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High resolution methods as an approach to the localization of evoked potential generators
ble we used the following procedure: 8-16 channel EEG for better localization of abnormalities and planning of next procedures: then drug dose was increased (e.g. thiopental) until burst suppression occurred; next, a two-channel CSA monitor was added. We draw the following conclusions: (1) with CSA help it was possible to detect the recurrence of crisis, as electrographical crisis may precede the clinical onset; (2) it is simple to assess CNS drug effects, thus monitoring the dosage required to attain EEG burst suppression; (3) intensive care staff can easily follow the procedure and actively participate in the monitoring; (4) control of crisis was generally attained with doses far exceeding those recommended.
LONG-LOOP
REFLEXES
IN MOVEMENT
DISORDERS.
C.H. Liicking and G. Deuschl
(Freiburg
University,
Freiburg,
F.R.G.)
Activation of muscle afferents by stretch elicits reflex activity of short and long latency (Ml, M2, M3). Electrical stimulation of peripheral mixed nerves also evokes early and late muscle responses: the Hoffmann Reflex (HR) as a pure spinal reflex, and long-latency reflexes (LLR I, II, III) which may be mediated by transcortical loops (!ong-loop reflexes). The enhancement of the M2 response in Parkinson’s disease is related to the amount of rigidity rather than to tremor. On the other hand there is often an enhanced early component of the long-loop reflexes (LLR I) in a certain tremor type of parkinsonian patients as well as in essential tremor with a reciprocal alternating burst activity in antagonistic muscles. In Huntington’s chorea. M2 and LLR II are reduced or abolished without any clear correlation to duration and severity of the disease. Antidopaminergic treatment has no influence on LLR despite clinical improvement. Healthy relatives and patients with symptomatic choreatic syndrome revealed normal LLR in all cases. Patients with focal or generalized dystonia do not present a consistent pathological feature of LLR. In essential myoclonus LLR are normal, whereas in reflex myoclonus the EMG bursts correspond to LLR I or LLR III. It remains open to discussion whether the modification of LLR is related to the pathophysiology of the movement disorders or whether it is only due to common underlying processes.
NOCTURNAL
to carbamazepine (C‘BZ). Because of the association with othclclearly epileptic seizures, and for the clinical feature:; of the attack, we suggest that NPD with short-lasting attacks may represent a variety of epilepsy. probably artsing from deep sited frontal foci. Other varieties of NPD are represented hi. short-lasting paroxysmal behavioural arousals during NREM sleep. often with abnormal motor pattern and without EEG epileptic discharges: atypical periodic movements in sleep. w 1111 fragments of a dystonic attack occurring periodically every 20 set-2 min during NREM sleep, both may respond to CBZ: and NPD with intermediate duration attacks (2-5 min), occurring in children during NREM sleep and wakefulness with peculiar jerky puppet-like movements. and refractory to treatment.
PAROXYSMAL DYSTONIA.
NEW SOLUTIONS TO METHODOLOGICAL PROBLEMS IN BRAIN ELECTRICAL ACTIVITY MAPPING. B. Lumeau
(CNRS,
and G. Rondouin
Gif-sur-Yvette,
France)
Brain mapping of EEG activity (BEAM) was recently proposed as a new tool in the exploration of brain function. Basic assumptions are the random characteristics of EEG signals and the quasi-stationary property of the EEG over a short period. The last assumption is only true for periods of 6-10 sec. so that longer durations of analysis must be used very carefully. Major problems resulting from signal acquisition and conditioning methods must be kept in mind: the characteristics of electrodes, choice of reference, amplifier characteristics and analogue-to-digital conversion may all induce severe errors. Rigorous choice of hardware may contribute to solving this first group of difficulties. Additional problems result from signal processing and interpolation methods. To estimate the power spectral density we propose a method of automatic determination of the convolution window, minimising the bias and variance used to smooth the periodogram. Moreover. the accuracy of EEG mapping is increased by a polynomial interpolation method. The value of these solutions is illustrated with clinical applications.
