Biomechanics--review of approaches for performance training in spinal manipulation.

Motor skills development is an inherent part of clinical training in health disciplines. The conscious use of educational theory to ground learning is receiving increasing attention across health care education. There are three distinct, yet overlapping, stages of motor skill learning; the cognitive, the integrative or associative, and the autonomous; in which a contextual framework for learning content may be structured. The learning is associated with a mapping of changes within the central nervous system by the interactive mechanisms of adaptation, use-dependent plasticity and operant reinforcement. Successful skill learning requires a sufficient amount of practice and the implementation of relevant feedback strategies in the form of knowledge of performance (KP) or knowledge of results (KR). There is a natural maturation of skills that may be accelerated by feedback. Several factors contribute to stronger skills development. "Mixture-of-experts" models systematically sequence tasks into logical blocks of theory, practice and student reflection on performance. Feedback should involve both KP and KR that compares performance to a tangible standard. Rehearsals should balance use of simulators and volunteer simulated patients to provide the full range of safe and effective learning opportunities prior to students accepting a role as care givers to the public in any clinical setting.

Developmental changes in prehension during childhood.

Recent evidence has shown that the anticipatory control of grip and load force is not innate and develops over several years in childhood. The present study examined the development of grasping behavior by quantifying the relationship between grip force and the vertical acceleration of an object. Children and adults were requested to use a precision grip to lift an instrumented object which varied in size and weight. Grip force, grip force rate and the vertical position and acceleration profiles of the test object were measured or calculated. The results demonstrated the presence of distinct developmental milestones in the maturation of precision grip from 2 to 9 years of age. With 2-year-old children, the peak acceleration was negatively correlated (r=-0.51, n=34, P<0.01) with peak grip force during lifting. By 3 years of age, peak acceleration and peak grip force during lifting became positively correlated (r=0.28, n=104, P<0.01) and the correlation continued to strengthen up to 9 years of age. Variations in the temporal coupling of both peak grip force and peak acceleration also decreased with maturation. Furthermore, starting at 4-years-old, children clearly controlled the acceleration and deceleration of the object in a symmetrical pattern and used a single burst of grip force rate to grasp the object with some regularity, suggesting that the emergence of an anticipatory control strategy had already begun.

Comparing cerebellar and motor cortical activity in reaching and grasping.

The activity of single cells in the cerebellar and motor cortex of awake monkeys was recorded during separate studies of whole-arm reaching movements and during the application of force-pulse perturbations to hand-held objects. Two general observations about the contribution of the cerebellum to the control of movement emerge from the data. The first, derived from the study of whole arm reaching, suggests that although both the motor cortex and cerebellum generate a signal related to movement direction, the cerebellar signal is less precise and varies from trial to trial even when the movement kinematics remain unchanged. The second observation, derived from the study of predictable perturbations of a hand-held object, indicates that cerebellar cortical neurons better reflect preparatory motor strategies formed from the anticipation of cutaneous and proprioceptive stimuli acquired by previous experience. In spite of strong relations to grip force and receptive fields stimulated by preparatory grip forces increase, the neurons of the percentral motor cortex showed very little anticipatory activity compared with either the premotor areas or the cerebellum.

Responses of cerebellar Purkinje cells to slip of a hand-held object.

1. Two monkeys were trained to grasp, lift, and hold a device between the thumb and forefinger for 1 s. The device was equipped with a position transducer and strain gauges that measured the horizontal grip force and the vertical lifting or load force. On selected blocks of 20-30 trials, a force-pulse perturbation was applied to the object during static holding to simulate object slip. The animals were required to resist this displacement by stiffening the joints of their wrists and fingers to obtain a fruit juice reward. Single cells in the hand representation area of the paravermal anterior lobe of the cerebellar cortex were recorded during perturbed and unperturbed holding. If conditions permitted, the cell discharge was also recorded during lifting of objects of various weights (15, 65, or 115 g) or different surface textures (sandpaper or polished metal), and when possible the cutaneous or proprioceptive fields of the neurons were characterized with the use of natural stimulation. 2. On perturbed trials, the force pulse was always applied to the manipulandum after it had been held stationary within the position window for 750 ms. The perturbation invariably elicited a reflexlike increase of electromyographic (EMG) activity in wrist and finger muscles, resulting in a time-locked increase in grip force that peaked at a latency between 50 and 100 ms. 3. The object-slip perturbation had a powerful effect on cerebellar cortical neurons at a mean latency of 45 +/- 14 (SD) ms. Reflexlike increases or decreases in simple spike discharge occurred in 55% (53/97) of unidentified cells and 49% (21/43) of Purkinje cells recorded in the anterior paravermal and lateral cerebellar cortex. 4. The perturbation failed to evoke complex spike responses from any of the Purkinje cells examined. All the perturbation-evoked activity changes involved modulation of the simple spike discharge. The perturbations stimulated the simple-spike receptive field of most Purkinje cells recorded here, which suggests that the short-latency unit responses were triggered by afferent stimulation. Only one Purkinje cell was found with a distinct complex-spike receptive field on the thumb, but this neuron did not respond to the perturbation. It appears that simple- and complex-spike to receptive fields are not always identical or even closely related. 5. The majority of Purkinje and unidentified neurons that responded to the perturbation had cutaneous receptive fields, although some had proprioceptive fields. Seventy-seven neurons were examined for peripheral receptive fields and were also tested with the perturbation.(ABSTRACT TRUNCATED AT 400 WORDS)

Cutaneous afferent activity in the median nerve during grasping in the primate.

