1831:

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.

1896:

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.

1902:

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.

1959:

Klein demonstrates stimulation of a frog muscle using a magnetic field.

1965:

The first magnetic stimulation of human nerves is conducted by Bickford and Fremming.

1970:

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 retina.

1985:

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).

1993:

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.

2002:

rTMS therapy was been approved by Health Canada for clinical delivery in Canada.

2006:

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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