HIGH RESOLUTION METHODS AS AN APPROACH TO THE LOCALIZATION OF EVOKED POTENTIAL GENERATORS. B. Lumeau, G. Rondouin
and H. Clergeot
E. Lugaresi
(CNRS, (University
of Bologna,
Bologna,
Gif-sur-Yvette,
France)
Italy)
Nocturnal paroxysmal dystonia (NPD) represents a syndrome of paroxysmal dystonic-dyskinetic attacks arising during NREM sleep. NPD with long-lasting attacks (from 2 min to 1 h) is refractory to therapy. NPD with short-lasting (15 set to 2 min) attacks is much more common, and often responds well
High resolution methods have been defined and developed in the fields of spatial processing, in order to localize sources, and spectral analysis, to determine the spectral density of signals. Numerous methods of spatial processing are based on properties of the eigenspace of the spectral density matrix. It is within this framework that the localization of generators relating to
S87 evoked potentials has been considered. This requires a series of 4 methods: (1) optimal estimation of the noisy spectral density matrix (composed of signals received by a network of captors placed on the scalp, the noisy part coming from the total cerebral activity); (2) estimation of the spectral density matrix freed from noise thus allowing the separation of the source space (that of the generators) from the noise space; (3) a method of parameterising the source vectors (associated with each generator) in terms of unknown position parameters of the sources (definition of an optimal propagation model); (4) a method for determining, on these bases, the position parameters (method of the generalized ‘goniometer’). This procedure was implemented for somatosensory evoked potentials in order to localize the generator of the P22 wave in man.
SUPPRESSION MANS WITH CORTEX.
OF LETTER RECOGNITION IN HUTHE MAGNETIC COIL OVER OCCIPITAL
P.J. Maccabee, V.E. Amassian, Rude11 and L. Eberle (SUNY
Health
Science Center,
R.Q. Cracco.
Brooklyn,
J.B. Cracco,
A.
NY, U.S.A.)
Using ourselves as subjects, we tested the effect of magnetic coil (MC) stimulation on the perception of briefly presented random alphabetic letter trigrams. The letters, 5 mm tall, were displayed horizontally or vertically, and were viewed at a distance of 57 cm. Against a light background the letters were darker or, against a dark background the letters were brighter, decaying substantially within 2 msec. Topographical relations were studied by placing a Cadwell round MC such that the distal edge was located 2 cm above the inion and then shifted to the right, left, or rostrally. Moving the MC laterally at visual stimulus-to-MC pulse intervals of 100 msec resulted in loss of perception of the contralateral letter; this implies a focal cortical effect. Similarly, shifting the MC rostrally caused suppression of the bottom letter of a vertical array. When the MC was midline, visual stimulus-to-MC pulse intervals less than 60-80 msec or greater than 120-140 msec had no consistent effect on letter perception. At intermediate intervals from 80-100 msec, letters were rarely reported correctly. Thus, by 120-140 msec after a brief visual stimulus, neural activity subserving letter recognition is relayed from human calcarine cortex.
UNMASKING OF VISUAL PERCEPTION BY MAGNETIC COIL STIMULATION OF HUMAN CEREBRAL CORTEX. P.J. Maccabee, V.E. Amassian, Eberle
R.Q. Cracco,
(SUNY
Brooklyn,
Health
Science Center,
stimulus (9, the target) is ‘masked’ by the second stimulus (S2, the mask); this is referred to as backward masking. Masking is defined as a perceptual interference resulting from the rapid presentation of temporally discrete, briefly exposed, different visual stimuli. In 3 normals (VEA, RQC, PJM), trigrams separated by an interval of 100 msec resulted in significant suppression of Sl and retention of S2. When a round or double-square magnetic coil was subsequently energized over occipital cortex (OC) at intervals of 80-100 msec after S2 (i.e., 180-200 msec after Sl) the perception of Sl was consistently unmasked and perception of S2 was consistently suppressed. When the MC was pulsed over left temporo-patieto-occipital cortex 100-150 msec after S2, similar but less robust findings were observed. Previous studies reveal that by 140-160 msec a single trigram stimulus has been relayed beyond OC. One possible explanation for our data is that the MC pulse, given 180-200 msec after Sl, prevents the neural representation of S2 from being transmitted beyond occipital cortex and interfering with the perception of Sl.
