**5. OCD as a circuit disorder**

Several inclusive models have been suggested to explain the neurobiology of OCD. One is an executive dysfunction model, where there are deficits in impulse control and inhibition of behaviors. Another is a modulatory control model, where the main dysfunction is in regulating socially appropriate behaviors. A recent model proposes OCD as an uncertainty disorder where there is an imbalance between input and input suppression [5]. Regardless of the model, there is abnormal activity in a region of the cortical-striatal-thalamic-cortical circuits. These are multiple parallel interconnected loops between cortical and subcortical areas whose role is to screen out which actions are selected and which are considered maladaptive and ignored. These regions include the dorsolateral prefrontal cortex (DLPFC), orbitofrontal cortex (OFC), medial prefrontal cortex (mPFC), cingulate cortex, caudate nucleus, striatum and thalamus. An abnormality in the functioning of this pathway results in impulsivity, compulsivity, obsessivity, uncertainty, deficits in attentional allocation, sensory-motor gating, modulation of motor activity and more [6, 7].

**6.3. Blinding system**

**refractory OCD**

frequency rTMS [9].

are felt, but no neuronal stimulation is induced.

right PFC with a circular coil for 6 weeks [8].

OCD are described in detail. For an overview, please see **Table 1**.

Clinical trials with TMS ideally should include blinding for the patient, rater and operator. However, in order for the operator of the TMS device to be blinded a unique research TMS system is required. Because of this many TMS studies do not have a blinded TMS operator and the sham arm has the operator rotate the coil 90° against the scalp delivering cutaneous stimulation with the identical sound. Magventure manufactures a double-blind coil, which is in one device; then, the computer tells the operator which side of the coil to use for the patient. Magstim has separate active and sham coils. When conducting a clinical trial, one can use coil A or coil B, as well as a third coil to determine the motor threshold. Both the Magstim and Magventure, require a cutaneous nerve stimulator to induce a superficial sensation during the sham train. Some single-blind studies do not even create a cutaneous sensation at all. Brainsway has the most practical approach, since the H-coil is in a helmet both the active and sham coil is in the same helmet. The subject is assigned a card that interacts with the stimulator and coil through an interface module. The motor threshold is determined with an operator card; then the coil is advanced to the treatment position, and the subject card is inserted, which selects whether the sham or active coil is activated. The sham coil is made of conical windings that do not penetrate the cortex; so, the identical sound and a superficial sensation

TMS for OCD

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http://dx.doi.org/10.5772/intechopen.73594

**7. Detailed review of sham-controlled trials using TMS for treatment** 

In the following paragraphs, the sham-controlled or multi-arm therapeutic studies of TMS for

In 2001, Pino Alonso published a sham-controlled TMS study whereby 18 OCD patients were administered active (N = 10) or sham (N = 8) rTMS for 18 sessions (3 times a week for 6 weeks). Active and sham treatments were administered using low frequency rTMS (1 Hz, 1200 pulses) to the right prefrontal cortex (PFC) using a 70 mm circular coil. The active group was administered 110% of the left hand resting motor threshold (MT) and the sham group was administered 20%MT. Raters and patients were blinded, and operators were unaware of the expected effects of the prescribed intensity. Neither the sham nor active treatment groups had significant reduction in their OCD symptoms following 18 sessions of low frequency rTMS over the

Sachdev et al. randomly designated 12 treatment-resistant OCD subjects to right (n = 6) or left (n = 6) prefrontal rTMS treatment groups. Both groups were administered a figure-8 coil for 10 treatments over 2 weeks at 10 Hz for 1500 pulses at 110% MT. An independent rater evaluated progress once a weekly during treatment then at the 1 month follow up. In both groups, there was a significant improvement after 2 weeks and at the 1 month follow up in the obsessions, compulsions, and total scores on the Yale-Brown Obsessive Compulsive Scale (Y-BOCS). There was not a significant difference between left and right-sided high

The greatest evidence for OCD as a circuit disorder comes from the success of circuit interventions at various locations along the pathway. Specifically, circuit interventions have demonstrated efficacy at the striatum, globus pallidus interna, substantia nigra, thalamus, subthalamic nucleus, anterior cingulate cortex (ACC), OFC and anterior capsulotomy [5].
