List of publications

List of abbreviations

1 Introduction

2 Basic principles and history

3 Modelling of magnetic stimulation

3.1 The induced electric field
3.2 Electrophysiology of excitation
3.3 Locus of excitation

4 Instrumentation

4.1 Available types of stimulators and coils
4.2 About optimisation of the stimulator
4.3 Coil construction and fabrication
4.4 Focality of stimulation

5 New advanced techniques

5.1 Computer-assisted TMS
5.2 Multichannel TMS
5.3 TMS-compatible EEG

6 Safety

6.1 Known adverse effects
6.2 Guidelines

7 Applications

7.1 Clinical use
7.2 Basic brain research
7.3 Therapeutic use

8 Summary

List of references

Summary of publications

List of publications

This thesis consists of an overview and the following publications:

  1. Jarmo Ruohonen, Paolo Ravazzani and Ferdinando Grandori. An analytical model to predict the electric field and excitation zones due to magnetic stimulation of peripheral nerves. IEEE Transactions on Biomedical Engineering 42, 158-161, 1995.
  2. Jarmo Ruohonen, Paolo Ravazzani, Jan Nilsson, Marcela Panizza, Ferdinando Grandori and Gabriella Tognola. A volume-conduction analysis of magnetic stimulation of peripheral nerves. IEEE Transactions on Biomedical Engineering 43, 669–678, 1996.
  3. Paolo Ravazzani, Jarmo Ruohonen, Ferdinando Grandori and Gabriella Tognola. Magnetic stimulation of the nervous system: induced electric field in unbounded, semi-infinite, spherical, and cylindrical media. Annals of Biomedical Engineering 24, 606–616, 1996.
  4. Jarmo Ruohonen, Marcela Panizza, Jan Nilsson, Paolo Ravazzani, Ferdinando Grandori and Gabriella Tognola. Transverse-field activation mechanism in magnetic stimulation of peripheral nerves. Electroencephalography and clinical Neurophysiology 101, 167–174, 1996.
  5. Jarmo Ruohonen, Paolo Ravazzani, Risto Ilmoniemi, Giuseppe Galardi, Jan Nilsson, Marcela Panizza, Stefano Amadio, Ferdinando Grandori and Giancarlo Comi. Motor cortex mapping with combined MEG and magnetic stimulation. Electroencephalography and clinical Neurophysiology Supplement 46, 317–322, 1996.
  6. Jarmo Ruohonen, Juha Virtanen and Risto Ilmoniemi. Coil optimization for magnetic brain stimulation. Annals of Biomedical Engineering 25, 840–849, 1997.
  7. Jarmo Ruohonen and Risto Ilmoniemi. Focusing and targeting of magnetic brain stimulation using multiple coils. Medical & Biological Engineering & Computing 36, 297-301, 1998.
  8. Risto Ilmoniemi, Juha Virtanen, Jarmo Ruohonen, Jari Karhu, Hannu Aronen, Risto Näätänen and Toivo Katila. Neuronal responses to magnetic stimulation reveal cortical reactivity and connectivity. NeuroReport 8, 3537-3540, 1997.

List of abbreviations

CT Computed tomography
EEG Electroencephalography
EMG Electromyography
EP Evoked potential
ERP Event-related potential
ES Electrical stimulation
FEM Finite element method
fMRI Functional magnetic resonance imaging
MEG Magnetoencephalography
MEP Motor-evoked potential
MNE Minimum-norm estimation
MRI Magnetic resonance imaging
MT Motor threshold
NIRS Near-infrared spectroscopy
PET Positron emission tomography
PNS Peripheral nervous system
rTMS Repetitive transcranial magnetic stimulation
SPECT Single photon emission computed tomography
TCES Transcranial electrical stimulation
TMS Transcranial magnetic stimulation
3D Three-dimensional

1 Introduction

    The use of non-invasive neuroimaging has increased explosively in recent years. Details of the functioning of the human brain are revealed by measuring electromagnetic fields outside the head or metabolic and hemodynamic changes using electroencephalography (EEG), magnetoencephalography (MEG), positron emission tomography (PET), near-infrared spectroscopy (NIRS) or functional magnetic resonance imaging (fMRI). This thesis deals with transcranial magnetic brain stimulation (TMS), which is a direct way of manipulating and interfering with the function of the cortex, thus complementing conventional neuroimaging.

    Brain stimulation with TMS is achieved from the outside of the head using pulses of electromagnetic field that induce an electric field in the brain. TMS has numerous applications in the study, diagnosis and therapy of the brain. TMS can either excite the cortex or disturb its function. The observed excitatory effects are normally muscle twitches or phosphenes, whereas in the "lesion" mode TMS can transiently suppress perception or interfere with task performance.

    The aim of this thesis was to develop physical understanding of magnetic stimulation and to build models that could provide new insights for utilising the technique. For this purpose, two principal issues had to be addressed: 1) macroscopic electromagnetic fields in the tissue, for which models are developed in Publications I-III, and 2) understanding of the neuronal responses, considered in Publications IV and V. Then, the models developed were used as a basis for engineering modifications that would increase the utility of TMS, the emphasis being on the optimisation of the stimulating coils (Publication VI) and on the use of multiple coils in a whole-scalp array (Publication VII). Publication VIII presents the concurrent use of TMS and high-resolution EEG, showing that the combination is effective for mapping the functional connections in the brain.

    The models and procedures were developed in parallel with the design and construction of TMS instrumentation for computer-assisted stimulation.

2 Basic principles and history

2.1 Basic principles

    Neurones can be excited by externally applied time-varying electromagnetic fields. In TMS, excitation is achieved by driving intense pulses of current I(t) through a coil located above the head. The source of activation is the electric field E induced in the tissue, obtained from Faraday’s law:

    , (1)

    where B is the magnetic field produced by the coil, given by the Biot-Savart law:

    . (2)

    The integration is performed with the vector dl along the coil windings C and m0 = 410-7 H/m is the permeability of free space.

    The pulses of current are generated with a circuit containing a discharge capacitor connected with the coil in series by a thyristor. With the capacitor first charged to 2-3 kV, the gating of the thyristor into the conducting state will cause the discharging of the capacitor through the coil. The resulting current waveform is typically a damped sinusoidal pulse that lasts about 300 ms and has a peak value of 5-10 kA. The electrical principles have been outlined, e.g., by Jalinous [72,73].

    Figure 1 summarises the chain of events in TMS. The induced E is strongest near the coil and typically stimulates a cortical area of a few centimetres in diameter. TMS pulses cause coherent firing of neurones in the stimulated area as well as changed firing due to synaptic input. At microscopic level, E affects the neurones’ transmembrane voltage and thereby the voltage-sensitive ion channels. Brain imaging tools can be used to detect the associated electrical currents and changes in blood flow of metabolism. In motor-cortex stimulation, peripheral effects can be observed as muscle activity with surface electromyography (EMG). Moreover, there may be behavioural changes, for instance, impaired task performance.

    Fig 1

    Figure 1. Principles of TMS. Current I(t) in the coil generates a magnetic field B that induces an electric field E. The lines of B go through the coil; the lines of E form closed circles. The upper-right drawing illustrates schematically a lateral view of the precentral gyrus in the right hemisphere. Two pyramidal axons are shown, together with a typical orientation of the intracranial E. The electric field affects the transmembrane potential, which may lead to local membrane depolarisation and firing of the neurone. Pyramidal axons are likely stimulated near bends, as illustrated here, but also other mechanisms exist (see, section 3.2) and other neurones may be stimulated. Macroscopic responses can be detected with functional imaging tools (EEG, PET, fMRI, NIRS and SPECT = single photon emission computed tomography), with surface EMG, or as behavioural changes.

