Schizophrenia is usually accompanied by reality distortion followed by frequent delusions and hallucinations. Hallucinations may be both visual and auditory, while the latter is more frequent. Auditory hallucinations are usually expressed by voices speaking to or about the patient . The biochemical mechanisms behind auditory hallucinations (AHs) remain elusive. Generally, AHs may be considered to stem from a default monitoring of inner states. As a result, the individual mislabels the inner speech as non-self .
Auditory hallucinations are reported by 50% to 70% of patients with schizophrenia, and the majority of cases are successfully treated with antipsychotic medications. However, 25% to 30% of hallucinating schizophrenic patients are refractory to antipsychotic medications, and therefore patients suffer associated distress, functional disability, lack of behavioral control  and violent behavior . It has also been known to be a contributing factor in up to 25% of cases of serious suicide attempts .
Transcranial magnetic stimulation (TMS) is a non-invasive tool that stimulates nerve cells in superficial areas of the brain. TMS, which was first introduced in 1985 , induces a magnetic field that can produce a substantive electrical field in the brain causing depolarization of nerve cells, which results in the stimulation or disruption of local brain activity. TMS may be applied as a single stimulus, or repeated many times per seconds (rTMS), with variation in intensity, site and orientation of the magnetic field . The first report of rTMS treatment for auditory hallucinations was described in 1999 by Hoffman et al.
. In that study, rTMS was applied over the left temporoparietal cortex of three patients over 4 days (for 4, 8, 12 and 16 min). Hoffman et al. reported an improvement in auditory hallucination severity in those patients, as rated on a visual analogue scale (VAS) . Since then, several studies have used rTMS to treat auditory hallucinations in schizophrenic patients, targeting almost exclusively the left temporoparietal cortex, with mixed results [3, 4, 7, 9, 10]. The physiological basis of the rTMS-induced beneficial effect on auditory hallucinations is not well understood, but may reflect reduced pyramidal neuron excitability or neuroplasticity changes analogous to those associated with long-term depression [3, 4, 10]. Imaging studies of patients with of auditory hallucinations demonstrated increased blood flow in the speech perception areas of the brain, such as the superior temporal cortex of the dominant hemisphere and the superior temporal cortex bilaterally , and therefore, neuronal hyperactivity in these areas has been associated with AHs. Overactivation of the left temporoparietal cortex, which is critical to speech perception and is easily accessible to rTMS, has been implicated to be involved in the onset of auditory hallucinations . In a 2003 study, Hoffman et al. detected improvement primarily in frequency and attentional salience of hallucinations, which were also associated with modest overall clinical improvement, but with no negative effects of rTMS on cognition .
The H1 coil, used for deep TMS, has been shown to be effective in the treatment of major depression [12–14]. Deep TMS coils are designed to maximize the electrical field in deep brain tissues by the summation of separate fields projected into the skull from several points around its periphery . The device is planned to minimize the accumulation of electrical charge on the surface of the brain, which can give rise to an electrostatic field that might reduce the magnitude of the induced electric field both at the surface and inside, and reduce the depth penetration of the induced electric field . Deep TMS could be more effective than rTMS due to the larger and deeper spread of field it can produce . In our study we examined the efficacy of deep TMS over the left temporoparietal cortex for the treatment of auditory hallucinations in refractory schizophrenic patients.