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ABSTRACT: Single pulses of transcranial magnetic stimulation (sTMS) restricted locally to the primary cortical areas for somatosensory and visual input, unlike the effects of repetitive stimulation, usually fail to elicit projected sensations. We tested the effect of sTMS over anterior frontal cortex in facilitating phosphenes from preceding sTMS over calcarine cortex, which alone was rarely effective in eliciting phosphenes. The combined sTMS elicited complex phosphenes, which changed with the site of frontal sTMS and the interstimulus interval. Our results show that sTMS over anterior frontal cortex also improved reporting of weakly illuminated, flashed four-letter stimuli, which permitted its statistical validation. We propose that the present demonstration of frontal cortical facilitation of visual awareness, when combined with the previous finding of projected paresthesias and sense of movement (Amassian et al, 1991 Brain 114 2505-2520), provide evidence of a general frontal opening effect on a thalamic gate. Opening this gate facilitates entry of information from primary cortical receiving areas to thalamus. Thereby, the reciprocal thalamocortical interrelations that subserve conscious awareness of sensory stimuli could be fostered.
Perception 02/2008; 37(3):375-88. · 1.31 Impact Factor
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Annals of the New York Academy of Sciences 12/2006; 388(1):412 - 425. · 3.15 Impact Factor
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ABSTRACT: Although transcranial magnetic stimulation (TMS) has been introduced only recently, it is safe and provides a painless, inexpensive noninvasive method for the evaluation of brain function. Determining central motor conduction time (CMCT) permits assessment of the corticospinal pathways. Mapping the central representation of muscles provides a method for investigating the cortical reorganization that follows training, amputation and injury to the central nervous system. Such studies of human plasticity may have important implications for neurorehabilitation. TMS also provides a method whereby cortical excitability can be noninvasively evaluated, which is likely to have important implications in the study of epilepsy, movement disorders and related conditions. TMS is useful in tracking the flow of information from one brain region to another and in investigations of cognition and functional localization, thereby complementing information obtained using functional imaging techniques, which have superior spatial but inferior temporal resolution. Finally, TMS is currently being investigated as a method for establishing cerebral dominance and as a therapeutic tool in the treatment of depression. Investigations for treatment of other neurologic and psychiatric conditions are likely to be undertaken.
Journal of Neuroscience Methods 02/1999; · 1.98 Impact Factor
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ABSTRACT: Focal stimulation over human cerebellum with a figure 8 magnetic coil (MC) results in an evoked wave recorded from bipolar scalp electrodes on the interaural line and more anteriorly. In 3 subjects, the wave responses along the interaural line had latencies of 8.8–13.8 msec, lasted 17.4–29.0 msec and had a maximum amplitude of 14.4–26.8 μV. The responses were recorded more anteriorly from leads midway between the interaural line and frontal leads; responses recorded from frontal leads were up to 3.5 msec later. The evoked wave was preceded by a diphasic EMG response with a latency of 1.2–2.0 msec. Analysis of the averaged responses recorded by adjoining bipolar leads indicated that the response was predominantly surface positive and crossed. Control experiments eliminated eye movement and somatosensory input as explanations of the evoked response, thereby identifying it as a cortical response. The surface positive wave in humans was compared with the responses recorded in cat and monkey to cerebellar stimulation. The responses in humans could reflect dysfacilitation through MC activation of Purkinje cells, or feed-forward facilitation through transsynaptic or antidromic activation of dentate neurons. The latency of the surface positive wave exceeds that of cerebellar inhibition of MC elicited hand muscle responses, but the discrepancy is at least partly accounted for by the extra delay required to set up the indirect cortico-spinal component required for motoneuron discharge.Estimates made of the cerebello-frontal cortical and peripheral feedback loop times suggest that the central has less than one quarter the delay of the peripheral loop, which would be especially advantageous during fast skilled movements of the fingers.
Electroencephalography and Clinical Neurophysiology 09/1992;
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ABSTRACT: The results of the following selected studies using magnetic coil (MC) stimulation are presented: (1) evidence for focality of MC stimulation, (2) MC stimulation of frontal areas related to speech, (3) transcallosal responses evoked by MC stimulation, and (4) suppression of visual perception with MC stimulation over occipital cortex. The authors served as subjects, and in most studies a standard Cadwell stimulator and round MC were used. Using a more vertical, rather than tangential, MC orientation and threshold stimulation, nearly isolated movements of individual digits were elicited implying focal cortical excitation. MC stimulation of frontal areas of either hemisphere elicited electromyography in contralateral laryngeal muscles. The shortest latency responses that were often accompanied by arm movement were thought to be elicited from intermediate areas of precentral gyrus and longer latency responses, from near Broca's area, extreme lateral precentral gyrus, and the supplementary motor area. MC stimulation over the occipital cortex resulted in suppression of visual perception of letters briefly flashed on a screen. The topography of suppression implicated the geniculocalcarine system as the site of MC effect. Focal MC stimulation of posterior frontal cerebral cortex elicited a transcallosal response from contralateral homologous cortex with a latency similar to that obtained with focal anodic stimulation but with considerably less excitation of cranial muscles.
