Prolonged Repetition Research Articles

Kinematic effects of repeated turns while running

In team sports, non-contact ACL and MCL injuries occur during abrupt changes of direction, like turns or cutting manoeuvres. Fatigue affects dynamic neuromuscular control and increases knee injury risk. This study analysed how lower limb joints and centre-of-mass kinematics are affected throughout a high-intensity running protocol involving repeated 180°-turns. Twenty young men (18–23 years, BMI: 20.8–24.4 kg m−2) completed a 5-m shuttle running trial lasting 5 min at an average speed of 75% of their maximum aerobic speed. During the test, cardio-metabolic parameters were obtained, together with joints and centre-of-mass kinematics, using a motion capture system. Kinematic data were compared between the first and the last minute of exercise. Perceived exercise intensity ranged from “hard” to “maximum exertion” and post-exercise lactate concentration ranged from 5.4 to 15.5 mM. The repetition of 180°-turns induced a substantial reduction of hip (−60%, p < .001, large effect) and knee flexion (−40%, p = .003, medium-to-large effect), and an increase of hip adduction and internal rotation (+25–30%, p < .05, medium-to-large effect). Since such movements are factors increasing the likelihood of non-contact knee injuries, we concluded that the prolonged repetition of turns may expose participants to increased risk of ligament failure. Prevention programmes should include discipline-specific neuromuscular training especially in late practices.

Transient and Persistent UP States during Slow-wave Oscillation and their Implications for Cell-Assembly Dynamics

The membrane potentials of cortical neurons in vivo exhibit spontaneous fluctuations between a depolarized UP state and a resting DOWN state during the slow-wave sleeps or in the resting states. This oscillatory activity is believed to engage in memory consolidation although the underlying mechanisms remain unknown. Recently, it has been shown that UP-DOWN state transitions exhibit significantly different temporal profiles in different cortical regions, presumably reflecting differences in the underlying network structure. Here, we studied in computational models whether and how the connection configurations of cortical circuits determine the macroscopic network behavior during the slow-wave oscillation. Inspired by cortical neurobiology, we modeled three types of synaptic weight distributions, namely, log-normal, sparse log-normal and sparse Gaussian. Both analytic and numerical results suggest that a larger variance of weight distribution results in a larger chance of having significantly prolonged UP states. However, the different weight distributions only produce similar macroscopic behavior. We further confirmed that prolonged UP states enrich the variety of cell assemblies activated during these states. Our results suggest the role of persistent UP states for the prolonged repetition of a selected set of cell assemblies during memory consolidation.

Exploring the repetition paradox: The effects of learning context and massed repetition on memory

Although repetition is generally assumed to enhance the accessibility of memory for rehearsed material, recent research has suggested that prolonged repetition might actually be detrimental under some conditions. In the present work, we manipulated repetition duration and learning condition (intentional vs. incidental) in an effort to clarify the relationship between repetition and memory. Replicating previous findings, memory for repeated items declined with increased repetition under incidental-learning conditions. However, increased repetition had the opposite effect under intentional-learning conditions. Taken together, these results provide evidence for distinctive mechanisms of memory acquisition during repetition that vary depending on learning context.

Differential cross-tolerance development between single and repeated immobilization stress on the antinociceptive effect induced by β-endorphin, 5-hydroxytryptamine, morphine, and WIN55,212-2 in the inflammatory mouse pain mode