2.2 History of non-invasive brain stimulation

3 Modelling of magnetic stimulation

3.1 The induced electric field

3.1.1 The relationship between TMS and MEG

3.1.2 Field shaping with multiple coils

3.1.3 No 3D focusing

3.1.4 Spherical head model

3.1.5 Models of the limbs and the spine

3.1.6 Realistic models

3.2 Electrophysiology of excitation

3.2.1 Cable model

3.2.2 Geometrical factors affecting the excitability

3.2.3 Strength-duration relationship


3.3 Locus of excitation

3.3.1 Distal nerve stimulation

3.3.2 Stimulation of the spine and spinal roots

3.3.3 Brain stimulation


4 Instrumentation

4.1 Available types of stimulators and coils

    There are two stimulator types: single-pulse devices and repetitive TMS (rTMS) devices that generate trains of stimuli at 1-60 Hz. Commercial equipment are provided by three main manufacturers: Cadwell Laboratories, Inc. (Kennewick, USA), Magstim Company, Ltd. (Whitland, UK) and Medtronic Dantec NeuroMuscular (Skovlunde, Denmark).

    Dantec and Magstim have add-on modules to their single-pulse devices that can be used to drive one coil with two to four pulses separated by 1 ms to 1 s. These devices are called paired-pulse or quadruple-pulse stimulators. Two stimulator units can be used together to drive separate coils to stimulate different regions at the same time or in quick succession. This TMS mode is called double-pulse TMS.

    The rTMS devices operate at 10-60 Hz at 40–100% of the maximum intensity of single pulses. The duration of sustained operation is limited by coil heating to 100–1,000 pulses at maximum power. With proper coil cooling, the duration of the stimulus train can be made unlimited. Cadwell makes coils with continuous water cooling, whereas Magstim makes air-cooled coils.

    The current pulse properties vary among manufacturers. Three pulse

    waveforms are available: i) monophasic, i.e., rapid rise from zero to peak and slower decrease to zero; ii) biphasic, i.e., one damped sine pulse; and iii) multiple-cycle damped sine pulse. The Dantec MagPro model is equipped with a switch that allows selection between monophasic and biphasic pulse shapes. Most of the Magstim devices use a monophasic pulse. Cadwell devices generate a biphasic pulse, although earlier MES-10 units had a multiple-cycle sine pulse. Rapid charging of the capacitors requires that the rTMS devices use biphasic currents. The initial direction of the current in the coil can be switched in some Dantec stimulators.

    The current pulse duration is typically 200-300 ms for biphasic and about 600 ms for monophasic pulses. The peak current generated by the commercial devices is 2-8 kA. Operating voltage of TMS devices is typically 2-3 kV and the power consumption 2–3 kW at maximum stimulus intensity.

    The standard stimulating coils are either circular or 8-shaped. Some Cadwell coils are drop-shaped with one rectangular edge (Focalpoint™); the benefit from the shape is questionable. Magstim sells 8-shaped cone coils with angled wings that fit the head and Dantec has a similar circular cone coil. The cone coils are somewhat more effective than planar ones, but at the cost of focality. The diameter of the coils ranges from 50 to 150 mm. The coils are usually wound of 10–30 concentric turns of rectangular copper wire (gauge, e.g., 1×5 mm2), resulting in an inductance of 15-30 mH.

    Prototype four-leaf coils have been presented with four coplanar wings [140] suitable for peripheral stimulation. Another new idea is the so-called half-toroid ("slinky") coil, which is wound with the turns in different angles while maintaining the tangency along one edge [134,171].

    The TMS equipment developed and used at the BioMag Laboratory has two independent stimulator channels that are controlled by a computer. The maximum stimulus repetition rate is 1 Hz at full intensity and the system operates at 3 kV. The coils are 8-shaped and water-cooled and their outer diameter ranges from 30 to 50 mm. The current pulse shape is biphasic with rise time ranging between 70 and 100 ms depending on the coil.

Figure of merit Quantity to be minimised Importance
Stimulator's efficacy Input power Stimulus repetition rate
Coil's efficacy Peak magnetic energy Price, weight and size of
Coil heating Temperature rise / pulse Duration of pulse trains and
of sustained operation
Focality Area bound by the half-
maximum of E
Spatial resolution

4.2 About optimisation of the stimulator

    Publication VI addresses the optimisation of the TMS coil and the selection of the power electronics components. The optimal design depends on the application and how different qualities are weighted. Optimisation should hence begin by selecting the quality criteria and the weighting rules for computing the costs. The key task is to identify the members of three variable categories:

    · constraints, e.g., safety regulations
    · quantity/quantities to be minimised, e.g., fabrication costs
    · adjustable parameters, e.g., coil dimensions.

    The most important physical quantities that determine the quality of magnetic stimulators are listed in Table 1; Publication VI gives the formulas to calculate their values. Unfortunately, the quantities are competing, e.g., focal coils have a lower efficacy than otherwise similar coils.

    As a rule, the coil is the main item to be optimised. Publication VI focused on minimising the stimulator’s power consumption by changing the coil’s winding structure and wire gauge. The procedure could improve especially the efficacy of small coils by winding them into solenoids instead of flat spirals. This procedure has been applied to design small water-cooled coils for the TMS equipment at the BioMag Laboratory. In the literature, the results of coil optimisation have remained of little use since

    the definition of the "optimum" has been omitted [86,105,116]. In one study, a mathematical method was used to maximise the focality by changing the coil shape [141]. The resulting most focal coil shape was found to be roughly 8-shaped.

4.3 Coil construction and fabrication

    Coil design must always be taken into account when constructing TMS equipment. Effective design is hindered by the high amount of energy that must be driven through the coil in a very brief time. In brain stimulation this energy is about 500 J, which would suffice to lift a weight of 1 kg to a height of 50 m.

    The intense submillisecond current pulses cause strong expanding and compressing forces in the coil. The forces are even tens of kilonewtons and thus the cross-sectional wire size must be large and the potting material resistant. The forces are proportional to the peak energy in the coil. Optimally, the coils are wound so that the forces are compressing in the direction where the coil touches the head.

    In rTMS, an additional trouble is that tens of W/Hz of power is dissipated in the coil. The coil being usually placed against the head, according to the safety standards its surface temperature must not exceed 41ºC. One should also avoid high wire temperatures (100-120ºC), since these deteriorate insulation, decreasing safety and the coil’s life time. Built-in temperature sensors and effective cooling can be used to guard against excessive temperatures.

    Problems with power consumption and coil heating can be alleviated by reducing the coil’s resistance, determined by the wire gauge and coil geometry [Publication VI]. When the cross-sectional dimensions of the wire exceed 1 to 2 mm, the skin and proximity effects change the current distribution in the wire [154], and may increase the direct current resistance significantly. Striped, foil or litz wire can be used to reduce the skin and proximity effects. The skin effect causes the current to flow mainly on the surface of thick wire; hence, tubular wire can be used without affecting the resistance. Liquid coolant can then flow inside the wire, as it is done in the BioMag Laboratory’s TMS coils.

