Neurobiology of Repeated Transcranial Magnetic Stimulation in the Treatment of Anxiety: a Critical Review Stefano Pallantia,B,C and Silvia Bernardia,B
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Review 163 Neurobiology of repeated transcranial magnetic stimulation in the treatment of anxiety: a critical review Stefano Pallantia,b,c and Silvia Bernardia,b Transcranial magnetic stimulation (TMS) has been applied the posttraumatic stress disorder symptom core can be to a growing number of psychiatric disorders as hypothesized. TMS remains an investigational intervention a neurophysiological probe, a primary brain-mapping tool, that has not yet gained approval for the clinical treatment of and a candidate treatment. Although most investigations any anxiety disorder. Clinical sham-controlled trials are have focused on the treatment of major depression, scarce. Many of these trials have supported the idea that increasing attention has been paid to anxiety disorders. TMS has a significant effect, but in some studies, the effect The aim of this study is to summarize published findings is small and short lived. The neurobiological correlates about the application of TMS as a putative treatment for suggest possible efficacy for the treatment of social anxiety disorders. TMS neurophysiological and mapping anxiety that still has to be investigated. Int Clin findings, both clinical and preclinical, have been included Psychopharmacol 24:163–173 c 2009 Wolters Kluwer when relevant. We searched Medline, PsycInfo, and the Health | Lippincott Williams & Wilkins. Cochrane Library from 1980 to January 2009 for the terms ‘generalized anxiety disorder’, ‘social anxiety disorder’, International Clinical Psychopharmacology 2009, 24:163–173 ‘social phobia’, ‘panic’, ‘anxiety’, or ‘posttraumatic stress Keywords: anxiety, cortical excitability, panic, posttraumatic stress disorder, disorder’ in combination with ‘TMS’, ‘cortex excitability’, repeated transcranial magnetic stimulation, social anxiety, transcranial ‘rTMS’, ‘motor threshold’, ‘motor evoked potential’, ‘cortical magnetic stimulation silent period’, ‘intracortical inhibition’, ‘neuroimaging’, or ‘intracortical facilitation’. Most of the therapeutic aDepartment of Psychiatry, The Mount Sinai School of Medicine, New York, USA, b c experiences with repetitive TMS available in the literature Universita` degli Studi di Firenze and Istituto di Neuroscienze, Firenze, Italy are in the form of case reports, not controlled or blinded Correspondence to Stefano Pallanti, Department of Psychiatry, Box 1230, studies. Stimulation of the right dorsolateral prefrontal The Mount Sinai School of Medicine, 1 Gustave Levy Place, New York, cortex, especially at high frequencies, has been reported to NY 10029, USA Tel: + 1 3933 8279 1581; fax: + 1 3905 5587 8789; reduce anxiety symptoms in posttraumatic stress disorder e-mail: [email protected] and panic disorder; nevertheless, results are mixed. A specific role for the right dorsolateral prefrontal cortex in Received 21 January 2009 Accepted 26 March 2009 Introduction with neuronal transmission, leading to word-finding Transcranial magnetic stimulation (TMS) is a noninvasive, difficulties and speech arrest (Pascual-Leone et al., 1991). relatively focal technique for directly stimulating cortical neurons. TMS causes a depolarization of neurons Emerging data suggest that different rTMS frequencies (Belmaker and Fleischmann, 1995) with cortical changes can lead to alterations of cerebral metabolism, with in monoamines (Ben-Shachar et al., 1997). However, the high-frequency stimulation (20 Hz) leading to increased effect of magnetic stimulation varies depending on the regional cerebral metabolism (George et al., 1996) and location, intensity, and frequency of the magnetic pulses lower-frequency stimulation (1–5 Hz) leading to decreased and it is still not completely understood. Examples of the regional cerebral metabolism in normal volunteers variety of effects and potentialities of TMS are: single (Speer et al., 2000). or paired-pulse magnetic stimulation over the motor cortex can lead to excitation of the motor cortex and Therapeutic potential for rTMS in the treatment of subsequent motor-evoked potential (MEP) and move- neuropsychiatric conditions has been hypothesized, and ment (Wassermann, 1992). Recordings of the MEP allow trials mostly using the focal figure-eight coil have been for noninvasive mapping of this cortical area in humans. applied to neuropsychiatric conditions. Most clinical trials Repeated pulses of magnetic stimulation (rTMS) to with rTMS have been focused on major depression. Broca’s area in the dominant hemisphere can interfere Today, therapeutic rTMS has been accepted as a standard treatment for resistant depression in Canada, Israel, and Part of the data presented in this article has been presented as poster format at recently in the US. A smaller number of rTMS studies the congress ‘XI CONGRESSO della Societa` Italiana di Psicopatologia’ 21–25 February 2006, Rome, Italy and at ‘Advanced Maudsley Forum 2008’, London, have also focused attention on rTMS’s therapeutic 8–12 September 2008. potential in anxiety disorders. 