无意识活动与静息态脑能量消耗

静息态脑活动的研究关注个体在清醒、静卧、闭眼时脑的活动情况,大量实验证明静息状态下大脑仍进行着持续不断的信息加工活动,并且消耗大量能量。本文在阐述无意识活动特性以及总结静息态脑能量消耗研究的基础上,提出用无意识活动解释静息态脑能量消耗的观点,强调在研究无意识活动的心理意义的同时,还要研究无意识活动的神经机制及其生理表现。     

Recruitment of lateral rostral prefrontal cortex in spontaneous and task-related thoughts

Behavioural and neuroimaging studies suggest that spontaneous and task-related thought processes share common cognitive mechanisms and neural bases. Lateral rostral prefrontal cortex (RPFC) is a brain region that has been implicated both in spontaneous thought and in high-level cognitive control processes, such as goal/subgoal integration and the manipulation of self-generated thoughts. We therefore propose that the recruitment of lateral RPFC may follow a U-shaped function of cognitive demand: relatively high in low-demand situations conducive to the emergence of spontaneous thought, and in high-demand situations depending on processes supported by this brain region. We used functional magnetic resonance imaging to investigate brain activity while healthy participants performed two tasks, each with three levels of cognitive demands, in a block design. The frequency of task-unrelated thoughts, measured by questionnaire, was highest in the low cognitive demand condition. Low and high cognitive demand conditions were each compared to the intermediate level. Lateral RPFC and superior parietal cortex were recruited in both comparisons, with additional activations specific to each contrast. These results suggest that RPFC is involved both when (a) task demands are low, and the mind wanders, and (b) the task requires goal/subgoal integration and manipulation of self-generated thoughts.     

Response-specific sources of dual-task interference in human pre-motor cortex

It is difficult to perform two tasks at the same time. Such performance limitations are exemplified by the psychological refractory period (PRP): when participants make distinct motor responses to two stimuli presented in rapid succession, the response to the second stimulus is increasingly slowed as the time interval between the two stimuli is decreased. This impairment is thought to reflect a central limitation in selecting the appropriate response to each stimulus, but not in perceptually encoding the stimuli. In the present study, it was sought to determine which brain regions are specifically involved in response selection under dual-task conditions by contrasting fMRI brain activity measured from a response selection manipulation that increased dual-task costs, with brain activity measured from an equally demanding manipulation that affected perceptual visibility. While a number of parieto-frontal areas involved in response selection were activated by both dual-task manipulations, the dorsal pre-motor cortex, and to a lesser extent the inferior frontal cortex, were specifically engaged by the response selection manipulation. These results suggest that the pre-motor cortex is an important neural locus of response selection limitation under dual-task situations.     

The role of the human extrastriate visual cortex in mirror symmetry discrimination: a TMS-adaptation study

The human visual system is able to efficiently extract symmetry information from the visual environment. Prior neuroimaging evidence has revealed symmetry-preferring neuronal representations in the dorsolateral extrastriate visual cortex; the objective of the present study was to investigate the necessity of these representations in symmetry discrimination. This was accomplished by the use of state-dependent transcranial magnetic stimulation, which combines the fine resolution of adaptation paradigms with the assessment of causality. Subjects were presented with adapters and targets consisting of dot configurations that could be symmetric along either the vertical or horizontal axis (or they could be non-symmetric), and they were asked to perform a symmetry discrimination task on the targets while fixating the center of the screen. TMS was applied during the delay between the adapter and the test stimulus over one of four different sites: Left or Right V1/V2, or left or right dorsolateral extrastriate cortex (DLO). TMS over both Left and Right DLO reduced the adaptation effect in detecting vertical and horizontal symmetry, although the Left DLO effect on horizontal symmetry and the Right DLO effect on both vertical and horizontal symmetry were present only when considering subjects who showed a behavioral adaptation effect in the baseline No-TMS condition. Application of TMS over the Left or Right V1/V2 did not modulate the adaptation effect. Overall, these data suggest that both the Left and Right DLO contain neuronal representations tuned to mirror symmetry which play a causal role in symmetry discrimination.     

Distributed processing and cortical specialization for speech and environmental sounds in human temporal cortex

Using functional MRI, we investigated whether auditory processing of both speech and meaningful non-linguistic environmental sounds in superior and middle temporal cortex relies on a complex and spatially distributed neural system. We found that evidence for spatially distributed processing of speech and environmental sounds in a substantial extent of temporal cortices. Most importantly, regions previously reported as selective for speech over environmental sounds also contained distributed information. The results indicate that temporal cortices supporting complex auditory processing, including regions previously described as speech-selective, are in fact highly heterogeneous.     

Bilaterally recorded multiple-unit activity of the cingulate cortex during head turning conditioning with unilateral medial forebrain bundle stimulation

Cats were conditioned to turn their heads using a tone conditioned stimulus (CS) and medial forebrain bundle stimulation (MFB) unconditioned stimulus (US). The CS+ was delivered to one ear at a time, in random order, followed by the US. A tone of a different frequency was used as a CS-. The cats learned to respond differentially to the CSs showing head movements of greater acceleration to the CS+ than CS- over sessions. Bilateral recordings of cingulate cortex multiple-unit activity showed increased response amplitudes over sessions and larger responses in the hemisphere ipsilateral to the US. Since ipsilateral multiple-unit responses did not differ for the CSs, the asymmetry was probably due to the sensitizing effect of the unilateral US. Although increases in cingulate cortex neural activity coincided with increases in conditioned head movements, larger activation of the cingulate cortex ipsilateral to the US suggests that the neural changes were independent of these movements.     