    The voltage over the coil’s connectors may be 3 kV and depending on how the coil is wound the voltage across adjacent turns can be from 200

    to 1,000 V. The wire insulation (varnish, film, mylar paper) must have the necessary dielectric strength and resist chemical solvents of the potting material (epoxy resin, polyurethane foam). The electrical and liquid coolant contacts must be tightly fastened and well insulated.

    The intense current gives rise to a clicking sound from the coil, cables and capacitor, exceeding 100 dB near the coil. To reduce the noise from the coil, researchers at the BioMag Laboratory are investigating the possibility to encapsulate the coil in vacuum or place a vacuum shield between the coil and the subject [67].

4.4 Focality of stimulation


5 New advanced techniques

5.1 Computer-assisted TMS

    In currently available commercial TMS systems the coil is positioned manually above the head, the location of the coil being determined on the basis of skull landmarks. Although TMS is used enthusiastically, users strongly criticise the difficulties of focusing the activation in desired targets. Because of the large coils and manual placement, the reproducibility and repeatability are often poor.

    Computer-assisted stereotactic TMS is under development at the HUCH BioMag Laboratory. The essence of computer-assisted TMS is an intelligent user-interface, by aid of which the operator may plan, perform, monitor and document the experiments in a controlled and reproducible manner. An important part of the software is the calculation of the electric field induced in the brain. Stereotactic stimulus targeting is made possible by 3D localisation of the coil/coils with respect to the head and by displaying the MR images on the computer screen. The BioMag system is realised using a motorised coil holder and frameless stereotaxy based on a 3D electromagnetic pointer. The concept of computer-assisted TMS is illustrated in Fig. 6.

    Figure 6. Computer-assisted TMS. System comprises gantry, patient chair, computer, control and power electronics circuits and power source. One or a few coils may be used, or an array of many coils.

    Computer-assisted TMS enables new useful concepts for brain research. Stereotactic targeting allows stimulation of a given location in the cortex or a given anatomical structure. For instance, the functional organisation of the brain can be studied with a greatly improved spatio-temporal resolution. The stimulus may be modified both spatially and temporally

    during tasks in order to identify the cortical areas that are necessary for the task and the order in which they process the data.

    In computer-assisted TMS, information from brain imaging techniques can be used in planning the stimulation parameters as well as in the display and interpretation of the results. In particular, digitisation of the coil position on the MRI provides anatomical information of the stimulated location [83,102], which enables stereotactic TMS, that is, precise stimulation of selected anatomical locations. Stereotaxy allows selection of the stimulation intensity level on the basis of calculating the actually induced electric field in the target area instead of defining it as a percentage of the maximum stimulator output or motor threshold. Frameless stereotaxy system and stimulus targeting software have been realised in the BioMag Laboratory.

    The merging of TMS with functional neuroimaging tools provides additional benefits. The concurrent use of TMS with PET, fMRI and EEG has already been demonstrated for the study of connectivity maps and the reactivity of the stimulated cortex [18,127,Publication VIII]. Likewise, MEG can give the location of specific cortical functional units in advance.

    5.2 Multichannel TMS

    Multichannel TMS [64], theoretically examined in Publication VII, refers to the use of multiple independently controlled stimulating coils. It has a number of advantages over stimulation with one coil, offering an alternative solution for stereotactic TMS. One can stimulate multiple loci in one shot, or with short delay between the pulses. The operator can also alleviate the nuisance caused by the activation of undesired structures by suppressing the field at selected locations. Moreover, it is possible to quickly scan brain regions since the coils need not to be moved during scanning. The use of multiple coils improves the mapping resolution since the stimulating field can be made more concentrated. The shaping of the field can be effectively solved using the MNE procedure described in Publication VII and chapter 3.1.2.

    Publication VII analysed the properties of multichannel TMS; Fig. 7 shows some of the results. Coil size is an important factor that determines the focality and the power required to obtain a given stimulation intensity; the number of coils is less important, yet significant. The focality depends

    on the location of the target point with respect to the coils, being the best below points where the coils touch each other. Multichannel TMS can clearly improve the focality; with the present commercial single-coil devices the focality is 10-15 cm2, while levels of a few cm2 are attainable with multiple small coils. The focality is improved at the cost of increased power consumption.


    Figure 7. Left: Focality of cap-shaped array as function of number of coils n. Coil diameter is between 15 and 40 mm. Right: Normalised power required to induce a given peak value of E. Adapted from Publication VII.

    Multichannel TMS can also be used to produce sham stimulation by selecting the coil currents so that the electric field induced in the brain is small, but the subjective sensations due to scalp stimulation and coil click can be predicted to be similar to real TMS [147].

    The main drawback of multichannel TMS is that it is much more expensive than computer-assisted stereotactic TMS with one coil. This is because the power electronics design as well as the power source and mechanical construction are more complicated.

5.3 TMS-compatible EEG



6 Safety

 6.1 Known adverse effects

    Some immediate side effects to TMS are known. Seizure induction is the most serious of them. Single-pulse TMS has produced seizures in patients [28,47,62,75], but never in healthy subjects. In epileptic patients, there is to date only one report of seizure definitely triggered by single-pulse TMS [28]. Instead, rTMS at rates of several Hz has caused seizures even in volunteers with no neurological problems or history of epilepsy [24,99,123,165].

    A frequent harmless, but uncomfortable, effect is a mild headache, which is probably caused by the activation of scalp and neck muscles. The headache may persist after the end of stimulation session and responds well to mild analgesics.

    TMS is accompanied by loud clicking sound from the coil that can exceed 100 dB near the coil [152]. Most sound energy is in the frequency range 2–7 kHz. The noise may exceed criteria limits for sensorineural hearing loss [31].

    It is assumed that harmful effects of TMS are related to the induced electric field, since the body tissue is transparent to low-frequency magnetic fields. Heating of the brain is of the order of 10-6 °C/pulse and unlikely to cause deleterious effects [5]. Theoretical maximum power dissipation from rTMS in the whole brain is about 3 mW/Hz [39]. Mild burns from scalp electrodes [123] can be avoided using special-designed electrodes [142].

    Many tests, including blood pressure, pulse rate, balance, gait and serum prolactin and cortisol levels [71,123,166], have revealed no statistically significant changes after TMS. The same is true for cognitive tests; naturally, naming and verbal fluency tasks can be transiently disturbed by TMS. Documented consistent changes include at least a lateralised effect on immune functions (T-lymphocytes) [4] and changes in thyroid-stimulating hormone levels after prefrontal stimulation [53].

    Spontaneous EEG following TMS has been found to be normal. Izumi et al. [69] reported slowing of the EEG at 150 ms post-TMS and other changes lasting 400-600 ms, but these findings are not necessarily relevant for the safety of TMS since similar changes are caused by sensory stimuli. Generally, EEG is not a good test of safety since it is not sensitive to mild or additive cellular dysfunction. However, monitoring of the EEG during rTMS may be useful in order to stop the experiment if abnormalities appear.

    The few existing histopathological studies have not found any definite TMS-related changes. In one study, rTMS (2,000 pulses at 20 Hz) was performed in two patients who were assigned to temporal lobectomies because of medically intractable epilepsy [48]. Histologic study of the surgical specimen did not show any lesions attributable to TMS. Most animal models have failed to find negative effects from TMS [169]. One study in rats reported microvacuolar changes when using very high stimulus intensities [94]; these findings have been criticised by other authors [163]. A study in the cat did not reveal any acute adverse changes following TMS, assessed by cortical blood flow, blood pressure and heart rate measurements [46].

