Variability In Cycle Duration Research Articles

Effects of a Cognitively Challenging Agility Boot Camp Program on Balance and Gait in People With Parkinson’s Disease: Does Freezing of Gait Status Matter?

Background and Aim: Individuals with Parkinson’s disease (PD) with and without freezing of Gait (FoG) may respond differently to exercise interventions for several reasons, including disease duration. This study aimed to determine whether both people with and without FoG benefit from the Agility Boot Camp with Cognitive Challenges (ABC-C) program. Methods: This secondary analysis of our ABC-C trial included 86 PD subjects: 44 without FoG (PD−FoG) and 42 with FoG (PD + FoG). We collected measures of standing sway balance, anticipatory postural adjustments, postural responses, and a 2-minute walk with and without a cognitive task. Two-way repeated analysis of variance, with disease duration as covariate, was used to investigate the effects of ABC-C program. Effect sizes were calculated using standardized response mean (SRM) for PD−FoG and PD + FoG, separately. Results: The ABC-C program was effective in improving gait performance in both PD−FoG and PD + FoG, even after controlling for disease duration. Specifically, dual-task gait speed (P < .0001), dual-cost stride length (P = .012), and these single-task measures: arm range of motion (P < .0001), toe-off angle (P = .005), gait cycle duration variability (P = .019), trunk coronal range of motion (P = .042), and stance time (P = .046) improved in both PD−FoG and PD + FoG. There was no interaction effect between time (before and after exercise) and group (PD−FoG/PD + FoG) in all 24 objective measures of balance and gait. Dual-task gait speed improved the most in PD + FoG (SRM = 1.01), whereas single-task arm range of motion improved the most in PD−FoG (SRM = 1.01). Conclusion: The ABC-C program was similarly effective in improving gait (and not balance) performance in both PD−FoG and PD + FoG.

The Last 1200 Years of Rainfall/Runoff Variability along the Central Mexico Pacific Coast Associated with the North American Monsoon

This study presents new evidence for long-term variability in the late Holocene North American Monsoon (NAM), Pacific coast of Mexico. We have carried out a rock magnetic study on two deep-sea sediment cores from the Pacific coast Pescadero Basin. The magnetic intensities estimate total magnetic material and are a proxy for total clastic sediment. Ratios of magnetic intensities estimate the grain size of magnetic material. The rock magnetic data show a decimeter scale, multi-decadal oscillation with fourteen cycles (A-N) over the last 1200 years. These oscillations reflect alternating intervals of stronger/coarser magnetic/clastic flux to the coastal ocean and intervals of weaker/finer magnetic flux. We think these variations are caused by variations in long-term dominance of the NAM; summer (wet) monsoons produce rainy conditions (with runoff) while winter (dry) monsoons produce significant offshore winds, increased upwelling/biological productivity. We can correlate our variability to two other published studies southeast of Pescadero Basin, coastal lake sediments in Laguna de Juanacatlan and a Juxtlahuaca Cave stalagmite. Both of these studies estimate local rainfall. We see evidence of the same pattern of multi-decadal rainfall-runoff variability in these records as we see in Pescadero Basin, which is synchronous to within ±25 years over the last 1200 years. The multi-dacadal pattern of hydrologic variability in all three records varies in cycle duration from ~90-years wet/dry cycles in the Little Ice Age (1400–1850 AD) to ~60-years cycles in the Medieval Climate Optimum (1100–1400 AD). This variability in cycle duration suggests some chaotic nature to the regional NAM climate pattern or some long-term non-linear forcing (PDO?).

Timing of Sierra Nevadan stadial/interstadial variations from 15 to 56 ka

We summarize proxy evidence for stadial/interstadial variability recorded in sediments of three Great Basin lakes – Owens, Mono, and Pyramid. These lakes lie along the eastern margin of the Sierra Nevada Ice Sheet and record environmental variability associated with it. We have applied new paleomagnetic secular variation measurements (PSV) to more carefully date the lake environmental variability. We have also used PSV to correlate the Great Basin environmental variability to North Atlantic records of oxygen isotope variability. We see evidence for 25 cycles in stadial/interstadial variability of the Great Basin lakes. These cycles can be correlated among all three lakes and are largely synchronous. We can also date the individual stadial and interstadial intervals present in the three lakes. They have an average cycle duration of 1430 ± 530 years. But, the cycle durations in all three lakes vary coherently from less than 1000 years to more than 2000 years between 20 and 56 ka. The variability in cycle duration suggests internal variability in the global climate engine as the cause of the observed variability rather than some (presumably more periodic) external forcing. We also correlate interstadial D/O cycles 2–16 recorded in the Atlantic Ocean region with interstadial intervals in the Great Basin lakes. These intervals are largely synchronous between the two regions. We see evidence of 5 more Great Basin lake interstadials synchronous with un-numbered light δ18O intervals in the Atlantic oxygen isotope stratigraphy. This suggests some kind of linkage between the North Atlantic and North Pacific climate variability during the period 15–56 ka.

