AIP Conference Proceedings 2344, 050001 (2021); https://doi.org/10.1063/5.0047216 2344, 050001
© 2021 Author(s).
Analysis of quantitative EEG (QEEG)
parameters on the effect of transcranial direct current stimulation (TDCS) on post- stroke patients
Cite as: AIP Conference Proceedings 2344, 050001 (2021); https://doi.org/10.1063/5.0047216 Published Online: 23 March 2021
Hasballah Zakaria, Odilia Valentine, and Adre Mayza
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Analysis of Quantitative EEG (QEEG) Parameters on the Effect of Transcranial Direct Current Stimulation (TDCS) on Post-
Stroke Patients
Hasballah Zakaria
1, a), Odilia Valentine
1, b), Adre Mayza
21School of Electrical Engineering and Informatics, Bandung Institute of Technology (ITB), Jl. Ganesha No. 10, Bandung 40132, Indonesia
2Neurology Department and Cluster of Medical Technology IMERI, Faculty of Medicine, Universitas Indonesia, Jl. Salemba Raya No.6, Senen, Central Jakarta 10430, Indonesia
Corresponding author: a)[email protected]
Abstract. Cerebrovascular accident (CVA) or stroke is a condition where the blood flow to the brain is impaired, which can be caused by a blockage (ischemic stroke) or rupture of blood vessels (hemorrhagic stroke), resulting in cell death in some brain areas.
Stroke can cause significant impairment in motoric, cognitive, and coordination skills of limbs and muscles. One of the non-invasive stimuli that can be applied in post-stroke patient rehabilitation is Transcranial Direct Current Stimulation (TDCS), aiming to improve the frequency spectrum towards normal. This study aimed to find the Quantitative Electroenchepalograph (QEEG) parameters that characterize the improvement of post-stroke patients' brain signals after the administration of TDCS. QEEG parameters included absolute power, relative power, ratio power Delta Theta Alpha Beta (DTAB), Delta Alpha (DA), and the percentage of each frequency wave band in the brain. EEG signals were recorded for 5 minutes before and after TDCS administration from 23 subjects, consisted of 12 post-stroke patients and 11 healthy subjects as a control. The result showed that there were significant differences in QEEG parameters before and after TDCS administration to both post-stroke patients and healthy subjects. The alpha frequency was dominant for healthy subjects, with the average of 25.67% before stimulus then increased by 1.91% after the stimulus. For post-stroke patients, delta frequency before the stimulus was dominant, with an average percentage of 43.03% then decreased by 10.44% after the stimulus.
These results show that with TDCS, there is a change in the EEG wave pattern in post-stroke patients, which followed the profile pattern of healthy subjects.
Keywords: Quantitative EEG (QEEG), Stroke, Transcranial Direct Current Stimulation (TDCS)
INTRODUCTION
Cerebrovascular accident (CVA) or stroke is a condition where the blood flow to the brain is impaired, which can be caused by a blockage (ischemic stroke) or rupture of blood vessels (hemorrhagic stroke), resulting in cell death in some areas of the brain [1]. According to the 2018 Basic Health Research data, the prevalence of stroke in Indonesia is quite large, at 10.9% out of 1,000. The numbers are increasing when compared to Basic Health Research data in 2013, which around 7%. Stroke has become the leading cause of death in almost all hospitals in Indonesia, which is 14.5%. The prevalence of stroke based on doctor's diagnosis in 2018 is highest in East Kalimantan (14.7%), followed by Yogyakarta (14.5%) and lowest in Papua Province (4.1%) [7].
Strokes can cause neurological abnormalities such as reduced motor abilities of limbs and muscles, cognitive, visual, and coordination. The reduced level of independence and mobility can affect the quality of life [2]. Stroke is one of the leading causes of disability throughout the world. Most strokes occur when blood clots block the arteries leading to the brain. Lack of sufficient blood supply may result in permanent brain damage or death.
In most cases, depending on which area of the damaged brain, a stroke can affect a variety of different muscle groups and often cause disruption of daily living activities and motor functions of patients, and may also cause permanent disabilities. An
attempt to solve this problem may require a rehabilitation strategy to improve a patient’s motor function to overcome their disabilities. However, the current stroke rehabilitation strategy is still not showing effective outcomes. Therefore, to improve the effectiveness, a new non-invasive brain stimulation technique known as transcranial direct current stimulation (TDCS) may be added to the rehabilitation strategy [15].