6.2 Guidelines


7 Applications

7.1 Clinical use

7.2 Basic brain research

7.3 Therapeutic use


8 Summary

List of references

[1] Abdeen MA and Stuchly MA. Modeling of magnetic field stimulation of bent neurons. IEEE Trans Biomed Eng. 41, 1092-1095. 1994.

[2] Amassian VE, Cracco RQ, Maccabee PJ and Cracco JB. Cerebello-frontal cortical projections in humans studied with the magnetic coil. Electroenceph clin Neurophysiol. 85, 265-272. 1992.

[3] Amassian VE, Cracco RQ, Maccabee PJ, Cracco JB, Rudell A and Eberle L. Suppression of visual perception by magnetic coil stimulation of human occipital cortex. Electroenceph clin Neurophysiol. 74, 458-462. 1989.

[4] Amassian VE, Henry K, Durkin H, Chice S, Cracco JB, Somasundaram M, Hassan N, Cracco RQ, Maccabee PJ and Eberle L. Human immune functions are differentially affected by left-sided versus right-sided magnetic stimulation of temporo-parieto-occipital cortex. Neurology. 44 (Suppl 2), A133. 1994.

[5] Barker AT. An introduction to the basic principles of magnetic nerve stimulation. J Clin Neurophysiol. 8, 26-37. 1991.

[6] Barker AT, Freeston IL, Jalinous R and Jarratt JA. Clinical evaluation of conduction time measurements in central motor pathways using magnetic stimulation of the human brain. Lancet. 1, 1325-1326. 1986.

[7] Barker AT, Freeston IL, Jalinous R and Jarratt JA. Magnetic stimulation of the human brain and peripheral nervous system: an introduction and the results of an initial clinical evaluation. Neurosurgery. 20, 100-109. 1987.

[8] Barker AT, Garnham CW and Freeston IL. Magnetic nerve stimulation: the effect of waveform on efficiency, determination of neural membrane time constants and the measurement of stimulator output. In Levy WJ, Cracco RQ, Barker AT and Rothwell JC. Editors. Magnetic Motor Stimulation: Basic Principles and Clinical Experience. Amsterdam: Elsevier Science. 227-237. 1991.

[9] Barker AT, Jalinous R and Freeston I. Non-invasive magnetic stimulation of the human motor cortex. Lancet. 1, 1106-1107. 1985.

[10] Barlow HB, Kohn HL and Walsh EG. Visual sensations aroused by magnetic fields. Am J Physiol. 148, 372-375. 1947.

[11] Bartholow R. Experimental investigations into the functions of the human brain. Am J Med Sci. 67, 305-313. 1874.

[12] Basser PJ and Roth BJ. Stimulation of myelinated nerve axon by electromagnetic induction. Med Biol Eng Comput. 29, 261-268. 1991.

[13] Basser PJ, Wijesinghe R and Roth BJ. The activating function for magnetic stimulation derived from a three-dimensional volume conductor model. IEEE Trans Biomed Eng. 39, 1207-1210. 1992.

[14] Beckers G and Zeki S. The consequences of inactivating areas V1 and V5 on visual motion perception. Brain. 118, 49-60. 1995.

[16] Berardelli A, Inghilleri M, Cruccu G, Mercuri B and Manfredi M. Electrical and magnetic transcranial stimulation in patients with corticospinal damage due to stroke or motor neurone disease. Electroenceph clin Neurophysiol. 81, 389-396. 1991.

[17] Bickford RG and Fremming BD. Neural stimulation by pulsed magnetic fields in animals and man. 6th Int Conf Med Electr Biol Eng. Tokyo. Abstract 7-6. 1965.

[18] Bohning DE, Shastri A, Nahas Z, Lorberbaum JP, Andersen SW, Dannels WR, Haxthausen EU, Vincent DJ and George MS. Echoplanar BOLD fMRI of brain activation induced by concurrent transcranial magnetic stimulation. Invest Radiol. 33, 336-340. 1998.

[19] Brown P. Shocking safety concerns. Lancet. 348, 959. 1996.

[20] Brunholzl C and Claus D. Central motor conduction time to upper and lower limbs in cervical cord lesions. Arch Neurol. 51, 245-249. 1994.

[21] Caramia MD, Iani C and Bernardi G. Cerebral plasticity after stroke as revealed by ipsilateral responses to magnetic stimulation. Neuroreport. 7, 1756-1760. 1996.

[22] Carter N and Zee DS. The anatomical localization of saccades using functional imaging studies and transcranial magnetic stimulation. Curr Opin Neurol. 10, 10-17. 1997.

[23] Cerri G, De Leo R, Moglie F and Schiavoni A. An accurate 3-D model for magnetic stimulation of the brain cortex. J Med Eng Technol. 19, 7-16. 1995.

[24] Chen R, Gerloff C, Classen J, Wassermann EM, Hallett M and Cohen LG. Safety of different inter-train intervals for repetitive transcranial magnetic stimulation and recommendations for safe ranges of stimulation parameters. Electroenceph clin Neurophysiol. 105, 415-421. 1997.

[25] Chokroverty S. Magnetic Stimulation in Clinical Neurophysiology. Boston: Butterworth. 1990.

[26] Chokroverty S, Deutsch A, Guha C, Gonzalez A, Kwan P, Burger R and Goldberg J. Thoracic spinal nerve and root conduction: a magnetic stimulation study. Muscle Nerve. 18, 987-991. 1995.

[27] Chokroverty S, Flynn D, Picone M, Chokroverty M and Belsh J. Magnetic coil stimulation of the human lumbosacral vertebral column: site of stimulation and clinical applications. Electroenceph clin Neurophysiol. 89, 54-60. 1993.

[28] Classen J, Witte OW, Schlaug G, Seitz RJ, Holthausen H and Benecke R. Epileptic seizures triggered directly by focal transcranial magnetic stimulation. Electroenceph clin Neurophysiol. 94, 19-25. 1995.

[29] Cohen D and Cuffin BN. Developing a more focal magnetic stimulator. Part I: some basic principles. J Clin Neurophysiol. 8, 102-111. 1991.

[30] Cohen LG, Celnik P, Pascual-Leone A, Corwell B, Faiz L, Dambrosia J, Honda M, Sadato N, Gerloff C, Catalá MD and Hallett M. Functional relevance of cross-modal plasticity in blind humans. Nature. 389, 180-183. 1997.

[31] Counter SA, Borg E and Olofsson A. Oto-traumatic effects of computer simulated magnetic coil impulse noise: analysis of mechanisms. Acta Oto-Laryngol. 113, 699-705. 1993.

[32] Cracco RQ, Amassian VE, Maccabee PJ and Cracco JB. Comparison of human transcallosal responses evoked by magnetic coil and electrical stimulation. Electroenceph clin Neurophysiol. 74, 417-424. 1989.

[33] Cracco RQ, Amassian VE, Maccabee PJ and Cracco JB. Flow of symbolic visual information from retina to vocalization. 6th Symp on Clinical Use of Magnetic Stimulation. Kyoto, Japan. 28-30. 1995.

[34] Cros D, Day TJ and Shahani BT. Spatial dispersion of magnetic stimulation in peripheral nerves. Muscle Nerve. 13, 1076-1082. 1990.

[35] Cuffin BN and Cohen D. Magnetic fields of a dipole in special volume conductor shapes. IEEE Trans Biomed Eng. 24, 372-381. 1977.

