Low vs. High Frequency TMS

Research into optimal TMS treatment parameters for a given disorder is ongoing. The paper we will consider here, by Kozel and colleagues, looks at frequency of pulse delivery, specifically low versus high frequency TMS in the treatment of PTSD.

The effect TMS has on the brain is contingent upon many factors – frequency being one of them. Broadly speaking, TMS is thought to induce one of two effects in the brain:  an inhibitory effect or an excitatory effect.  The former is a result of low frequency TMS, which corresponds to 1 to 5 hertz, making it less likely the receiving neurons will fire. The latter is a result of high frequency TMS – a frequency of 10 hertz or greater – making it more likely the receiving neurons will fire.

To further clarify the concept of frequency it is important to understand the hertz. The hertz (Hz) is a unit of measure used to describe frequency. 1 Hz is equal to 1 cycle per second. Supposing we were to use 1 Hz in the settings for a TMS treatment session, one pulse would be delivered per second, provided of course that the pulses are delivered continuously (i.e. an interval time of 0). A session that lasts 10 minutes would therefore deliver 600 pulses. This information is important in considering the study by Kozel et al.

They hypothesized that there would be a significant difference in improvement between the two frequencies. Holding other variables constant (i.e. “number of pulses, time for treatment, dose, and treatment location”) the only variable manipulated in their study was frequency. Participants were randomly assigned to the 1 Hz group or the 10 Hz group, which, to reiterate, correspond to low frequency and high frequency TMS, respectively.  Interestingly enough, while both groups did show significant improvement, the study did not reach statistical significance regarding its primary endpoint; suggesting there is no difference in clinical response between the two frequencies. Treatment using 1 Hz was just as effective as 10 Hz.

Given the differing effects low frequency and high frequency TMS are thought to induce, these results are a bit surprising. Perhaps frequency, as the authors mention, is not the main component in determining clinical outcome. Further research is needed to determine this.

This study helps explain why there are two widely used protocols for the treatment of depression.  A left sided, high frequency protocol is the most commonly used. However, a right sided, low frequency protocol has also been shown to be effective.  In some patients, both protocols are used in order to maximize the clinical response to treatment.

At Principium Psychiatry, patients receive an in depth assessment and treatment plan recommendation. The treatment plan will include whether TMS is appropriate, and which protocol will be most helpful in targeting the patient’s symptoms. Principium Psychiatry offers state of the art medicine in the heart of NYC, including TMS, ketamine, psychopharmacology, and other treatments. Principium offers four convenient locations; two offices in Manhattan, one near Grand Central Station and another office along Wall Street. In addition, we have an office in Greenwich Connecticut and Santa Monica California.

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