Compensatory Actions Research Articles

Functional organization of velar movements following jaw perturbation.

Mechanical perturbation of the articulators has been used to examine motor control principles underlying speech production. One common observation is that if one member of a group of functionally related articulators is perturbed during articulation, the other members compensate. The compensatory response patterns reflect sensorimotor organization for speech, and thus have implications for speech production theories. The present experiment examines such linkages by analyzing the spatiotemporal response patterns to jaw perturbation displayed by the anatomically linked and remote jaw, upper lip, lower lip, and velum. Subjects were fitted with a mandibular prosthesis to allow delivery of jaw-lowering, random (20% of the trials) perturbations during productions of the utterance /mabnab/. Lip, jaw, and velar kinematics were recorded optoelectronically and simultaneously with the acoustic signal. These movements exhibited compensatory actions including increased movement displacement and oral closing velocity. Movement duration changes were also observed. Coordinative timing among lips, jaw, and velum was generally maintained following the perturbation. Variations in that timing appear to depend on the temporal relations between the onset of the perturbation and the onset of the component speech event. [Work supported by NIH Grant Nos. DC-00121, and DC-00594 to Haskins Laboratories.]

The influence of limb alignment on the gait of above-knee amputees

Biomechanical gait tests on above-knee amputees were conducted in which the alignment of the prosthesis was changed systematically. An eight-segment biomechanical model of the above-knee amputee was developed to analyse and present the three-dimensional kinematic and kinetic data obtained. The effects of alignment changes on the above-knee amputees' gait were studied in terms of the angular displacements of the lower limbs, ground reactions and intersegmental moments. It was found that following the alignment changes the angular displacement at the hip joint on the prosthetic side showed compensatory actions by the amputee. The ground reaction force was sensitive to alignment changes, and in particular, the changes in the characteristics of the fore-aft component of the ground force could be related to the alignment changes. The antero-posterior intersegmental moments at the prosthetic ankle and knee joints were evidently influenced by alignment.

Site-directed mutagenesis of arginine 179 of thymidylate synthase. A nonessential substrate-binding residue.

X-ray structural studies have shown that Arg-179 of thymidylate synthase is complexed to bound inorganic phosphate or to the 5'-phosphate of the bound substrate dUMP. The importance of Arg-179 to the structure/function of thymidylate synthase is also indicated by its complete conservation among the 17 thymidylate synthases thus far sequenced. In the present work, Arg-179 has been replaced by Thr, Ala, Lys, and Glu using site-directed mutagenesis with a mixture of four synthetic oligonucleotides as primers. The mutant proteins complement thymidylate synthase-deficient Escherichia coli and show high enzyme activity. Each of these mutants has been purified to homogeneity, partially sequenced to verify the mutation, and has had its steady state kinetic parameters determined. The most significant effect of all mutations is localized to a decrease in the net rate of association of thymidylate synthase with dUMP; the Lys mutant also shows an apparent increase in the dissociation constant of the folate cofactor of the reaction. The high activity in the mutant enzymes is explained by "plasticity" of the enzyme and compensatory actions of the other Arg residues. Why the Arg-179 residue has been conserved during evolution remains an open question.

Rational drug therapy based on understanding the pathophysiology of hypertension.

Increased peripheral vascular resistance is the hemodynamic hallmark of chronic hypertension. Evidence suggests that Ca2+ is vital in mediating vasoconstrictive mechanisms. Calcium channel blockers correct the specific arteriolar vasoconstrictive mechanism without unwanted compensatory actions. Human primary hypertension may also be related to volume variations in which renal influences contribute to elevated arterial pressure and diuretics may be necessary to control the hypertension. Patients in whom neurogenic-mediated vasoconstriction predominates show increased catecholamine production and renin release. These patients can be treated with either alpha- or beta-receptor blocking agents or with converting enzyme inhibitors. Recent biochemical and pharmacological advances and a clear understanding of cardiovascular physiology have allowed more rational and individualized therapy for hypertensive patients, using minimal numbers of drugs in their minimal effective doses. Long-term monotherapy is now possible for different subgroups because of the specific and selective actions of newer antihypertensive agents.

Simulation of bipedal walking by model having zero moment joints. (2nd report. Reduction of compensatory actions and interpretation of numerical results).

