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21.
This study explored the neurophysiological mechanisms underlying the planning and execution of an overt goal-related handle rotation task. More specifically, we studied the neural basis of motor actions concerning the influence of the grasp choice. The aim of the present study was to differentiate cerebral activity between grips executed in a habitual and a non-habitual mode, and between specified and free grip choices. To our knowledge, this is the first study to differentiate cerebral activity underlying overt goal-related actions executed with a focus on the habitual mode. In a handle rotation task, participants had to use thumb-toward (habitual) or thumb-away (non-habitual) grips to rotate a handle to a given target position. Reaction and reach times were shorter for the habitual compared to the non-habitual mode indicating that the habitual mode requires less cognitive processing effort than the non-habitual mode. Neural processes for action execution (measured by event-related potentials (ERPs)) differed between habitual and non-habitual conditions. We found differential activity between habitual and non-habitual conditions in left and right frontal areas from −600 to 200 ms time-locked to reaching the target position. No differential neural activity could be traced for the specification of the grip. The results suggested that the frontal negativity reflected increased difficulty in movement precision control in the non-habitual mode compared to the habitual mode during the homing in phase of grasp and rotation actions. 相似文献
22.
The ability to discriminate between galactose and N- acetylgalactosamine,
observed in some lectins, is crucial for their biological activity as well
as their usefulness as tools in biology and medicine. However, the
molecular basis of differential binding of lectins to these two sugars is
poorly understood. Peanut agglutinin (PNA) is one of the few
galactose-specific legume lectins which does not bind N-
acetylgalactosamine at all and is, therefore, ideal for the study of the
basis of specificity towards C-2 substituted derivatives of
galactopyranosides. Examination of the three-dimensional structure of PNA
in complex with lactose revealed the presence of both a longer loop and
bulkier residues in the region surrounding the C-2 hydroxyl of the
galactopyranoside ring, which can sterically prevent the accommodation of a
bulky substituent in this position. One such residue, is a glutamic acid at
position 129 which protrudes into the binding site and perhaps directly
obstructs any substitution at the C-2 position. Two mutants in bacterially
expressed PNA were therefore constructed. These were E129D and E129A, in
which Glu129 was replaced by Asp and Ala, respectively. The specificity of
the mutants for galactose, galactosamine, and N- acetylgalactosamine was
examined through observing the inhibition of hemagglutination and binding
of the lectin to immobilized asialofetuin. The results showed that the
affinity of E129A and E129D for C-2-substituted derivatives of the
galactose varies. The mutant E129D showed significant binding towards N-
acetylgalactosamine, suggesting that the residue Glu 129 is crucial in
imparting exclusive galactose-specificity upon PNA. This study not only
attempts to provide an explanation for the inability of PNA to accommodate
C-2-substituted derivatives at its primary subsite, but also seeks to
present a basis for engineering lectins with altered specificities.
相似文献
23.
There is ample evidence that people plan their movements to ensure comfortable final grasp postures at the end of a movement. The end-state comfort effect has been found to be a robust constraint during unimanual movements, and leads to the inference that goal-postures are represented and planned prior to movement initiation. The purpose of this study was to examine whether individuals make appropriate corrections to ensure comfortable final goal postures when faced with an unexpected change in action goal. Participants reached for a horizontal cylinder and placed the left or right end of the object into the target disk. As soon as the participant began to move, a secondary stimuli was triggered, which indicated whether the intended action goal had changed or not. Confirming previous research, participants selected initial grasp postures that ensured end-state comfort during non-perturbed trials. In addition, participants made appropriate on-line corrections to their reach-to-grasp movements to ensure end-state comfort during perturbed trials. Corrections in grasp posture occurred early or late in the reach-to-grasp phase. The results indicate that individuals plan their movements to afford comfort at the end of the movement, and that grasp posture planning is controlled via both feedforward and feedback mechanisms. 相似文献
24.
The tangential neurons in the lobula plate region of the flies are known to respond to visual motion across broad receptive
fields in visual space.When intracellular recordings are made from tangential neurons while the intact animal is stimulated
visually with moving natural imagery,we find that neural response depends upon speed of motion but is nearly invariant with
respect to variations in natural scenery. We refer to this invariance as velocity constancy. It is remarkable because natural scenes, in spite of similarities in spatial structure, vary considerably in contrast, and
contrast dependence is a feature of neurons in the early visual pathway as well as of most models for the elementary operations
of visual motion detection. Thus, we expect that operations must be present in the processing pathway that reduce contrast
dependence in order to approximate velocity constancy.We consider models for such operations, including spatial filtering,
motion adaptation, saturating nonlinearities, and nonlinear spatial integration by the tangential neurons themselves, and
evaluate their effects in simulations of a tangential neuron and precursor processing in response to animated natural imagery.
We conclude that all such features reduce interscene variance in response, but that the model system does not approach velocity
constancy as closely as the biological tangential cell. 相似文献
25.
