经颅电刺激与视功能调控

经颅电刺激(Transcranial Electrical Stimulation, TES)通过电极将特定模式的低强度电流作用于大脑头皮以调控皮层活动, 是一种非侵入、无创的神经刺激方法。根据刺激电流的模式的不同, TES分为经颅直流电刺激(tDCS), 经颅交流电刺激(tACS)和经颅随机电刺激(tRNS)。TES能对视功能诸如光幻视阈值、视野、对比敏感度、视知觉运动等进行一定程度上的调控, 并且能够与传统的视觉知觉学习训练相结合以调控视觉功能。对于不同的视觉功能, 不同的TES参数和模式的调控效果有所不同。     

不同频率经颅交流电刺激在精神疾病中的应用

近年来, 研究者开始将经颅交流电刺激技术应用于精神疾病领域中, 其中, 以γ、α频率最受关注。tACS作用于精神疾病的可能机制包括两个方面, 直接调节异常的大脑神经活动和间接改善患者的认知功能。首先, 使用特定频率的tACS作用目标脑区, 可以调节对应频率的神经振荡和大脑功能连接, 通过作用于疾病相关的异常大脑活动, 直接改善患者的临床症状。其次, 并不针对某种疾病特异受损的大脑活动, 而是用tACS激活与认知功能相关的大脑环路, 广泛地提高患者的注意、记忆等多种认知功能, 进而整体上缓解不良症状。目前, 使用tACS治疗精神疾病这一领域还有一些尚未解决、值得探讨的问题。tACS的作用机制研究、刺激参数和范式改进、技术升级, 可以成为心理学、脑科学以及临床医学的重点研究方向。     

事件相关振荡与振荡脑网络

事件相关振荡是伴随认知、情感和行为过程的脑电磁振荡活动,观察到其各类调频、调幅和调相现象,这种介观和宏观尺度上大量神经元的集体活动与微观尺度上神经元平均发放率和发放定时相互影响,共同参与神经信息的编码、表征、通讯和调控。动态细胞集群假说认为大脑认知功能是神经网络通过同步振荡相互作用的结果,在基于振荡的大脑理论指引下,多尺度、跨脑区和跨频率事件相关振荡研究为揭开振荡脑网络的工作原理带来了希望     

重复经颅磁刺激对轻度认知障碍的干预效果

轻度认知障碍(mild cognitive impairment, MCI)是介于正常认知老化和老年痴呆的中间状态, 目前尚无有效的药物治疗方案。重复经颅磁刺激(repetitive transcranial magnetic stimulation, rTMS)可通过诱导突触可塑性的改变来改善大脑的认知功能。对rTMS干预MCI认知功能的有效性及神经机制进行分析。未来研究应优化定位手段, 延长对干预效果的随访评估, 考察不同刺激参数和刺激靶区对干预有效性的影响, 以及结合脑成像技术来探索rTMS的干预机制。     

经颅直流电刺激提高记忆功能

经颅直流电刺激是最近复兴的非侵入性无创脑刺激方法, 具有轻便、廉价、较为安全的特点。经颅直流电刺激能产生一系列生理变化, 相比传统脑成像方法具有优势, 在工作记忆、陈述性记忆、程序性记忆上已有应用, 可与传统认知训练相结合。经颅直流电刺激虽然不能进行精确定位, 但是能够基于脑区影响个体认知加工过程。经颅直流电刺激在临床上可以作为治疗手段, 对健康人可以作为神经训练的方法, 在心理学领域具有良好的研究前景。     

刺激前alpha振荡对视知觉的影响

人类对感觉阈限附近的视觉刺激的知觉不总是一致的。为探究这种视知觉不一致的现象及其神经机制, 一些研究者关注刺激前脑内自发alpha神经振荡(8~13 Hz)对视知觉的影响。近年来的研究发现, 刺激前alpha振荡能量的降低能提高被试的探测击中率, 但不能提高知觉精确度; 而刺激前alpha振荡的相位能预测被试能否成功探测刺激。刺激前alpha能量被认为调控了视皮层的基础活动强度; alpha能量的降低反映了皮层基础活动的增强, 进而提高了对较弱刺激的探测率。刺激前alpha相位则被认为调控了皮层兴奋和抑制的时间; 大脑在刺激呈现时的不同状态(兴奋/抑制)决定了最终的知觉结果。     

前额叶的无创神经干预对饮食控制的影响:基于rTMS和tDCS研究的综述

饮食控制缺陷可导致超重、肥胖和饮食失调。已有研究表明,肥胖和饮食失调者在前额叶认知控制神经环路上存在缺陷。无创神经干预-经颅直流电刺激(t DCS)和重复经颅磁刺激(r TMS)-通过调节前额叶皮层兴奋性来提高饮食控制能力,改善饮食失调症状。未来的研究应考虑不同刺激参数和刺激位点下的干预效应,融合其他神经生理技术考察无创神经干预改善饮食控制的作用机制,考虑个体差异性并结合客观的行为范式进行探究。     