[36] d'Arsonval A. Dispositifs pour la mesure des courants alternatifs de toutes fréquences. C R Soc Biol. (Paris). 3, 450-457. 1896.

[37] D'Inzeo G, Esselle KP, Pisa S and Stuchly MA. Comparison of homogeneous and heterogeneous tissue models for coil optimization in neural stimulation. Radio Sci. 30, 245-253. 1995.

[38] Day BL, Thompson PD, Dick JP, Nakashima K and Marsden CD. Different sites of action of electrical and magnetic stimulation of the human brain. Neurosci Lett. 75, 101-106. 1987.

[39] De Leo R, Cerri G, Balducci G, Moglie F, Scarpino O and Guidi M. Computer modelling of brain cortex excitation by magnetic field pulses. J Med Eng Technol. 16, 149-156. 1992.

[40] Devinsky O. Electrical and magnetic stimulation of the central nervous system. Historical overview. Adv Neurol. 63, 1-16. 1993.

[41] Dunlap K. Visual sensations from the alternating magnetic field. Science. 33, 68-71. 1911.

[42] Durand D, Ferguson S and Dalbasti T. Effect of surface boundary charge on neuronal magnetic stimulation. IEEE Trans Biomed Eng. 39, 58-64. 1992.

[43] Eaton H. Electric field induced in a spherical volume conductor from arbitrary coils: application to magnetic stimulation and MEG. Med Biol Eng Comput. 30, 433-440. 1992.

[44] Esselle KP and Stuchly MA. Quasi-static electric field in a cylindrical volume conductor induced by external coils. IEEE Trans Biomed Eng. 41, 151-158. 1994.

[45] Esselle KP and Stuchly MA. Cylindrical tissue model for magnetic field stimulation of neurons: effects of coil geometry. IEEE Trans Biomed Eng. 42, 934-941. 1995.

[46] Eyre J, Flecknell P, Kenyon B, Koh T and Miller S. Acute effects of electromagnetic stimulation of the brain on cortical activity, cortical blood flow, blood pressure and heart rate in the cat: an evaluation of safety. J Neurol Neurosurg Psychiatry. 53, 507-513. 1990.

[47] Fauth C, Meyer BU, Prosiegel M, Zihl J and Conrad B. Seizure induction and magnetic stimulation after stroke. Lancet. 339, 362. 1992.

[48] Gates JR, Dhuna A and Pascual-Leone A. Lack of pathological changes in human temporal lobe after transcranial magnetic stimulation. Epilepsia. 33, 504-508. 1992.

[49] Geddes LA. History of magnetic stimulation of the nervous system. J Clin Neurophysiol. 8, 3-9. 1991.

[50] Geller V, Grisaru N, Abarbanel JM, Lemberg T and Belmaker RH. Slow magnetic stimulation of prefrontal cortex in depression and schizophrenia. Prog Neuro-Psychopharm & Biol Psychiatry. 21, 105-110. 1997.

[51] George MS, Wassermann EM, Kimbrell TA, Little JT, Williams WE, Danielson AL, Greenberg BD, Hallett M and Post RM. Mood improvement following daily left prefrontal repetitive transcranial magnetic stimulation in patients with depression: a placebo-controlled crossover trial. Am J Psychiatry. 154, 1752-1756. 1997.

[52] George MS, Wassermann EM, Williams WA, Callahan A, Ketter TA, Basser P, Hallett M and Post RM. Daily repetitive transcranial magnetic stimulation (rTMS) improves mood in depression. Neuroreport. 6, 1853-1856. 1995.

[53] George MS, Wassermann EM, Williams WA, Steppel J, Pascual-Leone A, Basser P, Hallett M and Post RM. Changes in mood and hormone levels after rapid-rate transcranial magnetic stimulation (rTMS) of the prefrontal cortex. J Neurophychol Clin Neurosci. 8, 172-180. 1996.

[54] Grandori F and Ravazzani P. Magnetic stimulation of the motor cortex—theoretical considerations. IEEE Trans Biomed Eng. 38, 180-191. 1991.

[55] Greenberg BD, George MS, Martin JD, Benjamin J, Schlaepfer TE, Altemus M, Wassermann EM, Post RM and Murphy D. Effect of prefrontal repetitive transcranial magnetic stimulation in obsessive-compulsive disorder: a preliminary study. Am J Psychiatry. 154, 867-869. 1997.

[56] Hallett M. Transcranial magnetic stimulation: a useful tool for clinical neurophysiology. Ann Neurol. 40, 344-345. 1996.

[57] Hallett M, Cohen LG, Nilsson J and Panizza M. Differences between electrical and magnetic stimulation of human peripheral nerve and motor cortex. In Chokroverty S. Editors. Magnetic Stimulation in Clinical Neurophysiology. Stoneham, MA: Butterworth. 275-287. 1990.

[58] Hamdy S, Aziz Q, Rothwell JC, Singh KD, Barlow J, Hughes DG, Tallis RC and Thompson DG. The cortical topography of human swallowing musculature in health and disease. Nature Med. 2, 1217-1224. 1996.

[59] Hämäläinen M and Sarvas J. Realistic conductivity geometry model of the human head for interpretation of neuromagnetic data. IEEE Trans Biomed Eng. 26, 165-171. 1989.

[60] Hämäläinen MS and Ilmoniemi RJ. Interpreting magnetic fields of the brain: minimum norm estimates. Med Biol Eng Comput. 32, 35-42. 1994.

[61] Heller L and van Hulsteyn DB. Brain stimulation using electromagnetic sources: theoretical aspects. Biophys J. 129-138. 1992.

[62] Hömberg V and Netz J. Generalised seizures induced by transcranial magnetic stimulation of motor cortex. Lancet. 2, 1223. 1989.

[63] Hyodo A and Ueno S. Nerve excitation model for localized magnetic stimulation of finite neuronal structures. IEEE Trans Magn. 32, 5112-5114. 1996.

[64] Ilmoniemi RJ and Grandori F. Device for applying a programmable excitation electric field to a target. Patent FI/100458 (issued 15.12.1997), patent pending EP/94203134. Filed 13.10.1993.

[65] Ilmoniemi RJ, Hämäläinen MS and Knuutila J. The forward and inverse problems in the spherical model. In Weinberg H, Stroink G and Katila T. Editors. Biomagnetism, Applications and Theory. New York: Pergamon Press. 278-282. 1985.

[66] Ilmoniemi RJ, Karhu J, Ruohonen J and Virtanen J. Method and apparatus for mapping cortical connections. Patent pending FI/964387 and PCT/FI97/00664. Filed 30.10.1996.

[67] Ilmoniemi RJ, Ruohonen J, Kamppuri J and Virtanen J. Stimulator head and method for attenuating noise from the stimulating coil. Patent pending FI/974371. Filed 28.11.1997.

[68] Irwin DD, Rush S, Evering R, Lepeschkin D, Montgomery B and Weggel R. Stimulation of cardiac muscle by a time-varying magnetic field. IEEE Trans Magn. 6, 321-322. 1970.

[69] Izumi S, Takase M, Arita M, Masakado Y, Kimura A and Chino N. Transcranial magnetic stimulation-induced changes in EEG and responses recorded from the scalp of healthy humans. Electroenceph clin Neurophysiol. 103, 319-322. 1997.