Neural activity was recorded from the median nerve of a monkey during grasping and lifting, using a chronically implanted cuff electrode. At the onset of lifting, there was an initial dynamic response during which the intensity of the neural signal increased rapidly. This neural response attained its peak value well before the displacement, the load force or the grip force. The time course and peak of the rectified, integrated neurogram were best correlated with the rate of change of grip force. The neural activity declined exponentially to a steady value following the initial peak. During steady holding the mean amplitude of the neurogram was best correlated with the mean grip force. At the end of the holding phase there was a short burst of neural activity as the monkey relaxed the grip force and released the object. During some blocks of trials pulse perturbations were applied to the object. When the monkey did not increase the grip force in advance of the perturbation, the perturbation produced a relatively large displacement of the object and a burst of neural activity whose onset coincided with the onset of displacement. When the monkey anticipated the perturbation by increasing the grip force during the holding period preceding the perturbation, the perturbation produced a relatively small displacement and relatively little increase in neural activity.

[The evolution of ethnic structure in Quebec's peripheral regions]. / Composition et evolution ethniques de regions peripheriques du Quebec.

"The main purpose of this paper is to analyse, on the basis of census data, the evolution of the ethnic structure of the population in five peripheral regions of Quebec. After some methodological considerations and a brief discussion of the settlement structure, the author describes the evolution of ethnic structure over two sub-periods: 1871-1971 and 1971-1986." (SUMMARY IN ENG AND SPA)

Strategy and learning effects on perturbed movements: an electromyographic and kinematic study.

The effects of practice and movement strategy were studied in a goal-directed movement with different levels of perturbation applied in four independent groups (0%, 20%, 50% or 100%). The phase-plane trajectory data revealed that for all subjects there was a decrease in the mean trajectory variability with learning and that variability was affected by the level of uncertainty confronting the subjects. Both the average electromyographic (EMG) profiles and the mean subject variability for agonist and antagonist muscles decreased with learning. In each experimental group a specific interaction developed between reflex responses and voluntary activity to create a balanced level of EMG activity to improve the performance with learning.

Lateral diffusion in the plasma membrane of maize protoplasts with implications for cell culture.

Plasma-membrane dynamics in live protoplasts from maize (Zea mays L.) roots were characterized and examined for relationships as to the ability of the protoplasts to synthesize new cell walls and develop to cells capable of division. The lateral diffusion-coefficients and mobile fractions of fluorescence-labeled plasma-membrane proteins and lipids were measured by fluorescence photobleaching recovery. Small but significant effects on the diffusion of membrane proteins were observed after treatments with oryzalin or amiprophosmethyl, microtubule-disrupting drugs that increased the mobile fraction, and after treatments with cytochalasins B or D, microfilament-disrupting drugs that decreased the diffusion coefficient. A number of parameters were tested for correlative effects on membrane dynamics and protoplast performance in culture. Protoplasts isolated with a cellulase preparation from Trichoderma viride showed faster membrane-protein diffusion and a lower frequency of development to cells capable of division than did protoplasts isolated with a cellulase preparation from T. reesei. Membrane proteins in maize A632, a line less capable of plant regeneration from callus, diffused with a smaller diffusion coefficient but a greater mobile fraction than did membrane proteins in maize A634, a line with greater regeneration capacity. The plasma membranes of A632 and A634 protoplasts also differed with regard to lateral-diffusion characteristics of phospholipid and sterol probes, although the presence of both rapidly and slowly diffusing lipid components indicated the apparent existence of lipid domains in both A632 and A634. The protoplasts of the two lines did not differ significantly, however, in either wall regeneration or frequency of development to cells capable of division.

[Decision making by intercollegiate basketball players]. / Stratégie de décision d'un groupe de joueurs de basket-ball inter-universitaire.

The results of several studies suggest that in an event incertitude situation, elite athletes can select the appropriate response faster than the novice. There are at least two possibilities to explain such a difference. First, it could be that the elite athlete has more facility to reduce the amount of information he/she is confronted with, that is he/she is able to identify more easily certain sequences and patterns in the play of his/her opponents. Secondly, it is possible that the athlete uses the available information in a different manner. The purpose of this study was to verify the second hypothesis. 10 subjects (5 novices and 4 intercollegiate basketball players) were submitted to a choice time task where the required response was a total body displacement over 2 meters. The results suggest that elite athletes use their knowledge of probability of events in the same way as the novice subjects.