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P421 Metabolic changes produced by repetitive magnetic brain stimulation
Poster Session: Motor Evoked Potentials tremor in comparison to that of non-parkinsonian tremors. In this connection the author come to the conclusion that the obtained results can help the nosometricion of the PD (p < 0.05), PS (p < 0.05) and ET (p < 0.02).
Motor Evoked Potentials [P~
MATHEMATICALMODELLING OF EDDY CURRENTS IN HUMAN BRAIN DURING TMS
A. Krawczyk, S. Wiak, T. Zyss. Institute of Electrical Engineering,
Warsaw, Poland The paper deals with the problem of how to model eddy currents in neural cells in human brain while the transcranial magnetic stimulation (TMS) is considered. The magnetic stimulation uses low frequency pulse magnetic field in order to induce eddy currents in brain space. The value of current density which is required to occur in neural cells is somehow known, thus one needs to predict the magnetic field causes such a current. It can be done experimentally but then a lot of experiments should be carried out on physical models as well as on human subjects. This is very cumbersome way and we suggest that mathematical modelling should be employed here. The human brain can be modelled as a multilayer sphere and it is subjected to time-varying magnetic field that is homogenous. Prescribing values of electrical parameters to each particular layer, one establishes the mathematical model which is described by set of partial differential equations. In the paper such a model has been described and this is the first step. The next step is to solve this model and in order to do it the one of numerical methods should be applied. For the purpose considered, the finite element method has been used and the method is oriented towards some specific features of the brain. The numerical method as well as the results of calculations are presented.
DESIGN AND INSTRUMENTATION OF A REPETITIVE RAPID RATE MAGNETIC STIMULATOR A. Domino, A. Krawczyk, P. Kwasnowski, J. Waszczyszyn, T. Zyss.
Institute of Electrotechnics, Warsaw, Poland The repetitive rapid-rate transcranial magnetic stimulation (rr-TMS) opens totally new areas of interests in neurophysiology. This method is capable of stimulating at rates similar to those used for direct electrical stimulation. The currently brand and serially made magnetic stimulators (Dantec Mag Pro and Cadwell Rapid-Rate Magnetic Stimulator) used for the technique of rr-TMS have two major pitfalls. The devices may operate with frequencies of up to 30 (60) Hz, but at rates above 15-25 Hz, the power supply is incapable of charging the capacitors bank fully, and so the amplitude of the output drops. The second problem is that stimulation induces a rapid overheating of coil, which limits repetition rates and the total stimulation time. At our laboratory, we have begun a program to develop magnetic stimulator for rr-TMS with following parameters: induction of magnetic field B = 1-2 T, frequency up to 100 Hz, total stimulation time up to 1-5 minutes. Stimulators of similar characteristics are unavailable - for technological reasons they are not manufactured. Three main activities are described: a) fabrication of prototype stimulator coils with water/oil cooling in closed system, b) developing a high power supply with a high voltage, high current switching element, c) developing an electronics controller.
~
REPETITIVE MAGNETIC STIMULATIONS OF THE RAT
Poul Jennum, Henrik Klitgaard. Department of Clinical Neurophysiology,
UniversiO, of Copenhagen, Denmark As repetitive transcranial magnetic stimulation (RTMS) has been reported to induce epileptic seizures we studied the effect of acute or chronic stimulations with RTMS on the induction of pentylenetetrazol (PTZ) induced clonic seizures in the rat. Male Wistar rats were stimulated with a stimulus frequency of 50 hz. The motor threshold (Tm) was determined by single transcranial stimuli. Acute stimulation was performed with a stimulus
373
intensity of 0.9 x Tm and 1.5 × Tm using a duration of the train of stimuli of five seconds. Chronic stimulation was performed with a duration of the train of stimuli of one and five seconds using a stimulusintensity of 1.8 × Tm. The stimulations was performed every day in 30 days. Time to onset of PTZ induced clonic seizure was determined after the acute or the last stimulation in chronic RTMS. Some rats showed facial contractions, chewing or head movements during or immediately after the stimulations, but none of the rats developed tonic or clonic seizures. Time to onset of PTZ clonic seizures was reduced in both groups receiving chronic RTMS with a stimulus duration of one and five seconds compared control rats, whereas no differences were observed in the rats receiving acute RTMS. These results suggest that acute RTMS does not affect the induction of clonic PTZ seizures, whereas chronic stimulations possess a facilatory effect. This indicates that chronic stimulation with RTMS especially if the stimulus intensity is further increased - may induce a kindling process in the rat.