[70] Jackson JD. Classical Electrodynamics. New York: John Wiley & Sons. 1975.

[71] Jahanshahi M, Ridding MC, Limousin P, Profice P, Fogel W, Dressler D, Fuller R, Brown RG, Brown P and Rothwell JC. Rapid rate transcranial magnetic stimulation—a safety study. Electroenceph clin Neurophysiol. 105, 422-429. 1997.

[72] Jalinous R. Technical and practical aspects of magnetic stimulation. J Clin Neurophysiol. 8, 10-25. 1991.

[73] Jalinous R. Guide to Magnetic Stimulation. Magstim Company Ltd. 1997.

[74] Jennum P, Friberg L, Fuglsang-Frederiksen A and Dam M. Speech localization using repetitive transcranial magnetic stimulation. Neurology. 44, 269-273. 1994.

[75] Kandler R. Safety of transcranial magnetic stimulation. Lancet. 335, 469-470. 1990.

[76] Kew JJM, Ridding MC, Rothwell JC, Passingham RE, Leigh PN, Sooriakumaran S, Frackowiak RSJ and Brooks DJ. Reorganization of cortical blood flow and transcranial magnetic stimulation maps in human subjects after upper limb amputation. J Neurophysiol. 72, 2517-2524. 1994.

[77] Kirkcaldie M, Pridmore S and Reid P. Bridging the skull: electroconvulsive therapy (ECT) and repetitive transcranial magnetic stimulation (rTMS) in psychiatry. Convulsive Ther. 13, 83-91. 1997.

[78] Kobayashi M, Ueno S and Kurakawa T. Importance of soft tissue inhomogeneity in magnetic peripheral nerve stimulation. Electroenceph clin Neurophysiol. 105, 406-413. 1997.

[79] Kolin A, Brill NQ and Broberg PJ. Stimulation of irritable tissues by means of an alternating magnetic field. Proc Soc Exp Biol Med. 102, 251-253. 1959.

[80] Kong JA. Theory of Electromagnetic Waves. New York: John Wiley & Sons. 1975.

[81] Krassowska W and Neu JC. Response of a single cell to an external electric field. Biophys J. 66, 1768-1776. 1994.

[82] Krings T, Buchbinder BR, Butler W, Chiappa KH, Jiang HJ, Rosen BR and Cosgrove GR. Stereotactic transcranial magnetic stimulation: correlation with direct electrical cortical stimulation. Neurosurgery. 41, 1319-1326. 1997.

[83] Krings T, Naujokat C and Graf v Keyrserlink D. Representation of cortical motor function as revealed by stereotactic transcranial magnetic stimulation. Electroenceph clin Neurophysiol. 109, 85-93. 1998.

[84] Kujirai T, Sato M, Rothwell JC and Cohen LG. The effect of transcranial magnetic stimulation on median nerve somatosensory evoked potentials. Electroenceph clin Neurophysiol. 89, 227-234. 1993.

[85] Lewko JP, Tarkka IM and Dimitrijevic MR. Neurophysiological assessment of the motor and sensory spinal pathways in chronic spinal cord injury. Restor Neurol Neurosci. 7, 225-234. 1995.

[86] Liu JL and Faust U. Analysis of coil parameters for magnetic stimulation. Techn Health Care. 2, 43-52. 1994.

[87] Maass J and Asa M. Contactless nerve stimulation and signal detection by inductive transducer. IEEE Trans Magn. 6, 322-326. 1970.

[88] Maccabee PJ, Amassian VE, Cracco RQ and Eberle LP. Mechanisms of neuromagnetic stimulation of peripheral nerve. In Nilsson J, Panizza M and Grandori F. Editors. Advances in Magnetic Stimulation: Mathematical Modeling and Clinical Applications. Pavia, Italy: Salvatore Maugeri Foundation. 117-128. 1996.

[89] Maccabee PJ, Amassian VE, Cracco RQ, Eberle LP and Rudell AP. Mechanisms of peripheral nervous system stimulation using the magnetic coil. Electroenceph clin Neurophysiol Suppl. 43, 344-361. 1991.

[90] Maccabee PJ, Amassian VE, Eberle L and Cracco RQ. Magnetic coil stimulation of straight and bent amphibian and mammalian peripheral nerves in vitro: locus of excitation. J Physiol. 460, 201-219. 1993.

[91] Maccabee PJ, Amassian VE, Eberle L, Rudell A, Cracco RQ, Lai K and Somasundaram M. Measurement of the electric field induced into inhomogeneous conductors by magnetic coils: application to human spinal neurogeometry. Electroenceph clin Neurophysiol. 81, 224-237. 1991.

[92] Magnusson CE and Stevens HC. Visual sensations created by a magnetic field. Am J Physiol. 29, 124-136. 1911.

[93] Mathis J, Seemann U, Weyh T, Jakob C and Struppler A. The boundary effect in magnetic stimulation. Analysis at the peripheral nerve. Electroenceph clin Neurophysiol. 97, 238-245. 1995.

[94] Matsumiya Y, Yamamoto T, Yarita M, Miyauchi S and Kling JW. Physical and physiological specification of magnetic pulse stimuli that produce cortical damage in rats. J Clin Neurophysiol. 9, 278-287. 1992.

[95] McNeal DR. Analysis of a model for excitation of myelinated nerve. IEEE Trans Biomed Eng. 23, 329-337. 1976.

[96] Merton PA and Morton HB. Stimulation of the cerebral cortex in the intact human subject. Nature. 285, 227. 1980.

[97] Meyer BU and Röricht S. Scalp potentials recorded over the sensorimotor region following magnetic stimulation over the cerebellum in man: considerations about the activated structures and their potential diagnostic use. J Neurol. 242, 109-112. 1995.

[98] Meyer BU, Röricht S and Woiciechowsky C. Topography of fibers in the human corpus callosum mediating interhemispheric inhibition between the motor cortices. Ann Neurol. 43, 360-369. 1998.

[99] Michelucci R, Valzania F, Passarelli D, Santangelo M, Rizzi R, Buzzi AM, Tempestini A and Tassinari CA. Rapid-rate transcranial magnetic stimulation and hemispheric language dominance: usefulness and safety in epilepsy. Neurology. 44, 1697-1700. 1994.

[100] Miller MB, Fendrich R, Eliassen JC, Demirel S and Gazzaniga MS. Transcranial magnetic stimulation: delays in visual suppression due to luminance changes. Neuroreport. 7, 1740-1744. 1996.

[101] Mills KR. Magnetic brain stimulation: a tool to explore the action of the motor cortex on single human spinal motoneurons. Trends Neurosci. 14, 401-405. 1991.

[102] Miranda PC, de Carvalho M, Conceicao I, Sales Luis ML and Ducla-Soares E. A new method for reproducible coil positioning in transcranial magnetic stimulation mapping. Electroenceph clin Neurophysiol. 105, 116-123. 1997.

[103] Morioka T, Mizushima A, Yamamoto T, Tobimatsu S, Matsumoto S, Hasuo K, Fujii K and Fukui M. Functional mapping of the sensorimotor cortex: combined use of magnetoencephalography, functional MRI, and motor evoked potentials. Neuroradiol. 37, 526-530. 1995.

[104] Morioka T, Yamamoto T, Mizushima A, Tombimatsu S, Shigeto H, Hasuo K, Nishio S, Fujii K and Fukui M. Comparison of magnetoencephalography, functional MRI, and motor evoked potentials in the localization of the sensory-motor cortex. Neurol Res. 17, 361-367. 1995.

