomena display different topographical patterns and timecourses and therefore do not necessarily reflect the same underlying neuronal process. The ERD can be displayed topographically in the form of maps and as time courses for different electrodes or cortical regions. Data from replicated experiments with visual-verbal stimulation and semantic judgements are reported. It will be shown that the ERD mapping technique makes it possible to study encoding processes in space and time and to differentiate between task-specific and non-task-specific cognitive processes.
A. Filla and FUNCTIONAL PING.
Naples,
EEG DESYNCHRONIZATION.
BRAIN TOPOGRAPHY
AND ERD MAP-
Italy) G. Pfurtscheller and W. Klimesch
Nine patients affected by Friedreich’s ataxia, at different stages of the disease, according to the Inherited Ataxias Progressive Scale (IAPS), were investigated electrophysiologically by transcranial stimulation of the hand motor cortex. In all patients, ‘unifocal’ electrical stimulation of the motor cortex was performed at different intensities to elicit motor-evoked potentials (MEPs) from the contralateral abductor pollicis brevis muscle during moderate contraction. Central motor conduction time (CMCT) was calculated, indirectly, by subtracting F wave latency from MEP latency. Some of these patients also underwent “bifocal” and magnetic cortical motor stimulation of the motor cortex during contraction and relaxation of the target muscle.
(University
of Technology,
Graz,
Austria)
The human brain generates a great variety of alpha band rhythms, some of them closely linked to different cortical fields. When such a cortical field becomes activated, the intrinsic rhythm is desynchronized or blocked. Since such an amplitude attenuation is always connected with an externally or internally paced event, the phenomenon was named “event-related desynchronization” (ERD). Based on multichannel EEG data and the quantification and topographical display of the ERD in the form of maps, the functional topography of the human brain can be studied.