Asymmetric division events promote variability in cell cycle duration in animal cells and Escherichia coli

Asymmetric cell division is a major mechanism generating cell diversity. As cell cycle duration varies among cells in mammalian tissue culture cells, we asked whether their division asymmetry contributes to this variability. We identify among sibling cells an outlier using hierarchical clustering on cell cycle durations of granddaughter cells obtained by lineage tracking of single histone2B-labelled MDCKs. Remarkably, divisions involving outlier cells are not uniformly distributed in lineages, as shown by permutation tests, but appear to emerge from asymmetric divisions taking place at non-stochastic levels: a parent cell influences with 95% confidence and 0.5% error the unequal partitioning of the cell cycle duration in its two progenies. Upon ninein downregulation, this variability propagation is lost, and outlier frequency and variability in cell cycle durations in lineages is reduced. As external influences are not detectable, we propose that a cell-autonomous process, possibly involved in cell specialisation, determines cell cycle duration variability.

Effect of Trunk Muscle Strengthening on Gait Pattern and Falls in Parkinson's Disease.

BackgroundThe course of Parkinson’s disease is characterized by gait disturbance and falls, which affect patients’ quality of life and engender high healthcare costs. These factors are not greatly improved by levodopa therapy or deep brain stimulation of the subthalamic nuclei. Indeed, the symptoms may even worsen with these treatment. Physiotherapy may be the most appropriate treatment to reduce the incidence of falls in these cases; however, its benefits are modest.ObjectiveTo assess the effectiveness of trunk muscle strengthening in 10 patients with Parkinson’s disease being treated with deep brain stimulation of the subthalamic nuclei who are affected by gait disturbances and falls.MethodA standardized physiotherapy programme centred on trunk muscle strengthening was conducted. Its effectiveness was assessed using a clinical approach combined with video-based motion analysis.ResultsAfter 4 weeks of trunk muscle strengthening, the gait item on the Unified Parkinson’s Disease Rating Scale (UPDRS, part 3) together with several gait kinematic parameters (step length, walking cycle duration variability, gait speed) were significantly improved and the number of falls decreased.ConclusionThese preliminary findings suggest that physiotherapy centred on rachis mobility improves the quality of gait and reduces the number of falls in patients with Parkinson’s disease who are being treated with deep brain stimulation of the subthalamic nuclei. This is a potentially useful supplement to the traditional physiotherapy approach, in addition to the pharmacological and surgical treatment of Parkinson’s disease.LAY ABSTRACTOver time, patients with Parkinson’s disease treated operatively with subthalamic nucleus deep brain stimulation develop drug-resistant gait disturbance and falls. Traditional physiotherapy programmes for reducing the incidence of falls in these patients have modest effects. Thus, a physiotherapy programme based on trunk exercises could be helpful, since optimal axial motility and gait and posture quality are strongly linked. A specific programme was used for 10 patients with Parkinson’s disease treated operatively with subthalamic nucleus deep brain stimulation. The programme involved 2 physiotherapy sessions per day for 5 days a week over a period of 4 consecutive weeks. Quality of gait improved and the number of falls decreased significantly. In conclusion, specific standardized rehabilitation of axial motility is potentially a useful supplement to the traditional physiotherapy approach in order to reduce falls in patients with Parkinson’s disease who have been treated operatively with subthalamic nucleus deep brain stimulation.