The modulatory impact of reward and attention on global feature selection in human visual cortex

Reward powerfully influences human behaviour and perception, with reward effects being observed already on the level of basic sensory processing. Although reward-related modulations generally resemble those related to attentional selection, it is debated whether these effects indeed reflect the same selection operations. Here we focus on neuromagnetic indices of global colour-based attention in visual cortex, and ask whether reward elicits the same or separable underlying modulation effects. Observers performed a colour/orientation selection task where colour served to define the target as well as reward prospect. On each trial a target containing the target colour and one other colour was presented in the left visual field (VF) together with a bicoloured distractor in the right VF. Reward was delivered on correctly performed trials when the reward colour appeared in the target but not when it appeared in the distractor. The effect of global colour selection was assessed by comparing the brain response to the distractor depending on whether it contained the target colour, the reward colour, both, or neither. We observed that both the reward and target colour led to similar increases of the neuromagnetic response between ~200–260 ms originating from the same ventral extrastriate visual cortex areas, albeit slightly temporally lagged. Importantly, the response to the target and reward colour alone always added up to match the response size of their combined presentation. These results suggest that while reward and attention recruit the same global feature selection effects in extrastriate visual cortex, they are likely controlled by independent top-down influences.     

Spontaneous startle activity in newborn infants

Spontaneous startles have been reported to occur most frequently in quiet sleep, less frequently in active sleep and drowse, and relatively nonexistent in the waking states. These findings may be a result of a focus on infants whose prenatal histories reflect a restricted range of the conditions to which normal newborns are exposed. The present study examined the spontaneous startle behavior of 30 newborn infants characterized by high numbers of obstetric complications and by indicators of prenatal malnutrition, but within the range of normal, healthy newborns. In this sample, startles were not limited to the sleep and drowse states. Because individual differences in a number of neonatal behaviors have been related to autonomic nervous system (ANS) functioning, the different pattern of spontaneous startles observed in this sample may be related to the functional integrity of this system.     

Neurocognitive mechanisms underlying the experience of flow

Recent theoretical and empirical work in cognitive science and neuroscience is brought into contact with the concept of the flow experience. After a brief exposition of brain function, the explicit-implicit distinction is applied to the effortless information processing that is so characteristic of the flow state. The explicit system is associated with the higher cognitive functions of the frontal lobe and medial temporal lobe structures and has evolved to increase cognitive flexibility. In contrast, the implicit system is associated with the skill-based knowledge supported primarily by the basal ganglia and has the advantage of being more efficient. From the analysis of this flexibility/efficiency trade-off emerges a thesis that identifies the flow state as a period during which a highly practiced skill that is represented in the implicit system's knowledge base is implemented without interference from the explicit system. It is proposed that a necessary prerequisite to the experience of flow is a state of transient hypofrontality that enables the temporary suppression of the analytical and meta-conscious capacities of the explicit system. Examining sensory-motor integration skills that seem to typify flow such as athletic performance, writing, and free-jazz improvisation, the new framework clarifies how this concept relates to creativity and opens new avenues of research.     

A sensitive period for language in the visual cortex: distinct patterns of plasticity in congenitally versus late blind adults

Recent evidence suggests that blindness enables visual circuits to contribute to language processing. We examined whether this dramatic functional plasticity has a sensitive period. BOLD fMRI signal was measured in congenitally blind, late blind (blindness onset 9-years-old or later) and sighted participants while they performed a sentence comprehension task. In a control condition, participants listened to backwards speech and made match/non-match to sample judgments. In both congenitally and late blind participants BOLD signal increased in bilateral foveal-pericalcarine cortex during response preparation, irrespective of whether the stimulus was a sentence or backwards speech. However, left occipital areas (pericalcarine, extrastriate, fusiform and lateral) responded more to sentences than backwards speech only in congenitally blind people. We conclude that age of blindness onset constrains the non-visual functions of occipital cortex: while plasticity is present in both congenitally and late blind individuals, recruitment of visual circuits for language depends on blindness during childhood.     