工作记忆训练诱发的神经可塑性——基于系列fMRI实验的脑区分布递减时空模型

工作记忆训练(Working Memory Training, WMT)诱发神经可塑性, 但其具体机制尚不明晰。为探索WMT改变正常人群大脑功能的时空特性, 以“扩展的智力顶额整合理论”和“神经效率假说”为依据, 采用逐层递进的5种方法, 分6个步骤来查究近20年来正常人群WMT的37篇fMRI文献。第一步, 用叙述性综述、频数分析和卡方检验法比较脑区激活模式和脑网络功能连接在WMT前后发生的改变, 发现WMT改变了大脑的5个联合区、7个宏观区和3个子区。其中, 额上回、顶下小叶和扣带回这3个子区各自激活减弱的报道文献数量多于其激活增强的, 且这种差异分别具有统计学意义。第二步, 采用激活似然估计法对其中26篇开展元分析, 发现大脑的3个子区激活减弱水平在WMT前后的差异具有统计学意义, 即额中回(BA6和8)、额上回(BA6)和前扣带回(BA24和32)。第三步, 综合定性和定量分析结果, 提出WMT脑区分布递减时空模型, 产生5个结果和讨论。第四步, 采用非参数检验进一步追踪WMT效应的调节因素, 发现训练的任务类型和时间分别对脑区激活的影响具有统计学意义。第五步, 针对正常人群WMT诱发神经可塑性的时空特性, 得出3个结论：第一, WMT改变了正常人群相应脑区的神经活动, 表现为减弱或增强, 但减弱更加突出, 且更新和较短时间的WMT倾向于诱发较多减弱; 第二, 这些神经活动变化主要发生在额顶叶联合区, 但也包括分别以颞叶、枕叶、扣带回及纹状体为主的联合区, 在一定范围内体现了整脑功能联合。这体现了WMT诱发神经可塑性的空间特性, 且符合“扩展的智力顶额整合理论”; 第三, 额中回、额上回、顶下小叶和扣带回(尤其前扣带回)这4个子区在激活减弱水平上重点展示了WMT神经可塑性的时间特性, 且符合“神经效率假说”, 恰好体现出“聪明的大脑更懒惰”。第六步, 指出WMT诱发神经可塑性的未来研究可能关注脑可塑性中的低活跃性、辨析额中回、额上回、顶下小叶和扣带回(尤其前扣带回)这4个子区在激活减弱水平上体现的时间特性、找寻训练减弱或增强大脑活动的综合性影响因素。     

右侧背外侧前额叶在视觉工作记忆中的因果性作用

以往的影像学研究表明右侧背外侧前额叶皮层(DLPFC)在视觉工作记忆中发挥重要作用, 然而缺乏因果性的证据。本研究旨在考察右侧DLPFC的激活与视觉工作记忆容量的因果关系, 并探讨这一关系受到记忆负荷的调节及其神经机制。被试接受经颅直流电刺激之后完成视觉工作记忆变化检测任务, 根据被试在虚假刺激情况下从负荷4到负荷6任务记忆容量的增量将被试分为低记忆增长潜力组(简称低潜力组)和高记忆增长潜力组(简称高潜力组), 结果发现正性电刺激右侧DLPFC相对于虚假电刺激显著提升了高潜力组被试在低记忆负荷(负荷4)下的记忆容量及其对应的提取阶段的脑电指标SPCN成分。表明右侧DLPFC在视觉工作记忆的提取阶段发挥重要的因果性作用; 正性经颅直流电刺激右侧DLPFC可使工作记忆容量高潜力被试获得更多的脑活动增益, 并导致更好的行为提升效果。     

创造力产生过程中的神经振荡机制

创造力究竟是怎么产生的, 目前尚未得出一致的结论。神经电生理技术因其高时间分辨率, 可以准确地揭示创造力产生进程中的神经振荡机制, 从而帮助人们更深刻地理解创造力的本质。近年来的研究发现, 单节律alpha神经振荡会随着创造力的增加而增强, 这反映了创造力产生过程中的内部信息加工需求增加、自上而下的抑制控制增强。同时, 多频段神经振荡交叉节律耦合体现了创造性产生过程中额叶、颞叶和顶叶等多脑区之间信息交流的动态变化。未来研究应该以整合理论框架为基础, 结合多层次多方法的研究工具, 引进更生态化的数理计算方法, 并利用计算神经科学建模来预测个体创造力发展趋势, 从而全面深刻地认识创造力的本质。     

