Different Error Size During Locomotor Adaptation Affects Transfer to Overground Walking Poststroke

Background. Studies in neurologically intact subjects suggest that the gradual presentation of small perturbations (errors) during learning results in better transfer of a newly learned walking pattern to overground walking. Whether the same result would be true after stroke is not known. Objective. To determine whether introducing gradual perturbations, during locomotor learning using a split-belt treadmill influences learning the novel walking pattern or transfer to overground walking poststroke. Methods. Twenty-six chronic stroke survivors participated and completed the following walking testing paradigm: baseline overground walking; baseline treadmill walking; split-belt treadmill/adaptation period (belts moving at different speeds); catch trial (belts at same speed); post overground walking. Subjects were randomly assigned to the Gradual group (gradual changes in treadmill belts speed during adaptation) or the Abrupt group (a single, large, abrupt change during adaptation). Step length asymmetry adaptation response on the treadmill and transfer of learning to overground walking was assessed. Results. Step length asymmetry during the catch trial was the same between groups ( P = .195) confirming that both groups learned a similar amount. The magnitude of transfer to overground walking was greater in the Gradual than in the Abrupt group ( P = .041). Conclusions. The introduction of gradual perturbations (small errors), compared with abrupt (larger errors), during a locomotor adaptation task seems to improve transfer of the newly learned walking pattern to overground walking poststroke. However, given the limited magnitude of transfer, future studies should examine other factors that could impact locomotor learning and transfer poststroke.

WAYS FOR RECONSTRUCTION OF NONCOMMERCIAL COPPICE OAK STANDS IN LEFT-BANK FOREST-STEPPE ZONE

The article reports new results on the reconstruction of the noncommercial weakened coppice oak stands in the Left-bank Forest-Steppe zone, Ukraine. For the first time, a technology of reconstruction of coppice stands into the mixed seed natural or planted ones is proposed through regeneration felling with the elements of even gradual, group successive and strip gradual felling with a continuous cutting of 25 m width strips. The use of the technologies that combine regeneration felling, selective sanitary felling and thinning in conjunction with silvicultural activities will allow to form mixed seed natural or planted stands of different ages from noncommercial weakened coppice oak forests and significantly increase their productivity and sustainability.

Stability of visual acuity after cessation of occlusion therapy in patients of amblyopia

Background: It is generally recognized that most children with amblyopia have an improvement of visual acuity (VA) with treatment, little is known about the course of vision once treatment is decreased or stopped in a child. The treatment of amblyopia in children is frequently discussed in the literature; however, there is a lack of research into which method of treatment cessation is the most appropriate once therapy has been completed. We undertook this specifically designed prospective study to directly compare the potential relationship between the method of therapy cessation and the short-term (12-weeks) recurrence of amblyopia.Methods: Fifty children of 5-14 years of age group with different types of amblyopia fulfilling the inclusion criteria were included in the study. Once BCVA was achieved, the subjects were randomized into one of two groups; abrupt cessation group or therapy tapering group. In subjects of tapered group occlusion was reduced from full-time occlusion to 50% of waking hours at BCVA and then additional by 50% at the 4-week’s study visit with occlusion being discontinued completely at the 8-week’s visit. All subjects in the abrupt cessation group stopped their full-time occlusion completely at the Best corrected visual acuity (BCVA). All subjects were followed for 3 consecutive 4-weeks intervals, for a total of 12 weeks, to assess the short-term recurrence rate of amblyopia.Results: The overall results show that at 12-weeks study outcome visit, 9 of the 50 subjects developed recurrence. Out of the total of 9 recurrences, 5 (20%) occurred in abrupt cessation group and 4 (16%) occurred in gradual cessation group. Comparing the time of occurrence of recurrence of amblyopia between the 2 studied groups, the recurrence of amblyopia was more during first 4 weeks of study 60% in abrupt group, whereas in gradual group all the recurrences occurred between 8 and 12 weeks visits. The pre-treatment VA and BCVA had a significant impact on the recurrence of amblyopia.Conclusions: In present study, the results demonstrate that the overall risk of amblyopia recurrence is 18% and the difference in the risk of amblyopia recurrence between the abrupt cessation group and the gradual cessation group (20% vs. 16%) is not statistically significant.