Transcranial Direct Current Stimulation (TDCS) is a non-invasive technique for stimulating the brain using direct current.
Transcranial direct current stimulation (TDCS) has recently surfaced as a promising technique to modulate cognitive, motor functions, social skills, change behavior, help the memory process, and improve performance [7]. Tae-Gyu An et al. conducted a study in 2016, which showed that using transcranial direct current stimulation (TDCS) as a stimulus on stroke patients could improve their quality of life [11].
An approach that can be used to examine brain wave pattern is quantitative Electroenchelpalograph (qEEG) guided by Neurofeedback (NF) therapy. Electroenchelpalograph (EEG) is a device used to measure the brain's electrical activity, commonly known as brain waves, through electrodes attached to the scalp at a particular time. EEG measures the change in voltage produced by the flow of ions in the brain. EEG is widely used to diagnose epilepsy, coma, tumors, strokes, and other brain disorders [13]. In a study conducted by Sofiah in 2018, researchers used quantitative parameters to adopt visual readings of EEG signals to justify EEG signal abnormalities. The quantitative parameters used are the frequency and amplitude parameters of the Posterior Dominant Rhythm (PDR), the amplitude of the beta rhythm, and the percentage of theta and delta rhythm [11].
Another study that used the quantitative Electroenchelpalograph parameters (QEEG) was conducted by Cynthia. The researchers analyzed EEG signals in Vascular Cognitive Impairment (VCI) patients before and after sound wave therapy. The parameters used in the study are power, wave duration, and percentage of each frequency wave in the brain. The results of this study found that there is increasing power before and after therapy in VCI patients [3].
Finnigan et al. (2012) used quantitative Electroenchelpalograph (qEEG) to analyze EEG signals in ischemic stroke patients.
This study shows that the power parameters produced in the delta wave are higher than the power in the alpha wave. Analysis using quantitative EEG signal parameters are considered sensitive to the abnormality index in acute ischemic stroke patients [4].
Mangia et al. (2014) analyzed the effects of providing Transcranial Direct Current Stimulation (TDCS) and used quantitative EEG parameters to see EEG signal activity in 10 healthy subjects. The parameter used is the power parameter.
This study also shows that there is an increase in theta wave activity in the first minute of the stimulus and an increase in power in alpha and beta waves during and after the stimulus were applied, as well as the presence of extensive activation in regions of the brain [5].
Based on several studies that have been carried out, this study will analyze the characteristics of the quantitative Electroenchelpalograph (qEEG) parameters in post-stroke patients before and after administration of Transcranial Direct Current Stimulation (TDCS). Quantitative parameters that will be used are the power parameters named absolute power, relative power, and ratio power of DTAB (Delta Theta Alpha Beta) and DAR (Delta Alpha Ratio) on each brain wave (delta, theta, alpha, beta, and gamma) as well as the percentage parameters of each waveband against the whole wave.
SUBJECT AND METHODS
Twenty-three subjects were included in this study by voluntary participation, consisting of 12 post-stroke patients, ages ranging from 40 to 80 years old, and 11 healthy subjects ranging from 20 to 45 years old. All participants provided written, informed consent to participate in the experiment. EEG signals were recorded using the EEG Neuroelectrics Starstim 8 Channels with a sampling rate of 500 Hz before and after stimuli. The EEG signal was recorded by eight electrodes, namely F3, F4, C3, Cz, C4, P3, Pz, P4, that were placed following the 10-20 International System. EEG signal was recorded for five minutes before and after the stimulus was given. All signal recordings for this study were recorded while the patients are conscious and relaxed.
Transcranial Direct Current Stimulation (TDCS) used Sooma TDCS with a direct current of 2 mA for 10 minutes for each subject. The anode and cathode electrodes were placed at F3 and F4 points, respectively (10-20 International Standart System).
This stimulus is expected to improve the quality of EEG signals.