[105] Mouchawar GA, Nyenhuis JA, Bourland JD and Geddes LA. Guidelines for energy-efficient coils: coils designed for magnetic stimulation of the heart. Electroenceph clin Neurophysiol Suppl. 43, 255-267. 1991.

[106] Mouchawar GA, Nyenhuis JA, Bourland JD, Geddes LA, Schaefer DJ and Riehl ME. Magnetic stimulation of excitable tissue: calculation of induced eddy-currents with a three-dimensional finite-element model. IEEE Trans Magn. 29, 3355-3357. 1993.

[107] Muri RM, Rivaud S, Vermersch AI, Leger JM and Pierrot-Deseilligny C. Effects of transcranial magnetic stimulation over the region of the supplementary motor area during sequences of memory-guided saccades. Exp Brain Res. 104, 163-166. 1995.

[108] Nagarajan SS and Durand DM. Analysis of magnetic stimulation of a concentric axon in a nerve bundle. IEEE Trans Biomed Eng. 42, 926-933. 1995.

[109] Nagarajan SS and Durand DM. A generalized cable equation for magnetic stimulation of axons. IEEE Trans Biomed Eng. 43, 304-312. 1996.

[110] Nagarajan SS, Durand DM and Hsuing-Hsu K. Mapping location of excitation during magnetic stimulation: effects of coil position. Ann Biomed Eng. 25, 112-125. 1997.

[111] Nagarajan SS, Durand DM and Warman EN. Effects of induced electric fields on finite neuronal structures: a simulation study. IEEE Trans Biomed Eng. 40, 1175-1188. 1993.

[112] Netz J, Lammers T and Hömberg V. Reorganization of motor output in the non-affected hemisphere after stroke. Brain. 120, 1579-1586. 1997.

[113] Nielsen JF, Klemar B, Hansen HJ and Sinkjaer T. A new treatment of spasticity with repetitive magnetic stimulation in multiple sclerosis. J Neurol Neurosurg Psychiatry. 58, 254-255. 1995.

[114] Nilsson J, Panizza M and Grandori F. Advances in Magnetic Stimulation: Mathematical Modeling and Clinical Applications. Pavia, Italy: Salvatore Maugeri Foundation. 1996.

[115] Nilsson J, Panizza M, Roth BJ, Basser PJ, Cohen LG, Caruso G and Hallett M. Determining the site of stimulation during magnetic stimulation of a peripheral nerve. Electroenceph clin Neurophysiol. 85, 253-264. 1992.

[116] Nyenhuis JA, Mouchawar GA, Bourland JD and Geddes LA. Energy considerations in the magnetic (eddy-current) stimulation of tissues. IEEE Trans Magn. 27, 680-687. 1991.

[117] Olney RK, So YT, Goodin DS and Aminoff JA. A comparison of magnetic and electrical stimulation of peripheral nerves. Muscle Nerve. 13, 957-963. 1990.

[118] Öberg PÅ. Magnetic stimulation of nerve tissue. Med Biol Eng Comput. 11, 55-64. 1973.

[119] Panizza M, Nilsson J, Roth BJ, Grill SE, Demirci M and Hallett M. Differences between the time constant of sensory and motor peripheral nerve fibres: further studies and considerations. Muscle Nerve. 21, 48-54. 1998.

[120] Pascual-Leone A, Catalá MD and Pascual-Leone Pascual A. Lateralized effect of rapid-rate transcranial magnetic stimulation of the prefrontal cortex on mood. Neurology. 46, 499-502. 1996.

[121] Pascual-Leone A, Cohen LG, Brasil-Neto JP and Hallett M. Non-invasive differentiation of motor cortical representation of hand muscles by mapping of optimal current directions. Electroenceph clin Neurophysiol. 93, 42-48. 1994.

[122] Pascual-Leone A, Grafman J and Hallett M. Modulation of cortical motor output maps during development of implicit and explicit knowledge. Science. 263, 1287-1289. 1994.

[123] Pascual-Leone A, Houser CM, Reese K, Shotland LI, Grafman J, Sato S, Valls-Solé J, Brasil-Neto JP, Wassermann EM, Cohen LG and Hallett M. Safety of rapid-rate transcranial magnetic stimulation in normal volunteers. Electroenceph clin Neurophysiol. 89, 120-130. 1993.

[124] Pascual-Leone A, Rubio B, Pallardo F and Catalá MD. Rapid-rate transcranial magnetic stimulation of left dorsolateral prefrontal cortex in drug-resistant depression. Lancet. 348, 233-237. 1996.

[125] Pascual-Leone A, Valls-Solé J, Brasil-Neto JP, Cohen LG and Hallett M. Akinesia in Parkinson's disease. I. Shortening of simple reaction time with focal, single-pulse transcranial magnetic stimulation. Neurology. 44, 884-891. 1994.

[126] Pascual-Leone A, Valls-Solé J, Toro C, Wassermann EM and Hallett M. Resetting of essential tremor and postural tremor in Parkinson's disease with transcranial magnetic stimulation. Muscle Nerve. 17, 800-807. 1994.

[127] Paus T, Jech R, Thompson CJ, Comeau R, Peters T and Evans AC. Transcranial magnetic stimulation during positron emission tomography: a new method for studying connectivity of the human cerebral cortex. J Neurosci. 17, 3178-3184. 1997.

[128] Polson MJR, Barker AT and Freeston IL. Stimulation of nerve trunks with time-varying magnetic fields. Med Biol Eng Comput. 20, 243-244. 1982.

[129] Puri BK, Davey NJ, Ellaway PH and Lewis SW. An investigation of motor function in schizophrenia using transcranial magnetic stimulation of the motor cortex. Brit J Psychiatry. 169, 690-695. 1996.

[130] Rapisarda G, Bastings E, de Noordhaut AM, Pennisi G and Delwaide PJ. Can motor recovery in stroke patients be predicted by early transcranial magnetic stimulation. Stroke. 27, 2191-2196. 1996.

[131] Rattay F. Analysis of models for external stimulation of axons. IEEE Trans Biomed Eng. 33, 974-977. 1986.

[132] Rattay F and Aberham M. Modeling axon membranes for functional electrical stimulation. IEEE Trans Biomed Eng. 40, 1201-1209. 1993.

[133] Reilly JP. Peripheral nerve stimulation by induced electric currents: exposure to time-varying magnetic fields. Med Biol Eng Comput. 27, 101-110. 1989.

[134] Ren C, Tarjan PP and Popovic DB. A novel electric design for electromagnetic stimulation—the Slinky coil. IEEE Trans Biomed Eng. 42, 918-925. 1995.

[135] Rimpiläinen I, Pyykkö I, Blomstedt G, Kuurne T and Karma P. The site of impulse generation in transcranial magnetic stimulation of the facial nerve. Acta Oto-Laryngol. 113, 339-344. 1993.

[136] Rossini PM, Barker AT, Berardelli A, Caramia MD, Caruso G, Cracco RQ, Dimitrijevic MR, Hallett M, Katayama Y, Lücking CH, Maertens de Noordhout A, Marsden C, Murray N, Rothwell JC, Swash M and Thomberg C. Non-invasive electrical and magnetic stimulation of the brain, spinal cord and roots: basic principles and procedures for routine clinical application. Report of an IFCN committee. Electroenceph clin Neurophysiol. 91, 79-92. 1994.

