SAR-161206-transcranial-magnetic-stimulation-for-the-treatment-of-cocai_051818.pdf

44 on the other hand by stimulating the pfcx function

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44 On the other hand, by stimulating the PfCx, function- ing of the cortical network can be strengthened and hopefully improve executive-control circuits. 7,9,35,68 Key TMS factors At present, the need to find the best stimulation parameters to optimize the clinical outcome is the main target. Recent studies have pointed out the importance of the characteris- tics of the magnetic E-field inducted in association with the clinical outcome, theorizing that a deeper stimulation may have more chance of reaching dysfunctional brain areas, and through this “direct way” better odds of obtaining long-lasting effects, such as reduction in craving and drug consumption. 69–71 The activation of targeted brain areas depends on the shape of the magnetic E-field, spatial accuracy, and Substance Abuse and Rehabilitation downloaded from by 71.219.80.117 on 18-Aug-2018 For personal use only. 1 / 1
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Substance Abuse and Rehabilitation 2018:9 submit your manuscript | Dove press Dove press 13 TMS in cocaine addiction penetration depth of stimulation. 72 These factors are dictated by coil geometry, which then defines the capability of stimula- tion to activate the brain areas of interest aimed at restoring the dysfunctional neuronal network, eventually. Considering that the intensity of the E-field is maximal closest to the coil, stimulation intensity is strongest over the brain surface and rapidly attenuates with distance. 73 The most widely used coil implemented in the study of TMS effects is the figure-of-eight coil, which owing to its geometry (figure of eight), is able to project focal fields over the brain surface with high spatial resolution (2.5–3 cm 2 ). 74 However, the E-fields remain quite superficial and tend to dissipate in intensity rapidly, with little chance of reaching deeper brain areas disrupted by the neuropathology of addiction. 73 Moreover, discrepancies in the geometry of magnetic fields generated by the figure-of- eight coil and thus in the localization of the area targeted may account for the variability in effects observed. In 2002, Roth et al designed a new coil called a Hesed-coil (H-coil) able to stimulate the PfCx bilaterally and through the stimulation of frontostriatal projections activate midbrain DA neurons and other subcortical areas involved in dopa- minergic activity, at least in theory. 69,75 Recently, Malik et al tested the capacity of the H-coil to modulate DA release in eight healthy subjects, finding that low-frequency rTMS (1 Hz) significantly decreased DA levels in the substantia nigra and sensorimotor and associative striata. 76 This novel coil seems to have more chance of obtaining consistent and prolonged effects, presumably due to its ability to stimulate subcortical brain regions that are involved in the develop- ment of addiction’s neuropathology. However, since cortical thickness is contained within 2 cm from the skin surface, targeting fifth-layer cortical pyramidal neurons (efferent) may suffice to modulate subcortical circuitries involved in taking and relapse.
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