We have evaluated the possible underlying mechanisms of immobilization stress-induced analgesia (SIA) by behavioral cross-tolerance studies and molecular studies. In the behavioral studies, the cross-tolerance between single or repeated immobilization SIA and the antinociceptive effects of β-endorphin, morphine, 5-hydroxytryptamine (5-HT), or WIN55,212-2 were assessed. Both single and repeated (×7) immobilization stress significantly attenuated the β-endorphin and 5-hydroxytryptamine-induced antinociception in the 2nd phase of formalin response, respectively. However, these cross-tolerances disappeared in prolonged repetition of the stress (×14). Neither single nor repeated (×7 and ×14) immobilization stress affected the antinociceptive effect of morphine or WIN55,212-2 at all. We also found that immobilization stress activated hypothalamic proopiomelanocortin (POMC) gene and β-endorphin expression. Since, it has potent inhibitory activity on the noxious stimuli-induced POMC expression, immobilization stress seemed to dissipate the POMC gene expression process. Meanwhile, we did not find any changes in the opioid receptors' (mu-, delta- and kappa-receptor) and the cannabinoid receptors' (CB1 and CB2) expressions in the midbrain regions elicited by single or repeated stress. These results suggested that a single immobilization stress activates the descending pain modulatory system, which is mainly mediated through endorphinergic and serotonergic activation. Moreover, the tolerance of SIA induced by repeated stresses may be due to the prolonged activation of these systems induced by repeated immobilization.

Rate-dependent impairments in repetitive finger movements in patients with Parkinson's disease are not due to peripheral fatigue

Performance of repetitive finger movements is an important clinical measure of disease severity in patients with Parkinson's disease (PD) and is associated with a dramatic deterioration in performance at movement rates near 2 Hz and above. The mechanisms contributing to this rate-dependent movement impairment are poorly understood. Since clinical and experimental testing of these movements involve prolonged repetition of movement, a loss of force-generating capacity due to peripheral fatigue may contribute to performance deterioration. This study examined the contribution of peripheral fatigue to the performance of unconstrained index finger flexion movements by measuring maximum voluntary contractions (MVC) immediately before and after repetitive finger movements in patients with PD (both off- and on-medication) and matched control subjects. Movement performance was quantified using finger kinematics, maximum force production, and electromyography (EMG). The principal finding was that peak force and EMG activity during the MVC did not significantly change from the pre- to post-movement task in patients with PD despite the marked deterioration in movement performance of repetitive finger movements. These findings show that the rate-dependent deterioration of repetitive finger movements in PD cannot be explained by a loss of force-generating capacity due to peripheral fatigue, and further suggest that mechanisms contributing to impaired isometric force production in PD are different from those that mediate impaired performance of high-rate repetitive movements.

Fast T1 mapping on a whole-body scanner.

A method for the fast acquisition of quantitative T1 maps is presented. It is based on the acquisition of a series of snapshot fast low-angle shot (FLASH) images after inversion of the magnetization. A drawback of this method is the necessity for a sufficiently long relaxation delay before each inversion pulse, leading to long experimental times if averaging or segmentation is required. Thus implementation of this method on a whole-body scanner is problematic, as the longer gradient rise times provide prolonged repetition times, which makes segmentation indispensable to provide a sufficient temporal resolution. We present a modification of the method that allows for reduction in the intermediate relaxation delays and thus for considerably reduced experimental durations.

Halfscan: Clinical applications in MR imaging

A series of phantom experiments was performed to evaluate the effects of half-Fourier scanning, also known as Halfscan, on signal-to-noise and in-plane resolution. Resolution was not demonstrably effected with the available phantoms and signal-to-noise was seen to vary as the square root of time independent of the implementation of Halfscan. Evaluation of the Halfscan technique was made using data from 240 patients. The technique was found to “salvage” examination in an estimated 70% of uncooperative patients where motion artifact or other patient concerns would have precluded clinically useful studies. Halfscan was also combined with other techniques such as increased number of signal acquisitions, prolonged repetition times and three-dimensional Fourier transform technique.

The Effects of Prolonged Stimulus Repetition with Repeated Switching of Target Status on the Orienting Response in Schizophrenia and Depression

