Demographics and baseline scores.

IntroductionThis research explores the relationship between baseline performance in dementia patients and its impact on the effectiveness of transcranial direct current stimulation (tDCS) for improving executive function. Past research suggests that those participants who are more impaired at baseline will be those who then demonstrate the greatest improvements with tDCS. In addition, we examined if bilateral or unilateral stimulation would be more effective for improving the general level of cognition of these participants.Materials and MethodsThe study involved 24 participants, with 18 diagnosed with Alzheimer’s disease (AD) and 6 with Frontotemporal Dementia (FTD). These participants engaged in three rounds of N-back task training sessions, each separated by two months. The sessions included three types of stimulation: 4mA unilateral stimulation targeting the left Dorsolateral Prefrontal Cortex (DLPFC), 4mA bilateral stimulation targeting both the left and right DPFC, and sham stimulation. Additionally, a control group of elderly individuals without dementia was used to establish a benchmark for the normal average response time (RT) of the administered N-Back task. Evaluations, comprising of the N-Back task and the Mini-Mental State Examination (MMSE), were conducted before stimulation, at the final session, and two weeks post-stimulation in all rounds.ResultsParticipants were retrospectively allocated into those whose baseline N-Back response times (RTs) were found on average to be within the normal range versus those who performed more slowly than the normal range. For the group that performed within the normal range, no significant improvement was observed on the N-Back task after a series of sessions involving active tDCS. In contrast, the participants with slower than normal RTs at baseline demonstrated improvement both on the N-Back task (faster times) and the MMSE (higher scores) after receiving active tDCS, although accompanying improvement on the MMSE task was restricted to the condition where participants received bilateral tDCS.ConclusionThis study replicates a pervasive finding in the tDCS literature: participants who perform worse at baseline often demonstrate the greatest improvements with tDCS. Furthermore, these results have clinical implications, in that tDCS may be most beneficial in individuals when clear deficits or impairments are present. Attempts to treat less severe participants might fail to show improvement with tDCS. Ultimately, baseline condition should be routinely considered when evaluating tDCS results.引言 本研究探讨痴呆患者基线认知表现与经颅直流电刺激（transcranial direct current stimulation, tDCS）改善执行功能的疗效之间的关联。既往研究提示，基线受损程度更严重的受试者，在接受tDCS后往往表现出最显著的认知改善。此外，本研究还考察了双侧刺激与单侧刺激哪种更能有效提升受试者的整体认知水平。 材料与方法 本研究共纳入24名受试者，其中18名确诊为阿尔茨海默病（Alzheimer’s disease, AD），6名确诊为额颞叶痴呆（Frontotemporal Dementia, FTD）。所有受试者完成三轮N-back任务训练，每轮间隔两个月。训练过程中采用三种刺激方案：针对左侧背外侧前额叶皮层（Dorsolateral Prefrontal Cortex, DLPFC）的4mA单侧刺激、针对左右两侧DLPFC的4mA双侧刺激，以及假刺激。此外，本研究设置了无痴呆老年人群作为对照组，以建立所采用N-back任务的正常平均反应时（response time, RT）基准。在每轮研究中，均于刺激前、最后一次训练阶段以及刺激结束后两周，采用N-back任务与迷你精神状态检查（Mini-Mental State Examination, MMSE）进行评估。 结果 研究采用回顾性分组方式，将受试者分为基线N-back反应时处于正常范围组，以及基线反应时慢于正常范围组。对于基线反应时处于正常范围的受试者群体，在接受一系列主动tDCS训练后，其N-back任务表现未出现显著改善。与之相对，基线反应时慢于正常范围的受试者，在接受主动tDCS后，N-back任务表现（反应时缩短）与MMSE评分均得到提升；不过MMSE评分的改善仅在双侧tDCS刺激条件下才得以显现。 结论 本研究复现了tDCS相关研究中的普遍结论：基线表现更差的受试者，往往在接受tDCS后获得最显著的改善。此外，本研究结果具有临床指导意义，即tDCS或对存在明确认知缺损或受损的个体最为有益，而针对轻症受试者的治疗可能无法观察到改善效果。综上，在评估tDCS疗效时，应常规将基线状态纳入考量因素。