A. Rude11 and L.
NY, U.S.A.)
Typically, when briefly presenting random, alphabetic letter trigrams separated by intervals of less than 150 msec, the 1st
VOLTAGE GRADIENTS INDUCED IN HOMOGENOUS MEDIA VOLUME CONDUCTORS BY ROUND AND FIGURE-8 MAGNETIC COILS: RELATIONSHIP TO ACTIVATION OF SENSORY NERVE FIBERS.
P.J. Maccabee, L. Eberle, Rude11 and M. Jayachandra
(SUNY
Health
V.E. Amassian,
Science Center,
Brooklyn,
R.Q.
Cracco,
A.
NY, U.S.A.)
Physical modelling of voltage gradients induced in a saline-filled trough were performed using magnetic coils of diverse design and orientation. Recordings were obtained with a coaxial cable electrode (a linear probe) moved in 3 spatial dimensions. Voltage gradients (Z axis) were plotted as a function of (X, Y) space. Sensory nerve action potentials (SNAPS) elicited by MC stimulation of median nerve at the wrist were recorded from index finger, permitting various MC orientations uncomplicated by ulnar nerve co-activation. When the round MC remained parallel to the MC plane, maximal (or minimal) voltage gradients were recorded when the probe was parallel (or perpendicular) to the direction of current in the windings. Similiarly, maximal (or minimal) SNAPS were elicited by tangential edge (or symmetricaltangential) MC orientations over distal median nerve. The figure-8 MC elicited an extremely focal voltage gradient consisting of a sharp central peak adjacent to smaller peaks. SNAPS elicited by the figure-8 MC could be as precise as those elicited by cathodal stimuli. These findings are in accord with reports documenting focal MC stimulation of motor and visual cortex.
LONG-LOOP
REFLEXES
IN MOVEMENT
DISORDERS.
C.H. Liicking and G. Deuschl
(Freiburg
University,
Freiburg,
F.R.G.)
Activation of muscle afferents by stretch elicits reflex activity of short and long latency (Ml, M2, M3). Electrical stimulation of peripheral mixed nerves also evokes early and late muscle responses: the Hoffmann Reflex (HR) as a pure spinal reflex, and long-latency reflexes (LLR I, II, III) which may be mediated by transcortical loops (!ong-loop reflexes). The enhancement of the M2 response in Parkinson’s disease is related to the amount of rigidity rather than to tremor. On the other hand there is often an enhanced early component of the long-loop reflexes (LLR I) in a certain tremor type of parkinsonian patients as well as in essential tremor with a reciprocal alternating burst activity in antagonistic muscles. In Huntington’s chorea. M2 and LLR II are reduced or abolished without any clear correlation to duration and severity of the disease. Antidopaminergic treatment has no influence on LLR despite clinical improvement. Healthy relatives and patients with symptomatic choreatic syndrome revealed normal LLR in all cases. Patients with focal or generalized dystonia do not present a consistent pathological feature of LLR. In essential myoclonus LLR are normal, whereas in reflex myoclonus the EMG bursts correspond to LLR I or LLR III. It remains open to discussion whether the modification of LLR is related to the pathophysiology of the movement disorders or whether it is only due to common underlying processes.
