LB 015-018 T

(3) Developmental History of the Central Regulatory Mechanism

The logical argument offered by Lashley is supported by an impressive array of experimental findings. We have mentioned the experiments on salamander larvae in which limb buds were transplanted to inappropriate sites. If a left forelimb is amputated from a donor animal and transplanted as a supernumerary limb to a host animal where it is allowed to regenerate into the right armpit, the extra limb is soon found to be moving smoothly. No tonic rigidity is noticed, and therefore we must assume that agonist and antagonist muscles receive innervation that is appropriate to the muscle. Interestingly enough, the limb will move at the tome that is appropriate for a forelimb to move; since, however, we have changed sides in the process of transplantation, the super numerary limb will move in the opposite direction from the original limb that is next to it. Thus one limb cancels the effect of the other, and it is possible to have a preparation with totally paradoxical behavior.

Lashley所提出的邏輯辯論是根據一個印象深刻的實驗結果.我們可以注意到在蠑螈幼蟲的實驗中,對於幼蟲四肢的解釋並不恰當.如果由捐贈器官的動物切除其左前肢,並移植到另一隻腳到宿主動物身上,則這隻額外移植的腳能馬上行動自如,沒有任何僵硬或不適的情形,因此,我們可以假設收縮筋和頡頏肌的神經分布是適合肌肉生長的.有趣的是,前肢移動的時候也會帶動後肢的移動,然而,當我們將移植改變到另一側時,額外移植的另一隻腳則會往反方向移動.因此,一隻腳相對抵消了對另外一隻腳的影響.這對動物不合常理的行為提出了一種可能的解釋.

What is the nature of this relationship between the limb and the brain? How can reciprocal innervation of muscles and timing of the limb with respect to other limbs be established in a fairly orderly way where there could not have been any neuronal “wiring” for the additional leg? Inspection under the microscope of the regenerated tissues does not reveal any visible order. Never fibers seem to have sprouted every which way, and the established connections seem to be entirely random. Could this be a delusion due perhaps to insufficient power of resolution of the light microscope? Is it possible that the nerve sprouts actually find their way to the appropriate muscle because of some unknown biochemical affinity between muscle and nerve? At first this possibility was never entertained. Instead it was thought that muscles were physiologically tuned to specific neuronal messages and simply responded whenever they “heard their name over the public address system.” This hypothesis was known as the muscle-resonance theory. However, Wiersma(1931) disproved the theory by recording electrical potentials from the nerves. Subsequently, the orderly recovery of motor coordination in the transplanted limb was interpreted on the basis of structural connections. There are two essential possibilities here. Either the nervous system entirely fixed and proper connections are made at the periphery in the way first mentioned, that is, fibers that carry given messages have the capacity of finding their way into the appropriate muscle during regeneration; or the muscles have the capacity of influencing the nerves that grow into them and thus affect the central nervous system retrogradely.

而四肢和腦部之間在本質上存在著什麼樣的關係呢?肌肉組織的神經交互分布和四肢之間的關聯性要如何建立一個相當有秩序的方式,讓那隻額外移植的腳沒有發上任何神經系統上錯誤的?把肌肉重生的組織放在顯微鏡下觀察,似乎無法從肉眼得知.神經組織可能以任何方式生長以及發展,而其中所建立的連結似乎是隨機的.這會是由於顯微鏡的觀察沒有提供充分的解答所造成的誤解嗎?神經系統的生長有沒有可能是因為肌肉組織和神經之間存在生物化學上,異種物質間起化學作用所產生的吸引力?起初,這種可能性是完全不被接受的.當時是認為肌肉在生理學上調整成特有的神經訊息,只單純地在公開的演講系統聽到他們的命名時作回應,這樣的說法就是著名的肌肉共振理論.然而,Wierma(1931)以神經的電位來推論此理論.其次,針對經過一值得繳,其運動神經協調性的復原,說明了神經連結架構的基礎.在這裡,有兩種重要的可能性.第一種,神經系統是固有的,而其中的連結是根據一開始所提到的外圍方式,也就是說,在肌肉重生的過程中,帶有訊息的組織有能力去尋找到適合的肌肉組織.另外一種可能性是,肌肉擁有影響神經的能力,藉以降低中樞神經系統的影響力.

