Three-Dimensional Distribution of the Electric Field Induced in the Brain by Transcranial Magnetic Stimulation Using Figure-8 and Deep H-Coils

Advanced Technology Center, Sheba Medical Center, Tel-Hashomert, Israel.
Journal of Clinical Neurophysiology (Impact Factor: 1.43). 03/2007; 24(1):31-8. DOI: 10.1097/WNP.0b013e31802fa393
Source: PubMed

ABSTRACT The H-coils are a novel development in transcranial magnetic stimulation (TMS), designed to achieve effective stimulation of deep neuronal regions without inducing unbearable fields cortically, thus broadly expanding the potential feasibility of TMS for research and for treating various neurologic disorders. This study compared the field distribution of two H-coil versions, termed H1 and H2, and of a standard figure-of-eight coil. Three-dimensional electrical field distributions of the H1 and H2-coils, designed for effective stimulation of prefrontal regions, and of a standard figure-8 coil, were measured in a head model filled with physiologic saline solution. With stimulator output at 120% of the hand motor threshold, suprathreshold field is induced by the H1-coil at lateral and medial frontal regions at depths of up to 4 to 5 cm, and by the H2-coil at medial prefrontal regions up to 2 to 3 cm, and at lateral frontal regions up to 5 to 6 cm. The figure-8 coil induced suprathreshold field focally under the coil's central segment, at depths of up to 1.5 cm. The ability of the H-coils to stimulate effectively deeper neuronal structures is obtained at the cost of a wider electrical field distribution in the brain. However, the H-coils enable simultaneous stimulation of several brain regions, whereas the depth penetration in each region can be controlled either by adjusting the stimulator output, and/or by varying the distance between various coil elements and the skull.

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    • "For dTMS sessions we used Brainsway's H1 coil deep TMS System (Brainsway, Har Hotzvim, Jerusalem, Israel). The H1 coil is designed to elicit neuronal activation in medial and lateral prefrontal regions, including the orbitofrontal cortex, with a preference for the left hemisphere (Roth et al., 2007). H1 coils were positioned over patient's scalp. "
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    ABSTRACT: Introduction: Co-occurrence of Major Depressive (MDD) and Alcohol Use Disorders (AUDs) is frequent, causing more burden than each disorder separately. Since the dorsolateral prefrontal cortex (DLPFC) is critically involved in both mood and reward and dysfunctional in both conditions, we aimed to evaluate the effects of dTMS stimulation of bilateral DLPFC with left prevalence in patients with MDD with or without concomitant AUD. Methods: Twelve MDD patients and 11 with concomitant MDD and AUD (MDD+AUD) received 20 dTMS sessions. Clinical status was assessed through the Hamilton Depression Rating Scale (HDRS) and the Clinical Global Impressions severity scale (CGIs), craving through the Obsessive Compulsive Drinking Scale (OCDS) in MDD+AUD, and functioning with the Global Assessment of Functioning (GAF). Results: There were no significant differences between the two groups in sociodemographic (age, sex, years of education and duration of illness) and baseline clinical characteristics, including scores on assessment scales. Per cent drops on HDRS and CGIs scores at the end of the sessions were respectively 62.6% and 78.2% for MDD+AUD, and 55.2% and 67.1% for MDD (p<0.001). HDRS, CGIs and GAF scores remained significantly improved after the 6-month follow-up. HDRS scores dropped significantly earlier in MDD+AUD than in MDD LIMITATIONS: The small sample size and factors inherent to site and background treatment may have affected results. Conclusions: High frequency bilateral DLPFC dTMS with left preference was well tolerated and effective in patients with MDD, with or without AUD. The antidepressant effect of dTMS is not affected by alcohol abuse in patients with depressive episodes. The potential use of dTMS for mood modulation as an adjunct to treatment in patients with a depressive episode, with or without alcohol abuse, deserves further investigation.
    Journal of Affective Disorders 11/2014; 174. DOI:10.1016/j.jad.2014.11.015 · 3.38 Impact Factor
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    • "Rather than display each site as a single point in cortical space, this method represents each site as a spherical ROI (r = 8 mm) centered on the peak SMG voxel from the critical fMRI contrast between the picture–picture versus word–word conditions. This radius was chosen to illustrate the likely extent of rTMS effects on cortex, consistent with the estimate that using a standard figure-8 coil at an intensity of less than 120% of motor threshold is likely to stimulate cortex at a depth of up to roughly 1.5 cm (Roth et al., 2007). As clearly seen in Figure 2, there is a wide range of variation of rTMS stimulation within left SMG. "
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    ABSTRACT: What does it mean to have a "verbal cognitive style?" We adopt the view that a cognitive style represents a cognitive strategy, and we posit the conversion hypothesis - the notion that individuals with a proclivity for the verbal cognitive style tend to code nonverbal information into the verbal domain. Here we used repetitive transcranial magnetic stimulation (rTMS) to disrupt this hypothesized verbal conversion strategy. Following our previous research implicating left supramarginal gyrus (SMG) in the verbal cognitive style, we used an fMRI paradigm to localize left SMG activity for each subject, then these functional peaks became rTMS targets. Left SMG stimulation impaired performance during a task requiring conversion from pictures to verbal labels. The magnitude of this effect was predicted by individuals' level of verbal cognitive style, supporting the hypothesized role of left SMG in the verbal labeling strategy, and more generally supporting the conversion hypothesis for cognitive styles.
    Frontiers in Human Neuroscience 01/2014; 8:15. DOI:10.3389/fnhum.2014.00015 · 2.99 Impact Factor
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    • "This is an advantage in the context of magnetic seizure therapy, but in subconvulsive applications, this is a significant source of risk. A family of dTMS coil designs called Hesed (H) coils has been developed with the goal of effective stimulation of deep brain structures (Roth et al., 2002; Zangen et al., 2005; Roth et al., 2007a,b). More than twenty different types of H coils have been designed and manufactured for various applications (Roth et al., 2013). "
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    ABSTRACT: To explore the field characteristics and design tradeoffs of coils for deep transcranial magnetic stimulation (dTMS). We simulated parametrically two dTMS coil designs on a spherical head model using the finite element method, and compare them with five commercial TMS coils, including two that are FDA approved for the treatment of depression (ferromagnetic-core figure-8 and H1 coil). Smaller coils have a focality advantage over larger coils; however, this advantage diminishes with increasing target depth. Smaller coils have the disadvantage of producing stronger field in the superficial cortex and requiring more energy. When the coil dimensions are large relative to the head size, the electric field decay in depth becomes linear, indicating that, at best, the electric field attenuation is directly proportional to the depth of the target. Ferromagnetic cores improve electrical efficiency for targeting superficial brain areas; however magnetic saturation reduces the effectiveness of the core for deeper targets, especially for highly focal coils. Distancing winding segments from the head, as in the H1 coil, increases the required stimulation energy. Among standard commercial coils, the double cone coil offers high energy efficiency and balance between stimulated volume and superficial field strength. Direct TMS of targets at depths of ∼4cm or more results in superficial stimulation strength that exceeds the upper limit in current rTMS safety guidelines. Approaching depths of ∼6cm is almost certainly unsafe considering the excessive superficial stimulation strength and activated brain volume. Coil design limitations and tradeoffs are important for rational and safe exploration of dTMS.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 12/2013; 125(6). DOI:10.1016/j.clinph.2013.11.038 · 3.10 Impact Factor
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