Short theta burst stimulation to left frontal cortex prior to encoding enhances subsequent recognition memory

Deep semantic encoding of verbal stimuli can aid in later successful retrieval of those stimuli from long-term episodic memory. Evidence from numerous neuropsychological and neuroimaging experiments demonstrate regions in left prefrontal cortex, including left dorsolateral prefrontal cortex (DLPFC), are important for processes related to encoding. Here, we investigated the relationship between left DLPFC activity during encoding and successful subsequent memory with transcranial magnetic stimulation (TMS). In a pair of experiments using a 2-session within-subjects design, we stimulated either left DLPFC or a control region (Vertex) with a single 2-s train of short theta burst stimulation (sTBS) during a semantic encoding task and then gave participants a recognition memory test. We found that subsequent memory was enhanced on the day left DLPFC was stimulated, relative to the day Vertex was stimulated, and that DLPFC stimulation also increased participants’ confidence in their decisions during the recognition task. We also explored the time course of how long the effects of sTBS persisted. Our data suggest 2 s of sTBS to left DLPFC is capable of enhancing subsequent memory for items encoded up to 15 s following stimulation. Collectively, these data demonstrate sTBS is capable of enhancing long-term memory and provide evidence that TBS protocols are a potentially powerful tool for modulating cognitive function.     

Variable heart rate and a flexible mind: Higher resting-state heart rate variability predicts better task-switching

The neurovisceral integration model proposes that heart rate variability (HRV) is linked to prefrontal cortex activity via the vagus nerve, which connects the heart and the brain. HRV, an index of cardiac vagal tone, has been found to predict performance on several cognitive control tasks that rely on the prefrontal cortex. However, the link between HRV and the core cognitive control function “shifting” between tasks and mental sets is under-investigated. Therefore, the present study tested the neurovisceral integration model by examining, in 90 participants, the relationship between vagally mediated resting-state HRV and performance in a task-switching paradigm that provides a relatively process-pure measure of cognitive flexibility. As predicted, participants with higher resting-state HRV (indexed both by time domain and frequency domain measures) showed smaller switch costs (i.e., greater flexibility) than individuals with lower resting-state HRV. Our findings support the neurovisceral integration model and indicate that higher levels of vagally mediated resting-state HRV promote cognitive flexibility.     

Beyond arousal and valence: The importance of the biological versus social relevance of emotional stimuli

The present study addressed the hypothesis that emotional stimuli relevant to survival or reproduction (biologically emotional stimuli) automatically affect cognitive processing (e.g., attention, memory), while those relevant to social life (socially emotional stimuli) require elaborative processing to modulate attention and memory. Results of our behavioral studies showed that (1) biologically emotional images hold attention more strongly than do socially emotional images, (2) memory for biologically emotional images was enhanced even with limited cognitive resources, but (3) memory for socially emotional images was enhanced only when people had sufficient cognitive resources at encoding. Neither images’ subjective arousal nor their valence modulated these patterns. A subsequent functional magnetic resonance imaging study revealed that biologically emotional images induced stronger activity in the visual cortex and greater functional connectivity between the amygdala and visual cortex than did socially emotional images. These results suggest that the interconnection between the amygdala and visual cortex supports enhanced attention allocation to biological stimuli. In contrast, socially emotional images evoked greater activity in the medial prefrontal cortex (MPFC) and yielded stronger functional connectivity between the amygdala and MPFC than did biological images. Thus, it appears that emotional processing of social stimuli involves elaborative processing requiring frontal lobe activity.     

