Bernstein's Construction of Movements
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Bernstein's Construction of Movements

The Original Text and Commentaries

Mark L. Latash, Mark L. Latash

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eBook - ePub

Bernstein's Construction of Movements

The Original Text and Commentaries

Mark L. Latash, Mark L. Latash

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About This Book

Nikolai Aleksandrovich Bernstein was one of the great neuroscientists of the twentieth century and highly respected by Western scientists even though most have never read his most important book entitled On the Construction of Movements. Bernstein's Construction of Movements: The Original Text and Commentaries is the first English translation. It supplements the translated text with a series of commentaries by scientists who knew Bernstein personally, as well as leaders in related fields including physics, motor control, and biomechanics.

While written in 1947, Bernstein's book is anything but obsolete, making this English translation and accompanying commentaries an invaluable text. The translated original text presents in detail Bernstein's views on the evolutionary history of biological movement and his multi-level hierarchical scheme of the construction of movements in higher animals, including humans. The following commentaries address Bernstein's personality, the history of the book, and current views on different aspects of neuroscience covered in Bernstein's text. Ultimately, they present "a book within the book" to showcase how Bernstein's heritage has developed over the past years.

This classic, available for the first time to an English-speaking audience, will prove beneficial to students, instructors, and experts of neuroscience, physics, neurophysiology, motor control, motor rehabilitation, biomechanics, dynamical systems, and related fields.

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On the Origin of the Motor Function