Maize yields over Europe may increase in spite of climate change, with an appropriate use of the genetic variability of flowering time

Projections based on invariant genotypes and agronomic practices indicate that climate change will largely decrease crop yields. The comparatively few studies considering farmers' adaptation result in a diversity of impacts depending on their assumptions. We combined experiments and process-based modeling for analyzing the consequences of climate change on European maize yields if farmers made the best use of the current genetic variability of cycle duration, based on practices they currently use. We first showed that the genetic variability of maize flowering time is sufficient for identifying a cycle duration that maximizes yield in a range of European climatic conditions. This was observed in six field experiments with a panel of 121 accessions and extended to 59 European sites over 36 years with a crop model. The assumption that farmers use optimal cycle duration and sowing date was supported by comparison with historical data. Simulations were then carried out for 2050 with 3 million combinations of crop cycle durations, climate scenarios, management practices, and modeling hypotheses. Simulated grain production over Europe in 2050 was stable (-1 to +1%) compared with the 1975-2010 baseline period under the hypotheses of unchanged cycle duration, whereas it was increased (+4-7%) when crop cycle duration and sowing dates were optimized in each local environment. The combined effects of climate change and farmer adaptation reduced the yield gradient between south and north of Europe and increased European maize production if farmers continued to make the best use of the genetic variability of crop cycle duration.

Divergent acoustic properties of gelada and baboon vocalizations and their implications for the evolution of human speech.

Human speech has many complex spectral and temporal features traditionally thought to be absent in the vocalizations of other primates. Recent explorations of the vocal capabilities of non-human primates are challenging this view. Here, we continue this trend by exploring the spectro-temporal properties of gelada (Theropithecus gelada) vocalizations. First, we made cross-species comparisons of geladas, chacma baboons, and human vowel space area. We found that adult male and female gelada exhaled grunts-a call type shared with baboons-have formant profiles that overlap more with human vowel space than do baboon grunts. These gelada grunts also contained more modulation of fundamental and formant frequencies than did baboon grunts. Second, we compared formant profiles and modulation of exhaled grunts to the derived call types (those not shared with baboons) produced by gelada males. These derived calls contained divergent formant profiles, and a subset of them, notably wobbles and vocalized yawns, were more modulated than grunts. Third, we investigated the rhythmic patterns of wobbles, a call type shown previously to contain cycles that match the 3-8 Hz tempo of speech. We use a larger dataset to show that the wobble rhythm overlaps more with speech rhythm than previously thought. We also found that variation in cycle duration depends on the production modality; specifically, exhaled wobbles were produced at a slower tempo than inhaled wobbles. Moreover, the variability in cycle duration within wobbles aligns with a linguistic property known as 'Menzerath's law' in that there was a negative association between cycle duration and wobble size (i.e. the number of cycles). Taken together, our results add to growing evidence that non-human primates are anatomically capable of producing modulated sounds. Our results also support and expand on current hypotheses of speech evolution, including the 'neural hypothesis' and the 'bimodal speech rhythm hypothesis'.

Distinguishing between stochasticity and determinism: Examples from cell cycle duration variability.

We describe a recent approach for distinguishing between stochastic and deterministic sources of variability, focusing on the mammalian cell cycle. Variability between cells is often attributed to stochastic noise, although it may be generated by deterministic components. Interestingly, lineage information can be used to distinguish between variability and determinism. Analysis of correlations within a lineage of the mammalian cell cycle duration revealed its deterministic nature. Here, we discuss the sources of such variability and the possibility that the underlying deterministic process is due to the circadian clock. Finally, we discuss the "kicked cell cycle" model and its implication on the study of the cell cycle in healthy and cancerous tissues.

Dynamics of Revolution Time Variability in Cycling Pattern: Voluntary Intent Can Alter the Long-Range Autocorrelations

Long-range dependency has been found in most rhythmic motor signals. The origin of this property is unknown and largely debated. There is a controversy on the influence of voluntary control induced by requiring a pre-determined pace such as asking subjects to step to a metronome. We studied the cycle duration variability of 15 men pedaling on an ergometer at free pace and at an imposed pace (60 rpm). Revolution time was determined based on accelerometer signals (sample frequency 512 Hz). Revolution time variability was assessed by coefficient of variation (CV). The presence of long-range autocorrelations was based on scaling properties of the series variability (Hurst exponent) and the shape of the power spectral density (α exponent). Mean revolution time was significantly lower at freely chosen cadence, while values of CV were similar between both sessions. Long-range autocorrelations were highlighted in all series of cycling patterns. However, Hurst and α exponents were significantly lower at imposed cadence. This study demonstrates the presence of long-range autocorrelations during cycling and that voluntary intent can modulate the interdependency between consecutive cycles. Therefore, cycling may constitute a powerful paradigm to investigate the influence of central control mechanisms on the long-range interdependency characterizing rhythmic motor tasks.

Bimanual 1:1 with 90° continuous relative phase: difficult or easy!