The lost function at zero moment joint (ZMJ) is compensated by the remaining normal joints. The compensatory actions are so great that a stable walking can not be realized in some cases. Methods to reduce the compensation are introduced as follows: walking velocity, lateral motion of pelvis, and inclination of legs at the instant of heel contact. A gait that is realized by a slower waling with wider step width and lateral inward motion of pelivis during stance phase can reduce the strength of compensations. The walking style resembles to that of men or infants. passive elastic elements attached at both ankles (ZMJ) contribute to make the upper torso almost upright. The passive elements are effective for the correction of abnormal walking. Some applications of results are, also, discussed with respect to the design of locomotive robots.

Cardiac failure, the kidney, renin and atrial peptides.

Cardiac failure is characterised by a marked reduction in renal blood flow. However, urea excretion and glomerular filtration rate remain well preserved until the terminal stages. Intrarenal compensatory actions of the renin-angiotensin system probably effect this compensation. Important interrelations have recently been observed between the renin and atrial peptide systems. The latter, which is activated in cardiac failure, tends to emphasise the useful intrarenal effects while minimising the less valuable peripheral actions of the renin system in that condition.

An ecological theory of orientation and the vestibular system.

In this article we provide evidence against a fundamental assumption of traditional theories of orientation--that gravitoinertial force is perceived. We argue that orientation is based on information that is available in patterns of motion of the organism. We further argue that perception and control of orientation depend not only on information about an organism's motions relative to the local force environment but also on information about the surface of support and about the compensatory actions of the organism. We describe these kinds of information and discuss their availability to, and across, different perceptual systems. The use of this information for the control of orientation is emphasized. We conclude with recommendations for research based on the new approach. How do organisms orient themselves in the environment? To what do they orient? The answer to these questions has seemed so obvious for so long that it is taken for granted: Organisms orient to gravity. They sit, stand, walk, run, throw, catch, dance, and do gymnastics relative to the omnipresent force of gravity. Gravity is probably the most important spatial reference cue for an organism (Schone, 1984, p. 258). Within this context, what are the functions of the perceptual systems? How do the perceptual systems contribute to the achievement and maintenance of orientation in terrestrial environments and in such situations as flight and weightlessness? In this article we analyze the information for orientation that is available to the perceptual systems. Our analysis leads us to two important areas of disagreement with the classical approach to spatial orientation. One is in the nature of the information for orientation; this is discussed in the first half of the article. The other concerns cooperation between perceptual systems in the perception and control of orientation and is dis

The role of the monkey sensory cortex in the recovery from cerebellar injury.

The aim of the study was to investigate the contribution of the primary sensory cortex in the compensation of cerebellar deficits during self-paced movements. For this purpose, monkeys were trained on motor tasks which required goal-reaching and independent finger movements. The intermediate and lateral deep cerebellar nuclei and the sensory cortex were lesioned in isolation and in sequence and the course of motor recovery was studied on the test performances. The deep nuclei were lesioned by kainic acid injections, the sensory cortex was removed by ablation. Cerebellar lesions in isolation produced obvious deficits at proximal and distal joints, affecting both slow and fast motor adjustments. Only lesions of the anterior portions of the intermediate and lateral deep nuclear complexes produced deficiencies in voluntary movements. Lesions of the posterior portions produced postural disturbances. The process of recovery following cerebellar lesions was slow and, depending on the nature of the task, was found to be differentially disruptive for motor performances requiring fast and slow motor adjustments. The deficits at distal joints appeared to be more enduring than those at proximal joints. Sensory cortical lesions in isolation produced much less severe and more transient motor deficits. They consisted of hand clumsiness and their recovery was fast and reached higher levels of performance than following cerebellar lesions. When the sensory cortex was removed secondarily to a cerebellar lesion and after recovery from the cerebellar deficits, the initially recovered motor performance became much worse again (decompensation). Removal of the sensory cortex prior to a cerebellar lesion exaggerated the cerebellar deficits and severely limited their recovery. Slow and fast motor performances were completely abolished for three weeks following sequential lesions. Signs of recovery subsequently appeared and stabilized at low levels of performance by five to seven weeks. The effects of combined, sequential cerebellar and sensory cortical lesions were much worse than expected if the effects from the two lesions were merely additive. This indicates that there is some functional interrelationship between the sensory cortex and the cerebellum, which promotes compensation. The somatosensory cortex appears to play a crucial role in the process of recovery from cerebellar motor deficits and it is likely that sensation is an important component in the process of recovery. It is suggested that the sensory cortex exerts its compensatory actions via a structure or structures which receives convergent cerebellar and sensory cortical inputs.

