A mirror neuron is a neuron that fires both when an animal acts and when the animal observes the same action performed by another.[1][2][3] Thus, the neuron “mirrors” the behavior of the other, as though the observer were itself acting. Such neurons have been directly observed in primate species.[4] Birds have been shown to have imitative resonance behaviors and neurological evidence suggests the presence of some form of mirroring system.[4][5] In humans, brain activity consistent with that of mirror neurons has been found in the premotor cortex, the supplementary motor area, the primary somatosensory cortex and the inferior parietal cortex.[6] The function of the mirror system is a subject of much speculation. Many researchers in cognitive neuroscience and cognitive psychology consider that this system provides the physiological mechanism for the perception/action coupling (see the common coding theory).[3] They argue that mirror neurons may be important for understanding the actions of other people, and for learning new skills by imitation. Some researchers also speculate that mirror systems may simulate observed actions, and thus contribute to theory of mind skills,[7][8] while others relate mirror neurons to language abilities.[9] Neuroscientists such as Marco Iacoboni (UCLA) have argued that mirror neuron systems in the human brain help us understand the actions and intentions of other people. In a study published in March 2005 Iacoboni and his colleagues reported that mirror neurons could discern if another person who was picking up a cup of tea planned to drink from it or clear it from the table.[10] In addition, Iacoboni has argued that mirror neurons are the neural basis of the human capacity for emotions such as empathy.[11] It has also been proposed that problems with the mirror neuron system may underlie cognitive disorders, particularly autism.[12][13] However the connection between mirror neuron dysfunction and autism is tentative and it remains to be seen how mirror neurons may be related to many of the important characteristics of autism.[14]

Transcranial magnetic stimulation (TMS) is a noninvasive method used to stimulate small regions of the brain. During a TMS procedure, a magnetic field generator, or “coil” is placed near the head of the person receiving the treatment.[1]:3 The coil produces small electric currents in the region of the brain just under the coil via electromagnetic induction. The coil is connected to a pulse generator, or stimulator, that delivers electric current to the coil.[2] TMS is used diagnostically to measure the connection between the brain and a muscle to evaluate damage from stroke, multiple sclerosis, amyotrophic lateral sclerosis, movement disorders, motor neuron disease and injuries and other disorders affecting the facial and other cranial nerves and the spinal cord.[3] The use of single-pulse TMS was approved by the FDA for use in migraine[4] and repetitive TMS (rTMS) for use in treatment-resistant major depressive disorder.[5] Evidence suggests it is useful for neuropathic pain[6] and treatment-resistant major depressive disorder.[6][7] Evidence also suggests that TMS may be useful for negative symptoms of schizophrenia and loss of function caused by stroke.[6] As of 2014, all other investigated uses of rTMS have only possible or no clinical efficacy.[6] Matching the discomfort of TMS to distinguish true effects from placebo is an important and challenging issue that influences the results of clinical trials.[6][8][9] The greatest risks of TMS are the rare occurrence of syncope (fainting) and even less commonly, induced seizures.[8] Other adverse effects of TMS include discomfort or pain, transient induction of hypomania, transient cognitive changes, transient hearing loss, transient impairment of working memory, and induced currents in electrical circuits in implanted devices.[8]