EEG signals were pre-processed by filtering and manual segmentation before the calculation of QEEG parameters. The QEEG parameters included absolute power, relative power, Delta Theta Alpha Beta Ratio (DTABR), Delta Alpha Ratio (DAR), and the wave percentage parameters for each band of the delta, theta, alpha, beta, and gamma. QEEG parameters for post- stroke patients and healthy subjects were presented in average value and standard deviation for different frequencies.
The EEG signal was filtered by using a bandpass filter of 0.5 - 45 Hz. It is used to remove DC signals with frequencies below 1 Hz and noise of electric grids at rates ± 50 Hz. The next process after filtering was segmentation. The initial segmentation phase aimed to equalize the length of data for all subjects. This segmentation was conducted manually with a one-minute duration and 5 seconds time window. So, there were 12 segments in 1 (one) EEG signal data.
The windowed signal was processed with the bank filter to divide the EEG into several frequency bands. The frequency bands were delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-13 Hz), beta (13-30), and gamma (30-45 Hz). Then the power spectral density (PSD) estimation was calculated. The used method was the Welch method with windowing for 2 seconds and overlapped 50% using the MATLAB function [10]. For each frequency band, the maximum peak of the calculated PSD was selected. Then, it proceeded with the calculation of quantitative parameters in each frequency band.
RESULT
The following results are the quantitative parameters of EEG signals before and after administering the stimulus to post- stroke patients. Figure 1 shows that for absolute power before TDCS administration, the dominant frequency is found at the delta frequency. After the stimulus was given, there was an increase in alpha, beta, and gamma frequencies and decreased delta frequency. Likewise, the average relative power in some post-stroke patients obtained a dominant value in delta frequency.
Whereas in healthy subjects, the dominant EEG was in the alpha frequency band. This result is consistent with the research conducted previously [5].
Figure 2 shows that the power ratio of DTABR (Delta Theta Alpha Beta Ratio) in post-stroke patients and healthy subjects after the stimulus has decreased compared to the value of the power ratio of DTABR before the stimulus. This study indicates that post-stroke patients experience improvement after the administration of the stimulus.
Table 1 shows the differences in each frequency band before and after TDCS in healthy subjects and post-stroke patients.
Before the stimulus was administered in healthy subjects, the average percentage of delta wave is 15.63 ± 3.44%, while in post- stroke patients is 43.03 ± 5.06%. The average percentage of theta wave before the stimulus for healthy subjects is at 25.41 ± 2.19%, while the post-stroke patients are at 18.74 ± 2.66%.
TABLE 1. Average and standard deviation of the percentage of each frequency band.
Frequency Band
Healthy Subjects Post Stroke Patients Before
TDCS (%)
After TDCS (%)
Before TDCS (%)
After TDCS (%)
Delta Mean 15.63 10.59 43.03 32.60
SD 3.44 3.02 5.06 3.04
Theta Mean 25.41 27.88 18.74 22.02
SD 2.19 4.01 2.66 2.27
Alpha Mean 25.67 27.58 15.92 17.34
SD 3.26 4.78 1.53 1.38
Beta Mean 18.53 18.31 12.86 14.61
SD 2.24 2.32 1.83 1.55
Gamma Mean 14.76 15.65 9.45 13.44
SD 2.26 5.70 2.13 2.68
The average percentage of alpha is at 25.67 ± 3.26% for healthy subjects. This is higher than in post-stroke patients, which at 15.92 ± 1.53% before the stimulus. For beta and gamma waves in healthy subjects are at 18.53 ± 2.24% and 14.76 ± 2.26%
while in post-stroke patients are at 18.31 ± 2.32% and 15.65 ± 5.70%.
The average percentage of delta wave for the healthy subjects is 10.59 ± 3.02% after the stimulus, while for post-stroke patients is at 32.60 ± 3.04%. The theta wave in healthy subjects is 27.88 ± 4.01%, and in post-stroke patients is at 22.02 ± 2.27%. The result shows that the alpha wave in healthy subjects after the stimulus is higher than before the stimulus, which is at 27.58 ± 4.78. The same as healthy subjects, in post-stroke patients, the average value of alpha wave increases to 17.34 ± 1.38%. For beta and gamma wave, the average beta wave is at 18.31 ± 2.32%, and the gamma wave is at 15.65 ± 5.70% for healthy subjects, whereas in post-stroke patients the average beta wave is at 14.61 ± 1.55% and the gamma wave is at 13.44 ± 2.68%.
