Noninvasive brain stimulation: From physiology to network dynamics and back

1] Human Cortical Physiology and Neurorehabilitation Section, National Institute of Neurological Disorders and Stroke, US National Institutes of Health, Bethesda, Maryland, USA. [2].
Nature Neuroscience (Impact Factor: 16.1). 06/2013; 16(7):838-844. DOI: 10.1038/nn.3422
Source: PubMed


Noninvasive brain stimulation techniques have been widely used for studying the physiology of the CNS, identifying the functional role of specific brain structures and, more recently, exploring large-scale network dynamics. Here we review key findings that contribute to our understanding of the mechanisms underlying the physiological and behavioral effects of these techniques. We highlight recent innovations using noninvasive stimulation to investigate global brain network dynamics and organization. New combinations of these techniques, in conjunction with neuroimaging, will further advance the utility of their application.

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    • "Previous work has demonstrated that transcranial direct current stimulation (tDCS), the application of weak electric DC currents of 1-2mA through contact electrodes placed over the scalp, can modulate cortical excitability in a polarity specific way, and affect cognition (Nitsche et al., 2012; Monti et al., 2013; Santarnecchi et al., 2013), visuo-motor learning (Antal et al., 2004) or motor performance (Hendy and Kidgell, 2014; Hummel et al., 2005). The underlying neurophysiological mechanisms mediating these effects, however, are not understood (Dayan et al., 2013), partly because of the difficulty to record neural activity at high temporal and spatial resolution while transcranial electric currents are applied. The main difficulty is to eliminate electromagnetic artifacts that by many orders of magnitude exceed the brain's endogenous electric or magnetic activity. "
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    ABSTRACT: Transcranial direct current stimulation (tDCS) can influence cognitive, affective or motor brain functions. Whereas previous imaging studies demonstrated widespread tDCS effects on brain metabolism, direct impact of tDCS on electric or magnetic source activity in task-related brain areas could not be confirmed due to the difficulty to record such activity simultaneously during tDCS. The aim of this proof-of-principal study was to demonstrate the feasibility of whole-head source localization and reconstruction of neuromagnetic brain activity during tDCS and to confirm the direct effect of tDCS on ongoing neuromagnetic activity in task-related brain areas. Here we show for the first time that tDCS has an immediate impact on slow cortical magnetic fields (SCF, 0-4Hz) of task-related areas that are identical with brain regions previously described in metabolic neuroimaging studies. 14 healthy volunteers performed a choice reaction time (RT) task while whole-head magnetoencephalography (MEG) was recorded. Task-related source-activity of SCFs was calculated using synthetic aperture magnetometry (SAM) in absence of stimulation and while anodal, cathodal or sham tDCS was delivered over the right primary motor cortex (M1). Source reconstruction revealed task-related SCF modulations in brain regions that precisely matched prior metabolic neuroimaging studies. Anodal and cathodal tDCS had a polarity-dependent impact on RT and SCF in primary sensorimotor and medial centro-parietal cortices. Combining tDCS and whole-head MEG is a powerful approach to investigate the direct effects of transcranial electric currents on ongoing neuromagnetic source activity, brain function and behavior.
    NeuroImage 10/2015; DOI:10.1016/j.neuroimage.2015.09.068 · 6.36 Impact Factor
    • "The growing interest in non-invasive brain stimulation generated by transcranial magnetic stimulation (TMS) led to the revitalization of transcranial direct current stimulation (tDCS), a technique that has been being applied in animal studies since the 1960s (Dayan et al., 2013; Utz et al., 2010). It has been demonstrated that tDCS is able to induce polarity-dependent shifts in cortical excitability which can last for up to a few hours after stimulation with conventional protocols (Nitsche et al., 2003a; Nitsche and Paulus, 2000). "
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    ABSTRACT: Transcranial direct current stimulation (tDCS) is a promising and well-tolerated method of non-invasive brain stimulation, by which cortical excitability can be modulated. However, the effects of tDCS on the developing brain are still unknown, and knowledge about its tolerability in children and adolescents is still lacking. Safety and tolerability of tDCS was assessed in children and adolescents by self-reports and spectral characteristics of electroencephalogram (EEG) recordings Nineteen typically developing children and adolescents aged 11 to 16 years participated in the study. Anodal and cathodal tDCS as well as sham stimulation were applied for a duration of 10min over the left primary motor cortex (M1), each with an intensity of 1mA. Subjects were unable to identify whether they had received active or sham stimulation, and all participants tolerated the stimulation well with a low rate of adverse events in both groups and no serious adverse events. No pathological oscillations, in particular, no markers of epileptiform activity after 1mA tDCS were detected in any of the EEG analyses. In summary, our study demonstrates that tDCS with 1mA intensity over 10minutes is well tolerated, and thus may be used as an experimental and treatment method in the pediatric population.
    Brain research bulletin 10/2015; 119. DOI:10.1016/j.brainresbull.2015.09.011 · 2.72 Impact Factor
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    • "While it was shown that the application of electric currents to the brain can modulate mood, cognition and behavior, only the recent development of neurophysiological and neuroimaging tools allows systematic investigation of the mechanisms underlying these effects (Bolwig, 2014). Besides invasive stimulation techniques, such as deep brain stimulation or motor cortex stimulation, non-invasive forms of brain stimulation (NIBS), including transcranial direct current stimulation (tDCS) or transcranial magnetic stimulation (TMS) are increasingly used (Liew et al., 2014) and their effects on brain physiology are being investigated (Dayan et al., 2013). For instance, it was shown that tDCS, i.e. the application of weak electric direct currents (DC) of 1–2 mA through saline soaked sponges or electrodes, can improve learning and consolidation throughout different domains (Reis et al., 2008; Marshall et al., 2004). "

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