One cannot help but marvel at the accomplishments of a skilled pianist, athlete, or craftsman. Even those without exceptional proficiencies display remarkable abilities for fine motor control. As I am typing, my fingers are moving rapidly in varying order and with remarkable spatial and temporal precision. We all perform everyday tasks, such as tying our shoes, with so little effort that we fail to appreciate how complex they are. Performance of these “simple” behaviors far outstrips the abilities of even the most advanced robots.
Mechanisms Of Fine Motor Control
How are we capable of performing such sophisticated tasks? The most basic units of motor organization are found in the spinal cord. These circuits provide for the fundamental coordination between muscles as well as feedback control of movement. At a higher level, a group of brain structures, the basal ganglia, act as important “amplifiers” of movement. Damage to these structures in the neurodegenerative disorder, Parkinson’s disease, result in paucity of movement. Motor cortex is particularly important for controlling fine movements of the digits. It is the direct connection between motor cortex and spinal motoneurons that enable the fine, independent movements of the fingers necessary for typing or tying shoelaces. However, one could not type, play the piano, or conduct any other rapid sequence of complex movements without premotor and supplementary motor areas of the cortex. These regions are where sequences of movement are “programmed” in advance preparation for movement. Thus, during typewriting, premotor and supplementary motor areas develop a movement plan that is conveyed to the motor cortex, which in turn directs the movements of individual fingers as required. When one “visualizes” execution of a skilled motor behavior, these areas are activated, which is why previsualization and mental rehearsal of complex skills can improve performance. The cerebellum is another major structure of the nervous system of crucial importance for fine motor control. The cerebellum is best thought of as a structure that compares intended behavior, as dictated by motor cortex and the basal ganglia, to the actual output. The cerebellum acts to minimize the error between intended act and the actual behavior and also ensures proper timing of rapid movement sequences. As one reaches for a coffee cup, the trajectory of the hand is continually being modified by cerebellum-mediated error correction. The importance of the cerebellum is clearly illustrated in the effects of alcohol intoxication, which profoundly affects cerebellar function. The coffee cup gets knocked over instead of being picked up, and typing becomes error prone. Maturation of these different parts of the nervous system are thus of critical importance for the development of fine motor control.
Development Of Fine Motor Control
First 6 Months After Birth
The first 6 months after birth are dominated by spinal reflex mechanisms because brain mechanisms of motor control have yet to mature. So, for example, independent control of the digits is not possible. Instead, touching the palm of the newborn elicits a grasping reflex in which all digits act as a unit. Amplitude, direction, and force of movements are poorly controlled, and there is little evidence of goal directedness. Fundamental rhythms of movement that will later become organized into locomotion and other rhythmic behaviors are present, as are basic patterns of flexor–extensor alternation. Control of movement of the limbs progresses in a proximal to distal pattern, so that maturation of control of the shoulders and hips is more advanced than that of the fingers and toes. Infantile reflexes constitute a large part of the coordinated activity of newborns, but their relationship to later voluntary behavior is disputed. Whether they serve as essential precursors to later behavior, serve adaptive functions peculiar to the neonate, or simply reflect the state of maturation of the nervous and musculoskeletal systems is not clear. At about 6 months of age, most of these infantile reflexes disappear in anticipation of the development of voluntary control of movement. By about 6 months of age, most infants can visually direct their reach toward an object and correct that reach for movement of the object.
