Effects of Transcranial Direct Current Stimulation on Brain Networks Related to Creative Thinking

Targeting Method for rTMS for Treating Depression in Japanese Patients: A Comparison of the Standard, F3, and Neuronavigation Approaches

INTRODUCTION

The left dorsolateral prefrontal cortex (lDLPFC) is a commonly targeted brain region for repetitive transcranial magnetic stimulation (rTMS) for depression. The lDLPFC has been identified using the "5-cm rule." However, identification of the lDLPFC may deviate from the ideal stimulation site localized by neuronavigation. Therefore, we aimed to compare this method with other methods and examine the relationship between deviation from the ideal stimulation site and treatment effects. While most existing studies have focused on participants of European descent, this study focused on Japanese participants.

METHODS

The study participants were 16 patients who underwent rTMS and had the stimulus location identified using the 5-cm method. The lDLPFC was identified by the F3 electrode position and neuronavigation in addition to the 5-cm rule, and these locations were compared. We then performed a correlation analysis of the distance between the sites identified by the 5-cm method and by neuronavigation, as well as changes in scores on the 17-item Hamilton Depression Scale (HAMD-17).

RESULTS

The lDLPFC identified by the F3 site and neuronavigation was approximately 3 cm more anterolateral than that identified by the 5-cm method. A significant correlation was found between the distance between the sites identified by the 5-cm method and neuronavigation and the rate of change in HAMD-17 scores.

CONCLUSION

The ideal stimulation site may be approximately 3 cm anterior to the site identified by the 5-cm method, and stimulation of the F3 site may be a valid alternative to the 5-cm method.

Divergent thinking benefits from functional antagonism of the left IFG and right TPJ: a transcranial direct current stimulation study

Divergent thinking is assumed to benefit from releasing the constraint of existing knowledge (i.e. top-down control) and enriching free association (i.e. bottom-up processing). However, whether functional antagonism between top-down control-related and bottom-up processing-related brain structures is conducive to generating original ideas is largely unknown. This study was designed to investigate the effect of functional antagonism between the left inferior frontal gyrus and the right temporoparietal junction on divergent thinking performance. A within-subjects design was adopted for three experiments. A total of 114 participants performed divergent thinking tasks after receiving transcranial direct current stimulation over target regions. In particular, cathodal stimulation over the left inferior frontal gyrus and anodal stimulation over the right inferior frontal gyrus (Experiment 1), anodal stimulation over the right temporoparietal junction (Experiment 2), and both cathodal stimulation over the left inferior frontal gyrus and anodal stimulation over the right temporoparietal junction (Experiment 3) were manipulated. Compared with sham stimulation, the combination of hyperpolarization of the left inferior frontal gyrus and depolarization of the right temporoparietal junction comprehensively promoted the fluency, flexibility, and originality of divergent thinking without decreasing the rationality of generated ideas. Functional antagonism between the left inferior frontal gyrus (hyperpolarization) and right temporoparietal junction (depolarization) has a "1 + 1 > 2" superposition effect on divergent thinking.

The Effects of Transcranial Direct Current Stimulation (tDCS) on the Cognitive Functions: A Systematic Review and Meta-analysis

Previous studies have investigated the effect of transcranial direct current stimulation (tDCS) on cognitive functions. However, these studies reported inconsistent results due to differences in experiment design, measurements, and stimulation parameters. Nonetheless, there is a lack of meta-analyses and review studies on tDCS and its impact on cognitive functions, including working memory, inhibition, flexibility, and theory of mind. We performed a systematic review and meta-analysis of tDCS studies published from the earliest available data up to October 2021, including studies reporting the effects of tDCS on cognitive functions in human populations. Therefore, these systematic review and meta-analysis aim to comprehensively analyze the effects of anodal and cathodal tDCS on cognitive functions by investigating 69 articles with a total of 5545 participants. Our study reveals significant anodal tDCS effects on various cognitive functions. Specifically, we observed improvements in working memory reaction time (RT), inhibition RT, flexibility RT, theory of mind RT, working memory accuracy, theory of mind accuracy and flexibility accuracy. Furthermore, our findings demonstrate noteworthy cathodal tDCS effects, enhancing working memory accuracy, inhibition accuracy, flexibility RT, flexibility accuracy, theory of mind RT, and theory of mind accuracy. Notably, regarding the influence of stimulation parameters of tDCS on cognitive functions, the results indicated significant differences across various aspects, including the timing of stimulation (online vs. offline studies), population type (clinical vs. healthy studies), stimulation duration (< 15 min vs. > 15 min), electrical current intensities (1-1.5 m.A vs. > 1.5 m.A), stimulation sites (right frontal vs. left frontal studies), age groups (young vs. older studies), and different cognitive tasks in each cognitive functioning aspect. In conclusion, our results demonstrate that tDCS can effectively enhance cognitive task performance, offering valuable insights into the potential benefits of this method for cognitive improvement.

Development of Low-Contact-Impedance Dry Electrodes for Electroencephalogram Signal Acquisition

Dry electroencephalogram (EEG) systems have a short set-up time and require limited skin preparation. However, they tend to require strong electrode-to-skin contact. In this study, dry EEG electrodes with low contact impedance (<150 kΩ) were fabricated by partially embedding a polyimide flexible printed circuit board (FPCB) in polydimethylsiloxane and then casting them in a sensor mold with six symmetrical legs or bumps. Silver-silver chloride paste was used at the exposed tip of each leg or bump that must touch the skin. The use of an FPCB enabled the fabricated electrodes to maintain steady impedance. Two types of dry electrodes were fabricated: flat-disk electrodes for skin with limited hair and multilegged electrodes for common use and for areas with thick hair. Impedance testing was conducted with and without a custom head cap according to the standard 10-20 electrode arrangement. The experimental results indicated that the fabricated electrodes exhibited impedance values between 65 and 120 kΩ. The brain wave patterns acquired with these electrodes were comparable to those acquired using conventional wet electrodes. The fabricated EEG electrodes passed the primary skin irritation tests based on the ISO 10993-10:2010 protocol and the cytotoxicity tests based on the ISO 10993-5:2009 protocol.

tDCS Anodal Stimulation of the Right Dorsolateral Prefrontal Cortex Improves Creative Performance in Real-World Problem Solving

Brain regions associated with creativity is a focal point in research related to the field of cognitive neuroscience. Previous studies have paid more attention to the role of activation of the left dorsolateral prefrontal cortex in creativity tasks, which are mostly abstract conceptual tasks, and less attention to real-world creativity tasks. The right dorsolateral prefrontal cortex is involved in functions such as visuospatial processing, which may have a positive impact on innovative solutions to real-world problems. In this study, tDCS technology was used to explore the effect of anodal stimulation of the right dorsolateral prefrontal cortex on design creativity performance in a real-word problem-solving task related to product design. The experimental task comprised three stages, of which the first two were idea generation stages based on divergent thinking using text and graphics, respectively, whereas the third was the creative evaluation stage based on convergent thinking. Thirty-six design students were recruited to partake in the experiment. They were randomly assigned into anodal stimulation and sham stimulation groups. The results showed that anodal stimulation of the right dorsolateral prefrontal cortex produced a significant positive effect during the creative evaluation stage, promoting the usefulness of ideas (p = 0.009); thus, improving product creativity scores. However, there was no significant impact on the idea generation stage (p > 0.05), which is dominated by divergent thinking. The results suggest that activating the right dorsolateral prefrontal cortex with tDCS can improve people’s performance in creative activities by promoting convergent thinking rather than divergent thinking. It also provides further evidence that the right hemisphere of the brain has an advantage in solving complex problems that require the participation of visuospatial information.