Copyright (C) 1990 American Clinical Neurophysiology Society
Journal of Clinical Neurophysiology 12/1989; 7(1). · 1.45 Impact Factor
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ABSTRACT: Using ourselves as subjects, maximal compound motor action potentials (CMAPs) were evoked in ipsilateral nasal and orbicularis oculi muscles (onset latency 4.9–5.4 msec) by a magnetic coil (MC) tangentially oriented over parieto-occipital scalp. The facial nerve was also electrically stimulated sequentially at the posterior tragus near the stylomastoid foramen, anterior tragus and 3 cm more distally. Onset latency of the CMAP elicited at posterior tragus ranged from 1.0 to 1.3 msec less than that elicited by the MC over scalp. Because the measured distal facial nerve motor conduction velocity was 50–60 m/sec, the locus of impulse generation induced by magnetic coil stimulation was estimated to be approximately 6.5 cm proximal to the site of electrical stimulation at the posterior tragus, i.e., closer to the exit of the facial nerve from the brain-stem than to its entrance into the internal auditory meatus. This non-invasive technique should be useful in evaluating patients with peripheral facial nerve disorders including Bell's palsy.
Electroencephalography and Clinical Neurophysiology 11/1988;
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ABSTRACT: Lumbar spine and scalp short latency somatosensory evoked potentials (SSEPs) to stimulation of the posterior tibial, peroneal and sural nerves at the ankle (PTN-A, PN-A, SN-A) and common peroneal nerve at the knee (CPN-K) were obtained in 8 normal subjects. Peripheral nerve conduction velocities and lumbar spine to cerebral cortex propagation velocities were determined and compared. These values were similar with stimulation of the 3 nerves at the ankle but were significantly greater with CPN-K stimulation.CPN-K and PTN-A SSEPs were recorded from the L3, T12, T6 and C7 spines and the scalp in 6 normal subjects. Conduction velocities were determined over peripheral nerve-cauda equina (stimulus-L3), caudal spinal cord (T12-T6) and rostral spinal cord (T6-C7). Propagation velocities were determined from each spinal level to the cerebral cortex. With both CPN-K and PTN-A stimulation the speed of conduction over peripheral nerve and spinal cord was non-linear. It was greater over peripheral nerve-cauda equina and rostral spinal cord than over caudal cord segments. The CPN-K response was conducted significantly faster than the PTN-A response over peripheral nerve-cauda equina and rostral spinal cord but these values were similar over caudal cord. Spine to cerebral cortex propagation velocities were significantly greater from all spine levels with CPN-K stimulation.These data show that the conduction characteristics of SSEPs over peripheral nerve, spinal cord and from spine to cerebral cortex are dependent on the peripheral nerve stimulated.