~-2-~
METABOLICCHANGES PRODUCED BY REPETITIVE MAGNETIC BRAIN STIMULATION
A. Oliviero, V. Di Lazzaro, D. Restuccia, L. Ferrara, D. Iacono, F. Della Corte i, M.A. Pennisi i O. Piazza I p. Profice, P. Tonali. Institute of
Neurology, Catholic University, Rome; I Institute of Anesthesiology, Catholic University, Rome, Italy The hemodynamic effects of repetitive magnetic stimulation (RMS) of the human brain were investigated by several authors that reported an increase of the cerebral blood flow (CBF). CBF is closely coupled with brain metabolism. To evaluate if CBF changes induced by RMS are associated with metabolic activation we measured the brain oxygen availability and consumption before and after RMS using NIRS (Near Infra-Red Spectroscopy; CRITIKON Cerebral Redox Research Monitor 2001). NIRS is a non invasive technique based on the ability of near infrared light (650-1000 nm) to pass through tissues. We studied 10 healthy volunteers and evaluated cerebral variation in HHb, HbO2, and Cit aa3 correlated to magnetic stimulation. The M R S probe was placed on motor and premotor areas. Magnetic stimulation was performed using a Magstim 200 (Novamelrix, UK). Thirty stimuli (100% of the maximal stimulator output; 0.25 Hz) were delivered through a figure of 8 coil over the premotor and motor cortex. The data averaging of 10 minutes recording before and of 5 minutes after the magnetic stimulation were recorded. Immediately after stimulation a significant increase in HbO2 and a decrease in Cit aa3 was observed (p < 0.05). Our data suggest that RMS induces metabolic activation of the cerebral cortex together with an increase of CBE
[ - P ' 4 ~ STIMULATIONOF PERIPHERAL NERVES USING A NOVEL MAGNETIC COIL F. Binkofski l, j. Classen 2, R. Benecke 3. ~Dept. of Neurology,
Heinrich-Heine-University, Dusseldorf, Germany; "National Institutes of Health, Bethesda, USA; 3 University of Rostock, Germany The clinical use of magnetic peripheral nerve stimulation has been limited because of its inability to produce maximal compound action potentials (CMAP) and of the difficulty to assess the exact site of nerve excitation. We characterized the electrophysiological properties of a novel figure-8 magnetic coil (Magstim Co.) differing from conventional coils in size (O of one wing 25 mm) and peak magnetic field (4.6 T). Stimulation of motor nerves of upper and lower extremities (N. ulnaris, N. medianus, N, radialis, N. tibialis, N. peroneus, N. femoralis) was compared with conventional electric stimulation in 4 healthy volunteers and in 4 patients with conduction block at the ulnar groove. Single magnetic pulses were delivered through the coil connected with a magnetic stimulator (Magstim 200, Novametrix). Maximal CMAP could be elicited by magnetic stimulation in each nerve of the upper and lower extremity stimulated. Amplitudes and shapes of CMAPs, as well as motor conduction velocities were comparable with magnetic and electrical stimulation within 5% range. The virtual cathode of the small butterfly coil was empirically located at the anterior meeting point of the windings. Variability of latencies was minimal (< 0.1%) in maximal CMAPs. The differences in the latencies between the magnetic and electric stimulation did not exceed 0.1 ms. The conduction velocities obtained over shorter distances at the ulnar groove and over the caput fibulae were also similar with magnetic and electric stimulation in
Motor Evoked Potentials [P~
MATHEMATICALMODELLING OF EDDY CURRENTS IN HUMAN BRAIN DURING TMS
A. Krawczyk, S. Wiak, T. Zyss. Institute of Electrical Engineering,