The first of these two possibilities has gained plausibility in most recent investigations (Mark, 1965) , although it is still far from established. The second possibility is favored by many of the neuroembryologists who had made the original discoveries on lower vertebrates. In Weiss’s own words (1950b) : It is thought now that “each muscle has a specific biochemical differential, that it projects this differential into the motor nerve fibers that come to innervate it and thus tunes (modulates) the motor ganglion cells to a specificity appropriate for the particular muscle. The ganglion cells have received their specificity by a retrograde influence (modulation) from the muscle itself.” Until recently, Sperry (1958) believed that the biochemical influence exerted by the muscle upon the nerve actually induces synaptic changes in the central nervous system. But Eccles et al. (1962) found only limited support for this interpretation, lending credence to Mark’s (1965) interpretation, a point of view that is also now favored by Sperry (1963). For an up-to-date review of the entire topic see Weiss (1965).
此兩種假設雖然和以建立的理論有一段差距,但仍在之後的研究中逐漸取得合理性.其中,第二種假設最受到許多從事研究較低階脊椎動物的神經病理學者支持.在Weiss所提出的論述中:每一條肌肉都具有生物化學上的差異,並將這樣的差異性投射於運動神經的組織中,並且改變運動神經節細胞,成為只針對某特定肌肉發展的細胞.神經節細胞接收到這樣的訊息是受到肌肉本身調整的影響.一直到西元1958年,Sperry相信運用神經肌肉在生物化學上的影響,在中樞神經系統上確實減少了生殖細胞在進行減數分裂的前期,相同染色體互相結合的現象.但是,Eccles et.al在西元1962年發現只有少數研究支持這項理論,而對於Mark在西元1965年的研究給予肯定.同時也獲得了Sperry的支持.相關最新的且完整的論述可以參考Weiss (1965).

The importance of the original discovery is that in phylogenetically primitive vertebrates (and probably during fetal stages of most other vertebrates) there is an inescapable BaupIan (blueprint) for both the gross form and the sensory-motor integration. The surgical rearrangement experiments on lower forms show how difficult it is to interfere with the “preestablished harmony” of the movements of muscles throughout the body which accounts for smooth coordination.

最初的重要發現是對於脊椎動物一開始有關物種的變化(或者是在大多數脊椎動物的胚胎階段)有一個關於數量以及運動肌感知的整合性的藍圖.在較低階的外科手術重组實驗中顯示在流暢的身體協調度上肌肉運動前期在協調方面的困難

Compare this situation with rearrangement experiments in mammals and adult forms of lower vertebrates. If the nerves which normally feed a flexor and extensor pair of muscles, respectively, are interchanged surgically and are allowed to regenerate into the wrong muscle, subsequent coordination becomes disordered and remains so.

和較低階的脊椎動物中的哺乳類動物重组實驗的相比較之下,如果屈肌和伸肌在外科手術上互相交換,並且重新生長錯誤的肌肉,則協調性會受到阻礙,且阻礙的形況會一直持續下去.

The difference in the results of rearrangement between lower and higher forms is not as paradoxical as it might appear at first. Table 1.1 summarizes the situation for easier reference. We discern here the emergence of a specific theme. For all animals examined, rigid plans for development of form and motor coordination seem to exist. In primitive forms, tissues are less differentiated or specialized and thus participate in the organization responsible for motor coordination; end organs may influence the structure and function of centers as much as the centers may influence the periphery. The result is preservation of the original plan for integration. In adult and higher forms, tissues become more and more specialized and thus more independent of each other. The motor-integration plan is no longer “inscribed” in tissues other than those directly concerned with coordination, principally the brain. The basic plan or plans (the dispatch schedules) for sensory motor coordination are still as rigidly inherent in the internal organization of the animal but they are stored now in the central nervous system alone. In this context, the dimension of plasticity-rigidity refers exclusively to adaptation and readjustment of internal process, not to an animal’s adaptation to environmental conditions.
在較高階和低階的層次上,重组結果的不同,並非是不合理的.圖表1.1說明了先前所參考的情況.我們認知到了特殊命題的急迫性.在所有調查的動物中,較堅硬植物的生長和運動神經的協調性是存在的.對於運動神經的協調度而言,組織初期的形狀並無明顯不同.而最終器官或許會影響組織核心的架構和功能,就像是組織核心影響外圍一樣.其結果是在成熟或更高階的形式,組織變得越來越有個別性,越來越獨立於其他組織.而運動神經整合的計畫不再只是存在組織當中,而是直接參與協調.主要以腦部為主.最初對於感知運動在神經協調性的計畫,是嚴格地經由遺傳到動物的內部組織中.但它們現在仍獨立儲存於中樞神經系統中.在這裡,適應性和剛性所指的是內部過程中的適應性和重新調整的能力,而不是指動物對外界環境的適應性.