Electroencephalography and Clinical Neurophysiology 08/1987;
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ABSTRACT: Short latency SEPs to peroneal nerve stimulation were recorded in 26 normal adults. These potentials consisted of 3 positive potentials (P1, P2, P3) peaking at about 17, 21 and 27 msec, followed by a negative potential (N1) peaking at about 34 msec. P1 and P2 were small and incosistently recorded. P1 was widespread in its scalp distribution in noncephalic reference leads, and was poorly defined or absent in scalp bipolar and ear reference leads. P2 was widespread in its scalp distribution in both non-cephalic and ear reference leads. It was poorly defined in scalp bipolar leads. P3 and N1 were consistently recorded from the scalp in both reference and bipolar leads. They were much greater in amplitude than the earlier potentials and had steep potential gradients. They were most prominent around the vertex. They showed significant differences in their peak latencies at different scalp recording locations.The short latency, positive polarity and widespread scalp distribution of P1 and P2 suggest they are far-field events arising in subcortical structures. The longer latency and steep potential gradient of P3 and N1 suggest that they are near-field events arising in cerebral cortical structures. Both P3 and N1 were stable potentials and, therefore, may prove to be clinically useful.RésuméDes PES de courte latence à la stimulation du nerf péroné ont été enregistrés chez 26 adultes normaux. Ces potentiels consistent en 3 potentiels positifs (P1, P2, P3) dont le pic survient à environ 17, 21 et 27 msec, suivis par un potentiel négatif (N1) dont le pic se situe à 34 msec environ. P1 et P2 sont de faible amplitude et inconstants. P1 montre une large distribution sur le scalp dans les montages à référence non-céphalique, et est mal défini ou absent dans les montages de scalp bipolaires ou avec référence à l'oreille. P2 a une distribution étendue sur le scalp dans les montages non-céphaliques et avec référence à l'oreille. Il est mal défini dans les montages bipolaires. P3 et N1 sont constamment enregistrés sur le scalp aussi bien sur les montages référentiels que bipolaires. Ils sont beaucoup plus amples que les potentiels plus précoces et montrent des gradients de potentiels abrupts. Ils prédominent au voisinage du vertex. Ils montrent des différences significatives de latences de pics pour différentes localisations d'enregistrement sur le scalp.La latence courte, la polarité positive et la large distribution sur le scalp de P1 et P2 suggèrent qu'ils sont des événements projetés, provenant des structures sous-corticales. La latence plus longue et le gradient de potentiel abrupt de P3 et N1 suggèrent qu'ils sont des événements proches, prenant leur origine dans les structures corticales. P3 et N1 sont des potentiels stables et donc peuvent s'avérer cliniquement utiles.
Electroencephalography and Clinical Neurophysiology 08/1981;
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ABSTRACT: Spinal and cerebral somatosensory evoked potentials to peroneal nerve and median nerve stimulation were recorded in 17 children with CNS degenerative disease and compared with similar potentials obtained in a group of age-matched normal control subjects. Spinal potentials were increased in duration over caudal cord segments and were poorly defined or absent over the rostral cord in some patients. In 12 patients the conduction velocity of the spinal response was slow over spinal cord segments. However, conduction velocity over peripheral nerve and cauda equina was normal in all patients. The scalp recorded evoked potentials to both median and peroneal nerve stimulation which arise in neural structures rostral to the brain stem were absent in 14 patients. Cerebral responses and certain spinal potentials were greatly increased in amplitude in one patient with myoclonus.This study demonstrates that these methods permit an evaluation of the entire neuraxis from peripheral nerve to cerebral cortex and that they may be helpful in the evaluation of patients with diffuse or multifocal disease of the nervous system.RésuméLes potentiels somatosensitifs cérébraux et spinaux évoques par stimulation du nerf péroné et du nerf médian ont 'eté enregistrés chez 17 enfants avec maladie dégénérative du SNC et comparés aux mêmes potentiels obtenus dans un groupe de sujets de contrôle appariés par l'âge. La durée des potentiels spinaux est augmentée au niveau des segments caudaux de la moelle et sont mal définis ou absents au niveau de la moelle rostrale chez certains malades. Chez 12 malades la vitesse de conduction de la réponse spinale est lente au niveau des segments médullaires. Cependant, la vitesse de conduction au niveau du nerf périphérique et de la queue de cheval est normale chez tous les malades. Les potentiels évoqués enregistrés sur le scalp en réponse à la stimulation des nerfs péroné et med́ian qui surviennent dans des structures nerveuses en avant au tronc cérébral sont absentes chez 14 malades. Les réponses cérébrales et certains potentiels spinaux ont une amplitude très augmenée chez un malade avec myoclonies.Cette étude montre que cette méthode permet une évaluation du névraxe dans son entier, du nerf périphérique au cortex cérébral, et qu'elle peut être utile pour l'évaluation des malades avec maladies diffuses ou multi-focales dy système nerveux.
Electroencephalography and Clinical Neurophysiology 10/1980;
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ABSTRACT: Short latency visual evoked oscillatory potentials to bright light stimulation were recorded from the scalp of 15 normal human adult subjects. The onset latencies of these potentials recorded over anterior frontal and posterior scalp regions were 9–17 msec and 13–24 msec, respectively. The frequency of the oscillations was about 100 c/sec. These potentials were widespread in their distribution over the scalp but were most prominent at midline and parasagittal recording locations. Like similar potentials recorded in animals, it seems that these potentials arise in both subcortical and cortical visual structures. The mechanism underlying the generation of these potentials and their possible functional significance are discussed.RésuméLes potentials évoqués visuels de courte latence à des stimulations de lumière brillante oscillatoire ont été enregistrés sur le scalp chez 15 sujects adultes normaux. Les latences de début de ces potentiels enregistrés sur les régions frontales antérieures et sur les régions postérieures sont respectivement de 9–17 msec et 13–24 msec. La fréquence des oscillations est d'environ 100 c/sec. Ces potentiels ont une large distribution sur le scalp mais prédominent au niveau de localisations d'enregistrements médianes et parasagittales. Comme les potentiels similaires enregistrés chez l'animal, il semble que ces potentiels prennent naissance dans les structures visuelles sous-corticales et corticales. Les auteurs discutent le mécanisme sous-jacent à la production de ces potentiels et leur signification fonctionnelle possible.
