History of rTMS
Faraday discovers the principle of mutual induction.
Faraday’s law quantifies the conversion of
electrical energy into magnetic fields and magnetic
fields into electrical energy.
D’arsonval moves forward and places a subject’s
head inside a power magnetic coil. Subjects recorded
seeing “magneto phosphenes” (sparks) and
experiencing vertigo and syncope.
Pollacsek and Beer in Vienna, Australia file a
patent for treating depression by using an
electromagnetic coil placed over the skull to pass
vibrations into the skull.
These early innovations represent the
historical structures that have shaped today’s
modern version of rTMS but did not permit high
intensity or frequency usage.
Klein demonstrates stimulation of a frog muscle
using a magnetic field.
The first magnetic stimulation of human nerves is
conducted by Bickford and Fremming.
More research was conducted using different
magnetic stimulators constructed to study phosphene
production. As mentioned, these stimulators were
inadequate in the duration and intensity of the
magnetic pulse, the focality and shape of the
magnetic field, and also the capacity for rapid
frequency utilization. As such, is it unknown if the
phosphene production was as a result of stimulation
of the occipital cortex or direct stimulation of the
Anthony Barker at the University of Sheffield,
England built the first effective, modern
Transcranial Magnetic Stimulation (TMS) device. In
addition to the stimulation previously found with
the frog, researchers could now induce movement in
the finger and foot by placing the coil over the
motor cortex. This TMS device was capable of
producing an evoked potential in specific neurons in
the brain. However, these initial studies of TMS
were limited to functional brain imaging. The
procedure’s non-invasive and painless nature allowed
early researchers to utilize the TMS devices to map
and study regions of the brain that were involved in
memory, vision and muscle control.
Advanced technical developments in the
devices used to administer magnetic stimulation made
it possible to apply more and faster stimuli to
specific areas of the brain. This form of magnetic
stimulation is called repetitive TMS (rTMS). The
first TMS instruments were limited by their rate of
stimulation to less than one pulse per second (1
Hz). This is termed low-frequency rTMS (≤ 1 Hz). The
earliest studies of TMS therapy for depression were
limited by low-frequency stimulation and a lack of
awareness of the importance for precise coil
placement over the prefrontal region of the brain.
With technological improvements and newer coil
designs, magnetic fields became more focused and
magnetic pulses could be delivered in a series, or
repetitive "train" of 20 Hz or more, termed
high-frequency rTMS (≥ 1 Hz).
The first open trials of using TMS for depression
began. Hoflich et al. suggested that TMS, which was
applied over the vertex, has antidepressant effects.
The first clinical utilization of the early TMS
devices involved diagnostics for multiple sclerosis
and motor neuron disease. These early researchers
did not conceive of stimulating the frontal cortex
or areas associated with mood disorders.
rTMS therapy was been approved by Health Canada for
clinical delivery in Canada.
rTMS research has now been ongoing for over 20 years
around the world in Canada, the United States,
United Kingdom, Germany, Israel and Japan. More
recently, rTMS has been used to investigate sensory
and cognitive aspects of cortical processing.
Current research suggests that rTMS has a valuable
therapeutic potential for many other illness and
disorders, besides depression, because of its unique
capacity to selectively increase or decrease the
excitability of neurons in discrete brain regions.
This emerging technology represents the most
significant innovation in neuro-psychiatry in the
last 50 years.
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