首页 | 官方网站   微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   426篇
  国内免费   17篇
  完全免费   10篇
医药卫生   453篇
  2015年   4篇
  2014年   6篇
  2013年   21篇
  2012年   32篇
  2011年   77篇
  2010年   38篇
  2009年   42篇
  2008年   43篇
  2007年   29篇
  2006年   37篇
  2005年   34篇
  2004年   18篇
  2003年   30篇
  2002年   14篇
  2001年   11篇
  2000年   9篇
  1999年   4篇
  1998年   1篇
  1997年   1篇
  1995年   1篇
  1989年   1篇
排序方式: 共有453条查询结果,搜索用时 78 毫秒
1.
Studies of categories of objects, including tools, have spurred the development of the sensory-motor model of object concept representation. According to this model, information about objects is represented in the same neural subsystems that are active when we perceive and use them. In turn, this model has provided insight into the brain mechanisms of tool use. For tools, three types of information are especially important for identification: the characteristic motion with which they move (such as the up and down motion of a hammer), their visual form, and the way that they are manipulated. Evidence from neuropsychological, non-human primates, and neuroimaging studies suggest a mapping between specific brain regions and these fundamental identifying properties of tools. We focus on neuroimaging studies of the left posterior middle temporal gyrus. This brain region is active both when subjects perceive moving tools and when they answer questions about tools, and is responsive to the type of visual motion characteristic of tools: rigid, unarticulated motion. We describe a simple model that explains how low-level receptive field properties like those known to exist in area MT/V5 could give rise to the high-level category-related representations observed in functional imaging experiments.  相似文献   
2.
Internal models are neural mechanisms that can mimic the input-output properties of controlled objects. Our studies have shown that: 1) an internal model for a novel tool is acquired in the cerebellum (Imamizu et al., 2000); 2) internal models are modularly organized in the cerebellum (Imamizu et al., 2003); 3) their outputs are sent to the premotor regions after learning (Tamada et al., 1999); and 4) the prefrontal and parietal regions contribute to the blending of the outputs (Imamizu et al., 2004). Here, we investigated changes in global neural networks resulting from the acquisition of a new internal model. Human subjects manipulated three types of rotating joystick whose cursor appeared at a position rotated 60 degrees, 110 degrees, or 160 degrees around the screen's center. In a pre-test after long-term training (5 days) for the 60 degrees and 160 degrees joysticks, brain activation was scanned during manipulation of the three joysticks. The subjects were then trained for the 110 degrees for only 25 min. In a post-test, activation was scanned using the same method as the pre-test. Comparisons of the post-test to the pre-test revealed that the volume of activation decreased in most of the regions where activation for the three rotations was observed. However, there was an increase in volume at a marginally significant level (p < .08) only in the inferior-lateral cerebellum and only for the 110 degrees joystick. In the cerebral cortex, activation related to 110 degrees decreased in the prefrontal and parietal regions but increased in the premotor and supplementary motor area (SMA) regions. These results can be explained by a model in which outputs of the 60 degrees and 160 degrees internal models are blended by prefrontal and parietal regions to cope with the novel 110 degrees joystick before the 25-minute training; after the acquisition within the cerebellum of an internal model for the 110 degrees, output is directly sent to the premotor and SMA regions, and activation in these regions increases.  相似文献   
3.
Recent observations indicate that sex and level of steroid hormones may influence cortical networks associated with specific cognitive functions, in particular visuo-spatial abilities.

The present study probed the influence of sex, menstrual cycle, and sex steroid hormones on 3D mental rotation and brain function using 3-T fMRI. Twelve healthy women and 12 men were investigated. Menstrual cycle and hormone levels were assessed. The early follicular and midluteal phase of the menstrual cycle were chosen to examine short-term cyclical changes.

Parietal and frontal areas were activated during mental rotation in both sexes. Significant differences between men and women were revealed in both phases of menstrual cycle. In men we observed a significant correlation of activation levels with testosterone levels in the left parietal lobe (BA 40). In women, a cycle-dependent correlation pattern was observed for testosterone: brain activation correlated with this male hormone only during the early follicular phase. In both cycle phases females’ brain activation was significantly correlated with estradiol in frontal and parietal areas.

Our study provides evidence that fMRI-related activity during performance of cognitive tasks varies across sex and phases of the menstrual cycle. The variation might be partly explained by better task performance in men, but our results indicate that further explanations like basic neuronal or neurovascular effects modulated by steroid hormones must be considered. Both estradiol and testosterone levels may influence fMRI signals of cognitive tasks, which should affect selection of subjects for future fMRI studies.  相似文献   

4.