Monopoli MP Raghnaill MN Loscher JS O'Sullivan NC Pangalos MN Ring RH von Schack D Dunn MJ Regan CM Pennington S Murphy KJ 《Proteomics》2011,11(21):4189-4201
Information storage in the brain depends on the ability of neurons to alter synaptic connectivity within key circuitries such as the hippocampus. Memory-associated synaptic plasticity is mediated by a temporal cascade of de novo protein synthesis and altered protein processing. Here, we have used two-dimensional difference in gel electrophoresis (2-D DIGE) to investigate memory-specific protein changes in the hippocampal dentate gyrus at increasing times following spatial learning. We identified 42 proteins that were significantly regulated in the first 24 h of spatial memory consolidation. Two distinct waves of protein expression regulation were evident, at 3 and 12 h post-learning and this is in agreement with studies employing inhibitors of global translation. Functional classification of the memory-associated proteins revealed that the majority of regulated proteins contributed either to cellular structure or cellular metabolism. For example, actins, tubulins and intermediate filament proteins, core proteins of the three major cytoskeletal components, were dynamically regulated at times that suggest a role in memory-associated synaptic reorganization. Increased proteasome-mediated protein degradation was evident in the early post-training period including the down-regulation of phosphoprotein enriched in astrocytes 15 kDa, a key inhibitor of extracellular signal-regulated kinase signaling. Some of the most substantial protein expression changes were observed for secreted carrier proteins including transthyretin and serum albumin at 6-12 h post-learning, regulations that could serve an important role in increasing the supply of retinoic acid and thyroid hormone, key synaptic plasticity-promoting signals in the adult brain. Together these observations provide further insight into protein level regulations occurring in the hippocampus during spatial memory consolidation. 相似文献
26.
27.
Quantiles and their estimations are the basis for solving numerous problems of statistics. The paper presents adaptive recursive estimation methods for this statistical parameter. Its specifical properties are investigated and the possibilities of applications in computer assisted analysis of biological signals are demonstrated even satisfying real time requirements. 相似文献
28.
Maria Ellegaard Cansu Agca Solveig Petersen Ankita Agrawal Lars Schack Kruse Ning Wang Alison Gartland Jens-Erik Beck Jensen Niklas Rye Jørgensen Yuksel Agca 《Purinergic signalling》2017,13(4):545-557
It is now widely recognized that purinergic signaling plays an important role in the regulation of bone remodeling. One receptor subtype, which has been suggested to be involved in this regulation, is the P2Y2 receptor (P2Y2R). In the present study, we investigated the effect of P2Y2R overexpression on bone status and bone cell function using a transgenic rat. Three-month-old female transgenic Sprague Dawley rats overexpressing P2Y2R (P2Y2R-Tg) showed higher bone strength of the femoral neck. Histomorphometry showed increase in resorptive surfaces and reduction in mineralizing surfaces. Both mineral apposition rate and thickness of the endocortical osteoid layer were higher in the P2Y2R-Tg rats. μCT analysis showed reduced trabecular thickness and structural model index in P2Y2R-Tg rats. Femoral length was increased in the P2Y2R-Tg rats compared to Wt rats. In vitro, there was an increased formation of osteoclasts, but no change in total resorption in cultures from P2Y2R-Tg rats. The formation of mineralized nodules was significantly reduced in the osteoblastic cultures from P2Y2R-Tg rats. In conclusion, our study suggests that P2Y2R is involved in regulation of bone turnover, due to the effects on both osteoblasts and osteoclasts and that these effects might be relevant in the regulation of bone growth. 相似文献
29.
Two core elements for the coordination of different actions in sport are tactical information and knowledge about tactical situations. The current study describes two experiments to learn about the memory structure and the cognitive processing of tactical information. Experiment 1 investigated the storage and structuring of team-specific tactics in humans’ long-term memory with regard to different expertise levels. Experiment 2 investigated tactical decision-making skills and the corresponding gaze behavior, in presenting participants the identical match situations in a reaction time task. The results showed that more experienced soccer players, in contrast to less experienced soccer players, possess a functionally organized cognitive representation of team-specific tactics in soccer. Moreover, the more experienced soccer players reacted faster in tactical decisions, because they needed less fixations of similar duration as compared to less experienced soccer players. Combined, these experiments offer evidence that a functionally organized memory structure leads to a reaction time and a perceptual advantage in tactical decision-making in soccer. The discussion emphasizes theoretical and applied implications of the current results of the study. 相似文献
30.
Markham B. Schack 《Science activities》2013,50(1):3-4
It is natural to study astronomy outdoors, but it is not quite as natural to study astronomy during the daytime. This lesson uses the Earth's closest star as a subject of study within the schoolyard. The importance of the rising sun is combined with hands-on inquiry in which students explore the properties of shadows. Students (a) complete a modified Know and Need to Know (KNK) chart about shadows, (b) complete task cards to help direct their inquiry, (c) develop two rules about shadows and the sun, and (d) reflect upon the experience through a writing assignment. 相似文献