Low field magnetic stimulation

Low field magnetic stimulation (LFMS) is a form of non-invasive neurostimulation that uses broadly distributed, low field strength, oscillating magnetic stimulation to manipulate brain function.[1] LFMS is in the class of non-invasive brain stimulation techniques such as transcranial direct-current stimulation (tDCS), transcranial alternating current stimulation (tACS) and variants, transcutaneous electrical nerve stimulation (TENS), transcranial magnetic stimulation (TMS), and electroconvulsive therapy (ECT). However, LFMS has distinct parameter sets from each of these aforementioned approaches:

Mechanism of action

LFMS utilizes an oscillating magnetic field to induce an alternating electric field. While the effects of LFMS have not been explicitly tested on neurons, several pieces of evidence indicate it is affecting brain tissue. As described below, LFMS was first discovered to affect the mood of depressed patients (and thus must be affecting neural elements). The most direct test of LFMS efficacy to date measured glucose uptake in the human brain using PET imaging. The authors observed that glucose uptake levels were decreased following LFMS.[2] Relatedly, high frequency electric fields can modulate neuronal activity: 1–5 kHz tACS has been observed to increase the excitability of motor cortex.[3] These high frequencies are in the range of LFMS.

Therapeutic efficacy

LFMS is being tested as a potential rapidly-acting, anti-depressant therapy for the treatment of major depressive disorder and bipolar depressive disorder. This stimulation modality was discovered serendipitously by Aimee Parow and Perry Renshaw at McLean Hospital, after depressed patients were being scanned as part of a functional MRI (fMRI) research study using echo-planar spectroscopic imaging. Patients exiting the MRI scanner self-reported feeling calmer and having an improved mood within 20 minutes.[4] A research team, led by Michael Rohan, then specifically tested whether patients showed improved mood after active stimulation or after a control ‘sham’ treatment.[1] This study verified that LFMS can have an immediate effect on mood after a 20 minute treatment and thus has the potential to provide relief in emergency situations. Another report also suggests potential long-term anti-depressant efficacy.[5]

LFMS is currently being tested in a series of clinical trials by McLean hospital, NIMH, Weill-Cornell Medical Center, Medical University of South Carolina, and by Tal Medical.

Safety

LFMS, due to the use of magnetic stimulation, avoids skin and muscle irritation, as well as headache, associated with tDCS and tACS.[6][7] The low induced electric field strengths are subthreshold for most neural tissue,[8] though the direct effect of LFMS on neural tissue has not been rigorously tested. By comparison, however, seizure inducing approaches, such as electroconvulsive therapy (ECT), use a current amplitudes of about 800 mA, and magnetic seizure therapy (MST) creates field strengths of > 200 V/m.[9] Fields generated by LFMS and other neurostimulation techniques are less than 1% of the level required to generate seizure.

Furthermore, LFMS is not associated with the cognitive side effects of ECT. According to Rohan, "While other brain stimulation treatments like ECT and TMS are often effective for the treatment of depression, they typically take longer to impact mood, and ECT is associated with side effects such as memory loss."[10]

Comparison of Electromagnetic Treatment Modalities
Treatment Electric Field Strength (Volts per Meter)
Electroconvulsive therapy
200(Over 200 V/m)
Deep brain stimulation
100(V/m)
Transcranial magnetic stimulation
100(V/m)
Low field magnetic stimulation
1(V/m)

Low magnetic field stimulation exerts its effects with low powered electric fields, too weak to depolarize neurons while still influencing neuronal activity.[8]

See also

References

  1. 1 2 3 Rohan, ML (August 1, 2014). "Rapid Mood-Elevating Effects of Low Field Magnetic Stimulation in Depression". Biological Psychiatry 76: 186–193. doi:10.1016/j.biopsych.2013.10.024. PMID 24331545.
  2. ↑ Volkow, ND (2010). "Effects of low-field magnetic stimulation on brain glucose metabolism". NeuroImage 51: 623–628 Contents. doi:10.1016/j.neuroimage.2010.02.015. PMC 2862488. PMID 20156571.
  3. ↑ Chaieb, L (2011). "Transcranial alternating current stimulation in the low kHz range increases motor cortex excitability". Restorative Neurology and Neuroscience 29: 167–175 Contents. doi:10.3233/RNN-2011-0589. PMID 21586823.
  4. ↑ Rohan, ML (2004). "Low-Field Magnetic Stimulation in Bipolar Depression Using an MRI-Based Stimulator". American Journal of Psychiatry 161: 93–98. doi:10.1176/appi.ajp.161.1.93. PMID 14702256.
  5. ↑ Vaziri-Bozorg, S (2012). "Antidepressant effects of magnetic resonance imaging—based stimulation on major depressive disorder: a double-blind randomized clinical trial". Brain Imaging and Behavior 6: 70–76. doi:10.1007/s11682-011-9143-2. PMID 22069111.
  6. ↑ Rodríguez, N (2014). "Skin lesions induced by transcranial direct current stimulation (tDCS)". Brain stimulation 7: 765–7. doi:10.1016/j.brs.2014.06.005. PMID 25073936.
  7. ↑ Janicak, P. (2008-02-01). "Transcranial magnetic stimulation in the treatment of major depressive disorder: a comprehensive summary of safety experience from acute exposure, extended exposure, and during reintroduction treatment". The Journal of Clinical Psychiatry 69 (2): 222–232. ISSN 1555-2101. PMID 18232722.
  8. 1 2 Fröhlich, F (2010). "Endogenous electric fields may guide neocortical network activity". Neuron 67 (1): 129–143. doi:10.1016/j.neuron.2010.06.005. PMC 3139922. PMID 20624597.
  9. ↑ Deng, ZD (2011). "Electric field strength and focality in electroconvulsive therapy and magnetic seizure therapy: a finite element simulation study.". Journal of Neural Engineering 8: 016007. doi:10.1088/1741-2560/8/1/016007. PMC 3903509. PMID 21248385.
  10. ↑ Bobinchock, Adriana (July 28, 2014). "New treatment for depression shows immediate results". Harvard Gazette. McLean Hospital Communications. Retrieved 5 January 2015.
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