Electroencephalography and Clinical Neurophysiology 01/1979;
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ABSTRACT: BAERs were recorded in a patient who suffered spontaneous cardio-respiratory arrest after testing had begun. During the arrest the BAERs initially decreased in amplitude and then could not be recorded. After restoration of cardiac activity there was immediate recovery of waves I and II. Subsequent potentials also immediately reappeared but they did not recover their original peak latency values during the 50 min following resuscitation.RésuméLes réponses évoquées auditives du tronc cérébral (REATC) ont été recueillies chez un patient ayant présenté un arrêt cardio-respiratoire spontané aprés que l'examen ait commencé. Pendant l'arrêt, l'amplitude des REATC a diminué jusqu'à ne plus permettre leur enregistrement. Après reprise de l'activité cardiaque, la restauration des ondes I et II a été immédiate. Les ondes plus tardives, bien qu'ayant réapparu immédiatement n'ont pas retrouvé la latence de pic originale, ceci pendant les 50 min qui ont suivi la réanimation.
Electroencephalography and Clinical Neurophysiology.
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ABSTRACT: Magnetic coil (MC) stimulation percutaneously of human occipital cortex was tested on perception of 3 briefly presented, randomly generated alphabetical characters. When the visual stimulus-MC pulse interval was less than 40–60 msec, or more than 120–140 msec, letters were correctly reported; at test intervals of 80–100 msec, a blur or nothing was seen. Shifting the MC location in the transverse and rostro-caudal axes had effects consistent with the topographical representation in visual cortex, but incompatible with an effect on attention or suppression from an eyeblink. The MC pulse probably acts by eliciting IPSPs in visual stimulus.
Electroencephalography and Clinical Neurophysiology/Evoked Potentials Section.
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ABSTRACT: Human transcallosal responses (TCRs) were elicited by focal magnetic oil (MC) stimulation of homologous sites in contralateral frontal cortex and compared with those to focal anodic stimulation. With MC stimulation, the TCR consisted of an initially positive wave with an onset latency of 8.8–12.2 msec, a duration of 7–15 msec, and an amplitude which reached up to 20 μV, sometimes followed by a broad low amplitude negative wave. With anodic stimulation, a similar response was obtained in which the positive wave was similar in latency and maximum amplitude, but had a greater duration. With anodic stimulation, not only was the TCR threshold below that for contralateral movement, but it reached substantial size at intensities below motor threshold. With MC stimulation, contralateral arm movement and scalp corticomotor potentials were observed when the MC was displaced posteriorly towards the central sulcus. Unlike with anodic stimulation, the MC evoked TCR was usually not preceded by a prominent EMG potential from temporalis muscle and was not associated with subject discomfort.The TCR provides unique information concerning the functional integrity of callosal projection neurons, their axons and transsynaptic processes in recipient cortex. This information may prove useful in the evaluation of intrinsic cerebral mechanisms and in establishing cortical viability.
