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Investigate the effect of HD-tDCS on the prefrontal cortex using fNIRS for neurorehabilitation

M. Atif Yaqub1, Seong-Woo Woo1, Amad Zafar1 and Keum-Shik Hong1, 2*
  • 1 Pusan National University, School of Mechanical Engineering, Republic of Korea
  • 2 Pusan National University, Department of Cogno-Mechatronics Engineering, Republic of Korea

Objective This paper examines the usefulness and area selection of applying high definition transcranial direct current stimulation (HD-tDCS) on both (left and right) hemispheres of prefrontal cortex of human brain using functional near infrared spectroscopy (fNIRS). Introduction In this era, where the population of elderly is growing at a high rate, we are dealing with the problem of the brain degeneration in the form of diseases such as Alzheimer’s disease (AD), Parkinson's disease, fronto-temporal dementia. These patients are troubled in everyday settings of their lives even for simple tasks due to deficit in cognitive functions such as working memory, episodic memory, and attention/executive function impairments (De Lacoste and White, 1993). We have utilized tDCS, which involves supplying of electric current in small amounts to our brain (Nitsche and Paulus, 2001). The common type of electrodes in application are the patch type electrodes (pair of saline soaked sponge electrodes with size of 5 x 7 cm) for studying the effect of stimulation on prefrontal cortex for working memory enhancement (Jones et al., 2015), improvement of hemodynamic response (Ehlis et al., 2016), functional connectivity (Mancini et al., 2016), and brain perfusion changes (Stagg et al., 2013). Recently, HD-tDCS has opened new ways in controlling the electric field and consequently deliver the stimulation to a specific targeted cortical region (Edwards et al., 2013), which has shown the potential for increasing the duration of after-effects. We have used fNIRS, which is a noninvasive, easy to carry for outdoor experiments and repeatable technology that allows the regional assessment of the oxygenation state of hemoglobin in tissue (Chance et al., 1993). This technique uses the near-infrared spectrum of light within the 650 nm – 1000 nm range to measure oxy -hemoglobin (HbO) and deoxy-hemoglobin (HbR) in the blood due to their infrared light-absorbing property (Zafar and Hong, 2017). Methods To evaluate the effect of HD-tDCS using fNIRS, two equally age balanced groups were formed with each having five male subjects (age: mean 28.5 ± 2.5 years). All the subjects were reportedly healthy and did not observed any neurological or psychiatric disorders or head injuries in the past and none had ever used the neuroleptic, hypnotic, or anti-seizure medications. The experiment was designed in such a way that it had three stages, namely, pre-stimulation, stimulation, and post stimulation. The complete experiment covering all the stages continued for twenty five minutes in which the pre-stimulation phase lasted for 5 minutes, subsequently followed by the stimulation phase of 10 minutes, and ending with 10 minutes of post-stimulation phase. The subjects were told to remain awake by keeping their eyes open during the whole experiment, while they were positioned comfortably on the clinical bed in the Fowler’s position. During the first phase, fNIRS data was acquired to collect the baseline signal. In the second phase, active stimulation was applied with 15 seconds ramp up to 1mA which remained at this level during the entire phase and finishing with the last 15 seconds ramp down, while continuously acquiring data using fNIRS. The final phase of the experiment was planned for acquiring the fNIRS data to visualize the after effects of stimulation. The stimulation was delivered by a battery-driven Starstim tCS system (Neuroelectrics, Barcelona, Spain). The system has a total capacity of eight electrodes of which fives electrodes were utilized via an anodal 4 x 1 HD-tDCS electrode arrangement. The electrodes were positioned on the right or left side of the prefrontal cortex over the eyebrow. The distance between all the returning electrodes to the anode was 3.5 cm. The anodal current for the stimulation was regulated at 1 mA with each return electrode configured to receive equal amount of current at the rate of quarter of the anodal current. The tDCS device was charged and attached to the designed headgear during the experiment. The fNIRS recording was done using a continuous-wave imaging device (DYNOT: Dynamic Near-Infrared Optical Tomography; NIRx Medical Technologies, Brooklyn, New York). This system was used to continuously measure concentration changes in oxyhemoglobin (∆HbO) and deoxyhemoglobin (∆HbR) from 32 channels covering the scalp of the complete prefrontal cortex including left and right hemispheres. Results and conclusion The measured light intensities were converted to hemoglobin concentration changes, ∆HbO and ∆HbR, using the MATLAB® toolbox NIRS-SPM. The fNIRS data from all the channels was low-pass filtered to remove respiration and pulse-related physiological noises. The second phase of experiment involving active stimulation was compared to the first phase. The results from all the subjects show significant increase in the ∆HbO responses of left and right hemisphere due to HD-tDCS during the second phase of the experiments in comparison with the baseline obtained in the first phase of experiment. By further group based examination, it was observed that the group which was stimulated on the right prefrontal cortex had a better response to those who were stimulated on the left prefrontal cortex. The channels under stimulation were averaged to show that the right stimulated group has a much higher response to the HD-tDCS activation as compared to the left stimulated group as shown in Fig. 1. The left stimulated group also had an overall significant response as well. The final phase of post-stimulation showed that the HbO levels in all subjects in both groups remained high and did not returned to the baseline even after ten minutes. The obtained results are consistent with previous studies of improved hemodynamic response (Khan et al., 2013). The outcomes of this study are important in the rehabilitation and therapy of patients suffering for daily tasks due to brain degenerative diseases. The underlying biological reasons should be further examined which provides better stimulation reception in right hemisphere compared to left hemisphere. These experiments will be further expanded and the obtained results will be analyzed to see the effect on cortical plasticity in both hemispheres due to stimulation.

Figure 1
Image

Acknowledgements

This work was supported by the National Research Foundation (NRF) of Korea under the auspices of the Ministry of Science and ICT, Republic of Korea (grant nos. NRF-2017R1A2A1A17069430 & NRF-2017R1A4A1015627).

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Keywords: functional near-infrared spectroscopy (fNIRS), high definition transcranial direct current stimulation (HD-tDCS), Neurorehabilitation, Prefrontal Cortex, cortical stimulation

Conference: 2nd International Neuroergonomics Conference, Philadelphia, PA, United States, 27 Jun - 29 Jun, 2018.

Presentation Type: Poster Presentation

Topic: Neuroergonomics

Citation: Yaqub M, Woo S, Zafar A and Hong K (2019). Investigate the effect of HD-tDCS on the prefrontal cortex using fNIRS for neurorehabilitation. Conference Abstract: 2nd International Neuroergonomics Conference. doi: 10.3389/conf.fnhum.2018.227.00031

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Received: 02 Apr 2018; Published Online: 27 Sep 2019.

* Correspondence: Prof. Keum-Shik Hong, Pusan National University, School of Mechanical Engineering, Busan, 609-735, Republic of Korea, kshong@pusan.ac.kr