Of all the domains of general physiology, none is more specifically human as the field of physiology of motor function in spite of its obvious, continuous evolvement from phylogenetic ancestors. The point is that no other physiological function has shown such an intense and, moreover, accelerating phylogenetic progression. It would be hard to point out essential changes during evolutionary progression in any other functional domain between humans and other warm-blooded animals, for example, in the domain of autonomic functions such as breathing, circulation, metabolism, etc.1 There is a single obvious exception showing even more dramatic progress, which has been singled-out into a separate domain based on related methodology and has become a separate science – the domain of psychic life or, as we will address it here for convenience, the domain of central processing systems of the neural machinery. The methodological issue that contributed to turning it into an independent branch of science also created an insurmountable additional difficulty. If we drew this process as a graph for the functions of breathing or metabolism – within the phylogenesis of warm-blooded animals – the line would be nearly parallel to the abscissa axis. The development of psychic functions would look in such a graph as a steeply rising curve; unfortunately, we would have the right to draw only its rightmost part related to humans. The rest of the curve would reflect only hypotheses because of the total absence of objective material related to animals despite the united heroic efforts by researchers in the fields of animal psychology, behaviorism, and conditioned reflexes. Only for motor function can we draw a fully objective evolutionary curve, steeply increasing toward the right part of the graph and leaving far behind its morphological central nervous substrate, which, by itself, displays evolution that is anything but slow. Even this fact, by itself, makes movement physiology interesting for psychologists and neurologists, independently of its importance in the role of a necessary ornament for the much better developed field of psychophysiology of receptor functions.
Besides the mentioned factors, the overwhelming evolutionary importance of motor function has been emphasized by the total time when it dominated in the phylogenesis of the overall somatic apparatus. The highest rate of evolutionary growth of the central processing system is due to the fact that these systems, over the same time interval, had to develop from the effector apparatuses to higher functions. This system gained the leading role in both its position and leading importance in the phylogenetic evolution relatively recently, whereas earlier it played (and still plays in less developed organisms) much more modest, auxiliary roles related to integration of receptor and effector signals. The current picture of the animal world – the living book of phylogenetic history – keeps memories on the early biography of this organ, barely starting (in coelenterates and echinoderms) its future mind-boggling career with the modest role of a switchboard operator, just introducing into the physiological repertoire the new, bioelectrical, (telegraph) transmission method instead of the more ancient and substance-based, humoral (kind of postal) signal transmissions. However, the crucial step in the history of the central processing system was the emergence of elongated animal shapes instead of the ancient circular-symmetrical (ray-like) shapes. This defined the predominance of the front, mouth-bearing end of the body, which becomes the first to encounter both food and danger, thus confronting the biological necessity to signal all other metamers, to lead and unite their movements and initiatives to produce movements. The head end became the main end of the body. This is the embryo of centralized nervous systems instead of the ancient diffuse ones (Reflex-Republics, Üexkull). Further, the head metamers acquired all the prerequisites for the emergence and development of telereceptors, which transformed in the process of refinement and improvement from one of the ancient contact categories (olfaction from taste chemoreceptors, hearing from vibration receptors, and vision from skin photochemical sensitivity). Telereceptors turned out to be a powerful centralizing factor by giving the animal possibilities of reacting to stimuli from infinitely far away, compared to the body size. This brought about, as actions of primary importance, locomotor movements of the whole body in space, which moved aside, into the second-rate category, local metamer reactions, which had dominated in the era of tangoreceptors. The biological necessity of locomotion led to the development of powerful, integrative, synergic apparatuses of the central nervous system – the most ancient in the phylogenesis of actions by vertebrates of a central neural origin – which have not been exceeded, as we will see later, up to humans, with respect to their ability of vast motor integrations and muscle synergies: we speak now of the so-called thalamo-pallidar motor system or level, as we are going to address it in future (Chapter 4).
As correctly pointed out by Sherrington, “telereceptors created the brain” – or, more exactly, structures that we have so far addressed as central processing systems (at the same time, telereceptors contributed to the centralizing properties of the spinal cord, which used to be purely metamer-specific and acquired during later phylogenesis obvious properties of a central formation). The point is that receptors, namely telereceptors, are overwhelmingly secondary, derivative instruments, and here we have to continue and develop the line of thinking of Sherrington.
In the process of evolution of the somatic system (maybe with the exception of the latest phylogenetic period), the role of the dominating factor has been played by effector functions. The fate of an individual in the struggle for existence is defined by its actions – their being more or less adequate within the ever-complicating process of adaptation. In this process, the receptor function plays a secondary, service role. Nowhere in the phylogenesis, watching the world is the ultimate, something self-sufficient, goal. Receptor systems happen to be either signal systems – we have already discussed this role – and then any degree of their sophistication cannot by itself ensure biological advantage for the animal if the effector apparatus is defective, or they are part of the process ensuring adequate, coordinated work of the effectors – we will discuss this role later – and here the secondary character of their activity follows directly from the semantic content of performed tasks. Hence, both the signal and corrective roles of receptors is ensured only by effectors of the animal or species. In this aspect, central processing systems historically play the role of servant systems for servants. We will show further how the emergence and development of telereceptors themselves and of the even more important for coordination sensory syntheses, which are based on central processing systems, are defined by the increasing and complicating demands from the effector systems.
The complication of motor tasks faced by an organism and the resulting enrichment of coordination resources of the individual proceed along two paths. On the one hand, motor tasks become more and more complicated. Diversity of reactions required from the organism increases. These reactions have to become more varied. The reactions have to meet higher and higher demands with respect to their differentiation and accuracy. Ultimately, requirements to the meaning of movements, actions, and behaviors of an animal also increase. It is sufficient to recall, for example, that the aerodynamics of the bird’s flight is more complex compared to the almost completely hydrostatic swimming of a fish, and the hunting strategy of a team of mammal predators is more sophisticated compared to hunting by sharks. The young generation of warm-blooded mammals won over the Jurassic “zaurs” because of their more sophisticated motor abilities.2 On the other hand, the overall composition of emerging motor problems contains an ever-increasing percentage of problems that are unique, unexpected, and extemporaneous at the expense of more ancient, stereotypical situations. All the numerous studies of “plasticity of the nervous system” show, in addition to the evolutionary increase in adaptability of the central nervous system to unusual changes in external conditions, immediate, nearly instantaneous adjustments to the most fanciful experimental conditions. But even if we forget about exquisite experimental anastomoses of nerves and muscles, the much more mundane fact of the phylogenetic increase in the ability to accumulate individual experience and to create new conditional connections, i.e., once again to go beyond the species-specific stereotypes, supports the aforementioned thesis.
In a somewhat schematic way, one can say that the first of the aforementioned routes of the development of motor coordination is ensured and accompanied primarily by the evolution of receptor functions, whereas the second one – by the evolution of central processing systems. First, as far as receptor function is concerned, there is a systematic qualitative improvement of receptor devices, which originates from the most ancient phylogenesis: overlaying of the ancient (paleokinetic, see Chapter 3) protopathic tactile sensitivity and more novel and sophisticated epicritic sensitivity realized by the neokinetic process; the emergence of the younger (also neokinetic) forms of proprioceptors – geometrical that perceive postures and velocities and led by the neo-labyrinth of the semicircular canals – on the background of proprioceptors reflecting tropisms and led by the otolithic apparatus (the paleo-labyrinth) and adapted for measuring pressures, tensions, efforts, orientation in the gravity field, etc. Second, there is ongoing development of the system of telereceptors, which assume the leading role and contribute to the evolution of central processing systems and the brain and to the whole qualitative revolution, which has been described before and which follows the gradual dominance of receptors of this type. In particular, the main accompanying structural phenomena include: (1) The transition from the single-neuron thalamic scheme of ascending neuronal pathways to the schemes of cortical afferentation involving two or more neurons, which signifies not only the emergence of a couple of extra synaptic connections in the pathway of sensory signals but the profound qualitative signal processing in the intermediate ganglia; (2) The transition from a system of isolated sensory neural nuclei to a two-dimensional elaborate, layered system typical of the cortex of the large hemispheres; the importance of these transitions for the evolution of coordinative function will be clarified later; and (3) The adaptive evolution of sensory function develops in parallel to the formation of progressively more and more elaborate synthetic sensory fields, which will be discussed in Chapters 4 and 5. These sensory syntheses, where raw receptor signals from different sensory organs are combined with stored in memory components related to the individual experience of the animal related to the generation of deeply processed and generalized directives for future movements and actions, stimulate and direct growth and development of central processing systems at least as much as telereceptors do. The phylogenetic formation of these gradually elaborating fields is related to the continuous increase in the role of memory-related components – in other words, of individual memory.3
Following a similar schematic interpretation, the second line of development of effector function corresponding to the growing importance of singular reactions based on the accumulated and organized individual experience of the animal, is primarily related to the evolution of central processing systems located in the cortex of the large hemispheres. The development of the cortex provides a prerequisite for the ongoing elaboration of the purposive structure of the organism’s actions and an increase in its memory capabilities. This is how central processing systems, at a certain stage of the evolution, transform from a subordinate position to a leading position, thus directing further development of the entire neuro-somatic system.
The phylogenetic evolution of the central nervous system (Figure 1.1), unlike all other organs and systems within the body, is not only (and even, not so much) limited to quantitative growth but rather includes qualitative accretion with new formations that have no analogues at preceding stages of the phylogenesis and represent primarily superstructures by one (or more) neuronal level within the overall neural process. This principle leads to inevitable leaps in the development of the central nervous system, in particular due to the discrete nature of the neural scheme: The elaboration of a reflex arc or any other pathway for a neural impulse within the central nervous system is possible only if a discrete number of relay neurons have been a...

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