Warsaw, Poland The paper deals with the problem of how to model eddy currents in neural cells in human brain while the transcranial magnetic stimulation (TMS) is considered. The magnetic stimulation uses low frequency pulse magnetic field in order to induce eddy currents in brain space. The value of current density which is required to occur in neural cells is somehow known, thus one needs to predict the magnetic field causes such a current. It can be done experimentally but then a lot of experiments should be carried out on physical models as well as on human subjects. This is very cumbersome way and we suggest that mathematical modelling should be employed here. The human brain can be modelled as a multilayer sphere and it is subjected to time-varying magnetic field that is homogenous. Prescribing values of electrical parameters to each particular layer, one establishes the mathematical model which is described by set of partial differential equations. In the paper such a model has been described and this is the first step. The next step is to solve this model and in order to do it the one of numerical methods should be applied. For the purpose considered, the finite element method has been used and the method is oriented towards some specific features of the brain. The numerical method as well as the results of calculations are presented.
DESIGN AND INSTRUMENTATION OF A REPETITIVE RAPID RATE MAGNETIC STIMULATOR A. Domino, A. Krawczyk, P. Kwasnowski, J. Waszczyszyn, T. Zyss.
Institute of Electrotechnics, Warsaw, Poland The repetitive rapid-rate transcranial magnetic stimulation (rr-TMS) opens totally new areas of interests in neurophysiology. This method is capable of stimulating at rates similar to those used for direct electrical stimulation. The currently brand and serially made magnetic stimulators (Dantec Mag Pro and Cadwell Rapid-Rate Magnetic Stimulator) used for the technique of rr-TMS have two major pitfalls. The devices may operate with frequencies of up to 30 (60) Hz, but at rates above 15-25 Hz, the power supply is incapable of charging the capacitors bank fully, and so the amplitude of the output drops. The second problem is that stimulation induces a rapid overheating of coil, which limits repetition rates and the total stimulation time. At our laboratory, we have begun a program to develop magnetic stimulator for rr-TMS with following parameters: induction of magnetic field B = 1-2 T, frequency up to 100 Hz, total stimulation time up to 1-5 minutes. Stimulators of similar characteristics are unavailable - for technological reasons they are not manufactured. Three main activities are described: a) fabrication of prototype stimulator coils with water/oil cooling in closed system, b) developing a high power supply with a high voltage, high current switching element, c) developing an electronics controller.
~
REPETITIVE MAGNETIC STIMULATIONS OF THE RAT
Poul Jennum, Henrik Klitgaard. Department of Clinical Neurophysiology,
UniversiO, of Copenhagen, Denmark As repetitive transcranial magnetic stimulation (RTMS) has been reported to induce epileptic seizures we studied the effect of acute or chronic stimulations with RTMS on the induction of pentylenetetrazol (PTZ) induced clonic seizures in the rat. Male Wistar rats were stimulated with a stimulus frequency of 50 hz. The motor threshold (Tm) was determined by single transcranial stimuli. Acute stimulation was performed with a stimulus
373
intensity of 0.9 x Tm and 1.5 × Tm using a duration of the train of stimuli of five seconds. Chronic stimulation was performed with a duration of the train of stimuli of one and five seconds using a stimulusintensity of 1.8 × Tm. The stimulations was performed every day in 30 days. Time to onset of PTZ induced clonic seizure was determined after the acute or the last stimulation in chronic RTMS. Some rats showed facial contractions, chewing or head movements during or immediately after the stimulations, but none of the rats developed tonic or clonic seizures. Time to onset of PTZ clonic seizures was reduced in both groups receiving chronic RTMS with a stimulus duration of one and five seconds compared control rats, whereas no differences were observed in the rats receiving acute RTMS. These results suggest that acute RTMS does not affect the induction of clonic PTZ seizures, whereas chronic stimulations possess a facilatory effect. This indicates that chronic stimulation with RTMS especially if the stimulus intensity is further increased - may induce a kindling process in the rat.