Does Therapeutic Repetitive Transcranial Magnetic Stimulation Cause Cognitive Enhancing Effects in Patients with Neuropsychiatric Conditions? A Systematic Review and Meta-Analysis of Randomised Controlled Trials

Repetitive transcranial magnetic stimulation (rTMS) is increasingly used as a therapeutic intervention for neuropsychiatric illnesses and has demonstrated efficacy for treatment of major depression. However, an unresolved question is whether a course of rTMS treatment results in effects on cognitive functioning. In this systematic review and meta-analysis we aimed to quantitatively determine whether a course of rTMS has cognitive enhancing effects. We examined cognitive outcomes from randomised, sham-controlled studies conducted in patients with neuropsychiatric conditions where rTMS was administered to the dorsolateral prefrontal cortex (DLPFC) across repeated sessions, searched from PubMed/MEDLINE and other databases up until October 2015. Thirty studies met our inclusion criteria. Cognitive outcomes were pooled and examined across the following domains: Global cognitive function, executive function, attention, working memory, processing speed, visual memory, verbal memory and visuospatial ability. Active rTMS treatment was unassociated with generalised gains across the majority of domains of cognitive functioning examined. Secondary analyses revealed a moderate sized positive effect for improved working memory in a small number of studies in patients with schizophrenia (k = 3, g = 0.507, 95 % CI = [0.183–0.831], p < .01). Therapeutic rTMS when administered to the DLPFC in patients with neuropsychiatric conditions does not result in robust cognitive enhancing effects.     

Effects of tDCS over the right DLPFC on attentional disengagement from positive and negative faces: An eye-tracking study

The aim of this study was to increase insight in the neural substrates of attention processes involved in emotion regulation. The effects of right dorsolateral prefrontal cortex (i.e., DLPFC) stimulation on attentional processing of emotional information were evaluated. A novel attention task allowing a straightforward measurement of attentional engagement toward, and attentional disengagement away from emotional faces was used. A sample of healthy participants received 20 minutes of active and sham anodal transcranial direct current stimulation (i.e., tDCS) applied over the right DLPFC on 2 separate days and completed the attention task after receiving real or sham stimulation. Compared to sham stimulation, tDCS over the right DLPFC led to impairments in attentional disengagement from both positive and negative faces. Findings demonstrate a causal role of right DLPFC activity in the generation of attentional impairments that are implicated in emotional disturbances such as depression and anxiety.     

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。     

A general mechanism for decision-making in the human brain?

A new fMRI study by Heekeren and colleagues suggests that left dorsolateral prefrontal cortex (DLPFC) contains a region that integrates sensory evidence supporting perceptual decisions. DLPFC meets two criteria posited by Heekeren et al. for such a region: (1) its activity is correlated in time with the output of sensory areas of the visual cortex measured simultaneously, and (2) as expected of an integrator, its activity is greater on trials for which the sensory evidence is substantial than on trials for which the sensory evidence is weak. Complementary experiments in humans and monkeys now offer a realistic hope of elucidating decision-making networks in the primate brain.     

触觉二维图像识别中2D-3D空间信息转换的认知机制

可触摸的触觉二维图像是视觉障碍人群获取图像信息的重要方式。目前大多数触觉二维图像都是直接由视觉二维图像转化为的可触摸线条图。在视觉二维图像中, 通常运用透视和视角等视觉原理将三维空间关系转换为二维平面关系。视觉系统经过长期大量知觉学习, 习得了这种二维到三维的映射关系。但是触觉识别二维图像时, 触觉系统如何建立二维平面与三维空间的映射, 目前尚有待进一步的研究。影响触觉识别二维图像中二维-三维空间信息转换的视觉因素主要有透视、视角、遮挡、纹理梯度和镂空, 直接将视觉二维图像转化为的触觉二维图像时, 图像中包含的上述视觉因素通常会干扰触觉识别。结合已有研究, 试图提出“双表象加工模型”来解释触摸二维图像时二维到三维空间信息转换的认知机制。该模型认为触觉识别二维图像依赖于两个表象系统的整合, 即物体表象系统(涉及物体的大小、形状和纹理)与空间表象系统(涉及物体的空间关系、透视和视角)。两种表象系统的信息最终进行整合, 在物体表象和空间表象成功匹配的基础上建立二维图像与三维空间之间的映射, 通达长时记忆中的三维物体表征。双表象加工模型将有助于我们深入认识触知觉的认知机制, 也将为触觉二维图像的设计提供理论依据。     

Cerebellum and processing of negative facial emotions: cerebellar transcranial DC stimulation specifically enhances the emotional recognition of facial anger and sadness

