RTMS Parameters

November 18, 2011 · Posted in Current Treatments 

rTMSAs we wrote yesterday, repeated transcranial magnetic stimulation (rTMS) is a treatment in which a magnetic field is applied to a patient’s head, where it is able to affect tissue 2-3 centimeters into the brain.  The major studies of rTMS, by O’Reardon and colleagues (2007) and George et al. (2010), were performed with patients who were medication-free during the course of rTMS treatment. However, it is routine clinical practice to use rTMS as an adjunctive treatment to ongoing antidepressant therapy, and in these cases, response rates appear to be close to 50%, even in patients with considerable treatment resistance to prior antidepressants.

Using the FDA-approved parameters, treatment is typically delivered with with an rTMS machine that stimulates the left prefrontal cortical area of the brain at a stimulation intensity of 120% of the patient’s motor threshold at a frequency of magnetic impulses of 10 per second or 10 Hz.  The motor threshold is the intensity of stimulation necessary to cause the thumb to move when the motor cortex is stimulated, but the treatment is given over the frontal cortex which does not produce any movements or other sensations.

Each treatment lasts for about 20 minutes and does not require any anesthesia or premedication. The patient is awake and alert during the procedure, and cognitive side effects are minimal.  Patients occasionally experience some pain from contraction of the scalp muscles under the magnet.

The rapid reversal of the magnetic field occurring ten times per second induces electrical stimulation of the brain at the same frequency and causes discharge of neurons. High frequency (at 10 or 20Hz) neuronal activity appears to increase activity (blood flow or metabolism) in the brain, while lower frequency stimulation, such as at 1 Hz, appears to decrease brain activity. In both cases, the effects last at least 48 hours after the last of a two- or three-week series of treatments.  RTMS increases brain-derived neurotrophic factor (BDNF) in the brain, and BDNF is released when nerves fire at a fast frequency. The release of BDNF appears to be necessary for long-term learning and memory.

Sitting passively versus receiving therapy during rTMS

In clinical practice, most treatments are administered by a technician. However, in some instances, clinicians engage patients in forms of active psychotherapy while they are receiving the rTMS. In several review chapters this editor Post and Andrew Speer contributed to the books TMS in Clinical Psychiatry, Magnetotherapy: Potential Therapeutic Benefits and Adverse Effects, and Transcranial Magnetic Stimulation in Neuropsychiatry, we recommended the exploration of such a practice based on a variety of clinical and theoretical grounds as discussed below.

If a patient participates in psychotherapeutic maneuvers such as desensitization therapy or other forms of new learning, it is theoretically possible that stimulating the brain with rTMS could enhance their effects. There is already some evidence that pairing psychotherapy with another type of treatment can increase the benefits of both. The compound d-cycloserineis a glutamate agonist that improves neuronal activity, and it has been shown to enhance treatment when paired with desensitization therapy in patients with anxiety disorders and phobias. New neurophysiological and biological data indicate that active new learning is required for the process of densensitization or habituation to previous anxiety-inducing stimuli, and d-cycloserineis may contribute to the new learning.

Thus, it is possible that a non-pharmacological means of enhancing glutamate NMDA receptors such as rTMS could also enhance new learning during systematic psychotherapeutic approaches. Using studies of animals’ hippocampi, scientists have developed a model of learning and memory at the synaptic level called long-term potentiation, in which high-frequency stimulation of the brain enhances the specific synaptic inputs that are being engaged, but not other inputs. In a process known as activity-dependent neuroplasticity, only those stimulated synapses show long-term enhancement.  Thus, engaging (activating) appropriate synaptic connections with psychotherapy could lead to rTMS enhancement of these selectively activated synapses, achieving what is sometimes referred to as experience-dependent neuroplasticity. RTMS applied simultaneously with psychotherapy to achieve experience-dependent neuroplasticity might be more effective than rTMS applied while the patient sits passively and or while the patient experiences the recurrent negative thoughts typically associated with clinical depression.  While systematic controlled clinical trials of rTMS with and without psychotherapy have not yet been conducted, there appears to be little downside to making such attempts in clinical treatment settings.  Anecdotal reports from several physicians who do employ this combined therapy approach suggest that they have seen a high response rate.

More articles about rTMS will be posted next week!

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