NOCTURNAL
to carbamazepine (C‘BZ). Because of the association with othclclearly epileptic seizures, and for the clinical feature:; of the attack, we suggest that NPD with short-lasting attacks may represent a variety of epilepsy. probably artsing from deep sited frontal foci. Other varieties of NPD are represented hi. short-lasting paroxysmal behavioural arousals during NREM sleep. often with abnormal motor pattern and without EEG epileptic discharges: atypical periodic movements in sleep. w 1111 fragments of a dystonic attack occurring periodically every 20 set-2 min during NREM sleep, both may respond to CBZ: and NPD with intermediate duration attacks (2-5 min), occurring in children during NREM sleep and wakefulness with peculiar jerky puppet-like movements. and refractory to treatment.
PAROXYSMAL DYSTONIA.
NEW SOLUTIONS TO METHODOLOGICAL PROBLEMS IN BRAIN ELECTRICAL ACTIVITY MAPPING. B. Lumeau
(CNRS,
and G. Rondouin
Gif-sur-Yvette,
France)
Brain mapping of EEG activity (BEAM) was recently proposed as a new tool in the exploration of brain function. Basic assumptions are the random characteristics of EEG signals and the quasi-stationary property of the EEG over a short period. The last assumption is only true for periods of 6-10 sec. so that longer durations of analysis must be used very carefully. Major problems resulting from signal acquisition and conditioning methods must be kept in mind: the characteristics of electrodes, choice of reference, amplifier characteristics and analogue-to-digital conversion may all induce severe errors. Rigorous choice of hardware may contribute to solving this first group of difficulties. Additional problems result from signal processing and interpolation methods. To estimate the power spectral density we propose a method of automatic determination of the convolution window, minimising the bias and variance used to smooth the periodogram. Moreover. the accuracy of EEG mapping is increased by a polynomial interpolation method. The value of these solutions is illustrated with clinical applications.
HIGH RESOLUTION METHODS AS AN APPROACH TO THE LOCALIZATION OF EVOKED POTENTIAL GENERATORS. B. Lumeau, G. Rondouin
and H. Clergeot
E. Lugaresi
(CNRS, (University
of Bologna,
Bologna,
Gif-sur-Yvette,
France)
Italy)
Nocturnal paroxysmal dystonia (NPD) represents a syndrome of paroxysmal dystonic-dyskinetic attacks arising during NREM sleep. NPD with long-lasting attacks (from 2 min to 1 h) is refractory to therapy. NPD with short-lasting (15 set to 2 min) attacks is much more common, and often responds well
High resolution methods have been defined and developed in the fields of spatial processing, in order to localize sources, and spectral analysis, to determine the spectral density of signals. Numerous methods of spatial processing are based on properties of the eigenspace of the spectral density matrix. It is within this framework that the localization of generators relating to
S87 evoked potentials has been considered. This requires a series of 4 methods: (1) optimal estimation of the noisy spectral density matrix (composed of signals received by a network of captors placed on the scalp, the noisy part coming from the total cerebral activity); (2) estimation of the spectral density matrix freed from noise thus allowing the separation of the source space (that of the generators) from the noise space; (3) a method of parameterising the source vectors (associated with each generator) in terms of unknown position parameters of the sources (definition of an optimal propagation model); (4) a method for determining, on these bases, the position parameters (method of the generalized ‘goniometer’). This procedure was implemented for somatosensory evoked potentials in order to localize the generator of the P22 wave in man.
SUPPRESSION MANS WITH CORTEX.
OF LETTER RECOGNITION IN HUTHE MAGNETIC COIL OVER OCCIPITAL
P.J. Maccabee, V.E. Amassian, Rude11 and L. Eberle (SUNY
Health
Science Center,
R.Q. Cracco.
Brooklyn,
J.B. Cracco,
A.
NY, U.S.A.)