Some evidence suggests that the cerebellum participates in the complex network processing emotional facial expression. To evaluate the role of the cerebellum in recognising facial expressions we delivered transcranial direct current stimulation (tDCS) over the cerebellum and prefrontal cortex. A facial emotion recognition task was administered to 21 healthy subjects before and after cerebellar tDCS; we also tested subjects with a visual attention task and a visual analogue scale (VAS) for mood. Anodal and cathodal cerebellar tDCS both significantly enhanced sensory processing in response to negative facial expressions (anodal tDCS, p=.0021; cathodal tDCS, p=.018), but left positive emotion and neutral facial expressions unchanged (p>.05). tDCS over the right prefrontal cortex left facial expressions of both negative and positive emotion unchanged. These findings suggest that the cerebellum is specifically involved in processing facial expressions of negative emotion.     

Mental relaxation improves long-term incidental visual memory

Experimental evidence has linked increased arousal to enhanced memory retention. There is also evidence that procedures reducing arousal, i.e., mental relaxation, might improve memory, but conflicting results have been reported. To clarify this issue, we studied the effects of a single session of relaxation training on incidental visual long-term memory. Thirty-two relaxation-naive subjects viewed 280 slides without being told that there would be subsequent memory testing. Afterwards, subjects listened to a 12 min relaxation tape; 16 subjects relaxed by following the instructions (relaxation group), and the other 16 subjects pressed a button whenever a body part was mentioned (control group). While listening to the relaxation tape, high frequency heart rate variability (HRV) was greater and low frequency HRV was lower in the relaxation group, implying effective relaxation and increasing parasympathetic activation. The relaxation group had superior memory retention 4 weeks later (p = .004), indicating enhancement of long-term memory performance. This effect could not be explained by retroactive interference experienced in the control group because short-term memory performance immediately after the tape was slightly better in the control group. Retention of materials acquired after the relaxation session remained unaffected, suggesting relaxation has retrograde effects on memory consolidation. Our data demonstrate a favorable influence of relaxation on at least this aspect of learning. Our data also extend previous knowledge on the beneficial effects of ascending parasympathetic stimulation on memory retention in that enhanced long-term memory consolidation may also occur in the presence of central and descending parasympathetic activation triggered by willful psychomotor activity.     

Cerebellum and processing of negative facial emotions: Cerebellar transcranial DC stimulation specifically enhances the emotional recognition of facial anger and sadness

Some evidence suggests that the cerebellum participates in the complex network processing emotional facial expression. To evaluate the role of the cerebellum in recognising facial expressions we delivered transcranial direct current stimulation (tDCS) over the cerebellum and prefrontal cortex. A facial emotion recognition task was administered to 21 healthy subjects before and after cerebellar tDCS; we also tested subjects with a visual attention task and a visual analogue scale (VAS) for mood. Anodal and cathodal cerebellar tDCS both significantly enhanced sensory processing in response to negative facial expressions (anodal tDCS, p=.0021; cathodal tDCS, p=.018), but left positive emotion and neutral facial expressions unchanged (p>.05). tDCS over the right prefrontal cortex left facial expressions of both negative and positive emotion unchanged. These findings suggest that the cerebellum is specifically involved in processing facial expressions of negative emotion.     

Emotional appraisal is influenced by cardiac afferent information

Influential models highlight the central integration of bodily arousal with emotion. Some emotions, notably disgust, are more closely coupled to visceral state than others. Cardiac baroreceptors, activated at systole within each cardiac cycle, provide short-term visceral feedback. Here we explored how phasic baroreceptor activation may alter the appraisal of brief emotional stimuli and consequent cardiovascular reactions. We used functional MRI (fMRI) to measure brain responses to emotional face stimuli presented before and during cardiac systole. We observed that the processing of emotional stimuli was altered by concurrent natural baroreceptor activation. Specifically, facial expressions of disgust were judged as more intense when presented at systole, and rebound heart rate increases were attenuated after expressions of disgust and happiness. Neural activity within prefrontal cortex correlated with emotionality ratings. Activity within periaqueductal gray matter reflected both emotional ratings and their interaction with cardiac timing. Activity within regions including prefrontal and visual cortices correlated with increases in heart rate evoked by the face stimuli, while orbitofrontal activity reflected both evoked heart rate change and its interaction with cardiac timing. Our findings demonstrate that momentary physiological fluctuations in cardiovascular afferent information (1) influence specific emotional judgments, mediated through regions including the periaqueductal gray matter, and (2) shape evoked autonomic responses through engagement of orbitofrontal cortex. Together these findings highlight the close coupling of visceral and emotional processes and identify neural regions mediating bodily state influences on affective judgment.     

