Here's a little bit of clarity as to how TMS works (in its inhibitory, rather than excitory, mode) (uh, meaning when in slows down neurons rather than speeding them up):
The Lancet
Volume 352, Number 9131 12 September 1998
Decreased neuronal inhibition in cerebral cortex in obsessive-compulsive disorder on transcranial magnetic stimulation
Benjamin D Greenberg, Ulf Ziemann, Ann Harmon, Dennis L Murphy, Eric M Wassermann
Transcranial magnetic stimulation (TMS), initially developed as a non-invasive probe of brain motor physiology, has been applied to research of neuropsychiatric illness. TMS can assess the degree of neuronal inhibition in the cerebral cortex. Cortical motor-output cells are activated with powerful magnetic pulses produced by an electromagnetic coil placed on the scalp. The subsequent motor-evoked potentials (MEPs) are decreased when subthreshold TMS pulses precede by 25 ms stimuli above the threshold. This phenomenon of intracortical inhibition is thought to be due to activation of inhibitory interneurons by the subthreshold pulse. One study found that intracortical inhibition was defective in patients with Tourette's syndrome,2 which suggests an influence on the intrusive motor phenomena characterising that illness. Because obsessive-compulsive disorder and Tourette's syndrome seem to be related by clinical phenomena and heritability, we used TMS to test for intracortical inhibitory abnormalities in patients with obsessive-compulsive disorder.
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National Institute of Mental Health (B D Greenberg), and National Institute of Neurological Disorders and Stroke, Bethesda 20892, MD, USA
I have no idea *what* an "interneuron" is. Sounds like a neuron between other neurons, as opposed to ones that make muscles twitch or tell the difference between hot and cold.
Here's another article excerpt (italics mine, and I apologize if the science lingo is a bit thick):
The Lancet
Volume 353, Number 9171 26 June 1999
Low-frequency repetitive transcranial magnetic stimulation improves intractable epilepsy
Frithjof Tergau, Ute Naumann, Walter Paulus, Bernhard J Steinhoff
Repetitive transcranial magnetic stimulation (rTMS) induces lasting effects on cortical excitability. In particular, long trains of low-frequency rTMS are described to reduce cortical excitability.1 Epilepsy is associated with TMS-assessed cortical hyperexcitability.2 We sought to find out whether patients with epilepsy benefit from low-frequency rTMS treatment on the following grounds: animal experiments have shown that low-frequency repetitive electrical stimulation blocked the development of seizures in rats;3 and 0·3 Hz rTMS in complex-partial epilepsy of mesiobasal limbic onset has led to a decrease in epileptic spike frequency....
...Low-frequency rTMS may temporarily improve intractable epilepsy. Long-term depression as a phenomenon of synaptic plasticity, which can be induced by long-term low-frequency repetitive electric stimulation, may be part of the underlying physiology.3 The reduction of seizures was of similar range as seen under intermittent repetitive vagus nerve stimulation.5
"Synaptic plasticity" refers to the ability of neurons to take on different tasks or alter their behavior.
Most of these studies seem to focus on the inhibitory aspects rather than the excitory aspects of the magnetic fields - that is, they're using low Hz fields rather than higher Hz fields (apparently). I suppose an overexcited brain is more likely to go into seizures. |