Role of renal prostaglandins and the effects of nonsteroidal anti-inflammatory drugs in patients with liver disease

Renal prostaglandins have several key functions in patients with severe liver disease and ascites. Increased activity of vasodilatory prostaglandins counters the underlying impairment in renal perfusion and the effects of vasoactive hormones. Prostaglandins also participate in renin secretion, renal diluting ability, sodium excretion, the action of diuretics, and, possibly, the development of the hepatorenal syndrome. Nonsteroidal anti-inflammatory drugs inhibit these compensatory actions of prostaglandins and cause a functional reduction in glomerular filtration rate and an impairment in sodium and fluid excretion. The severity of these nephrotoxic effects depends on the potency of the drug in inhibiting renal prostaglandins and on patient susceptibility. Patients with ascites and avid sodium retention, sodium-restricted diets, or concurrent diuretic use are most at risk. If nonsteroidal anti-inflammatory drugs must be administered to these patients, the type of drug should be carefully selected and renal function should be closely monitored.

Effects of premotor cortex cooling upon visually initiated hand movements in the monkey

The premotor cortex was temporarily impaired with a local cooling method and effects of the cooling upon visually initiated hand movement and upon cortical field potentials associated with the movement were examined in the monkey. Bilateral cooling of the premotor cortex (the dorsolateral part of presumed area 6) disorganized the well-trained reaction-time movement, in which a lever was lifted within duration of the light stimulus (about 0.5 s) delivered at random time intervals. Accordingly the monkey showed nearly self-paced, random movements with little regard to the light stimulus during the cooling. To obtain a certain number of appropriate reaction-time movements, about twice as many as trials in normal conditions were required during the premotor cooling. Unilateral (contralateral to the moving hand) cooling of the premotor cortex produced similar but weak effects. No appreciable paresis was observed by cooling. Such effects of cooling the premotor cortex faded in successive experimental days of several weeks or even in successive cooling sessions on the same day. This was in contrast with effects of motor cortex cooling which were reported to be almost unfaded on repetition. It is suggested that compensatory actions are quickly elicited in some other structure even on temporal impairment of the premotor cortex and that the actions are gradually accumulated on repetitive cooling with days and weeks.

Dynamic control of the perioral system during speech: kinematic analyses of autogenic and nonautogenic sensorimotor processes.

Afferent contributions to the motor control of speech were evaluated by applying unanticipated loads to the lower lip during the combined upper lip-lower lip gesture associated with the oral closing movements for a "b" sound. Loads were introduced randomly in approximately 15% of the trials to minimize subject anticipation or adaptation. A total of 490 load trials (in five naive subjects) were distributed within a restricted interval (100 ms) centered on the initiation of agonist muscle contraction associated with the lip-closing movements. Kinematic adjustments of the upper and lower lips to these perturbations were examined in detail. In all subjects, load-induced changes in upper and lower lip displacement, movement time, and closing velocity were statistically significant and observed the first time a perturbation was introduced. Load timing variations within the target interval resulted in systematic changes in the site of the compensatory adjustments (upper versus lower lip) and in the magnitude of the kinematic responses. These kinematic changes appeared to reflect the dynamic nature of underlying control processes and clearly contrasted the different response characteristics of autogenic (lower lip) and nonautogenic (upper lip) compensatory actions. Although both upper and lower lip adjustments contributed to perturbation compensations, autogenic responses were found to predominate when loads occurred 20-55 ms before muscle activation. For these early loads, autogenic responses provided approximately 75% of the total compensation. For later loads, when the evolving speech motor action was more time constrained, nonautogenic (open-loop) compensations predominated, providing approximately 65% of the total compensation. The variations in upper and lower lip compensatory response magnitude did not parallel the time course of facial muscle activation. Lower lip kinematic adjustments were reduced 10-15 ms prior to the onset of agonist muscle activation, whereas upper lip adjustments increased in magnitude 10-20 ms after agonist onset. Apparently the dynamic modulation of these responses is controlled independently from facial motoneuron excitation, possibly involving sensorimotor processing via supranuclear centers. Overall the compensatory movement displacements were highly related to the magnitude of the perturbation displacement, especially for loads introduced prior to agonist muscle onset, reflecting a well-calibrated readjustment.(ABSTRACT TRUNCATED AT 400 WORDS)

Bulimia and alcoholism: Two sides of the same coin?

