Introduction

Transcranial Magnetic Stimulation (TMS) is a non-invasive method that is adopted to study various cognitive functions in biopsychology. TMS is a painless method that has been employed to understand the brain-behavior of normal individuals as well as people with certain neuropsychological disorders (Dougall et al., 2015). The ability of the TMS method to specifically modulate distinct regions of the brain has contributed to its wide application as a therapeutic tool in a number of neuropsychological disorders. According to Freitas, Fregni and Pascual-Leone (2009), TMS has been adopted in the study of sub-cortical and cortical functions of the brain, brain mapping, and neural plasticity further justifying its applicability in the study of various neuropsychological disorders. Previous studies have indicates that the Repetitive Transcranial Magnetic stimulation method is the most promising method for the treatment of depression as opposed to other methods such as electroconvulsive (Stanford et al., 2008). It is also reported that TMS methods are also likely to be useful in the treatment of other mental disorders such as mania, epilepsy, and schizophrenia (Biswa et al., 2011). The current study focuses on the analysis and evaluation of the contributions of the TMS method in the study of   schizophrenia. Major emphasis is on the contributions of the methods towards the treatment of the disease. The paper begins with the description of the principle of TMS. This is followed with the evaluation of the contributions of the method towards the study and treatment of the mental disorder.

The principle of Transcranial Magnetic Stimulation

Transcranial Magnetic Stimulation (TMS) works on the principle of electromagnetic induction that involves capacitors. The capacitors discharge a large amount of current (approx 5000 amps) that flows rapidly through a circuit and a copper-wire coil resulting into a pulsed magnetic field (Du et al., 2012). When the coil is held on an individual’s head, the magnetic field induced generates an electric current that is of an adequate intensity capable of causing localized depolarization of sub- cortical and superficial cortical neurons. This generates an action that is used to study a number of neuronal functions (Stanford et al., 2008). The application of TMS to a subject can release immediate effects such as changes in perception of light or flashes or jerky movements. According to Biswa et al. (2011) repeated stimulation of the brain neurons at low frequency is likely to yield a long-term inhibition of cell-cell communication referred to as long-term depression. On the other hand, high-frequency inhibition is likely to improve the cell-cell communication. The action generated following the stimulation of the brain neurons by the TMS method is therefore used in the study of different neuronal functions.

Schizophrenia

Schizophrenia is one of the most debilitating psychotic disorders. The condition mainly begins at the adolescent age, to early adulthood and can equally lead to a lifelong course. The psychological disorder is characterized by a number of symptoms that can either be categorized as either positive or negative. The positive symptoms include disorganized speech, hallucinations, catatonic behavior and delusions. On the other hand, the negative symptoms include avolition, anhedonia, and alogia (Voineskos & Zafiris, 2013). Being a psychotic disorder, schizophrenia can be managed by administering antipsychotic drugs. However, the majority of the patients fail to respond to the antipsychotic treatment offered presenting the need for other alternative methods to be adopted.

Contributions of the TMS method towards the study of schizophrenia

The treatment of schizophrenia has mainly been based on pharmacotherapy through the use of antipsychotic medications. However, in his analysis Dougall et al (2015) pointed out that the first, second and third generations of the antipsychotic medicines have only succeeded in reducing the positive symptoms of schizophrenia. Negative responses have been reported by individuals who experienced the negative symptoms of the disorder. Research has also indicated that more than one-third of the individuals who suffers from the positive symptoms of schizophrenia do not respond to the antipsychotic drugs (Kubera et al., 2015). In addition, non-adherence to the antipsychotic medication is another challenge that is faced by this category of individuals (Stanford et al., 2008). As much as the pharmacotherapy approach may be suitable for the management of the condition, the majority of the patients that suffer from the condition are unlikely to benefit from the use of the antipsychotic medicines presenting the need for the use of other methods in the maintenance of the schizophrenia symptoms.

