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.     

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.     

情绪对注意功能网络的调制

情绪性注意是一种对具有情绪意义的刺激进行选择和加工的注意.由于刺激的情绪效价能调制人脑的感知和注意系统,因而,与对中性刺激的注意相比,情绪性注意的神经机制更加复杂.较早的研究显示,杏仁核对感知皮层的调制对情绪性注意起关键作用.近期的证据表明,杏仁核对注意功能网络的调制可能是其重要的神经机制.本文梳理了相关领域的研究证据,主要强调情绪性刺激对注意的警觉、定向和执行控制网络的调制,发现情绪性注意加工的认知神经机制可能涉及一个以杏仁核为核心的多重功能网络.     

自我控制资源与认知资源相互影响的机制:整合模型

尽管有学者认为自我控制资源和认知资源应该是两种独立的资源,但近期的研究却表明两种资源是互相影响的.以往研究从执行控制的角度解释两种资源为什么相互影响,但却没有指出两种资源如何影响执行控制,以及缺乏考虑神经机制和自我控制资源调节变量在其中的作用.为更系统地解释两种资源相互影响的机制,作者提出了一个整合模型,该模型指出:(1)两种资源相互影响的主要原因是两者都受到执行控制和前额叶皮层的影响;(2)个体进行自我控制或认知加工会消耗能量,产生心理疲劳,降低执行任务的动机,表现为前额叶皮层激活水平下降;(3)前额叶皮层激活不足进一步限制了执行控制在随后的自我控制和认知加工任务中的作用,因而影响后续自我控制或认知加工任务的表现;(4)自我控制资源调节变量通过提高个体对疲劳的耐受性、补充能量和提高动机等方法,使前额叶皮层和执行控制在完成前一阶段任务后仍然能够正常发挥作用,从而维持个体在后续自我控制或认知加工任务上的表现.未来的研究可考察自我控制资源与其他认知加工的关系;用动态的认知神经研究方法,建立前额叶皮层激活水平在前后两阶段任务之间的中介作用模型,以及研究自我控制资源调节变量的神经机制.     

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.     

The representation and perception of 3D space: Interactions between 2D location and depth

ABSTRACT

We live in a 3D world, and yet the majority of vision research is restricted to 2D phenomena, with depth research typically treated as a separate field. Here we ask whether 2D spatial information and depth information interact to form neural representations of 3D space, and if so, what are the perceptual implications? Using fMRI and behavioural methods, we reveal that human visual cortex gradually transitions from 2D to 3D spatial representations, with depth information emerging later along the visual hierarchy, and demonstrate that 2D location holds a fundamentally special place in early visual processing.     

Age-Related Changes in Executive Function: An Event-Related Potential (ERP) Investigation of Task-Switching

ABSTRACT

Older adults have difficulty when executive control must be brought on line to coordinate ongoing behavior. To assess age-related alterations in executive processing, task-switching performance and event-related potential (ERP) activity were compared in young and older adults on switch, post-switch, pre-switch, and no-switch trials, ordered in demand for executive processes from greatest to least. In stimulus-locked averages for young adults, only switch trials elicited fronto-central P3 components, indicative of task-set attentional reallocation, whereas in older adults, three of the four trial types evinced frontal potentials. In response-locked averages, the amplitude of a medial frontal negativity (MFN), a component reflecting conflict monitoring and detection, increased as a function of executive demands in the ERPs of the young but not those of the older adults. These data suggest altered executive processing in older adults resulting in persistent recruitment of prefrontal processes for conditions that do not require them in the young.     

