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Up to 40% of OCD patients fail to respond satisfactorily to generally adequate treatment options, and 10% cannot be helped at all. Because OCD may be related to increased neural activity in prefrontal subcortical circuits, the inhibitory effect of rTMS was hypothesized to be beneficial in OCD treatment. rTMS has recently demonstrated remote effects, with left prefrontal stimulation inducing changes in cerebral perfusion in the bilateral anterior cingulate and orbitofrontal cortex. In conclusion, in open-label studies, high-frequency rTMS of the right and/or left DLPFC appears to be effective in reducing obsessive-compulsive symptoms. However, this could not be replicated in double-blind, sham-controlled studies. As the efficacy of rTMS is often time limited, the necessity of a second rTMS after several weeks should be investigated and functional MRI studies of rTMS in OCD are needed to clarify the specific stimulation region of rTMS. Otherwise, as the improvement of symptoms is often noted in sham settings, it would be interesting to investigate the neural underpinnings of the placebo effect caused by sham rTMS.
Several initial studies on negative symptoms of schizophrenia have suggested that the condition seems to respond to high frequency (20 Hz, 10 Hz) repetitive transcranial magnetic stimulation (rTMS). Low frequency rTMS ( <= 1 Hz) inhibits cortical excitability and leads to a weakening of the transfer at the synapses. Some authors documented the superiority of 10 Hz rTMS using a sham-controlled parallel design (110% of motor threshold, over left dorsolateral prefrontal cortex), and found a statistically significant improvement in negative symptoms of schizophrenia patients. Interestingly, in this study, positive symptoms deteriorated from baseline. However, in another recent study with a similar controlled design, some authors failed to find significant improvement. Positive symptoms, as globally assessed by PANSS-P, do not show a statistically significant improvement after rTMS but a marked and significant improvement in severity of auditory hallucinations is obtained. More studies need to be conducted for further investigation of the effects of short term and prolonged application of TMS on negative and positive symptoms in schizophrenia.
TMS has also been applied to study motor cortex changes in patients with cognitive disorders such as AD, frontotemporal dementia, and dementia with Lewy bodies. Further investigations with larger sample sizes are needed to identify MCI and AD subjects and separate them from the healthy population, and to identify connectivity changes occurring during the development of AD. Active rTMS with exposure may have symptomatic and physiological effects. Larger studies are needed to confirm and verify whether rTMS plus exposure therapy has a role in the treatment of PTSD.
Some authors reported antimanic effects from rapid transcranial magnetic stimulation of the right prefrontal cortex. Further systematic studies are needed.
The prefrontal cortex may be a promising TMS target for reducing pain in neuropathic, rheumatologic and post-surgical populations although the mechanisms by which it might work remain unclear. Future studies are needed to determine TMS treatment parameters and cortical targets that can optimize its effects and duration