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Journal of Integrative Neuroscience  2019, Vol. 18 Issue (2): 107-115    DOI: 10.31083/j.jin.2019.02.159
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Electrophysiological modulation and cognitive-verbal enhancement by multi-session Broca's stimulation: a quantitative EEG transcranial direct current stimulation based investigation
Zahra Kheradmand Saadi1, 2, 3, Mahboobeh Saadat1, Ali-Mohammad Kamali2, 3, 4, Seyedeh-Saeedeh Yahyavi2, 3, 4, Mohammad Nami2, 3, 4, 5, *()
1 Department of Foreign Languages and Linguistics, Shiraz University, Shiraz, 7194685115, Iran
2 DANA Brain Health Institute, Iranian Neuroscience Society, Fars Chapter, Shiraz, 7183611557, Iran
3 Neuroscience Laboratory-NSL (Brain, Cognition and Behavior), Department of Neuroscience, School of Advanced Medical Sciences and Technologies, Shiraz University of Medical Sciences, Shiraz, 7184737798, Iran
4 Department of Neuroscience, School of Advanced Medical Sciences and Technologies, Shiraz University of Medical Sciences, Shiraz, 7184737798, Iran
5 Academy of Health, Senses Cultural Foundation, Sacramento, CA, 95826, USA
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Abstract  

To evaluate transcranial direct current stimulation-induced changes in resting state quantitative EEG and cognitive-verbal performance of second language learners, 16 healthy individuals were randomly recruited to sham and real transcranial direct current stimulation groups receiving eight sessions of second language instruction accompanied by a 2 mA transcranial direct current stimulation over Broca's area with the cathode placed over the left arm. Quantitative EEG was recorded during the resting state after the stimulation session and second language instruction. Reduced theta activity at Fp1, F7, F3, and T5 caused by the stimulus current was reported. Multisession stimulation resulted in a significant increase in current density for beta power (25 Hz) in the language network. Cognitive-verbal pre-post stimulation performances suggest that anodal vs. sham transcranial direct current stimulation significantly improved the subjects test score on digit span, a cognitive-verbal ability. It is concluded that transcranial direct current stimulation of Broca's area increase cognitive-verbal performance by modulating brain electrical activity in language-related regions.

Key words:  qEEG      transcranial direct current stimulation      Broca's area      cognitive-verbal function      current density     
Submitted:  27 April 2019      Accepted:  26 June 2019      Published:  30 June 2019     
Fund: 
  • DANA Brain Health Institute (DBHI), Shiraz, Iran
*Corresponding Author(s):  Mohammad Nami     E-mail:  torabinami@sums.ac.ir

Cite this article: 

Zahra Kheradmand Saadi, Mahboobeh Saadat, Ali-Mohammad Kamali, Seyedeh-Saeedeh Yahyavi, Mohammad Nami. Electrophysiological modulation and cognitive-verbal enhancement by multi-session Broca's stimulation: a quantitative EEG transcranial direct current stimulation based investigation. Journal of Integrative Neuroscience, 2019, 18(2): 107-115.

URL: 

https://jin.imrpress.com/EN/10.31083/j.jin.2019.02.159     OR     https://jin.imrpress.com/EN/Y2019/V18/I2/107

Table 1  Demographic information of the participants.
Real tDCS arm (n = 8) Sham tDCS arm (n = 8)
Male/female 3/5 3/5
Mean age in years 23.8 ± 4.5 23.5 ± 3.6
Mean years of formal education 15.50 ± 2 14.25 ± 1.5
Figure 1.  Effect of real vs. sham tDCS on linguistic ROI absolute power (μV2) for frequency bands theta (4-8 Hz), alpha (8-12 Hz), beta (12--30 Hz) and high beta (25-30 Hz) in sessions 1 (S1) and 8 (S8) of tDCS. Multi-session real vs. sham tDCS induced a significant decrease in theta power in linguistic ROI and significantly increased beta power at F7 and T5. Statistical significance assumed for P < 0.05, results given as mean ± standard error of the mean (SEM).

Figure 2.  Dot plots give mean CSD z-score of language network centers at 25 Hz oscillation that showed significant loading during the resting state. Real vs. sham tDCS resulted in a significant mean CSD z-score in sessions 1 (S1) and 8 (S8) during the resting state (P < 0.05). Intra-group comparisons revealed no significant difference between the two group mean values in S1 and S8. Statistical comparison: mean ± standard error of the mean (SEM), significance level: P < 0.05 indicated by asterisk (*).

Figure 3.  Average effect of sham vs. real tDCS on the mean language network CSD z-score at 25 Hz for the resting state EEG. Panel a, b: Real tDCS group average CSD z-score after one and eight sessions of tDCS. Panel c, d: Average CSD z-score of the sham group in the first and eight sessions of tDCS.

Figure 4.  Subject performance in verbal trials of CBS-CP before and after tDCS intervention. Panel A: No significant difference between the performance of the subjects on three verbal tasks in the sham and real tDCS groups. Panel B: tDCS accompanying L2 grammar instruction significantly improves subject performance in the Digit span task compared with sham stimulation (P < 0.05). Panel C: Significant difference in Grammatical reasoning task from preto post-intervention in the sham group (P < 0.05). Panel D: Significant improvement of the tDCS group from preto post-intervention on Digit Span and Grammatical Reasoning tasks (P < 0.05). Significant P-value 0 .05. Asterisk (*) indicates significant differences, data summarized as mean ± standard error of the mean (SEM).

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