Neurocognitive,physiological, and biophysical effects of transcranial alternating current stimulation

Transcranial alternating current stimulation (tACS) can modulate human neural activity and behavior. Accordingly, tACS has vast potential for cognitive research and brain disorder therapies. The stimulation generates oscillating electric fields in the brain that can bias neural spike timing, causing changes in local neural oscillatory power and cross-frequency and cross-area coherence. tACS affects cognitive performance by modulating underlying single or nested brain rhythms, local or distal synchronization, and metabolic activity. Clinically, stimulation tailored to abnormal neural oscillations shows promising results in alleviating psychiatric and neurological symptoms. We summarize the findings of tACS mechanisms, its use for cognitive applications, and novel developments for personalized stimulation.     

Attention training improves aberrant neural dynamics during working memory processing in veterans with PTSD

Posttraumatic stress disorder (PTSD) is associated with executive functioning deficits, including disruptions in working memory (WM). Recent studies suggest that attention training reduces PTSD symptomatology, but the underlying neural mechanisms are unknown. We used high-density magnetoencephalography (MEG) to evaluate whether attention training modulates brain regions serving WM processing in PTSD. Fourteen veterans with PTSD completed a WM task during a 306-sensor MEG recording before and after 8 sessions of attention training treatment. A matched comparison sample of 12 combat-exposed veterans without PTSD completed the same WM task during a single MEG session. To identify the spatiotemporal dynamics, each group’s data were transformed into the time-frequency domain, and significant oscillatory brain responses were imaged using a beamforming approach. All participants exhibited activity in left hemispheric language areas consistent with a verbal WM task. Additionally, veterans with PTSD and combat-exposed healthy controls each exhibited oscillatory responses in right hemispheric homologue regions (e.g., right Broca’s area); however, these responses were in opposite directions. Group differences in oscillatory activity emerged in the theta band (4–8 Hz) during encoding and in the alpha band (9–12 Hz) during maintenance and were significant in right prefrontal and right supramarginal and inferior parietal regions. Importantly, following attention training, these significant group differences were reduced or eliminated. This study provides initial evidence that attention training improves aberrant neural activity in brain networks serving WM processing.     

The influence of theta transcranial alternating current stimulation (tACS) on working memory storage and processing functions

The study aimed to explore the role of the fronto-parietal brain network in working memory function—in temporary storage and manipulation of information. In a single blind sham controlled experiment 36 respondents solved different working memory tasks after theta transcranial alternating current stimulation (tACS) was applied to left frontal, left parietal and right parietal areas. Both verum tACS protocols stimulating parietal brain areas (target electrodes positioned at location P3, or P4) had a positive effect on WM storage capacity as compared with sham tACS, whereas no such influence was observed for the stimulation of the left frontal area (target electrode positioned at location F3). A second finding was that left parietal theta tACS had a more pronounced influence on backward recall than on forward recall, which was not related to task content (spatial or verbal). The influence of theta tACS on WM executive processes was most pronounced for right parietal stimulation. The results are discussed in the broad theoretical framework of the multicomponent model of working memory.     

Working memory training: improving intelligence--changing brain activity

The main objectives of the study were: to investigate whether training on working memory (WM) could improve fluid intelligence, and to investigate the effects WM training had on neuroelectric (electroencephalography - EEG) and hemodynamic (near-infrared spectroscopy - NIRS) patterns of brain activity. In a parallel group experimental design, respondents of the working memory group after 30 h of training significantly increased performance on all tests of fluid intelligence. By contrast, respondents of the active control group (participating in a 30-h communication training course) showed no improvements in performance. The influence of WM training on patterns of neuroelectric brain activity was most pronounced in the theta and alpha bands. Theta and lower-1 alpha band synchronization was accompanied by increased lower-2 and upper alpha desynchronization. The hemodynamic patterns of brain activity after the training changed from higher right hemispheric activation to a balanced activity of both frontal areas. The neuroelectric as well as hemodynamic patterns of brain activity suggest that the training influenced WM maintenance functions as well as processes directed by the central executive. The changes in upper alpha band desynchronization could further indicate that processes related to long term memory were also influenced.     

Does cross‐frequency phase coupling of oscillatory brain activity contribute to a better understanding of visual working memory?

Nesting of fast rhythmical brain activity (gamma) into slower brain waves (theta) has frequently been suggested as a core mechanism of multi‐item working memory (WM) retention. It provides a better understanding of WM capacity limitations, and, as we discuss in this review article, it can lead to applications for modulating memory capacity. However, could cross‐frequency coupling of brain oscillations also constructively contribute to a better understanding of the neuronal signatures of working memory compatible with theoretical approaches that assume flexible capacity limits? Could a theta‐gamma code also be considered as a neural mechanism of flexible sharing of cognitive resources between memory representations in multi‐item WM? Here, we propose potential variants of theta‐gamma coupling that could explain WM retention beyond a fixed memory capacity limit of a few visual items. Moreover, we suggest how to empirically test these predictions in the future.     

