Imitation of Finger Movements--论文代写范文精选

人类及其同系动物也会有罕见的额上沟。最有可能找到它相对的后方,只是前面的前运动皮层。考虑细胞结构,缺乏一个颗粒层。从从生理的角度来看这两个领域应该分享一些特性。下面的paper代写范文进行阐述。

Abstract
Some neuroanatomical considerations suggest that area F5 of the macaque brain is the evolutionary precursor of Brodmann area 44 (BA 44) of the human brain (von Bonin & Bailey, 1947; Petrides & Pandya, 1994; Rizzolatti & Arbib, 1998). Brodmann area 44 is a cytoarchitectonic area that probabilistically maps onto pars opercularis of the inferior frontal cortex (Mazziotta et al., 2001a,b), an area that we have seen is strongly implicated in imitation and belongs to what we call the minimal neural architecture for imitation. BA 44 is part of Broca’s area (some authors assign Broca’s area to BA 44 only), the most important cortical region for language processing in the human brain. The simultaneous involvement of BA 44 in language and imitation, and the evolutionary anatomical considerations that I address later, suggest functional links between imitation and language. 

A discussion of these possible links is the focus of this section. In the macaque frontal lobe, there is a major sulcus that divides the anterior granular prefrontal cortex from the posterior agranular motor and premotor cortex. This sulcus is called the arcuate sulcus since its shape resembles an arc. It has been suggested that the evolutionary process has transformed the dorsal sector of the arcuate sulcus of the macaque brain into the superior frontal sulcus of the human brain. The same process would have transformed the ventral sector of the arcuate sulcus into the inferior frontal sulcus of the human brain. Area F5 is ventral to the arcuate sulcus, and its human homologue would also be located ventrally with respect to the inferior frontal sulcus. Thus one would expect to find the human homologue of area F5 in the inferior frontal gyrus. And one would most likely find it relatively posteriorly located, sitting just in front of the premotor cortex represented in the precentral gyrus, given that F5 is a rostral premotor area. 

If one then considers the cytoarchitecture of F5, which is devoid of a granular layer, one would expect the human homologue of F5 to be an agranular cortical area. If one considers all these points, the most likely candidate as a human homologue of F5 is BA 44 (Rizzolatti & Arbib, 1998; Geyer et al., 2000). In fact, BA 44 is the rostralmost agranular cortical field in the inferior frontal gyrus and is located right anteriorly to the ventralmost sector of the precentral gyrus. If BA 44 were the human homologue of macaque F5, then one would expect that from a physiological standpoint these two areas should share some features. 

In terms of motor representation of body parts, F5 in the macaque contains a representation for hand movement and one for mouth movements. Thus one would expect motor representation for the hand and the mouth in BA 44 also. In fact, several imaging studies have reported activation in BA 44 for motor tasks that engage the hand (Krams et al., 1998; Binkofski et al., 1999b; Iacoboni et al., 1999; Ehrsson et al., 2000) and the mouth (Fox et al., 2001). This also means that in an imaging experiment on, say, imitation of foot movements, one should not expect to observe activation of BA 44 if this activation reflects the motor aspect of BA 44 and not its linguistic (supposedly disembodied) one. The activation studies that we have performed on imitation of hand movements have demonstrated that a sector of pars opercularis is activated during imitation and observation of hand actions. Its activity is also modulated by the type of imitation (specular versus anatomical) and by goal-oriented imitation. 

Our meta-analysis of hand imitation (MolnarSzakacs et al., 2002) points to the dorsal sector of pars opercularis as the sector of Broca’s area with these characteristics. Also, a meta-analysis of language tasks (Chein et al., 2002) suggests that the dorsal sector of pars opercularis is a critical language region. The convergence of the empirical data is impressive and suggests shared neural structures for imitation and language. It could be objected, however, that the activation observed in Broca’s area during imitation is simply due to some kind of silent and perhaps unconscious verbalization (Heyes, 2001a). This objection does not really explain why there should be more verbalization in some imitative conditions but not in others. It also does not explain why the observation of hand movements activates Broca’s area but the observation of foot movements does not. At any rate, the silent verbalization hypothesis cannot be dismissed too lightly. 

To test whether the involvement of Broca’s area in imitation is due to silent verbalization or to mirror activity for hand or mouth movements, we used repetitive transcranial magnetic stimulation (rTMS). This technique allows one to create a kind of temporary, transient lesion in the brain area stimulated (Walsh & Cowey, 2000). We stimulated the pars opercularis of the inferior frontal gyrus during imitation of hand actions and during a control visuomotor task. We also stimulated a control site. If activation of Broca’s area in imaging studies of imitation is due only to an epiphenomenal silent verbalization, then producing a transient lesion in pars opercularis should not affect the imitative performance. 

If, in contrast, Broca’s area is essential to imitation, then producing a transient lesion in pars opercularis should have an effect on imitation. And if this effect reflects impairment in functional processes that are specific to imitation and to BA 44, then performance in the control task should be unaffected by stimulation of pars opercularis, and performance in the imitation tasks should be unaffected by stimulation of the control site. The results we obtained in a recent rTMS study performed in our laboratory (Heiser et al., 2003) are consistent with the hypothesis of an essential role for Broca’s area, namely BA 44, in imitation (figure 2.5). The possibility remains that the effect we observed is language mediated, so that one has to name a finger movement in order to imitate it. However, this is quite unlikely if one looks at human development. In fact, infants can imitate much earlier than they can talk (Meltzoff & Moore, 1977). If Broca’s area has an essential role in imitation, then it must be concluded that this area is not exclusively dedicated to language processing. It also suggests an evolutionary continuity between action recognition, imitation, and language.(paper代写)

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