Article

Biophysical foundation underlying TMS: Setting the stage for an effective use of neurostimulation in the cognitive neurosciences

Highland Instruments, Cambridge, MA 02138, USA.
Cortex (Impact Factor: 5.13). 11/2008; 45(9):1025-34. DOI: 10.1016/j.cortex.2008.10.002
Source: PubMed

ABSTRACT

Transcranial Magnetic Stimulation (TMS) induces electrical currents in the brain to stimulate neural tissue. This article reviews our present understanding of TMS methodology, focusing on its biophysical foundations. We concentrate on how the laws of electromagnetic induction apply to TMS; addressing issues such as the location, area (i.e., focality), depth, and mechanism of TMS. We also present a review of the present limitations and future potential of the technique.

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Available from: Richard J Rushmore
    • "Recently there has been considerable interest on the effects of repetitive transcranial magnetic stimulation (rTMS) on cortical excitability. Biophysical foundations underlying TMS effects are reviewed in Wagner et al. (2009), while results of investigation of connectivity of the cortical structures during TMS using positron emission tomography (PET) was reported by Paus et al. (1997). TMS operates based on Faraday's law of electromagnetic induction, which describes the process by which a changing magnetic field induces the flow of electric current in a nearby conductor, one preferentially standing at 90% to the magnetic field. "
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    ABSTRACT: Autism spectrum disorder (ASD) is a developmental disorder marked by difficulty in social interactions and communication. ASD also often present symptoms of autonomic nervous system (ANS) functioning abnormalities. In individuals with autism the sympathetic branch of the ANS presents an over-activation on a background of the parasympathetic activity deficits, creating an autonomic imbalance, evidenced by a faster heart rate with little variation and increased tonic electrodermal activity. The objective of this study was to explore the effect of 12 sessions of 0.5 Hz repetitive transcranial magnetic stimulation (rTMS) over dorsolateral prefrontal cortex (DLPFC) on autonomic activity in children with ASD. Electrocardiogram and skin conductance level (SCL) were recorded and analyzed during each session of rTMS. The measures of interest were time domain (i.e., R-R intervals, standard deviation of cardiac intervals, NN50-cardio-intervals >50 ms different from preceding interval) and frequency domain heart rate variability (HRV) indices [i.e., power of high frequency (HF) and low frequency (LF) components of HRV spectrum, LF/HF ratio]. Based on our prior pilot studies it was proposed that the course of 12 weekly inhibitory low-frequency rTMS bilaterally applied to the DLPFC will improve autonomic balance probably through improved frontal inhibition of the ANS activity, and will be manifested in an increased length of cardiointervals and their variability, and in higher frequency-domain HRV in a form of increased HF power, decreased LF power, resulting in decreased LF/HF ratio, and in decreased SCL. Our post-12 TMS results showed significant increases in cardiac intervals variability measures and decrease of tonic SCL indicative of increased cardiac vagal control and reduced sympathetic arousal. Behavioral evaluations showed decreased irritability, hyperactivity, stereotype behavior and compulsive behavior ratings that correlated with several autonomic variables.
    No preview · Article · Sep 2015 · Applied Psychophysiology and Biofeedback
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    • "Neuromodulatory brain stimulation can induce plastic reorganization of cortical circuits which persist beyond the period of stimulation [1]. A variety of neuromodulation techniques are currently used to modulate brain activity, the most common of which are repetitive Transcranial Magnetic Stimulation (rTMS) and transcranial Direct Current Stimulation (tDCS). "
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    ABSTRACT: Neuromodulatory brain stimulation can induce plastic reorganization of cortical circuits that persist beyond the period of stimulation. Most of our current knowledge about the physiological properties has been derived from the motor cortex. The integration of transcranial magnetic stimulation (TMS) and electroencephalography (EEG) is a valuable method for directly probing excitability, connectivity and oscillatory dynamics of regions throughout the brain. Offering in depth measurement of cortical reactivity, TMS-EEG allows the evaluation of TMS-evoked components that may act as a marker for cortical excitation and inhibition. A growing body of research is using concurrent TMS and EEG (TMS-EEG) to explore the effects of different neuromodulatory techniques such as repetitive TMS and transcranial direct current stimulation on cortical function, particularly in non-motor regions. In this review, we outline studies examining TMS-evoked potentials and oscillations before and after, or during a single session of brain stimulation. Investigating these studies will aid in our understanding of mechanisms involved in the modulation of excitability and inhibition by neuroplasticity following different stimulation paradigms. Copyright © 2015 Elsevier Inc. All rights reserved.
    Full-text · Article · Jul 2015 · Brain Stimulation
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    • "One of our recent studies showed that application of rTMS can prevent kindling-induced synaptic potentiation (Yadollahpour et al., 2014). This synaptic potentiation has been suggested to be accompanied with different changes in electrophysiological properties of neurons (Hallett et al., 1999; Wagner et al., 2009; Pell et al., 2011 ) in various brain areas involved in seizure generation or propagation of amygdala kindling, including the hippocampus. Previous studies showed that CA1 region of the hippocampus is one of the most important areas involved in the propagation of seizure in amygdala-kindled rats (Dasheiff and McNamara, 1982; MirnajafiZadeh et al., 2002). "
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    ABSTRACT: Introduction: Considering the antiepileptogenic effects of repeated transcranial magnetic stimulation (rTMS), the effect of rTMS applied during amygdala kindling on spontaneous activity of hippocampal CA1 pyramidal neurons was investigated. Materials and Methods: A tripolar electrode was inserted in basolateral amygdala of Male Wistar rats. After a recovery period, animals received daily kindling stimulations until they reached stage 5 seizure. In one group of animals, rTMS at frequency of 1 Hz were applied to hippocampus once daily at 5 min after termination of kindling stimulations. 24 h after the last kindling stimulation, spontaneous activity of CA1 pyramidal neurons of the hippocampus was investigated using whole cell patch clamp technique. Results: Kindling-induced seizures resulted in increment of spontaneous activity of hippocampal CA1 neurons, but application of rTMS during amygdala kindling prevented it. Moreover, rTMS administration inhibited the kindling-induced enhancement of afterdepolarization (ADP) amplitude and action potential duration. Conclusion: Results of this study suggest that rTMS exerts its anticonvulsant effect, in part, through preventing the amygdala kindling-induced increase in spontaneous activity and excitability of hippocampal CA1 pyramidal neurons. © 2015, Iranian Society of Physiology and Pharmacology. All rights reserved.
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