Electroencephalography and Clinical Neurophysiology
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ABSTRACT: In a longitudinal neonatal study, biweekly EEGs and summed auditory evoked responses (AERs) were recorded during sleep from 23 premature infants between the ages of 28 and 41 weeks post-conception. Seventy-eight EEG tracings were obtained and 60–74 min of each were visually analyzed. Each 20 sec epoch was classified into one of 6 EEG patterns according to specific criteria relating to amplitude, frequency, and persistence or intermittancy of activity. With increasing post-conceptional age, the relative and absolute occurrences of 3 patterns decreased and 2 patterns increased significantly in a general linear fashion.During each EEG session, 9–12 summed AERs to loud click stimuli were recorded from the vertex with combined ears as the reference electrode. The amplitude and latency of the N1 and P2 potentials were, in general, positively related to 3 intermittent, relatively immature EEG patterns, and negatively related to a high voltage continuous pattern, but significant relationships were noted mainly in subjects older than 34 weeks post-connection. Post-conceptional and gestational age but not post-natal age influenced the relationship between EEG patterns and AER measurements. The average regression coefficients between AER measurements and some EEG patterns were determined for every 2 week age period permitting a quantitative estimate of these relationships related to age post-conception. The intra-subject, intra-recording variability in amplitude and latency of 2 major waves of the neonatal AER recorded from premature infants was therefore related to two measurable variables, background EEG and age post-conception.RésuméAu cours d'études néo-natales longitudinales des EEG bi-hebdomadaires et des AERs sommés ont été enregistrés au cours du sommeil chez 23 enfants prématurés de 28 à 41 semaines d'âge conceptionnel. Soixante dix-huit tracés EEG ont été obtenus dont 60 à 74 min ont été analysées visuellement pour chacun d'eux. Chaque époque de 20 sec a été classée en l'un des 6 patterns EEG définis suivant des critères spécifiques tenant compte de l'amplitude, de la fréquence et de la perisistance ou de l'intermittence de l'activité. Avec l'accroissement de l'âge post-conceptionnel les survenues relatives et absolues de 3 de ces patterns diminuent et 2 patterns augmentent significativement d'une façon généralement linéaite.Au cours de chaque session EEG, 9 à 12 réponses évoquées auditives sommées à des stimuli sonores graves ont été enregistrées au niveau du vertex relié à des électrodes de référence situćes sur les oreilles. L'amplitude et la latence des potentiels N1 et P2 sont en général liées positivement à 3 des patterns EEG intermittents relativement immatures et de façon négative à un pattern continu de haut voltage, mais des relations significatives ont été notées principalement chez des sujets âgés de plus de 34 semaines d'âge post-conceptionnel. L'âge gestationnel et postconceptionnel influence les relations entre les patterns EEG et les mesures des AERs mais non l'âge post-natal. Les coefficients moyens de régression entre les mesures des AERs et certains patterns EEG ont été déterminés pour chaque période d'âge de deux semaines, permettant une estimation quantitative de ces relations par rapport à l'âge post-conceptionnel. La variabilité intra-sujet et intra-enregistrement de l'amplitude et de la latence des deux ondes principales de l'AER néo-natal enregistrée chez des enfants prématurés est ainsi liée à deux variables mesurables, l'activité de fond EEG et l'âge post-conceptionnel.
Electroencephalography and Clinical Neurophysiology.
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ABSTRACT: Spine and scalp somatosensory evoked potentials (SEPs) to peroneal nerve stimulation were recorded from 20 normal subjects using 1 restricted and 3 open frequency filter bandpasses. Spine to spine and spine to scalp propagation velocities were calculated. Of those recording parameters investigated, optimal recordings were obtained using an open bandpass (5–1500 or 30–1500 Hz) and recording from 3 surface spine bipolar channels and 1 scalp bipolar channel. This method was then investigated in 40 patients with disease of the spinal cord and peripheral nervous system. Focal spinal cord compressive lesions generally resulted in slowing of spine to spine and spine to scalp propagation velocities. Diffuse or multifocal lesions of the spinal cord generally resulted in the absence of scalp responses. Although there was no consistent correlation of the SEP findings with the sensory exam, there was a correlation of the SEP findings with the clinical prognosis.RésuméDes potentiels évoqués somatosensoriels (PES) de moelle et de scalp, à la stimulation du nerf péronier ont été enregistrés chez 20 sujets normaux en utilisant des filtres de fréquence l'un avec bande passante restreinte, 3 autres avec bandes ouvertes. Les vitesses de conduction à l'intérieur de la moelle (d'apophyse à apophyse) et de la moelle au scalp ont été calculées. Pour ces paramètres étudiés, les meilleurs enregistrements ont été obtenus en utilisant une bande passante ouverte (5–1500 ou 30–1500 Hz) et l'enregistrement en surface des apophyses par 3 canaux bipolaires et 1 canal bipolaire sur le scalp. Cette méthode a ensuite étéétudiée chez 40 patients avec atteinte de la moelle épinière ou du système nerveux périphérique. Des lésions par compression focale de la moelle ont généralement entraîné un ralentissement de la vitesse de conduction à l'intérieur de la moelle et de la moelle au scalp. Des lésions diffuses ou multiples de la moelle ont entraîné une absence de réponse sur le scalp. Il n'y avait aucune relation consistante entre ces résultats sur les PES et l'examen de capacité sensorielle, en revanche, une relation existait entre les résultats des PES et le pronostic clinique.
Electroencephalography and Clinical Neurophysiology/Evoked Potentials Section.