Interacting Learning Processes during Skill Acquisition: Learning to control with gradually changing system dynamics

ABSTRACTThere is increasing evidence that sensorimotor learning under real-life conditions relies on a composition of several learning processes. Nevertheless, most studies examine learning behaviour in relation to one specific learning mechanism. In this study, we examined the interaction between reward-based skill acquisition and motor adaptation to changes of object dynamics. Thirty healthy subjects, split into two groups, acquired the skill of balancing a pole on a cart in virtual reality. In one group, we gradually increased the gravity, making the task easier in the beginning and more difficult towards the end. In the second group, subjects had to acquire the skill on the maximum, most difficult gravity level. We hypothesized that the gradual increase in gravity during skill acquisition supports learning despite the necessary adjustments to changes in cart-pole dynamics. We found that the gradual group benefits from the slow increment, although overall improvement was interrupted by the changes in gravity and resulting system dynamics, which caused short-term degradations in performance and timing of actions. In conclusion, our results deliver evidence for an interaction of reward-based skill acquisition and motor adaptation processes, which indicates the importance of both processes for the development of optimized skill acquisition schedules.

Changes in corticospinal excitability during reach adaptation in force fields

Both abrupt and gradually imposed perturbations produce adaptive changes in motor output, but the neural basis of adaptation may be distinct. Here, we measured the state of the primary motor cortex (M1) and the corticospinal network during adaptation by measuring motor-evoked potentials (MEPs) before reach onset using transcranial magnetic stimulation of M1. Subjects reached in a force field in a schedule in which the field was introduced either abruptly or gradually over many trials. In both groups, by end of the training, muscles that countered the perturbation in a given direction increased their activity during the reach (labeled as the on direction for each muscle). In the abrupt group, in the period before the reach toward the on direction, MEPs in these muscles also increased, suggesting a direction-specific increase in the excitability of the corticospinal network. However, in the gradual group, these MEP changes were missing. After training, there was a period of washout. The MEPs did not return to baseline. Rather, in the abrupt group, off direction MEPs increased to match on direction MEPs. Therefore, we observed changes in corticospinal excitability in the abrupt but not gradual condition. Abrupt training includes the repetition of motor commands, and repetition may be the key factor that produces this plasticity. Furthermore, washout did not return MEPs to baseline, suggesting that washout engaged a new network that masked but did not erase the effects of previous adaptation. Abrupt but not gradual training appears to induce changes in M1 and/or corticospinal networks.

Is there a specific weakness in staple strength around the break of season?

In a Mediterranean climate the weak point of the staple normally occurs at the break of season in autumn, but it is not clear whether the staple simply breaks at the minimum fibre diameter or whether there is a specific weakness at this time. Three hypotheses were tested to determine if specific environmental effects on staple strength could be detected under field conditions. First, environmental stresses associated with rainfall and low temperature, resulting in a sudden disruption of warm summer–autumn conditions and lack of feed, may cause follicle shutdown. Second, the sudden decline in feed available following the rain event and the response of sheep to chase the green pick rather than eat the available dry feed may reduce the flow of nutrients to wool. Third, the slow adaptation by rumen microorganisms to changes in the diet from dry to green pasture may result in a further reduction of nutrients available to the wool follicle. We compared a group of sheep managed to minimise nutrient intake fluctuations at the break of season with a group grazing under normal farm practice and tested the hypothesis that a specific lowering of staple strength is associated with the break of season. On 2 April (3 days after the first rains of the season), 120, 18-month-old Merino wethers were allocated to 2 groups, paddock and yard. The paddock group comprised sheep following normal farm practice. The yard group was confined to yards and fed to maintain liveweight, to determine whether the break in the staple was associated with the rainfall event or with the subsequent changes in feed intake. These animals were left off feed for 4 days beginning 24 April. Within each group, 2 separate treatments were imposed. The paddock group was split, and half were moved into covered pens inside a shearing shed on 15 May, a few days before a second major rainfall event, to examine directly stresses associated with rainfall. The sheep from the yard group were kept as a single mob until 3 June, when they were split into 2 groups, sudden and gradual, in relation to their release onto green pasture, to examine the effect of adaptation time to green feed on the flow of nutrients to wool and staple strength. The sudden group was released onto green pasture, while the gradual group was given access to the pasture for increasing periods over the next week. The point of break was delayed by moving sheep into yards after the initial rainfall, suggesting that the rain event per se was not the direct cause of the break in the staple in this experiment. Furthermore, protecting the paddock sheep against the second major rainfall event by shedding half of them did not affect staple strength. The point of break in the staple in the yard group occurred after an accidental 4-day feed deprivation period. This indicates that even short periods of liveweight loss from feed deprivation due to poor or inattentive management when sheep are in low nutritional condition at this time of the year may precipitate the point of break. The rate of release onto green feed after yarding did not significantly affect staple strength and we conclude this was not an important factor. We conclude that neither stress associated with rainfall nor adaptation of ruminal microorganisms to the change in feed weakened the wool.