DISCUSSION
Based on the calculation of quantitative parameters of EEG signals in healthy subjects and post-stroke patients before Transcranial Direct Current Stimulation (tDCS), it was found that there are differences in power parameters. The absolute power quantitative parameters in healthy subjects were dominant at the alpha frequency in the parietal (P) channel. However, some subjects were prevailing in the Central (C) channel. This result was consistent with the research conducted by Widmaier and Strang [14]. The value of the DTAB ratio on healthy subjects produced was quite low compared to post-stroke patients, which might be caused by the frequency of healthy subjects were dominated by alpha frequency. Similar to the DTAB ratio, the Delta-Alpha ratio in healthy subjects was also quite low.
The absolute and relative power parameters in the post-stroke patients before giving the stimulus were dominant at a low frequency, which was delta and theta frequency and might be occurred because brain function had decreased, resulting in a decrease in the level of consciousness or alpha rate and increased delta frequency. This result was also consistent with previous research [4]. The comparison of DTABR and DAR in post-stroke patients was dominant in the frontal lobe at F3 and F4 channels. The value generated by the DTAB ratio was also quite high compared to the DTAB ratio value of healthy subjects before the stimulus. The DAR parameter value was also quite high compared to the DAR value in healthy subjects. In post-
0,00 1,00 2,00 3,00 4,00 5,00 6,00
Delta Theta Alfa Beta Gamma
Frequency Band Before TDCS After TDCS μV2/Hz
0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00
Delta Theta Alfa Beta Gamma Frequency Band
Before TDCS After TDCS μV2/Hz
(a)
FIGURE 1. The absolute power of (a) post-stroke patients and (b) healthy subjects before and after TDCS administration.
0,00 0,20 0,40 0,60 0,80 1,00 1,20 1,40
F3 F4 C3 Cz C4 P3 Pz P4
EEG Channel Before TDCS After TDCS 0,00
2,00 4,00 6,00 8,00 10,00 12,00 14,00
F3 F4 C3 Cz C4 P3 Pz P4
EEG Channel
Before TDCS After TDCS
(a)
FIGURE 2. DTAB Ratio of (a) post-stroke patients and (b) healthy subjects before and after TDCS administration.
(b)
(b)
stroke patients, the delta frequency value was high, so that the DTABR and DAR values were also high. Simultaneously, in healthy subjects, the frequency of the delta wave frequency was low and dominant in the alpha frequency so that the DTAB and DAR were low.
The quantitative parameters of EEG signals after TDCS administration in healthy subjects showed an increase in the value of power at the alpha frequency and a decrease in power value at delta frequency, consistent with previous research [5]. The post-stroke patients also showed the same result where the power value increased at alpha and theta frequency wave. This condition showed that after TDCS, there was a shift in the dominant frequency value towards the dominant frequency in healthy subjects. The power ratio of DTABR and DAR in post-stroke patients decreased after the stimulus was given compared to the power ratio before the stimulus was administered. This condition indicated that post-stroke patients experience improvement after the administration of the stimulus. The decreased DTAB and DAR ratio happened because, in post-stroke patients, the power value decreased at the delta frequency, while at the alpha frequency, the power value was increasing.
CONCLUSION
The results showed that there were significant differences in QEEG parameters before and after TDCS administration to both post-stroke patients and healthy subjects. Before the stimulus, healthy subjects were dominant at alpha frequency waves, with the average percentage was 25.67 ± 3.26%. After the stimulus was administered, there was a significant increase in the average alpha frequency wave by 1.91 ± 1.52% and a decrease in the average delta wave by 5.04 ± 0.42%. While in post-stroke patients, before the stimulus, were dominant at delta frequency wave with the average percentage was 43.03 ± 5.06%. After the stimulus, the alpha frequency increased by 1.42 ± 0.15%, and the delta frequency decreased by 10.44 ± 2.02%. These results show that with TDCS, there is a change in the EEG wave pattern in post-stroke patients, which followed the profile pattern of healthy subjects.
ACKNOWLEDGMENTS
Thanks to Mandiri Stroke & Neuro Rehabilitation Center Clinic, which has permitted me to conduct this research and the PT. Eracita Astamida for providing us access to EEG and Sooma TDCS equipment.
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