Anterior cingulate cortex and cognitive control: Neuropsychological and electrophysiological findings in two patients with lesions to dorsomedial prefrontal cortex

Whereas neuroimaging studies of healthy subjects have demonstrated an association between the anterior cingulate cortex (ACC) and cognitive control functions, including response monitoring and error detection, lesion studies are sparse and have produced mixed results. Due to largely normal behavioral test results in two patients with medial prefrontal lesions, a hypothesis has been advanced claiming that the ACC is not involved in cognitive operations. In the current study, two comparably rare patients with unilateral lesions to dorsal medial prefrontal cortex (MPFC) encompassing the ACC were assessed with neuropsychological tests as well as Event-Related Potentials in two experimental paradigms known to engage prefrontal cortex (PFC). These included an auditory Novelty Oddball task and a visual Stop-signal task. Both patients performed normally on the Stroop test but showed reduced performance on tests of learning and memory. Moreover, altered attentional control was reflected in a diminished Novelty P3, whereas the posterior P3b to target stimuli was present in both patients. The error-related negativity, which has been hypothesized to be generated in the ACC, was present in both patients, but alterations of inhibitory behavior were observed. Although interpretative caution is generally called for in single case studies, and the fact that the lesions extended outside the ACC, the findings nevertheless suggest a role for MPFC in cognitive control that is not restricted to error monitoring.     

Representations in the Human Prefrontal Cortex

ABSTRACT— The prefrontal cortex (PFC) in humans has been studied for more than a century, but many crucial questions about its functions remain unanswered. This paper will highlight a few key differences between human and animal PFCs, and between the human PFC (HPFC) and other parts of the human brain. We then make a case that the HPFC is critically important for executing behaviors over time and integrating disparate information from throughout the brain. Finally, we will focus on our position in the current debate regarding how the HPFC performs its functions and discuss future directions for research.     

前额叶在老年阶段的可塑性及相关机制

大量研究表明, 前额叶的结构和功能更容易受年老化影响; 然而, 近年来的研究发现, 前额叶的结构和功能在老年阶段具有一定的可塑性。对老年人进行认知训练, 能够延缓前额叶皮层厚度的萎缩, 提高白质完整性, 改善神经网络的功能连接和分化, 并可能通过调节多巴胺系统的活动改变前额叶皮质和皮质下结构的功能激活模式。有氧锻炼能够改善心脑血管功能, 保护和促进神经元的存活和生长, 引起前额叶灰质、白质体积的增加及功能激活的变化。认知训练与有氧锻炼等相结合的整合性训练不仅引起前额叶及相关认知功能的改变, 而且具有更好的生态学效度, 使老年人日常认知能力和生活质量得到提高。未来研究应采用多种技术手段, 从多个层面理解老年阶段前额叶的可塑性及相关机制; 加强对与前额叶关系密切的多种认知功能可塑性神经机制的研究; 并重视与整合性训练有关的前额叶可塑性。     

We are more selfish than we think: The endowment effect and reward processing within the human medial-frontal cortex

Perceived ownership has been shown to impact a variety of cognitive processes: attention, memory, and—more recently—reward processing. In the present experiment we examined whether or not perceived ownership would interact with the construct of value—the relative worth of an object. Participants completed a simple gambling game in which they gambled either for themselves or for another while electroencephalographic data were recorded. In a key manipulation, gambles for oneself or for another were for either small or large rewards. We tested the hypothesis that value affects the neural response to self-gamble outcomes, but not other-gamble outcomes. Our experimental data revealed that while participants learned the correct response option for both self and other gambles, the reward positivity evoked by wins was impacted by value only when gambling for oneself. Importantly, our findings provide additional evidence for a self-ownership bias in cognitive processing and further demonstrate the insensitivity of the medial-frontal reward system to gambles for another.     

左侧背外侧前额叶在程序性运动学习中的作用

程序性运动学习包括序列学习和随机学习。神经影像学研究表明背外侧前额叶皮层(DLPFC)和初级运动皮层(M1)在程序性运动学习中发挥重要作用,但DLPFC和M1之间的联通性及其与不同程序性运动学习的关系尚不明确。本研究采用连续反应时间任务,结合经颅磁刺激(TMS)方法,探讨左侧DLPFC到M1的联通性在不同程序性运动学习中的差异。实验1采用两连发TMS探测DLPFC到M1的最佳投射时间点;实验2,被试分为2组,分别进行序列学习和随机学习,在学习前、后采集行为学数据,以及M1的运动诱发电位和DLPFC-M1联通性的电生理学数据。行为学结果发现序列学习组的学习效果更佳;电生理学结果发现,两组被试学习前、后M1的运动诱发电位均未发生改变;在最佳时间投射点、适当刺激强度下,序列学习组DLPFC-M1联通性发生改变,且与学习成绩相关,而随机学习组没有改变。结果说明DLPFC到M1的联通性增强可能是序列学习成绩更佳的重要原因,这一结果从电生理角度为DLPFC在运动学习中的作用提供了重要证据。     

The representation of category typicality in the frontal cortex and its cross-linguistic variations

When asked to judge the membership of typical (e.g., car) vs. atypical (e.g., train) pictures of a category (e.g., vehicle), native English (N = 18) and native Chinese speakers (N = 18) showed distinctive patterns of brain activity despite showing similar behavioral responses. Moreover, these differences were mainly due to the amount and pervasiveness of category information linguistically embedded in the everyday names of the items in the respective languages, with important differences across languages in how pervasive category labels are embedded in item-level terms. Nonetheless, the left inferior frontal gyrus and the bilateral medial frontal gyrus are the most consistent neural correlates of category typicality that persist across languages and linguistic cues. These data together suggest that both cross- and within-language differences in the explicitness of category information have strong effects on the nature of categorization processes performed by the brain.