Transcranial magnetic stimulation over MT/MST fails to impair judgments of implied motion

The medial temporal and medial superior temporal cortex (MT/MST) is involved in the processing of visual motion, and fMRI experiments indicate that there is greater activation when subjects view static images that imply motion than when they view images that do not imply motion at all. We applied transcranial magnetic stimulation (TMS) to MT/MST in order to assess the functional necessity of this region for the processing of implied motion represented in static images. Area MT/MST was localized by the use of a TMS-induced misperception of visual motion, and its location was verified through the monitored completion of a motion discrimination task. We controlled for possible impairments in general visual processing by having subjects perform an object categorization task with and without TMS. Although MT/MST stimulation impaired performance in a motion discrimination task (and vertex stimulation did not), there was no difference in performance between the two forms of stimulation in the implied motion discrimination task. MT/MST stimulation did, however, improve subjects’ performance in the object categorization task. These results indicate that, within 150 msec of stimulus presentation, MT/MST is not directly involved in the visual processing of static images in which motion is implied. The results do, however, confirm previous findings that disruption of MT/MST may improve efficiency in more ventral visual processing streams.     

Effects of 1 mA and 2 mA transcranial direct current stimulation on working memory performance in healthy participants

Anodal transcranial current stimulation (tDCS) to the left dorsolateral prefrontal cortex (DLPFC) has been shown to enhance working memory (WM) in neuropsychiatric patients. In healthy populations, however, tDCS obtains inconclusive results, mostly due to heterogeneous study and stimulation protocols. Here, we approached these issues by investigating effects of tDCS intensity on simultaneous WM performance with three cognitive loads by directly comparing findings of two double-blind, cross-over, sham-controlled experiments. TDCS was administrated to the left DLPFC at intensity of 1 mA (Experiment 1) or 2 mA (Experiment 2), while participants completed a verbal n-back paradigm (1-, 2-, 3-back). Analysis showed no overall effects of tDCS on WM, but a significant interaction with cognitive load. The present study suggests that cognitive load rather than tDCS intensity could be a decisive factor for effects on WM. Moreover, it emphasizes the need of thorough investigation on study parameters to develop more efficient stimulation protocols.     

Neurophysiologic markers of primary motor cortex for laryngeal muscles and premotor cortex in caudal opercular part of inferior frontal gyrus investigated in motor speech disorder: a navigated transcranial magnetic stimulation (TMS) study

Transcranial magnetic stimulation studies have so far reported the results of mapping the primary motor cortex (M1) for hand and tongue muscles in stuttering disorder. This study was designed to evaluate the feasibility of repetitive navigated transcranial magnetic stimulation (rTMS) for locating the M1 for laryngeal muscle and premotor cortical area in the caudal opercular part of inferior frontal gyrus, corresponding to Broca’s area in stuttering subjects by applying new methodology for mapping these motor speech areas. Sixteen stuttering and eleven control subjects underwent rTMS motor speech mapping using modified patterned rTMS. The subjects performed visual object naming task during rTMS applied to the (a) left M1 for laryngeal muscles for recording corticobulbar motor-evoked potentials (CoMEP) from cricothyroid muscle and (b) left premotor cortical area in the caudal opercular part of inferior frontal gyrus while recording long latency responses (LLR) from cricothyroid muscle. The latency of CoMEP in control subjects was 11.75 ± 2.07 ms and CoMEP amplitude was 294.47 ± 208.87 µV, and in stuttering subjects CoMEP latency was 12.13 ± 0.75 ms and 504.64 ± 487.93 µV CoMEP amplitude. The latency of LLR in control subjects was 52.8 ± 8.6 ms and 54.95 ± 4.86 in stuttering subjects. No significant differences were found in CoMEP latency, CoMEP amplitude, and LLR latency between stuttering and control-fluent speakers. These results indicate there are probably no differences in stuttering compared to controls in functional anatomy of the pathway used for transmission of information from premotor cortex to the M1 cortices for laryngeal muscle representation and from there via corticobulbar tract to laryngeal muscles.     