Incidental regulation of attraction: The neural basis of the derogation of attractive alternatives in romantic relationships

Although a great deal of research addresses the neural basis of deliberate and intentional emotion-regulation strategies, less attention has been paid to the neural mechanisms involved in implicit forms of emotion regulation. Behavioural research suggests that romantically involved participants implicitly derogate the attractiveness of alternative partners, and the present study sought to examine the neural basis of this effect. Romantically committed participants in the present study were scanned with functional magnetic resonance imaging (fMRI) while indicating whether they would consider each of a series of attractive (or unattractive) opposite-sex others as a hypothetical dating partner both while under cognitive load and no cognitive load. Successful derogation of attractive others during the no cognitive load compared to the cognitive load trials corresponded with increased activation in the ventrolateral prefrontal cortex (VLPFC) and posterior dorsomedial prefrontal cortex (pDMPFC), and decreased activation in the ventral striatum, a pattern similar to those reported in deliberate emotion-regulation studies. Activation in the VLPFC and pDMPFC was not significant in the cognitive load condition, indicating that while the derogation effect may be implicit, it nonetheless requires cognitive resources. Additionally, activation in the right VLPFC correlated with participants' level of relationship investment. These findings suggest that the RVLPFC may play a particularly important role in implicitly regulating the emotions that threaten the stability of a romantic relationship.     

Aberrant neural mediation of verbal fluency in autism spectrum disorders

Objective

Contrasts of verbal fluency and automatic speech provide an opportunity to evaluate the neural underpinnings of generativity and flexibility in autism spectrum disorders (ASD).

Method

We used functional magnetic resonance imaging (fMRI) to contrast brain activity in high functioning ASD (n = 17, mean verbal IQ = 117) and neurotypical (NT; n = 20, mean verbal IQ = 112) adolescent and young adult males (12–23 years). Participants responded to three word generation conditions: automatic speech (reciting months), category fluency, and letter fluency.

Results

Our paradigm closely mirrored behavioral fluency tasks by requiring overt, free recall word generation while controlling for differences in verbal output between the groups and systematically increasing the task demand. The ASD group showed reduced neural response compared to the NT participants during fluency tasks in multiple regions of left anterior and posterior cortices, and sub-cortical structures. Six of these regions fell in cortico-striatal circuits previously linked to repetitive behaviors (Langen, Durston, Kas, van Engeland, & Staal, 2011), and activity in two of them (putamen and thalamus) was negatively correlated with autism repetitive behavior symptoms in the ASD group. In addition, response in left inferior frontal gyrus was differentially modulated in the ASD, relative to the NT, group as a function of task demand.

Conclusions

These data indicate a specific, atypical brain response in ASD to demanding generativity tasks that may have relevance to repetitive behavior symptoms in ASD as well as to difficulties generating original verbal responses.     

A model of amygdala–hippocampal–prefrontal interaction in fear conditioning and extinction in animals

Empirical research has shown that the amygdala, hippocampus, and ventromedial prefrontal cortex (vmPFC) are involved in fear conditioning. However, the functional contribution of each brain area and the nature of their interactions are not clearly understood. Here, we extend existing neural network models of the functional roles of the hippocampus in classical conditioning to include interactions with the amygdala and prefrontal cortex. We apply the model to fear conditioning, in which animals learn physiological (e.g. heart rate) and behavioral (e.g. freezing) responses to stimuli that have been paired with a highly aversive event (e.g. electrical shock). The key feature of our model is that learning of these conditioned responses in the central nucleus of the amygdala is modulated by two separate processes, one from basolateral amygdala and signaling a positive prediction error, and one from the vmPFC, via the intercalated cells of the amygdala, and signaling a negative prediction error. In addition, we propose that hippocampal input to both vmPFC and basolateral amygdala is essential for contextual modulation of fear acquisition and extinction. The model is sufficient to account for a body of data from various animal fear conditioning paradigms, including acquisition, extinction, reacquisition, and context specificity effects. Consistent with studies on lesioned animals, our model shows that damage to the vmPFC impairs extinction, while damage to the hippocampus impairs extinction in a different context (e.g., a different conditioning chamber from that used in initial training in animal experiments). We also discuss model limitations and predictions, including the effects of number of training trials on fear conditioning.