~-2-~
METABOLICCHANGES PRODUCED BY REPETITIVE MAGNETIC BRAIN STIMULATION
A. Oliviero, V. Di Lazzaro, D. Restuccia, L. Ferrara, D. Iacono, F. Della Corte i, M.A. Pennisi i O. Piazza I p. Profice, P. Tonali. Institute of
Neurology, Catholic University, Rome; I Institute of Anesthesiology, Catholic University, Rome, Italy The hemodynamic effects of repetitive magnetic stimulation (RMS) of the human brain were investigated by several authors that reported an increase of the cerebral blood flow (CBF). CBF is closely coupled with brain metabolism. To evaluate if CBF changes induced by RMS are associated with metabolic activation we measured the brain oxygen availability and consumption before and after RMS using NIRS (Near Infra-Red Spectroscopy; CRITIKON Cerebral Redox Research Monitor 2001). NIRS is a non invasive technique based on the ability of near infrared light (650-1000 nm) to pass through tissues. We studied 10 healthy volunteers and evaluated cerebral variation in HHb, HbO2, and Cit aa3 correlated to magnetic stimulation. The M R S probe was placed on motor and premotor areas. Magnetic stimulation was performed using a Magstim 200 (Novamelrix, UK). Thirty stimuli (100% of the maximal stimulator output; 0.25 Hz) were delivered through a figure of 8 coil over the premotor and motor cortex. The data averaging of 10 minutes recording before and of 5 minutes after the magnetic stimulation were recorded. Immediately after stimulation a significant increase in HbO2 and a decrease in Cit aa3 was observed (p < 0.05). Our data suggest that RMS induces metabolic activation of the cerebral cortex together with an increase of CBE
[ - P ' 4 ~ STIMULATIONOF PERIPHERAL NERVES USING A NOVEL MAGNETIC COIL F. Binkofski l, j. Classen 2, R. Benecke 3. ~Dept. of Neurology,
Heinrich-Heine-University, Dusseldorf, Germany; "National Institutes of Health, Bethesda, USA; 3 University of Rostock, Germany The clinical use of magnetic peripheral nerve stimulation has been limited because of its inability to produce maximal compound action potentials (CMAP) and of the difficulty to assess the exact site of nerve excitation. We characterized the electrophysiological properties of a novel figure-8 magnetic coil (Magstim Co.) differing from conventional coils in size (O of one wing 25 mm) and peak magnetic field (4.6 T). Stimulation of motor nerves of upper and lower extremities (N. ulnaris, N. medianus, N, radialis, N. tibialis, N. peroneus, N. femoralis) was compared with conventional electric stimulation in 4 healthy volunteers and in 4 patients with conduction block at the ulnar groove. Single magnetic pulses were delivered through the coil connected with a magnetic stimulator (Magstim 200, Novametrix). Maximal CMAP could be elicited by magnetic stimulation in each nerve of the upper and lower extremity stimulated. Amplitudes and shapes of CMAPs, as well as motor conduction velocities were comparable with magnetic and electrical stimulation within 5% range. The virtual cathode of the small butterfly coil was empirically located at the anterior meeting point of the windings. Variability of latencies was minimal (< 0.1%) in maximal CMAPs. The differences in the latencies between the magnetic and electric stimulation did not exceed 0.1 ms. The conduction velocities obtained over shorter distances at the ulnar groove and over the caput fibulae were also similar with magnetic and electric stimulation in