Using ourselves as subjects, we tested the effect of magnetic coil (MC) stimulation on the perception of briefly presented random alphabetic letter trigrams. The letters, 5 mm tall, were displayed horizontally or vertically, and were viewed at a distance of 57 cm. Against a light background the letters were darker or, against a dark background the letters were brighter, decaying substantially within 2 msec. Topographical relations were studied by placing a Cadwell round MC such that the distal edge was located 2 cm above the inion and then shifted to the right, left, or rostrally. Moving the MC laterally at visual stimulus-to-MC pulse intervals of 100 msec resulted in loss of perception of the contralateral letter; this implies a focal cortical effect. Similarly, shifting the MC rostrally caused suppression of the bottom letter of a vertical array. When the MC was midline, visual stimulus-to-MC pulse intervals less than 60-80 msec or greater than 120-140 msec had no consistent effect on letter perception. At intermediate intervals from 80-100 msec, letters were rarely reported correctly. Thus, by 120-140 msec after a brief visual stimulus, neural activity subserving letter recognition is relayed from human calcarine cortex.
UNMASKING OF VISUAL PERCEPTION BY MAGNETIC COIL STIMULATION OF HUMAN CEREBRAL CORTEX. P.J. Maccabee, V.E. Amassian, Eberle
R.Q. Cracco,
(SUNY
Brooklyn,
Health
Science Center,
stimulus (9, the target) is ‘masked’ by the second stimulus (S2, the mask); this is referred to as backward masking. Masking is defined as a perceptual interference resulting from the rapid presentation of temporally discrete, briefly exposed, different visual stimuli. In 3 normals (VEA, RQC, PJM), trigrams separated by an interval of 100 msec resulted in significant suppression of Sl and retention of S2. When a round or double-square magnetic coil was subsequently energized over occipital cortex (OC) at intervals of 80-100 msec after S2 (i.e., 180-200 msec after Sl) the perception of Sl was consistently unmasked and perception of S2 was consistently suppressed. When the MC was pulsed over left temporo-patieto-occipital cortex 100-150 msec after S2, similar but less robust findings were observed. Previous studies reveal that by 140-160 msec a single trigram stimulus has been relayed beyond OC. One possible explanation for our data is that the MC pulse, given 180-200 msec after Sl, prevents the neural representation of S2 from being transmitted beyond occipital cortex and interfering with the perception of Sl.
A. Rude11 and L.
NY, U.S.A.)
Typically, when briefly presenting random, alphabetic letter trigrams separated by intervals of less than 150 msec, the 1st
VOLTAGE GRADIENTS INDUCED IN HOMOGENOUS MEDIA VOLUME CONDUCTORS BY ROUND AND FIGURE-8 MAGNETIC COILS: RELATIONSHIP TO ACTIVATION OF SENSORY NERVE FIBERS.
P.J. Maccabee, L. Eberle, Rude11 and M. Jayachandra
(SUNY
Health
V.E. Amassian,
Science Center,
Brooklyn,
R.Q.
Cracco,
A.
NY, U.S.A.)
Physical modelling of voltage gradients induced in a saline-filled trough were performed using magnetic coils of diverse design and orientation. Recordings were obtained with a coaxial cable electrode (a linear probe) moved in 3 spatial dimensions. Voltage gradients (Z axis) were plotted as a function of (X, Y) space. Sensory nerve action potentials (SNAPS) elicited by MC stimulation of median nerve at the wrist were recorded from index finger, permitting various MC orientations uncomplicated by ulnar nerve co-activation. When the round MC remained parallel to the MC plane, maximal (or minimal) voltage gradients were recorded when the probe was parallel (or perpendicular) to the direction of current in the windings. Similiarly, maximal (or minimal) SNAPS were elicited by tangential edge (or symmetricaltangential) MC orientations over distal median nerve. The figure-8 MC elicited an extremely focal voltage gradient consisting of a sharp central peak adjacent to smaller peaks. SNAPS elicited by the figure-8 MC could be as precise as those elicited by cathodal stimuli. These findings are in accord with reports documenting focal MC stimulation of motor and visual cortex.