Noninvasive Brain Stimulation over the M1 Enhances Bimanual Force Control Ability: A Randomized Double-Blind Sham-Controlled Study

Well-coordinated bimanual force control is common in daily life. We investigated the effects of anodal transcranial direct current stimulation (tDCS) over the primary motor cortex on bimanual force control. Under a cross-over study, young adults (n = 19; female = 6, male = 13) completed three bimanual force control tasks at 5%, 25%, and 50% of bimanual maximum voluntary force (BMVF) before and after real or sham tDCS. Real tDCS enhanced accuracy at all BMVF, reduced variability at 5% BMVF, and increased coordination at 5% BMVF. Real tDCS improved force control at 5% and 25% BMVF, and especially increased bimanual coordination at 5% BMVF. These findings might have implications for establishing interventions for patients with hand force control deficits.     

Using Neuroimaging to Measure Mental Representations: Finding Color-OpponentNeurons in Visual Cortex

To date, most neuroimaging studies have tried to localize large regions in the brain that are responsible for specific behaviors or mental operations. Psychological theory, however, is more concerned with the nature of mental functions than with the locations of their neural substrates. This article reviews work that moves beyond functional anatomy to measure how color is represented by neurons in visual cortex. The general approach has three basic steps: First, the areas under investigation are localized in the brain. Second, responses of these areas are measured to sets of systematically varying stimuli, designed to uncover the nature of cortical representations. Third, the neuroimaging data are compared with behavioral data measured with the same stimuli. Results obtained using this approach support the hypothesis that primary visual cortex contains color-opponent neurons that support perception.     

传递性推理的ERP研究

以抽象的内容作为实验材料,测定15名大学生在完成三种不同类型的传递性推理任务和基线任务(记忆判断任务)时的事件相关电位(ERP),探讨传递性推理过程的脑内时程动态变化。研究发现,三种推理任务所诱发的波形基本一致,而推理任务与基线任务之间的ERP波形存在明显的差异。这说明对于传递性推理,被试可能是根据视觉的空间表征对信息进行加工的,结果进一步支持了心理模型理论。     

反馈负波及其近10年理论解释

个体决策后的反馈对随后的结果监控和行为调整起着至关重要的作用。事件相关脑电位研究发现, 反馈负波(feedback-related negativity, FRN)是与决策后反馈加工过程紧密相关的脑电成分。近10年来关于FRN的理论解释, 在最初经典的强化学习理论和情绪动机假说的基础上又提出了反应-结果的预测模型、奖赏正波理论以及积极情绪启动模型。未来的研究应该立足于大样本, 采用互补的研究手段和多样的分析技术来探讨FRN的心理意义; 同时考虑将FRN作为奖赏加工的脑电指标, 研究社会互动情境下的人类行为。     

Structural brain abnormalities in patients with Parkinson’s disease with visual hallucinations: A comparative voxel-based analysis

The objective is to evaluate clinical characteristics and cerebral alterations in Parkinson’s disease (PD) patients with diurnal visual hallucinations (VHs). Assessment was performed using magnetic resonance image (MRI) and voxel-based morphometry (VBM). Thirty-nine patients with PD (53.8%) and ten controls were studied. Voxel based morphology analysis was performed. Eleven patients presented diurnal VHs and among these, six had cognitive dysfunction. Patients with VHs performed worse in the mentation-related UPDRS I (p = 0.005) and motor-related UPDRS III (p = 0.02). Patients with VHs showed significant clusters of reduced grey matter volume compared to controls in the left opercula frontal gyrus and left superior frontal gyrus. PD without hallucinations demonstrated reduced grey matter volume in the left superior frontal gyrus compared to controls. Comparisons between patients with VHs regarding the presence of cognitive dysfunction showed that cases with cognitive dysfunction as compared to those without cognitive dysfunction showed significant clusters of reduced grey matter volume in the left opercular frontal gyrus. Cases without cognitive dysfunction had reduced grey matter substance in the left insula and left trigonal frontal gyrus. Judging from our findings, an abnormal frontal cortex, particularly left sided insula, frontal opercular, trigonal frontal gyrus and orbital frontal would make PD patients vulnerable to hallucinations. Compromise of the left operculum distinguished cases with VHs and cognitive dysfunction. Our findings reinforce the theoretical concept of a top-down visual processing in the genesis of VHs in PD.     

