Transcranial
magnetic stimulation (TMS) is based on Faraday’s principles of
electromagnetic induction [1]. A pulse of current flowing through a coil of
wire generates a magnetic field. If its magnitude changes with time, then it
will induce a secondary current in any nearby conductor. The rate of change
of the field determines the size of the induced current. In TMS studies, the
stimulating coil is held over a subject’s head and, as a brief pulse of
current is passed through it, a magnetic field is generated that passes
through the subject’s scalp and skull with a small attenuation. This
time-varying magnetic field induces a current in the subject’s brain that
stimulates the neural tissue. To induce enough current to excite neurons in
the brain, the current passed through the coil must change within a few
hundred microseconds [2]. The stimulators and coils, used to develop about
1.5–2 Tesla (T) at the face of the coil, are thought to activate cortical
neurons at a depth of 1.5–2 cm beneath the scalp [3, 4]. There are basically
two types of TMS applications: a) single-pulse TMS, wherein repeated pulses
are not applied faster than once every few seconds, and, b) repeated TMS (rTMS),
wherein a train of magnetic pulses is delivered during milliseconds to even
seconds [4, 5].
Jackson J D, Classical Electrodynamics. 1965, John Wiley and
Sons: New York.
Hallett M, Transcranial magnetic stimulation and the human brain.
Nature, 2000. 406: 147-50.
Rudiak D and Marg E, Finding the depth of magnetic brain stimulation:
a re-evaluation. Electroencephalogr Clin Neurophysiol., 1994. 93:
358-71.
Wassermann E M, 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. Electroencephalography and Clinical Neurophysiology, 1998. 108:
1-16.
Anand S and Hotson J, Transcranial magnetic stimulation:
neurophysiological applications and safety. Brain Cogn, 2002. 50:
366-86.
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and technology organization.
Transcranial
magnetic stimulation (TMS) is based on Faraday’s principles of
electromagnetic induction [1]. A pulse of current flowing through a coil of
wire generates a magnetic field. If its magnitude changes with time, then it
will induce a secondary current in any nearby conductor. The rate of change
of the field determines the size of the induced current. In TMS studies, the
stimulating coil is held over a subject’s head and, as a brief pulse of
current is passed through it, a magnetic field is generated that passes
through the subject’s scalp and skull with a small attenuation. This
time-varying magnetic field induces a current in the subject’s brain that
stimulates the neural tissue. To induce enough current to excite neurons in
the brain, the current passed through the coil must change within a few
hundred microseconds [2]. The stimulators and coils, used to develop about
1.5–2 Tesla (T) at the face of the coil, are thought to activate cortical
neurons at a depth of 1.5–2 cm beneath the scalp [3, 4]. There are basically
two types of TMS applications: a) single-pulse TMS, wherein repeated pulses
are not applied faster than once every few seconds, and, b) repeated TMS (rTMS),
wherein a train of magnetic pulses is delivered during milliseconds to even
seconds [4, 5]. 