Development From 6 Months to 5 Years
During the period from 6 months to 5 years of age, there is remarkable maturation of the peripheral and central mechanisms that control fine movement, which is greatly facilitated by practice and other experiential effects. Among the most notable milestones are the development of language and upright locomotion, both of which typically appear at the end of the first year after birth. It is generally thought that development of cortical areas important for planning and initiating movement and that maturation of the error-correcting cerebellum are crucial for effective execution of those movements. In the progression from crawling (belly on the floor) to creeping (belly elevated during quadrupedal locomotion) to assisted bipedal walking to independent walking, increasing demands are placed on the musculoskeletal system as well as on cerebellar assistance in maintaining balance and responses to perturbations. There is very little evidence to suggest that learning plays an important role in the onset of walking, despite the fact that this accomplishment is referred to as “learning” to walk. However, early walking is typically characterized by lifting and placing of the foot as a whole, rather than by the smooth heel-strike, rolling, and toe push-off that characterizes the adult. In early development, many movements are “mirror-image” movements, in which the intentional movement of one limb is reflected in the opposite limb. These mirror-image movements are thought to be a consequence of immature connections between the left and right sides of the cerebral cortex, which later in life serve to inhibit such movements. It is very clear, however, that after the first year of infancy, practice and learning play a large role in the acquisition and refinement of skills. During locomotion, one sees an improvement in the posture of the limbs and arms, more efficient movements of those limbs, and increasingly differentiated movements, especially of the digits. Thus, the toddler begins to grasp and throw objects. Initial attempts are not very skilled, and the result is not very effective. Toddlers typically begin to throw by stepping forward with the foot on the same side as the throwing hand rather than more effectively stepping forward with the opposite foot. Continued maturation of the motor areas of cortex and cerebellum contribute to these experience-dependent improvements. During this period, there is also increasing control of individual digits. Whereas the newborn uses all digits in unison, as the child matures, increasing control of individual digits becomes possible, so that by about 5 or 6 years of age, most children are able to tie their own shoes.
Development From 5 Years Into Adulthood
Once the basic sensory and motor controls are in place, experience and increases in muscular strength become the primary factors in the further development of motor skills. Errors in movement are detected visually and by sensory structures in our joints and muscles. Visual feedback generally tells us the effectiveness of the movement, whereas feedback from our muscles and joints tells us how we achieved that end. Both the outcome and feedback from our muscles and joints are used to improve skills. Thus, improvement of motor skills in late childhood and adolescence is dependent on maturation of peripheral tissues (e.g., muscles), but also on improving central and peripheral coordination through practice. Thus, the little league pitcher learns to throw a curve ball, or the pianist learns to play piano compositions of increasing spatial complexity (different combinations of digits) and temporal complexity (rhythms). Sex differences in skilled motor behaviors typically appear during this time and are probably due to differences in peripheral anatomy and physiology that emerge during puberty and to social influences that lead to differential practice of different skills in males and females.
There is little evidence to suggest that there is a “critical period” for learning specific skills. For every childhood athletic prodigy, there is one who did not take up the sport until high school. There is little evidence that taping a tennis racket to a 5-year-old will enhance his or her chances of winning at Wimbledon. Thus, although there are generalized benefits from engaging in skilled motor behaviors in the form of improving strength and hand–eye coordination, specific expert skills can be acquired throughout adulthood. In this context, it is interesting to note that in the past 20 years, it has become apparent that the representation of movement control in the brain is not static, but that continued practice results in increased cortical representation of the associate skill throughout adulthood.
Aging And Fine Motor Control
As during development, changes in fine motor skills during aging are dependent on changes in peripheral strength and flexibility and changes in central control of those skills. In the normal aging process, the amount of time it takes to preprogram fine motor sequences increases. However, this effect is much less for highly practiced movements, probably because the earlier practice has made areas of the brain responsible for planning those movements less susceptible to decrement due to age. For example, a skilled piano player who experiences a 20% loss of motor processing ability may experience little decline in piano playing skill relative to the decline experienced for less-practiced skills (e.g., playing ping-pong). Loss of muscle strength may also play an important role in declining motor skills during aging, so that the same little leaguer who could throw a curve ball or fast ball may find a significant loss of these skills during aging. Recent findings are encouraging in that both nervous system controls and muscular strength are responsive to exercise, so that continued engagement in fine motor skills serves to minimize decline of those skills.
- Cheatum, A., & Hammond, A. A. (2000). Physical activities for improving children’s learning and behavior: A guide to sensory motor development. Champaign, IL: Human Kinetics.
- Gallahue, L., & Ozmun, J. C. (1995). Understanding motor development: Infants, children, adolescents, adults. Madison, WI: Brown & Benchmark.
- Haywood, K. M. (2001). Life span motor deChampaign, IL: Human Kinetics.