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Antipsychotic medications are the cornerstone in the management of schizophrenia as they greatly reduce the symptoms and allow the patients to function better and improve their quality of life. Most patients would respond after two to four weeks. The newer class of antipsychotics is associated with lesser side effects. However, they are also more expensive. As such, alternative therapies are currently being explored like transcranial magnetic stimulation (TMS).
One of the earliest studies was done by Hoffman et al in 1999, where they used low-frequency TMS to treat auditory hallucinations. It was hypothesized that auditory hallucinations occurred as a result of overactivation of the left temporoparietal cortex, the part of the brain responsible for speech perception. As such, Hoffman et al applied TMS on this specific site in three patients over four days. They were able to demonstrate a reduction of auditory hallucinations based on a rating scale. Their study was successfully replicated by Rosenberg et al in 2011, which involved 8 participants with refractory hallucinations. An interesting finding was that participants subjected to TMS over a period of 20 days reported lesser hallucinations after 1-month follow-up compared to those who received it for only 10 days.
Due to the rather robust therapeutic effects of TMS on auditory hallucinations, low-frequency stimulation has also been used to treat positive symptoms of schizophrenia including the other forms of hallucinations and disorganized speech. In 2009, when Freitas et al conducted an analysis on trials using this protocol, they reported a lack of improvement in the positive symptoms and hypothesized that the left temporoparietal cortex might not be the site responsible for such symptoms.
On the other hand, high-frequency TMS has been applied to the prefrontal cortex in the hopes of ameliorating the negative symptoms of schizophrenia like catatonic state or lack of affect. Strafella et al explained that this may be due to TMS modulating the release of a substance called dopamine. However, Freitas et al was only able to demonstrate a modest but statistically insignificant improvement of negative symptoms compared to those given sham stimulation. They pointed out several factors that may have caused this like varying degrees of severity of the symptoms as well as different frequencies or duration of TMS therapy. It is also possible that the prefrontal cortex is just one of many dysfunctional sites in the brain that produce the negative symptoms of schizophrenia.
Overall, larger trials must be carried out to clearly demonstrate the efficacy of TMS in treating the positive and negative symptoms of schizophrenia. Furthermore, there is a need to come up with a uniform treatment protocol before TMS can be mainstream therapy for schizophrenia.
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