0268-1315 c 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI: 10.1097/YIC.0b013e32832c2639 Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. 164 International Clinical Psychopharmacology 2009, Vol 24 No 4 Anxiety, fear, and stress responses are conditions the amygdala/limbic system. In contrast, disorders such as characterized by cognitive arousal accompanied by bodily generalized anxiety disorder (GAD) and OCD that sensation because of activation of the peripheral nervous involve worry and rumination seem to be characterized system, with subsequent autonomic and sympathetic by increased activity of the PFC. Thus, differences in the responses (hyperventilation, dizziness, tachycardia, activity of the PFC and, subsequently, the cortical/limbic increased blood pressure, gastrointestinal disease). The network, might underlie the puzzling results obtained for peripheral activation seems to reflect a central increase in the application of rTMS as a treatment for anxiety. Given cortical excitability in different regions of the brain. In the current mixed results of the actual research on the fact, an association between relative electroencephalogram topic, and given the recent hypothesis of Berkowitz et al. (EEG) right-frontal hyperactivity and the state or trait (2007), there is a need to critically revisit the area. This measures of anxiety has been shown (Sutton and study also cites neurophysiological investigations relevant Davidson, 1997; Davidson et al., 2000; Crost et al., to the future anxiolytic potential of rTMS. Neuronal 2008). This increase in cortical excitability in association correlates and current opinions in neurobiology, with a with increased cognitive arousal and autonomic system special focus on cortical excitability, are reviewed for each responses may provide a rationale for the potential disorder to provide critical knowledge of the hypotheses therapeutic effect of rTMS in anxiety. regarding the treatment potential of rTMS. Transcranial magnetic stimulation and anxiety TMS also serves as an investigational tool for cortical excitability in anxiety, revealing a correlation between the The aim of this review paper is to critically revisit the amplitude ratio of the MEP threshold and neuroticism evidence regarding the effect of rTMS on anxiety (N), a stable measure of trait-level anxiety (Wassermann disorders. We excluded obsessive compulsive disorder et al., 2001). Oathes et al. (2008) assessed corticospinal (OCD), which we consider separately because of its motor responses during worry induction, motor imagery, peculiar clinical features, which seem to involve distinct and mental arithmetic. TMS applied over the primary brain circuitries and systems (Berkowitz et al., 2007). motor cortex elicited larger corticospinal motor responses rTMS has been hypothesized to have anxiolytic potential during worry than during mental arithmetic and smaller in humans. The first studies in humans were conducted responses than during motor imagery of the maximum on healthy volunteers. Schutter et al. (2001) reported voluntary contraction of targeted muscles. a reduction in self-rated anxiety levels after slow rTMS in the right dorsolateral prefrontal cortex (DLPFC), associated with a contralateral increase in y-activity. Low-frequency Search strategy rTMS of the right DLPFC was followed by selective We searched Medline, PsycInfo, and the Cochrane attention to angry faces, which was interpreted as an Library from 1980 to April 2008 for the terms ‘generalized anxiolytic effect through right-hemispheric inhibition anxiety disorder’, ‘social anxiety disorder’, ‘social phobia’, (D’Alfonso et al., 2000). There is also a preclinical study ‘panic’, ‘anxiety’, or ‘posttraumatic stress disorder’ in supporting the anxiolytic potential of rTMS. Kanno et al. combination with ‘TMS’, ‘cortex excitability’, ‘rTMS’, (2003) investigated the effects of TMS in Wistar rats ‘motor threshold’, ‘motor evoked potential’, ‘cortical using the elevated plus-maze test. After a 3-day series silent period’, ‘intracortical inhibition’, ‘neuroimaging’, of rTMS, a significant improvement in anxiety-related or ‘intracortical facilitation’. Owing to the small number behavior was observed. of studies identified, all reports including controlled randomized clinical trials, open-label trials and case However, opposing findings have also been published. reports were included in this review. The review was Other reports suggested that rTMS may instead induce limited to published reports