Seeing the future: Natural image sequences produce “anticipatory” neuronal activity and bias perceptual report

This paper relates human perception to the functioning of cells in the temporal cortex that are engaged in high-level pattern processing. We review historical developments concerning (a) the functional organization of cells processing faces and (b) the selectivity for faces in cell responses. We then focus on (c) the comparison of perception and cell responses to images of faces presented in sequences of unrelated images. Specifically the paper concerns the cell function and perception in circumstances where meaningful patterns occur momentarily in the context of a naturally or unnaturally changing visual environment. Experience of visual sequences allows anticipation, yet one sensory stimulus also “masks” perception and neural processing of subsequent stimuli. To understand this paradox we compared cell responses in monkey temporal cortex to body images presented individually, in pairs and in action sequences. Responses to one image suppressed responses to similar images for ～500 ms. This suppression led to responses peaking 100 ms earlier to image sequences than to isolated images (e.g., during head rotation, face-selective activity peaks before the face confronts the observer). Thus forward masking has unrecognized benefits for perception because it can transform neuronal activity to make it predictive during natural change.     

The effect of bicephalic stimulation of the dorsolateral prefrontal cortex on the attentional bias for threat: A transcranial direct current stimulation study

Previous stimulation studies demonstrated that the dorsolateral prefrontal cortex (DLPFC) is involved in threat processing. According to a model of emotional processing, an unbalance between the two DLPFCs, with a hyperactivation of right frontal areas, is involved in the processing of negative emotions and genesis of anxiety. In the present study, we investigated the role of the right and left DLPFC in threat processing in healthy women who also completed the State-Trait Anxiety Inventory (STAI). We simultaneously modulated the activity of the right and left dorsolateral prefrontal cortex by applying bicephalic transcranial direct current stimulation (tDCS) before participants completed a modified version of the classic Posner task using threatening and nonthreatening stimuli as spatial cues. Anodal stimulation on the right DLPFC with a simultaneous cathodal stimulation over the left side induced a disengagement bias in individuals with low STAI scores and a facilitation bias in individuals with high STAI scores. Anodal stimulation on the left DLPFC with the simultaneous cathodal stimulation over the right side did not affect threat processing. The findings of the present study provided specific support to the hypothesis that unbalanced activation between left and right hemispheres with enhanced activation of the right DLPFC is critical in early top-down threat processing in healthy individuals.     

Neural representations of faces and limbs neighbor in human high-level visual cortex: evidence for a new organization principle

Neurophysiology and optical imaging studies in monkeys and functional magnetic resonance imaging (fMRI) studies in both monkeys and humans have localized clustered neural responses in inferotemporal cortex selective for images of biologically relevant categories, such as faces and limbs. Using higher resolution (1.5 mm voxels) fMRI scanning methods than past studies (3–5 mm voxels), we recently reported a network of multiple face- and limb-selective regions that neighbor one another in human ventral temporal cortex (Weiner and Grill-Spector, Neuroimage, 52(4):1559–1573, 2010) and lateral occipitotemporal cortex (Weiner and Grill-Spector, Neuroimage, 56(4):2183–2199, 2011). Here, we expand on three basic organization principles of high-level visual cortex revealed by these findings: (1) consistency in the anatomical location of functional regions, (2) preserved spatial relationship among functional regions, and (3) a topographic organization of face- and limb-selective regions in adjacent and alternating clusters. We highlight the implications of this structure in comparing functional brain organization between typical and atypical populations. We conclude with a new model of high-level visual cortex consisting of ventral, lateral, and dorsal components, where multimodal processing related to vision, action, haptics, and language converges in the lateral pathway.