Neuroimaging studies have suggested that left inferior frontal gyrus, left inferior parietal lobule and left middle temporal gyrus are critical for semantic processing in normal children. The goal of the present functional magnetic resonance imaging (fMRI) study was to determine whether these regions are systematically related to semantic processing in children (9- to 15-year-old) diagnosed with reading disorders (RD). Semantic judgments required participants to indicate whether two words were related in meaning. The strength of semantic association varied continuously from higher association pairs (e.g., king-queen) to lower association pairs (e.g. net-ship). We found that the correlation between association strength and activation was significantly weaker for RD children compared to controls in left middle temporal gyrus and left inferior parietal lobule for both the auditory and the visual modalities and in left inferior frontal gyrus for the visual modality. These results suggest that the RD children have abnormalities in semantic search/retrieval in the inferior frontal gyrus, integration of semantic information in the inferior parietal lobule and semantic lexical representations in the middle temporal gyrus. These deficits appear to be general to the semantic system and independent of modality.  相似文献   
5.
Stout D  Chaminade T 《Neuropsychologia》2007,45(5):1091-1100
The appearance of the first intentionally modified stone tools over 2.5 million years ago marked a watershed in human evolutionary history, expanding the human adaptive niche and initiating a trend of technological elaboration that continues to the present day. However, the cognitive foundations of this behavioral revolution remain controversial, as do its implications for the nature and evolution of modern human technological abilities. Here we shed new light on the neural and evolutionary foundations of human tool making skill by presenting functional brain imaging data from six inexperienced subjects learning to make stone tools of the kind found in the earliest archaeological record. Functional imaging of this complex, naturalistic task was accomplished through positron emission tomography with the slowly decaying radiological tracer (18)flouro-2-deoxyglucose. Results show that simple stone tool making is supported by a mosaic of primitive and derived parietofrontal perceptual-motor systems, including recently identified human specializations for representation of the central visual field and perception of three-dimensional form from motion. In the naïve tool makers reported here, no activation was observed in prefrontal executive cortices associated with strategic action planning or in inferior parietal cortex thought to play a role in the representation of everyday tool use skills. We conclude that uniquely human capacities for sensorimotor adaptation and affordance perception, rather than abstract conceptualization and planning, were central factors in the initial stages of human technological evolution.  相似文献   
6.
The empirical and theoretical consideration of ethical decision making has focused on the process of moral judgment; however, a precondition to judgment is moral sensitivity, the ability to detect and evaluate moral issues [Rest, J. R. (1984). The major components of morality. In W. Kurtines & J. Gewirtz (Eds.), Morality, moral behaviour, and moral development (pp. 24-38). New York, NY: Wiley]. Using functional magnetic resonance imaging (fMRI) and contextually standardized, real life moral issues, we demonstrate that sensitivity to moral issues is associated with activation of the polar medial prefrontal cortex, dorsal posterior cingulate cortex, and posterior superior temporal sulcus (STS). These activations suggest that moral sensitivity is related to access to knowledge unique to one's self, supported by autobiographical memory retrieval and social perspective taking. We also assessed whether sensitivity to rule-based or "justice" moral issues versus social situational or "care" moral issues is associated with dissociable neural processing events. Sensitivity to justice issues was associated with greater activation of the left intraparietal sulcus, whereas sensitivity to care issues was associated with greater activation of the ventral posterior cingulate cortex, ventromedial and dorsolateral prefrontal cortex, and thalamus. These results suggest a role for access to self histories and identities and social perspectives in sensitivity to moral issues, provide neural representations of the subcomponent process of moral sensitivity originally proposed by Rest, and support differing neural information processing for the interpretive recognition of justice and care moral issues.  相似文献   
7.