Neuromagnetic correlates of intra- and extra-dimensional set-shifting

Set-shifting is essential to cognitive flexibility and relies on frontal lobe function. Previous studies have mostly focused on feedback processes following shifting rather than set-shifting itself. We designed an MEG paradigm without feedback to directly investigate the neural correlates of set-shifting. Adults (n = 16) matched one of two coloured images with a third stimulus, the target, by either the colour or shape dimension of the target. Half of the shift trials involved colour-to-colour or shape-to-shape (intra-dimensional: ID) shifting and the other half involved colour-to-shape or shape-to-colour (extra-dimensional: ED) shifting. MEG was continuously recorded on a 151 channel CTF system. We used beamforming to analyze responses to the first (shift) and the third (repeat) trials in each set. These trials were contrasted separately for ID and ED sets. Shift versus repeat trials showed larger MEG activations for intra-dimensional shifting in the right inferior frontal gyrus (BA 47), left medial frontal gyrus (BA 10) and right superior frontal gyrus (BA 9) as early as 100 ms, and in left middle frontal gyrus (BA 11) between 250–500 ms. Activations related to extra-dimensional shifting were detected in left inferior frontal gyrus (BA 44), left middle frontal gyrus (BA 11), and right middle frontal gyrus (BA 46) between 100 ms and 350 ms, followed by superior frontal gyrus (BA 8/BA 10) between 250–500 ms. Intra-dimensional and extra-dimensional shifting also activated bilateral and right parietal areas, respectively. This study establishes the location and timing of frontal and parietal activations during an intra-dimensional versus extra-dimensional shifting task.     

Role of medial prefrontal cortex in representing one’s own subjective emotional responses: A preliminary study

The medial prefrontal cortex (mPFC) has been implicated in attending to one’s own emotional states, but the role of emotional valence in this context is not understood. We examined valence-specific BOLD activity in a previously validated functional magnetic resonance imaging (fMRI) paradigm. Ten healthy subjects viewed emotional pictures and categorized their experience as pleasant, unpleasant or neutral. All three categories activated a common region within mPFC. Subtraction of neutral from pleasant or unpleasant conditions instead revealed ventromedial PFC (vmPFC), suggesting that this region represents emotional valence. During exteroceptive attention, greater mPFC responses were observed in response to emotional relative to neutral stimuli, consistent with studies implicating mPFC in the top-down modulation of emotion-biased attention. These findings may help to integrate the two proposed roles of mPFC in emotional representation and top-down modulation of subcortical structures.     

Relationships between executive function,working memory,and decision-making on the Iowa Gambling Task: Evidence from ventromedial patients,dorsolateral patients,and normal subjects

The results of previous studies are inconsistent in regard to the relationship between the Iowa Gambling Task (IGT), working-memory (WM), and executive tasks, and whether these cognitive processes could be considered as mechanisms underlying a decision-making deficit. Moreover, the relationship between the IGT and executive measures is examined based on a limited number of executive tasks, within different populations showing diffuse damage. In addition, there are fewer studies carried out within control participants, with those studies also being inconclusive. It is also suggested that the association of the IGT performance with executive tasks depends on whether the IGT was running under ambiguity or under risk. In this work, all of these issues are studied. Results showed that both patients with ventromedial (VMPFC, N = 10) and dorsolateral (DLPFC, N = 10) prefrontal cortex lesions are significantly impaired on almost all executive tasks, WM tasks, and the IGT. Furthermore, when the IGT is run under risk, there are significant correlations between executive measures and the IGT for the DLPFC patients and the control participants (N = 34) but not the VMPFC patients. No correlation was found between WM tasks and the IGT for both frontal subgroups and control participants. These findings suggested that the mechanisms underlying the IGT deficit differ according to the lesion locations.