工作记忆刷新及其训练效应——经颅直流电刺激的作用

工作记忆刷新是执行功能的重要成分之一。以往研究结合n-back任务和经颅直流电刺激（transcranial direct current stimulation ,tDCS）技术探究刷新能力,发现tDCS技术能够一定程度上增强刷新训练效果并引起大脑神经元相关活动的变化,其增强效果能够维持一定的时间,且能够迁移到其他认知任务之中。但tDCS的干预效果在各项研究中存在一定的差异性。其作用效果会受到训练任务与训练方式、电流强度、电极布局和训练时间间隔等因素的影响。未来研究可以探索tDCS结合刷新训练的最佳刺激参数,以获得最优化的干预效果。     

急性应激对工作记忆的影响受工作记忆负荷调节:来自电生理的证据

急性应激如何影响工作记忆还不清楚。采用电影片断诱发被试的急性应激或中性状态后,让其完成数字N-back任务并同时记录脑电。结果发现,低负荷工作记忆诱发的P3显著大于高负荷工作记忆;在0-back任务中,急性应激组诱发的P3显著大于控制组;而在2-back任务中,这种差异不显著。这些结果表明急性应激对工作记忆的影响受工作记忆负荷调节,支持了双竞争理论模型。     

Personality predicts working-memory-related activation in the caudal anterior cingulate cortex

Behavioral studies suggest that two affective dimensions of personality are associated with working memory (WM) function. WM load is known to modulate neural activity in the caudal anterior cingulate cortex (ACC), a brain region critical for the cognitive control of behavior. On this basis, we hypothesized that neural activity in the caudal ACC during a WM task should be associated with personality: correlated negatively with behavioral approach sensitivity (BAS) and positively with behavioral inhibition sensitivity (BIS). Using functional magnetic resonance imaging, we measured brain activity in 14 participants performing a three-back WM task. Higher self-reported BAS predicted better WM performance (r = .27) and lower WM-related activation in the caudal ACC (r = -.84), suggesting personality differences in cognitive control. The data bolster approach-withdrawal (action control) theories of personality and suggest refinements to the dominant views of ACC and personality.     

Working memory improvement with non-invasive brain stimulation of the dorsolateral prefrontal cortex: A systematic review and meta-analysis

Recent studies have used non-invasive brain stimulation (NIBS) techniques, such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), to increase dorsolateral prefrontal cortex (DLPFC) activity and, consequently, working memory (WM) performance. However, such experiments have yielded mixed results, possibly due to small sample sizes and heterogeneity of outcomes. Therefore, our aim was to perform a systematic review and meta-analyses on NIBS studies assessing the n-back task, which is a reliable index for WM. From the first data available to February 2013, we looked for sham-controlled, randomized studies that used NIBS over the DLPFC using the n-back task in PubMed/MEDLINE and other databases. Twelve studies (describing 33 experiments) matched our eligibility criteria. Active vs. sham NIBS was significantly associated with faster response times (RTs), higher percentage of correct responses and lower percentage of error responses. However, meta-regressions showed that tDCS (vs. rTMS) presented only an improvement in RT, and not in accuracy. This could have occurred in part because almost all tDCS studies employed a crossover design, possibly due to the reliable tDCS blinding. Study design was also associated with no improvement in correct responses in the active vs. sham groups. To conclude, rTMS of the DLPFC significantly improved all measures of WM performance whereas tDCS significantly improved RT, but not the percentage of correct and error responses. Mechanistic insights on the role of DLPFC in WM are further discussed, as well as how NIBS techniques could be used in neuropsychiatric samples presenting WM deficits, such as major depression, dementia and schizophrenia.     

Oscillatory gamma activity in humans and its role in object representation

We experience objects as whole, complete entities irrespective of whether they are perceived by our sensory systems or are recalled from memory. However, it is also known that many of the properties of objects are encoded and processed in different areas of the brain. How then, do coherent representations emerge? One theory suggests that rhythmic synchronization of neural discharges in the gamma band (around 40 Hz) may provide the necessary spatial and temporal links that bind together the processing in different brain areas to build a coherent percept. In this article we propose that this mechanism could also be used more generally for the construction of object representations that are driven by sensory input or internal, top-down processes. The review will focus on the literature on gamma oscillatory activities in humans and will describe the different types of gamma responses and how to analyze them. Converging evidence that suggests that one particular type of gamma activity (induced gamma activity) is observed during the construction of an object representation will be discussed.