Schizophrenic patients are frequently orienting nonresponders to innocuous stimuli, become responsive to significant target signals, and become hyporesponsive again on prolonged repetition. We wish to a) determine whether schizophrenic patients can display orienting response (OR) flexibility, responding to newly designated targets and ceasing to respond to newly designated nontargets; b) determine whether renewed hyporesponding can be averted with reminders of target relevance and repeated introduction of new targets; and c) compare schizophrenics with depressives and normal controls. Fifty schizophrenics (14 drug free), 50 depressives (20 drug free), and 50 normal controls receive four trial blocks involving the same sequence of 16 1000- or 2000-Hz tones delivered to either the right or left ear. A subsample of each group (N = 14) receives all blocks as a simple habituation series; others (N = 36) have to press a pedal for designated target signals (left ear or right ear, 1000 Hz or 2000 Hz), ignoring all nontarget tones. On each trial block, a new target signal is defined, and previous targets are discarded. Skin conductance and finger pulse amplitude analyses are presented. Both patient groups show enhanced ORs to newly relevant targets and ceased ORs to newly irrelevant former targets as well as normals. Both show OR decline with target repetition despite reminders and new targets.

Semantic satiation affects category membership decision time but not lexical priming.

Experiments 1 and 2 examined the effects of semantic satiation on category membership decision latency. Subjects overtly repeated the name of a category either 3 or 30 times, and then decided whether or not a target exemplar was a member of the repeated category. Experiment 1 obtained some evidence that member decisions are slower and nonmember decisions are faster following 30 repetitions, but only the interaction was reliable. Experiment 2 confirmed only that member decisions are slower following satiation of the category name. The results support the hypothesis that prolonged repetition of a word reduces the availability of semantic information related to that word. Experiment 3 showed that the magnitude of priming in the lexical decision task is unaffected by satiation of the prime. Several general approaches to understanding semantic satiation are discussed. The most parsimonious account assumes that satiation affects the links or pathways connecting concepts in the satiated category. The net effect is to decrease the rate of search and associative spread of activation in conceptual structures.

Changes in frequency and distress during prolonged repetition of obsessional thoughts.

Five obsessive-compulsive patients were treated for intrusive thoughts by three sessions of repetition of the thought. Within- and between-session changes in both frequency and subjective distress lent only partial support to the habituation and conditioned inhibition models which have been used to account for the effects of prolonged repetition. Alternative explanations should be sought.

Slow potentials and spike activity of cortical neurons during development of internal inhibition.

1. During the formation of different forms of internal inhibition to unreinforced flashes similar changes in electrical activity are observed in the cortex of waking rabbits, in the form of weakening of EP and a decrease in the activation of neurons of the sensomotor cortex and strengthening of the late components of EP with a corresponding alternation of inhibition and an increase in the discharge frequency of neurons in the visual cortex. 2. When reinforcement stimuli were used in the experiments (the formation of delaying inhibition, conditioned inhibition, differentiation) and in the first stage of extinction, changes in electrical indices are located mainly in the analyzer of the conditioned stimulus. 3. During prolonged repetition of unreinforced stimuli the changes in electrical activity become more generalized. High-amplitude polyrhythmic waves of potentials, which correspond to irregular grouped discharges of neurons, separated by inhibitory pauses, develop in the cortical representation of both conditioned and reinforcing stimuli. 4. The results are evidence in support of the view that during the formation of internal inhibition conditions favorable for strengthening of hyperpolarization are created in the cortex and, possibly, in other brain structures; recurrent inhibition probably plays an important role in the organization of this hyperpolarization.

Arousal and intracranial self-stimulation in split-brain monkeys

Split-brain monkeys were delivered noncontingent unilateral stimulation at sites in the vicinity of the lateral hypothalamus and the internal capsule. At self-stimulation sites, this produced suppression of alpha rhythm in both hemispheres of animals with either telencephalic or diencephalic commissurotomies. The time course of the alpha suppression in each hemisphere was identical and no habituation was seen with prolonged repetition of stimulation. Bilateral nonhabituating arousal was still obtained after lesion of the hypothalamus, including the medial forebrain bundle, contralateral to the self-stimulation site. Non-self-stimulation sites showed habituation. Bilateral nonhabituating cortical arousal may be involved in the bilateral reinforcement of learning produced by unilateral intracranial self-stimulation in split-brain animals.

Human eeg during formation of conditioned reflexes

The EEG changes, with prolonged repetition of conditioned reflexes (elaborated according to the method of defensive and speech-motor conditioned reflexes), were studied in 60 healthy individuals.