TMS is one of the neuromodulation methods that have been investigated to have significant contributions to the study of schizophrenia and treatment of the arising symptoms of the condition. According to Aleman, Sommer & Kahn (2007), TMS can be used in the management of auditory hallucination, one of the primary symptoms of schizophrenia. The TMS method has enabled the researchers to understand the neurocognitive basis of auditory hallucination making it possible for the symptom to be effectively managed. Adopting the TMS method on antipsychotic treatment-resistant patients, previous researchers demonstrated that there is hyperactivity in the left temporoparietal cortex (TPC). Through the exploitation of the inhibitory role of the TMS method, its application at a low frequency of 1 Hz resulted in the reduction of auditory hallucination (Kubera et al., 2015). Further improvements have been observed by subjects who went through the treatment 15 weeks later confirming the effectiveness of the method in reducing auditory hallucination amongst the antipsychotic treatment-resistant subjects. The effectiveness of the TMS therapy in the reduction of auditory hallucination across all subjects is however not known. It is important to note that most of the studies conducted by previous researchers have been centered on individuals with antipsychotic medication-resistant auditory hallucination. Very little information has been availed on the effects of TMS treatment on antipsychotic treatment responsive subjects (Voineskos & Zafiris, 2013). It is, therefore, important that future studies involve the antipsychotic-responsive subjects for the TMS method to be generalized as an effective tool in the reduction of auditory hallucination in schizophrenia patients.

Most of the previous studies have indicated that low-frequency TMS treatment is effective in the treatment of auditory hallucination. Nevertheless, Kubera et al (2015) have pointed out that not every feature of hallucination as reported by the patient seem to respond adequately and equally to the TMS treatments. Kubera et al (2015) obtained that there was a significant reduction in all the six items of the AHRS Scale except loudness after subjecting the subjects to TMS treatment. In contrast, Anna Marras and Pallanti (2013) found a significant effect for the loudness of voices as a manifestation of hallucination. The results on the effect of TMS treatment on every element of hallucination are still mixed up presenting the need for further research that will focus on the specific characteristics of auditory hallucination.

The reduction of auditory hallucination is more significant in the active phase of TMS as opposed to the sham phase.  Voineskos and Zafiris (2013) in their study subjected schizophrenia patients to 1Hz TMS over the left temporoparietal cortex that lasted for 16 minutes at 90%. This was followed by the assessment of the auditory hallucination using the Hallucination Change Scale. The study findings indicated that a higher positive response in the management of the auditory hallucination was experienced in the active phase as opposed to a lower positive change that was observed in the sham phase. From the results gathered, it is observed that the TMS treatment is likely to reduce auditory hallucination amongst the schizophrenia patients; however, the reduction is likely to be observed more in the active phase of TMS as opposed to the sham phase.

The number of TMS sessions that is administered to the subject also influences the efficacy of the method in managing hallucination. According to Du et al (2012) 12 sessions of TMS treatment is considered the most effective in reporting a higher level of reduction of auditory hallucination. Irrespective of the brain region that is stimulated, the schizophrenia patients are only likely to report a higher improvement when subjected to a relatively higher number of TMS treatment sessions. Previous studies have indicated that significant positive improvement was only reported by patients that underwent not less than 10 sessions in the treatment process (Oliveira et al., 2016). As such, the efficacy and possible of reporting a higher positive change in auditory hallucination are likely to be observed when the number of treatment sessions is expanded.

TMS treatment is repeated as less effective in the management of the positive symptoms of schizophrenia other than the hallucination. According to Biswa et al. (2011) low-frequency TMS treatment to the left temporoparietal cortex (TPC) does not seem to be a suitable approach in the treatment of other positive symptoms of schizophrenia other than the auditory hallucination. In a study where a placebo was used, the results of the effects of TMS treatment on the schizophrenia patients indicated that there were small and non-significant effects of the treatment on the changes in the positive symptoms. Similar findings were also obtained in a different study where Freitas, Fregni and Pascual-Leone (2009) obtained that there was no significant improvement in the overall positive symptoms of the patients included in the study. The possible reason for the stated outcome is that positive symptoms of schizophrenia other than hallucination are associated with certain dysfunction on the orbitofrontal cortex.  Dougall et al. (2015) have posited that the altered distribution of orbitofrontal cortex that is mainly observed amongst the patients with schizophrenia is associated with a thought disorder that is a positive symptom of the psychotic disorder. The medial temporal lobe dysfunction also causes most of the positive symptoms of schizophrenia apart from the hallucination that occurs as a result of the dysfunction of the lateral temporal cortex (Dougall et al., 2015). The analysis above suggests that positive symptoms of schizophrenia other than hallucinations are experienced due to the dysfunctions of other parts of the brain apart from temporoparietal cortex (TPC). As such, the positive symptoms such as delusions can be best addressed when other parts of the brain other than the TPC is targeted. This, therefore, justifies the inability of the low-frequency TMS treatment that targets the TPC region to manage the other positive symptoms of schizophrenia.