There has been an epidemic rise recently in the number of women evidencing bulimia, an addictive cycle of binge eating and purging of food. A significant number of bulimics are reported to abuse alcohol and drugs as well. There is a need to account for the serious problem of symptom substitution in substance abusing populations. Substance abuse is considered within the framework of ego growth, with a particular focus on developmental deficits and compensatory actions. Alcohol, food, and drugs all serve as attempts to minimize the impact of ego deficits. In this regard, the function the substance serves is more crucial than the specific substance abused. A treatment model for bulimia is outlined which addresses both the addiction at hand and the underlying developmental deficits.

ENERGY: GOVERNMENT POLICY OR MARKET RESULT?

ABSTRACTFrom the Truman presidency through that of Carter, the United States worked fitfully toward the development of an energy policy. Now, consistent with the “free market — get government off the backs of the people” philosophy of the Reagan Administration, the 1981 National Energy Policy Plan proposes that “individual choices” and “reliance on market decisions” replace regulations and subsidies in the nation's strategy for energy.This paper starts from the assumption that the Spring, 1982 oil “glut” may turn out to be a rather temporary thing. If one therefore wants to pursue a policy strategy that will protect us in the case of sudden short‐term supply disruptions and also work toward long‐term energy supply diversification, how far will market reliance carry us? What is a range of policies and programs that might usefully supplement the market? What are the externalities for which compensatory actions may still be needed if one would like to employ the market strategy as a basic thrust?The scope of the paper includes contingency planning, synthetic fuel development, renewables (especially solar energy), conservation, equity issues, environmental externalities, and the conceptualization of policies differentiated as “energy,”“environmental,” or “economic.”

Skull growth after coronal suturectomy, periostectomy, and dural transection.

Using radiocephalometric procedures, the authors examined the separate effects of suturectomy, periostectomy, and dural transection on the growing skull in young rabbits. When the coronal suture was surgically removed during normal growth, The freed frontal and parietal bones separated at a significantly accelerated rate. No accelerated separation was found when only the overlying periosteum and aponeurosis were transected. Furthermore, no additional separation was observed when the dura mater and falx cerebri were transected following suturectomy. Analysis of growth at the adjacent frontonasal and anterior lambdoid sutures suggested that the accelerated separation of bones after suturectomy was compensated for by reduced growth at these adjacent sutures. The result of these compensatory actions was that the total length of the skull remained unchanged. This study not only supports earlier observations that sutures grow in response to extrinsic separative forces but, significantly, that the suture tissue itself, rather than the dura or pericranium, acts as a restraint during normal translatory growth.

A Decision-Theoretic Model of the Sampling Behavior of the Human Process Monitor: Experimental Evaluation

Subjective sampling behavior was compared with that of an optimal dynamic decision model for a process monitoring task with and without compensatory actions. The cost structure (ratio of cost of sampling to cost of the process exceeding certain critical threshold limits) and the threshold limit were the two independent variables. The performance of the subjects tended to be suboptimal with significant differences between the subjective and the normative sampling intervals. The extent and direction of these differences depended on the values of the two independent variables. However, for the no-control task, significant correlations existed between the subjective and the normative sampling intervals for all subjects and all experimental conditions, while only three of the eight control cases produced such significant correlations.

Regulatory actions of human stretch reflex.

1. The stretch reflex in the elbow flexor musculature was studied in 23 human subjects. The subjects were required to establish an initial force equivalent to 10% maximum at a prescribed initial length; mechanical disturbances delivered at random times increased load force to 15% or reduced it to 5%. We measured arm force, displacement, and EMG (usually biceps); acceleration was calculated from displacement, and average responses from sets of 10 like trials. 2. Modification of the stretch reflex was studied by comparing average responses obtained with different instructions, but with the same disturbance. The usual introductions were "compensate for arm deflection" and "do not intervene voluntarily". The initial response did not depend on instruction; changes in response that depended on instruction began abruptly after a latent period which ranged from 70 to 320 ms (measured from force and acceleration), depending on conditions and subject. The latency became longer (10-50 ms) and more variable when the subject did not know the direction of disturbance in advance. This and other observations indicate that modifications of the stretch reflex are not produced by servo actions. They are produced by triggered reactions, which occur at both short and long latencies and which have properties resembling the movements produced in a reaction-time task. 3. We confirmed that most subjects can suppress triggered reactions when the instruction calls for no intervention, leaving an unmodified reflex response. This response consists of a compliant deflection of the arm in the direction of the disturbance. 4. The compensatory actions associated with unmodified stretch (and unloading) reflexes were assessed from EMG responses of biceps. During a 300-ms transient phase, EMG changes were notably asymmetric when responses to symmetric disturbances were compared. Increased force stretched biceps and produced a prominent increase in EMG, whereas decreased force allowed biceps to shorten and produced either an EMG decrease of smaller magnitude or an actual increase. These asymmetric reflex actions produced quite symmetric mechanical responses (arm displacements and forces), which implies the existence of and compensation for nonlinear muscle mechanical properties. This result is discussed in relation to the hypothesis that the function of the stretch reflex is to compensate for variations in muscle properties, thus maintaining stiffness. 5. Effective control of muscle length or joint position does not result from servo action by the stretch reflex. Errors in position are corrected only when triggered reactions are superimposed on the reflex response.

