Comparing transcranial direct current stimulation and transcranial random noise stimulation over left dorsolateral prefrontal cortex and left inferior frontal gyrus: Effects on divergent and convergent thinking

Abstract

The essential role of creativity has been highlighted in several human knowledge areas. Regarding the neural underpinnings of creativity, there is evidence about the role of left dorsolateral prefrontal cortex (DLPFC) and left inferior frontal gyrus (IFG) on divergent thinking (DT) and convergent thinking (CT). Transcranial stimulation studies suggest that the left DLPFC is associated with both DT and CT, whereas left IFG is more related to DT. However, none of the previous studies have targeted both hubs simultaneously and compared transcranial direct current stimulation (tDCS) and random noise stimulation (tRNS). Additionally, given the relationship between cognitive flexibility and creativity, we included it in order to check if the improvement in creativity may be mediated by cognitive flexibility. In this double-blind, between-subjects study, 66 healthy participants were randomly assigned to one of three groups (N = 22) that received a transcranial direct current stimulation (tDCS), transcranial random noise stimulation (tRNS), or sham for 20 min. The tDCS group received 1.5 mA with the anode over the left DLPFC and cathode over the left IFG. Locations in tRNS group were the same and they received 1.5 mA of high frequency tRNS (100–500 Hz). Divergent thinking was assessed before (baseline) and during stimulation with unusual uses (UU) and picture completion (PC) subtests from Torrance Creative thinking Test, whereas convergent thinking was evaluated with the remote association test (RAT). Stroop test was included to assess cognitive flexibility. ANCOVA results of performance under stimulation (controlling for baseline performance) showed that there were significant differences in PC (F = 3.35, p = 0.042, n2pnp2 = 0.10) but not in UU (F = 0.61, p = 0.546) and RAT (F = 2.65, p = 0.079) scores. Post-hoc analyses showed that tRNS group had significantly higher scores compared to sham (p = 0.004) in PC. More specifically, tRNS showed higher performance in fluency (p = 0.012) and originality (p = 0.021) dimensions of PC compared to sham. Regarding cognitive flexibility, we did not find any significant effect of any of the stimulation groups (F = 0.34, p = 0.711). Therefore, no further mediation analyses were performed. Finally, the group that received tDCS reported more adverse effects than sham group (F = 3.46, p = 0.035). Altogether, these results suggest that tRNS may have some advantages over tDCS in DT.

摘要

创造力在多个人类知识领域中均被证实具有核心作用。关于创造力的神经基础，已有研究证实左侧背外侧前额叶皮层（left dorsolateral prefrontal cortex, DLPFC）和左侧额下回（left inferior frontal gyrus, IFG）在发散思维（divergent thinking, DT）与聚合思维（convergent thinking, CT）中发挥关键作用。经颅刺激相关研究表明，左侧DLPFC与发散思维、聚合思维均存在关联，而左侧IFG则更多与发散思维相关。但此前尚无研究同时针对这两个脑区进行刺激，并对比经颅直流电刺激（transcranial direct current stimulation, tDCS）与经颅随机噪声刺激（transcranial random noise stimulation, tRNS）的干预效果。此外，考虑到认知灵活性与创造力的内在关联，本研究纳入认知灵活性指标，以探究创造力的提升是否可通过认知灵活性介导。

本研究为双盲、被试间设计实验，共招募66名健康被试，按随机原则分配至3组（每组n=22），分别接受20分钟的tDCS、tRNS或伪刺激。tDCS组采用1.5mA电流，阳极置于左侧DLPFC，阴极置于左侧IFG。tRNS组的刺激靶点与tDCS组一致，采用1.5mA的高频tRNS（100–500Hz）。

发散思维通过托兰斯创造性思维测验（Torrance Creative Thinking Test）的非常规用途（unusual uses, UU）和图片补全（picture completion, PC）分测验，在刺激前（基线）与刺激过程中进行评估；聚合思维则通过远程联想测验（remote association test, RAT）进行评估。本研究同时采用斯特鲁普测验（Stroop Test）评估认知灵活性。

以基线成绩为协变量的协方差分析（analysis of covariance, ANCOVA）结果显示，PC分测验成绩存在显著组间差异（F=3.35, p=0.042, ηp²=0.10），但UU（F=0.61, p=0.546）与RAT（F=2.65, p=0.079）成绩无显著组间差异。事后检验结果表明，tRNS组的PC成绩显著高于伪刺激组（p=0.004）；具体而言，相较于伪刺激组，tRNS组在PC分测验的流畅性（p=0.012）与独创性（p=0.021）维度上表现更优。

关于认知灵活性，各刺激组均未表现出显著效应（F=0.34, p=0.711），因此未进行后续的中介效应分析。最后，tDCS组报告的不良反应显著多于伪刺激组（F=3.46, p=0.035）。

综上，本研究结果提示，在发散思维任务中，tRNS或许较tDCS更具优势。