TMS treatment has a significant reduction in the negative symptoms of schizophrenia. Treatment of the schizophrenia patients with a high-frequency TMS resulted in a decrease in the anhedonia scale. In a study conducted by Oliveira et al (2016) 12 patients were subjected to high-frequency TMS treatment at left prefrontal cortex on a daily basis for two weeks. The study findings indicated that there is a significant negative reduction in the negative symptoms of the patients. The depression symptoms also reduced significantly. However, the positive symptoms such as auditory hallucinations that were reported by these patients increased. According to Freitas, Fregni & Pascual-Leone (2009) a high-frequency TMS treatment is only capable of reducing the negative symptoms of schizophrenia but has the ability to improve significantly the positive symptoms. Varying opinions have also been presented on whether the high-frequency TMS treatment is likely to manage the negative symptoms of schizophrenia effectively.

 Apart from the above scholars who demonstrated that there is a possibility of reducing the negative effects of schizophrenia, other researchers such as Du et al (2012) noted that high-frequency TMS treatment has no therapeutic effect on the schizophrenia patients. Dougall et al (2015) were also unable to demonstrate that high-frequency TMS treatment over the left dorsolateral cortex would reduce the negative symptoms of schizophrenia amongst patients that had reported predominant negative symptoms and were under antipsychotic medication. The mixed results obtained on the effects of TMS treatment on the management of the negative symptoms of schizophrenia makes its efficacy in the reduction of the symptoms questionable.

The positive and negative symptoms that are experienced by schizophrenia patients often fail to respond to the antipsychotic medication. As much as the medication is mainly given to control auditory hallucination that is the major symptom, in most cases, the medication does not offer the desired benefits to many patients (Aleman, Sommer & Kahn, 2007). The ability of the TMS to manage the schizophrenia symptoms at different frequency have resulted in the proposition that the TMS method can be used as an alternative method for the treatment of the condition. However, a number of studies have also indicated that the improvement in the positive symptoms of schizophrenia is only experienced amongst the schizophrenia patients that have gained stability following the administration of the antipsychotic drug (Rabany, Deutsch & Levkovitz, 2014). As such, it is not clear whether the TMS treatment method can fully and successfully eliminate antipsychotic medication as a treatment for the schizophrenia symptoms presenting a need for further studies to establish the same.

Based on the currently available information, it is insufficient to refute or support the assertion that TMS method can be used in the treatment of schizophrenia symptoms. Although there is significant evident to ascertain that TMS method can be used to treat auditory hallucination as long as the conditions for higher efficacy attainment are met, it is not clear whether the approach can be effective in the treatment of other positive symptoms of schizophrenia. In addition, the use of high-frequency TMS treatment has proved to be less beneficial since as much as it reduces the negative symptoms, it makes enhance the positive symptoms bringing additional problems to the patients. There is equally insufficient evidence to suggest that the TMS method can be used as a replacement of the antipsychotic medicine treatment for the patients that have reported some resistance or the TMS method has additional benefits when it is used as an adjunctive therapy for antipsychotic medication. The findings that have been obtained by most of the researchers have not been robust enough to unequivocally state that TMS method can be adopted in the treatment of schizophrenia symptoms.

Conclusion

The TMS method has been adopted in the study of various cognitive functions in biopsychology. The non-invasive method has had significant contributions in the study as well as in the treatment of schizophrenia, a psychotic disorder that is characterized by symptoms such as hallucination, delusion, and anhedonia amongst others. The TMS method has enabled the researchers to understand the various parts of the brain that are associated with every symptom of schizophrenia and that when targeted can lead to the management and control of the same symptom. This understanding has equally led to the treatment of some of the symptoms through the subjecting the patients to the TMS treatment session.

From the critical analysis low-frequency, TMS administered at the TPC, side of the brain has significant effects in the treatment of auditory hallucination. Greatest efficacy is achieved when the patient is subjected to more than 10 treatment sessions. Significant improvement in the other positive symptoms is however not achieved since they are in most cases associated with the dysfunction of other parts of the brain other than the TPC. Subjecting the schizophrenia patients to high-frequency TMS treatment improves the negative symptoms; however, the treatment has negative effects on the positive symptoms making them worse. Although the TMS method has significant contributions to the understanding of the causes of the various symptoms of schizophrenia, it is inaccurate to assert that the method can be effectively adopted in the treatment of the symptoms. There is evidence that TMS can assist in the reduction of some symptoms such auditory hallucination, however, there is insufficient evidence to justify that the method can be used in the reduction of other symptoms as well due to the mixed results that have been reported by various researchers. Nevertheless, if future studies on the use of TMS method in the management of schizophrenia symptoms are done more accurately, there is a high possibility that TMS method may be useful in the management and treatment of most of the schizophrenia symptoms.