Cerebral compensation during motor imagery in Parkinson's disease   总被引:2,自引:1,他引:1  
In neurodegenerative disorders, neural damage can trigger compensatory mechanisms that minimize behavioural impairments. Here, we aimed at characterizing cerebral compensation during motor imagery in Parkinson's disease (PD), while controlling for altered motor execution and sensory feedback. We used a within-patient design to compare the most and least affected hand in 19 right-handed PD patients with markedly right-lateralized symptoms. We used a motor imagery (MI) task in which the patients were required to judge the laterality of hand images, rotated either in a lateral or in a medial orientation with respect to the body sagittal plane. This design allowed us to compare cerebral activity (using fMRI) evoked by MI of each hand separately, while objectively monitoring task performance. Reaction times and parieto-premotor activity increased in a similar manner as a function of stimulus rotation during motor imagery of left and right hands. However, patients were markedly slower when judging images of the affected hand in lateral orientations, and there was a corresponding increase in activity in the right extrastriate body area (EBA) and occipito-parietal cortex during mental rotation of the affected hand. Furthermore, these regions increased their connectivity towards the left PMd for right (affected) hands in a lateral orientation. We infer that, in strongly lateralized PD patients, motor imagery of the most-affected hand exploits additional resources in extrastriate visual areas. These findings characterize the cerebral bases of the increased dependence on visual information processing during the generation of motor plans in PD, pointing to its compensatory role.  相似文献   
8.
The human mirror system: a motor resonance theory of mind-reading   总被引:6,自引:0,他引:6  
Electrophysiological data confirm the existence of neurons that respond to both motor and sensory events in the macaque brain. These mirror neurons respond to execution and observation of goal-orientated actions. It has been suggested that they comprise a neural basis for encoding an internal representation of action. In this paper the evidence for a parallel system in humans is reviewed and the implications for human theory of mind processing are discussed. Different components of theory of mind are discussed; the evidence for mirror activity within subtypes is addressed. While there is substantial evidence for a human mirror system, there are weaknesses in the attempts to localize such a system in the brain. Preliminary evidence indicates that mirror neurons may be involved in theory of mind; however, these data by their very nature are reliant on the presence, and precise characterization, of the human mirror system.  相似文献   
9.
Voluntary attention changes the speed of perceptual neural processing   总被引:1,自引:0,他引:1  
While previous studies in psychology demonstrated that humans can respond more quickly to the stimuli at attended than unattended locations, it remains unclear whether attention also accelerates the speed of perceptual neural activity in the human brain. One possible reason for this unclarity would be an insufficient spatial resolution of previous electroencephalography (EEG) and magnetoencephalography (MEG) techniques in which neural signals from multiple brain regions are merged with each other. Here, we addressed this issue by combining MEG with a novel stimulus-presentation technique that can focus on neural signals from higher visual cortex where the magnitude of attentional modulation is prominent. Results revealed that the allocation of spatial attention induces both an increase in neural intensity (attentional enhancement) and a decrease in neural latency (attentional acceleration) to the attended compared to unattended visual stimuli (Experiment 1). Furthermore, an attention-induced behavioural facilitation reported in previous psychological studies (Posner paradigm) was closely correlated with the neural 'acceleration' rather than 'enhancement' in the visual cortex (Experiment 2). In addition to bridging a gap between previous psychological and neurological findings, our results demonstrated a temporal dynamics of attentional modulation in the human brain.  相似文献   
10.
Sensing movements of the upper and lower extremities is important in controlling whole-body movements. We have shown that kinesthetic illusory hand movements activate motor areas and right-sided fronto-parietal cortices. We investigated whether illusions for the upper and lower extremities, i.e. right or left hand or foot, activate the somatotopical sections of motor areas, and if an illusion for each limb engages the right-sided cortices. We scanned the brain activity of 19 blindfolded right-handed participants using functional magnetic resonance imaging (fMRI) while they experienced an illusion for each limb elicited by vibrating its tendon at 110 Hz (ILLUSION). As a control, we applied identical stimuli to the skin over a nearby bone, which does not elicit illusions (VIBRATION). The illusory movement (ILLUSION vs. VIBRATION) of each immobile limb activated limb-specific sections of the contralateral motor cortex (along with somatosensory area 3a), dorsal premotor cortex (PMD), supplementary motor area (SMA), cingulate motor area (CMA), and the ipsilateral cerebellum, which normally participate in execution of movements of the corresponding limb. We found complex non-limb-specific representations in rostral parts of the bilateral SMA and CMA, and illusions for all limbs consistently engaged concentrated regions in right-sided fronto-parietal cortices and basal ganglia. This study demonstrated complete sets of brain representations related to kinesthetic processing of single-joint movements of the four human extremities. The kinesthetic function of motor areas suggests their importance in somatic perception of limb movement, and the non-limb-specific representations indicate high-order kinesthetic processing related to human somatic perception of one's own body.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司    京ICP备09084417号