Transcranial Magnetic Stimulation Elicits Coupled Neural and Hemodynamic Consequences

Helen Wills Neuroscience Institute, Group in Vision Science, School of Optometry, University of California, Berkeley, CA 94720, USA.
Science (Impact Factor: 33.61). 10/2007; 317(5846):1918-21. DOI: 10.1126/science.1146426
Source: PubMed


Transcranial magnetic stimulation (TMS) is an increasingly common technique used to selectively modify neural processing.
However, application of TMS is limited by uncertainty concerning its physiological effects. We applied TMS to the cat visual
cortex and evaluated the neural and hemodynamic consequences. Short TMS pulse trains elicited initial activation (∼1 minute)
and prolonged suppression (5 to 10 minutes) of neural responses. Furthermore, TMS disrupted the temporal structure of activity
by altering phase relationships between neural signals. Despite the complexity of this response, neural changes were faithfully
reflected in hemodynamic signals; quantitative coupling was present over a range of stimulation parameters. These results
demonstrate long-lasting neural responses to TMS and support the use of hemodynamic-based neuroimaging to effectively monitor
these changes over time.

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    • "These data suggest that the TMS, eliciting neural and haemodynamic changes, although for short-term after the pulse, could itself produce phenomena associated with the induction of spike timing-dependent modulation (for a review see Feldman, 2012). Therefore, a potential mechanism underlying the observed MEP changes could be the continuous elevation of neural activity induced through sequential TMS pulses (Allen et al., 2007) that promote a corticospinal excitability modulation by reducing the synaptic firing threshold. Thus, repeated single TMS pulses might depolarise the neuronal membrane and induce the pre-activation of motor cortical synapses, determining an increase in the peripheral outcome. "
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    ABSTRACT: To evaluate the effects of several single TMS pulses, delivered at two different inter-trial intervals (ITIs), on corticospinal excitability. Twelve healthy volunteers participated in two experimental sessions, during which TMS pulses were delivered at random or at fixed ITIs. The TMS single pulse-induced modulation of corticospinal output (motor evoked potential amplitude - MEP) was evaluated on-line. Each session began with a baseline block, followed by 10 blocks, with 20 TMS pulses each. Intra- and inter-block effects were valuated using an ANOVA model, through nested random effect on subjects considering the subject-specific variability. The delivery of successive TMS pulses significantly changed both intra-block and inter-block cortical excitability, as demonstrated by an increase in the amplitude of MEPs (p<0.001) and supported through trend analyses, showing a perfect linear trend for inter-block levels (R(2)=1) and nearly linear trend for intra-block levels (R(2)=0.97). The MEPs significantly increased when the TMS pulses were delivered at both random and fixed ITIs. Single TMS pulses induce cumulative changes in neural activity during the same stimulation, resulting in a motor cortical excitability increase. Particular attention should be taken when several single TMS pulses are delivered in research and clinical settings for diagnostic and therapeutic purposes. Copyright © 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
    Full-text · Article · Mar 2015 · Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology
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    • "Transcranial magnetic stimulation (TMS) is one of the noninvasive tools to stimulate neurons in the human brain [Allen et al., 2007; Barker et al., 1985; Merton and Morton, 1980], and has recently been used for treating neurological or neuropsychiatric diseases such as Parkinson disease and severe depression [George et al., 1999; Post et al., 1999; Pridmore and Belmaker, 1999]. For experimental purposes , repetitive TMS (rTMS) has been applied as one of the valuable tools to induce reversible changes in an intact human brain [Fox et al., 2012; Pascual-Leone et al., 2000]. "
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    ABSTRACT: Several recent studies using functional magnetic resonance imaging (fMRI) have shown that repetitive transcranial magnetic stimulation (rTMS) affects not only brain activity in stimulated regions but also resting-state functional connectivity (RSFC) between the stimulated region and other remote regions. However, these studies have only demonstrated an effect of either excitatory or inhibitory rTMS on RSFC, and have not clearly shown the bidirectional effects of both types of rTMS. Here, we addressed this issue by performing excitatory and inhibitory quadripulse TMS (QPS), which is considered to exert relatively large and long-lasting effects on cortical excitability. We found that excitatory rTMS (QPS with interstimulus intervals of 5 ms) decreased interhemispheric RSFC between bilateral primary motor cortices, whereas inhibitory rTMS (QPS with interstimulus intervals of 50 ms) increased interhemispheric RSFC. The magnitude of these effects on RSFC was significantly correlated with that of rTMS-induced effects on motor evoked potential from the corresponding muscle. The bidirectional effects of QPS were also observed in the stimulation over prefrontal and parietal association areas. These findings provide evidence for the robust bidirectional effects of excitatory and inhibitory rTMSs on RSFC, and raise a possibility that QPS can be a powerful tool to modulate RSFC. Hum Brain Mapp, 2013. © 2013 Wiley Periodicals, Inc.
    Full-text · Article · May 2014 · Human Brain Mapping
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    • "The main motivations for the proposed study are to deepen the understanding of this prospective mode of neural communication and to investigate whether the externally induced electrical fields (e.g., through Transcranial Magnetic Stimulation (TMS) (Barker et al., 1985; Hallett, 2000; Walsh and Cowey, 2000; Allen et al., 2007), Transcranial Electrical Stimulation (TEC) (Deans et al., 2007; Kirov et al., 2009; Ozen et al., 2010; Reato et al., 2010) and Deep Brain Stimulation (DBS) (Benabid et al., 2009; Joucla and Yvert, 2012) might promote the ephaptic coupling. Modifying the ephaptic coupling could alter synchrony of the neural assemblies and potentially help to correct pathological network dynamics. "
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    ABSTRACT: Neural communication generates oscillations of electric potential in the extracellular medium. In feedback, these oscillations affect the electrochemical processes within the neurons, influencing the timing and the number of action potentials. It is unclear whether this influence should be considered only as noise or it has some functional role in neural communication. Through computer simulations we investigated the effect of various sinusoidal extracellular oscillations on the timing and number of action potentials. Each simulation is based on a multicompartment model of a single neuron, which is stimulated through spatially distributed synaptic activations. A thorough analysis is conducted on a large number of simulations with different models of CA3 and CA1 pyramidal neurons which are modeled using realistic morphologies and active ion conductances. We demonstrated that the influence of the weak extracellular oscillations, which are commonly present in the brain, is rather stochastic and modest. We found that the stronger fields, which are spontaneously present in the brain only in some particular cases (e.g., during seizures) or that can be induced externally, could significantly modulate spike timings.
    Full-text · Article · Feb 2014 · Frontiers in Computational Neuroscience
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