[137] Roth BJ. Mechanisms for electrical stimulation of excitable tissue. Crit Rev Biomed Eng. 22, 253-305. 1994.

[138] Roth BJ and Basser PJ. A model of the stimulation of a nerve fiber by electromagnetic induction. IEEE Trans Biomed Eng. 37, 588-597. 1990.

[139] Roth BJ, Cohen LG, Hallett M, Friauf W and Basser PJ. A theoretical calculation of the electric field induced by magnetic stimulation of a peripheral nerve. Muscle Nerve. 13, 734-741. 1990.

[140] Roth BJ, Maccabee PJ, Eberle LP, Amassian VE, Hallett M, Cadwell J, Anselmi GD and Tatarian GT. In vitro evaluation of a 4-leaf coil design for magnetic stimulation of peripheral nerve. Electroenceph clin Neurophysiol. 93, 68-74. 1994.

[141] Roth BJ, Momen S and Turner R. Algorithm for the design of magnetic stimulation coils. Med Biol Eng Comput. 32, 214-216. 1994.

[142] Roth BJ, Pascual-Leone A, Cohen LG and Hallett M. The heating of metal electrodes during rapid-rate magnetic stimulation: a possible safety hazard. Electroenceph clin Neurophysiol. 85, 116-123. 1992.

[143] Roth BJ, Saypol JM, Hallett M and Cohen LG. A theoretical calculation of the field induced in the cortex during magnetic stimulation. Electroenceph clin Neurophysiol. 81, 47-56. 1991.

[144] Rothwell JC, Burke D, Hicks D, Stephen J, Woodforth I and Crawford M. Transcranial electrical stimulation of the motor cortex in man: further evidence for the site of activation. J Physiol. 481, 243-250. 1994.

[145] Rothwell JC, Day BL and Amassian VE. Near threshold electrical and magnetic transcranial stimuli activate overlapping sets of cortical neurones in humans. J Physiol. 452, 109P. 1992.

[146] Ruohonen J, Huotilainen M, Korvenoja A, Aronen H, Ilmoniemi RJ, Kahri P, Karp P, Lehmus S, Näätänen R and Virtanen J. Motor maps with whole-head MEG and magnetic stimulation. 3rd Eur Conf Eng Med. Firenze, Italy. 120. 1995.

[147] Ruohonen J, Ilmoniemi RJ, Ollikainen M and Virtanen J. Method and apparatus for sham magnetic stimulation. Patent pending FI/981595. Filed 10.7.1998.

[148] Sarvas J. Basic mathematical and electromagnetic concepts of the biomagnetic inverse problem. Phys Med Biol. 32, 11-22. 1987.

[149] Saypol JM, Roth BJ, Cohen LG and Hallett M. A theoretical comparison of electric and magnetic stimulation of the brain. Ann Biomed Eng. 19, 317-328. 1991.

[150] Scivill IJ, Barker AT and Freeston IL. Finite element modelling of magnetic stimulation of the spine. Proc 18th Ann Int Conf IEEE EMBS. Amsterdam, the Netherlands. 1996.

[151] Seyal M, Browne JK, Masuoka LK and Gabor AJ. Enhancement of the amplitude of somatosensory evoked potentials following magnetic pulse stimulation of the human brain. Electroenceph clin Neurophysiol. 88, 20-27. 1993.

[152] Starck J, Rimpiläinen I, Pyykkö I and Toppila E. The noise level in magnetic stimulation. Scand J Audiol. 25, 223-226. 1996.

[153] Stuchly MA and Esselle KP. Factors affecting neural stimulation with magnetic fields. Bioelectromagnetics Supplement. 1, 191-204. 1992.

[154] Terman FE. Electronic and Radio Engineering. New York: McGraw-Hill Book Company. 1955.

[155] Thompson SP. A physiological effect of an alternating magnetic field. Proc R Soc Lond [Biol]. B82, 396-399. 1910.

[156] Tokimura H, Tokimura Y, Oliviero A, Asakura T and Rothwell JC. Speech-induced changes in corticospinal excitability. Ann Neurol. 40, 628-634. 1996.

[157] Ueno S, Tashiro T and Harada K. Localized stimulation of neural tissue in the brain by means of a paired configuration of time-varying magnetic fields. J Appl Phys. 64, 5862-5864. 1988.

[158] Virtanen J, Ruohonen J, Ilmoniemi RJ and Näätänen R. Instrumentation for measuring electrical brain responses to transcranial magnetic stimulation. Helsinki University of Technology, Applied Electronics Laboratory. Research Report B1. 1998.

[159] Walsh P. Magnetic stimulation of the human retina. Fed Proc. 5, 109-110. 1946.

[160] Walsh V. Brain mapping: Faradization of the mind. Curr Biol. 8, R8-R11. 1998.

[161] Walsh V and Cowey A. Magnetic stimulation studies of visual cognition. Trends Cogn Sci. 2, 103-110. 1998.

[162] Wang W and Eisenberg SR. A Three-dimensional finite element method for computing magnetically induced currents in tissues. IEEE Trans Magn. 30, 5015-5023. 1994.

[163] Wassermann EM. Risk and safety of repetitive transcranial magnetic stimulation: report and suggested guidelines from the International Workshop on the Safety of Repetitive Transcranial Magnetic Stimulation, June 5-7, 1996. Electroenceph clin Neurophysiol. 108, 1-16. 1998.

[164] Wassermann EM, Blaxton TA, Hoffman E, Pascual-Leone A, Hallett M and Theodore WH. Repetitive transcranial magnetic stimulation (rTMS) of the dominant hemisphere can disrupt visual naming as well as speech in temporal lobe epilepsy patients. Ann Neurol. 40, T138. 1996.

[165] Wassermann EM, Cohen LG, Flitman SS, Chen R and Hallett M. Seizure in healthy people with repeated 'safe' trains of transcranial magnetic stimulation. Lancet. 347, 825. 1996.

[166] Wassermann EM, Grafman J, Berry C, Hollnagel C, Wild K, Clark K and Hallett M. Use and safety of a new repetitive transcranial magnetic stimulator. Electroenceph clin Neurophysiol. 101, 412-417. 1996.

[167] Wassermann EM, Wang B, Zeffiro TA, Sadato N, Pascual-Leone A, Toro C and Hallett M. Locating the motor cortex on the MRI with transcranial magnetic stimulation and PET. Neuroimage. 3, 1-9. 1996.

[168] Wunderlich G, Knorr U, Herzog H, Kiwit JCW, Freund H-J and Rudiger JS. Precentral glioma location determines the displacement of cortical hand representation. Neurosurgery. 42, 18-27. 1998.

[169] Yamada H, Tamaki T, Wakano K, Mikami A and Transfeldt EE. Effect of transcranial magnetic stimulation on cerebral function in a monkey model. Electroenceph clin Neurophysiol. 97, 140-144. 1995.

[170] Ziemann U, Lönnecker S, Steinhoff BJ and Paulus W. Effects of antiepileptic drugs on motor cortex excitability in humans: a transcranial magnetic stimulation study. Ann Neurol. 40, 367-378. 1996.

[171] Zimmermann KP and Simpson RK. "Slinky" coils for neuromagnetic stimulation. Electroenceph clin Neurophysiol. 101, 145-152. 1996.

Summary of publications

Publication I

Publication II

Publication III

Publication IV

Publication V

Publication VI

Publication VII

 Publication VIII