The lengthening effect in sequential estimations of a short interval: an alternative explanation.

Experiments were carried out on the lengthening effect in sequential time estimations. It appeared that lengthening only occurred in the case of intuitive evaluation of an interval. Autocorrelation functions revealed that the estimation process may be described as a series of compensatory actions with respect to the last trial. It was assumed that the last estimate is more or less always experienced as too long or too short. In the resulting correction process the positive corrections reach higher mean values than the negative ones since the upper limit of the interval is not defined. In view of the negative autocorrelation in the last trial it was postulated that the correction process is not random, but is related to sequential response bias, i.e. too many alternations. Subsequently, several presentation and estimation modes were compared. The possibility that lengthening might result from trace decay of the standard stored in memory was doubtful since the phenomenon was also observed in the case of pure production on the basis of verbal instructions only. Apparently, it makes no difference whether a standard is presented or not. The distribution of the time estimates under various conditions revealed that the subject becomes more uncertain in proportion as the amount of external reference given increases, so that estimation process variables seem to be of greater importance than stimulus factors (standard presentation). It was assumed that the temporal memory could be described as a register in which only one event (the last) remains available and forms the subject's frame of reference. Since lengthening appeared to be connected with several cognitive variables of a general nature it was postulated that the effect is not only inherent in time estimation, but may be considered as a phenomenon occurring in repeated estimations of various stimuli as well. This assumption appeared to be correct, as analogous effects were observed in the case of repeated line drawing. It was shown that the increase of the time estimates could be influenced significantly by introducing different risk levels, i.e. the degree of lengthening is a function of the subject's decision criterion. Furthermore, there was some correlation between the compensatory actions and sequential response bias in a randomization task. It is concluded that the lengthening effect does not only show a general character, but that it might be described and explained adequately within the framework of the cognitive theory of time experience in which memory mechanisms, decision theory, and sequential response bias play a significant role.

Det fleirkulturelle perspektivet i grunnskolelærarutdanningane

The article focuses on multicultural education in the Norwegian teacher education programs. We ask to what extent the student teachers experience achieving relevant competence. The findings indicate that the student teachers are relatively satisfied with the competence and skills they achieve. However, they ask for more specific knowledge about the pupils’ religious and cultural background. Knowledge about these factors could, according to the student teachers, be given through a compulsory element in the curriculum focusing on religion and culture. The findings seem to be in accordance with other researches which show that multicultural competence requires that the teachers have knowledge about the cultural background of the different minority groups. On the other hand, it seems like the students are not to any great extent aware that minority students tend to be overrepresented in special education and compensatory actions in schools. This finding indicates that there is a need for putting more emphasis on critical thinking with regards to multiculturalism in the teacher education programs in Norway, and an analytical approach in this context.Keywords: teacher education, multicultural education, critical multiculturalism, religion, culture, BanksNøkkelord: lærerutdanning, flerkulturell utdanning, kritisk multikulturalisme, religion, kultur, Banks

EFFECTS OF BRADYKININ ON FOREARM VENOUS TONE AND VASCULAR RESISTANCE IN MAN.

The effects of intravenous injections of synthetic bradykinin on the vascular dynamics of the forearm were studied in nine normal subjects. A plethysmographic technique was used to measure forearm blood flow and to estimate forearm venous tone. Bradykinin decreased mean systemic arterial pressure, elevated forearm blood flow, and reduced calculated forearm vascular resistance and also venous tone. The venodilatation was preceded by brief venoconstriction which was prevented in five subjects pretreated with the antiadrenergic agent, guanethidine. It is postulated (a) that this venoconstriction is one of the compensatory reflex actions that accompany reduction of systemic arterial pressure, and (b) that the prime effect of bradykinin on both the arterial and the venous beds of the forearm is a direct vasodilatation.