Functional near-infrared spectroscopy maps cortical plasticity underlying altered motor performance induced by transcranial direct current stimulation

University of Texas at Arlington and University of Texas Southwestern Medical Center at Dallas, Joint Graduate Program in Biomedical Engineering, 500 UTA Boulevard, Arlington, Texas 76010.
Journal of Biomedical Optics (Impact Factor: 2.86). 11/2013; 18(11):116003. DOI: 10.1117/1.JBO.18.11.116003
Source: PubMed


Transcranial direct current stimulation (tDCS) of the human sensorimotor cortex during physical rehabilitation induces plasticity in the injured brain that improves motor performance. Bi-hemispheric tDCS is a noninvasive technique that modulates cortical activation by delivering weak current through a pair of anodal-cathodal (excitation-suppression) electrodes, placed on the scalp and centered over the primary motor cortex of each hemisphere. To quantify tDCS-induced plasticity during motor performance, sensorimotor cortical activity was mapped during an event-related, wrist flexion task by functional near-infrared spectroscopy (fNIRS) before, during, and after applying both possible bi-hemispheric tDCS montages in eight healthy adults. Additionally, torque applied to a lever device during isometric wrist flexion and surface electromyography measurements of major muscle group activity in both arms were acquired concurrently with fNIRS. This multiparameter approach found that hemispheric suppression contralateral to wrist flexion changed resting-state connectivity from intra-hemispheric to inter-hemispheric and increased flexion speed (p<0.05). Conversely, exciting this hemisphere increased opposing muscle output resulting in a decrease in speed but an increase in accuracy (p<0.05 for both). The findings of this work suggest that tDCS with fNIRS and concurrent multimotor measurements can provide insights into how neuroplasticity changes muscle output, which could find future use in guiding motor rehabilitation.

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    • "Even though tACS induces changes in brain activity in a different way than tDCS (Herrmann et al., 2013), it may be a general implication of these studies that either an existing BOLD response is more easily manipulated than resting activity, or that a manipulation of the baseline BOLD signal is an effect so small, it cannot be detected by fMRI. In favor of the latter notion is the finding that regional cerebral blood flow as well as the concentration of oxygenated blood can be manipulated by tDCS as measured using positron emission tomography after stimulation during rest (Lang et al., 2005), and during stimulation using functional near-infrared spectroscopy (Khan et al., 2013). "
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    ABSTRACT: Many studies have proven transcranial alternating current stimulation (tACS) to manipulate brain activity. Until now it is not known, however, how these manipulations in brain activity are represented in brain metabolism or how spatially specific these changes are. Alpha-tACS has been shown to enhance the amplitude of the individual alpha frequency (IAF) and a negative correlation between alpha amplitude and occipital BOLD signal was reported in numerous EEG/fMRI experiments. Thus, alpha-tACS was chosen to test the effects of tACS on the BOLD signal. A reduction thereof was expected during alpha-tACS which shows the spatial extend of tACS effects beyond modeling studies. Three groups of subjects were measured in an MRI scanner, receiving tACS at either their IAF (N=11), 1 Hz (control; N=12) or sham (i.e. no stimulation - a second control; N=11) while responding to a visual vigilance task. Stimulation was administered in an interleaved pattern of tACS-on runs and tACS-free baseline periods. The BOLD signal was analyzed in response to tACS-onset during resting state and in response to seldom target stimuli. Alpha-tACS at 1.0 mA reduced the task-related BOLD response to visual targets in the occipital cortex as compared to tACS-free baseline periods. The deactivation was strongest in an area where the BOLD signal was shown to correlate negatively with alpha amplitude. A direct effect of tACS on resting state BOLD signal levels could not be shown. Our findings suggest that tACS-related changes in BOLD activity occur only as a modulation of an existing BOLD response.
    NeuroImage 10/2015; DOI:10.1016/j.neuroimage.2015.10.003 · 6.36 Impact Factor
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    • "(2010)reportedontheanteriorprefrontalcortexeffectsoftDCS beforeandafterstimulationusingaprefrontalsensorpadbased fNIRSmeasurement.ResultsindicatedthatfNIRSsuccessfully capturedtheactivationchangesinducedbythetDCSstimulation. Khanetal.(2013)comparedalteredhemodynamicpatternsin thesensorimotorcortexinresponsetobi-hemispherictDCS polaritiesandtheirrelationshiptomuscleactivityandmotor taskperformance.Muthalibetal.(2013)utilizedanodaltDCS "
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    ABSTRACT: Contemporary studies with transcranial direct current stimulation (tDCS) provide a growing base of evidence for enhancing cognition through the non-invasive delivery of weak electric currents to the brain. The main effect of tDCS is to modulate cortical excitability depending on the polarity of the applied current. However, the underlying mechanism of neuromodulation is not well understood. A new generation of functional near infrared spectroscopy (fNIRS) systems is described that are miniaturized, portable, and include wearable sensors. These developments provide an opportunity to couple fNIRS with tDCS, consistent with a neuroergonomics approach for joint neuroimaging and neurostimulation investigations of cognition in complex tasks and in naturalistic conditions. The effects of tDCS on complex task performance and the use of fNIRS for monitoring cognitive workload during task performance are described. Also explained is how fNIRS + tDCS can be used simultaneously for assessing spatial working memory. Mobile optical brain imaging is a promising neuroimaging tool that has the potential to complement tDCS for realistic applications in natural settings.
    Frontiers in Systems Neuroscience 03/2015; 9(27). DOI:10.3389/fnsys.2015.00027
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    • "Secondly, two studies used fNIRS to measure changes in motor cortex activity following tDCS to primary motor cortex (Khan et al., 2013; Muthalib et al., 2013). The results showed modulation in the rate of motor movements and increased HbO levels at the stimulation site (Khan et al., 2013). These findings confirm the feasibility of combining fNIRS with tDCS and extending them into cognitive tasks to gain insight regarding underlying neural changes. "
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    ABSTRACT: Working memory (WM) capacity falls along a spectrum with some people demonstrating higher and others lower WM capacity. Efforts to improve WM include applying transcranial direct current stimulation (tDCS), in which small amounts of current modulate the activity of underlying neurons and enhance cognitive function. However, not everyone benefits equally from a given tDCS protocol. Recent findings revealed tDCS-related WM benefits for individuals with higher working memory (WM) capacity. Here, we test two hypotheses regarding those with low WM capacity to see if they too would benefit under more optimal conditions. We tested whether supplying a WM strategy (Experiment 1) or providing greater extrinsic motivation through incentives (Experiment 2) would restore tDCS benefit to the low WM capacity group. We also employed functional near infrared spectroscopy to monitor tDCS-induced changes in neural activity. Experiment 1 demonstrated that supplying a WM strategy improved the high WM capacity participants' accuracy and the amount of oxygenated blood levels following anodal tDCS, but it did not restore tDCS-linked WM benefits to the low WM capacity group. Experiment 2 demonstrated that financial motivation enhanced performance in both low and high WM capacity groups, especially after anodal tDCS. Here, only the low WM capacity participants showed a generalized increase in oxygenated blood flow across both low and high motivation conditions. These results indicate that ensuring that participants' incentives are high may expand cognitive benefits associated with tDCS. This finding is relevant for translational work using tDCS in clinical populations, in which motivation can be a concern.
    NeuroImage 11/2014; 105. DOI:10.1016/j.neuroimage.2014.11.012 · 6.36 Impact Factor
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