Minimal Human Neural Architecture for Imitation--论文代写范文精选

最初的研究结果，只有在某种程度上，可能由于技术的局限性，掌握电路的测试是否在人类大脑区域显示,我们进行了功能性磁共振成像，早期的研究把握一个概念性的限制。即使连续性是非常重要的。下面的paper代写范文进行详述。

Abstract
The first attempts to demonstrate an action recognition system in the human brain similar to the one in the macaque brain were made using positron emission tomography (PET) and, as activation tasks, execution and observation of grasping (Grafton et al., 1996; Rizzolatti et al., 1996b). The idea behind these studies was the following. If there is a human action recognition system that is similar to the one described in macaques, motor areas in the human brain belonging to this system should be active during both execution and observation of grasping. Ideally, there should also be some anatomical correspondence between the human and the macaque areas. The early PET attempts were not entirely successful, even though some aspects of the empirical findings were encouraging. 

The two broadly defined regions of superior temporal cortex and inferior frontal cortex were indeed activated during both observation and execution of action. The areas activated within inferior frontal and superior temporal cortex during execution of grasping, however, did not spatially match the areas activated within inferior frontal and superior temporal cortex during observation of grasping. Furthermore, the posterior parietal cortex was found to be activated only during execution of grasping (Rizzolatti et al., 1996b). However, a second study comparing observation of grasping with imagination of this action did report activation of posterior parietal cortex during observation (Grafton et al., 1996). The reason the results of these first studies were successful only in part is probably due to technical limitations of the 2-D PET methodology used.

The second important feature of the action recognition system described in the macaque is that it is driven by goal-directed actions. To test whether human brain areas of the grasping circuit show a similar feature, we performed a functional magnetic resonance imaging (fMRI) experiment in which subjects either performed an object-directed action (grasping or touching an object) or simply pantomimed the action without actually interacting with the object. The prediction is that a hand–object interaction should yield greater activity in regions coding goal-oriented behavior. Consistently with the macaque single-cell data, we found that the inferior frontal cortex had this pattern of activity (figure 2.1).

The early studies on grasping, however, had a conceptual limitation. Even though continuity is important, so that it makes sense to see some features of the action recognition system of the macaque in the human brain, one must also factor in the changes that the evolutionary process might have produced. Thus, to keep focusing on grasping seemed to us a mistake. Imitation seemed a much more promising paradigm to use. In fact, the action recognition system of the macaque has the property of being active both when the monkey performs an action and when it observes an action. These neural properties make this system an ideal candidate for being involved in or at least facilitating imitation. 

It is true that the imitative abilities of monkeys are limited, but even if one wants to apply the most stringent definition of imitation and thus conclude that monkeys do not imitate at all, one can also conceivably argue that the action recognition system made monkeys ‘‘imitation-ready.’’ Thus it is plausible to predict an involvement of this system in imitation. The way we conceptualized it is captured in figure 2.2. The idea behind this conception is simply that during imitation there is both observation and execution of an action. Thus, one can predict that areas endowed with mirror properties would show an activity pattern similar to the one graphed in the figure, with activity during imitation corresponding roughly to the sum of the activity during observation and execution of action. With the use of fMRI, we found two areas with these properties (Iacoboni et al., 1999). The first area was located in the pars opercularis of the inferior frontal gyrus, in inferior frontal cortex, and the second one was located rostrally in the posterior parietal cortex. 

Thus there was a convincing anatomical correspondence between the areas identified in the human brain as having mirror properties and the macaque mirror areas. We initially proposed some sort of ‘‘division of labor’’ between the frontal and the posterior parietal mirror areas, so that frontal mirror areas would code the goal of the imitated action and the posterior parietal mirror areas would code somatosensory information relevant to the imitated action. This division of labor was based on considerations inspired by single-cell (Sakata et al., 1973; Mountcastle et al., 1975; Kalaska et al., 1983; Lacquaniti et al., 1995) and neuroimaging data (Decety et al., 1997; Gre`zes et al., 1998). Empirical support for this proposed division of labor has been provided recently by an imaging study from our group. 

The study shows a modulation of activity in inferior frontal mirror areas during imitation of goal-oriented action, with greater activity during goal-oriented imitation than nongoal-oriented imitation (Koski et al., 2002). To go back to the first experiment on imitation (Iacoboni et al., 1999), the third region identified by single-cell studies in the macaque as relevant to action recognition, STS, demonstrated a somewhat unexpected pattern of activity. As expected, there was greater activity in STS for action observation than for control visual tasks and for imitation compared with control motor tasks. However, there was also greater activity in STS for imitation than for action observation. (paper代写)

This was a somewhat unexpected finding because the observed action was the same during imitation and during action observation. If STS simply encodes the visual description of actions, its activity should be the same during imitation and action observation. Two possible explanations of this finding are as follows: First, the increased activity during imitation may simply reflect increased attention to the visual stimulus because the subjects are supposed to imitate it. Alternatively, the increased STS activity may be due to efferent copies of motor commands originating from the frontoparietal mirror areas. These efferent copies would allow a prediction of the sensory consequences of the planned imitative action that would be compared with the description of the observed action provided by STS. If a good match is obtained, then the planned imitative action can be performed.(paper代写)

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