The purpose of the present experiment was to observe the performance of participants attempting to produce a 1:1 bimanual coordination pattern with 90 degrees relative phase between the arms when feedback concerning the movement of the two limbs was integrated within a Lissajous plot and when this information was withdrawn. One group was paced with an auditory metronome and the other was encouraged to increase frequency when they fell below the goal frequency. We predicted that providing a salient integrated feedback display without a metronome would allow participants to effectively tune-in the goal relative phase pattern within several minutes; instead of several days as typically found in the literature when the metronome was used. The data indicated remarkably effective performances after 5 min of practice when the metronome was not used, with motion of both limbs harmonic in nature, and continuous relative phase errors (approximately 10 degrees) and standard deviation of continuous relative phase (approximately 10 degrees) relatively small. This seems remarkable given that this coordination pattern has proven relatively difficult to perform under normal and Lissajous feedback conditions even after several days of practice. As predicted relative phase errors and variability increased substantially when the metronome was used. When the extrinsic feedback was withdrawn all participants tended to drift from the required 90 degrees relative phase, but the cycle duration variability in the two limbs remained stable and limb motion remained harmonic in nature. The current findings suggest that some of the difficulty typically associated with producing various relative phase patterns is due to the less than optimal perceptual information available in the various testing situations and the use of pacing metronomes.

Variabilité phénotypique des sorghos locaux de deux régions du Burkina Faso : la Boucle du Mouhoun et le Centre-Ouest

The racial classification of 190 sorghum landraces collected in two regions of Burkina Faso and characterized for 27 agro-morphological traits shows the preponderance of Guinea varieties (96.8%). Durra and Caudatum varieties are rare, respectively 1.6% and 0.5%, whereas 1.1% of the varieties were not classified. Among the Guinea sorghums, the gambicum are more frequent than the margaritiferum which present an important variability in cycle duration. The phenotypic diversity of the landraces is high and poorly explained by geographic factors (villages or climatic zones). The differences between varieties are mainly based on vegetative duration and red-grained sorghums are generally earlier than white-grained sorghums. An initial multivariate analysis of data shows stratification based on racial aspects. In a second analysis, plant cycle and grain type characteristics discriminate two clusters: a group of early and medium cycle sorghum varieties with rather big and floury grain and a group of late cycle sorghum varieties with lower grain weight and vitreous grains. The red sorghums other than the margaritiferum form a specific cluster. In contrast, white sorghums show less homogeneity.

Chewing cycle kinematics of subjects with deepbite malocclusion

The notion that chewing cycle shape and cycle dynamics differ between subjects with and without malocclusion is largely based on qualitative studies that combined various types of malocclusion. The purpose of this prospective study was to determine whether chewing cycle kinematics of untreated young adults with deepbite malocclusion differ from those with normal occlusion. Twenty-three deepbite subjects (>50% overbite) and 24 controls with normal occlusion chewed gum (right side only) while their jaw movements were recorded at 100 Hz by using an optoelectric jaw tracking system. Differences in cycle duration between deepbite and control subjects were small and not significant (P >.05). The deepbite subjects showed significantly (P <.05) less maximum inferior excursion (7.7 vs 9.0 mm) and significantly greater maximum posterior excursion (5.1 vs 4.0 mm) than subjects with normal occlusion. In addition, the deepbite subjects had significantly smaller maximum vertical velocities than subjects with normal occlusion (49.2 vs 60.8 mm per second). Deepbite subjects also showed significantly (P <.05) less cycle-to-cycle variability in maximum velocities and excursions to the balancing side but significantly (P <.05) greater variability in cycle duration and maximum posterior excursions. A deepbite malocclusion alters the shape of chewing cycles and the consistency of chewing cycle kinematics.

Organization of Myocardial Activation During Ventricular Fibrillation After Myocardial Infarction

Studies of ventricular fibrillation (VF) in small mammals have revealed localized sustained stationary reentry. However, studies in large mammals with surface mapping techniques have demonstrated only relatively short-lived rotors. The purpose of this study was to identify whether sustained high-frequency activation with low beat-to-beat variability was present at intramural sites in a postinfarct ovine model of VF. VF was induced in 12 sheep 77+/-40 days after anterior myocardial infarction. Electrical activation was recorded with 20 multielectrode transmural plunge needles. Unipolar electrogram frequency content and local cycle duration variability were studied in 30-second recordings beginning 5 seconds after the onset of VF. Higher mean beat frequency was associated with lower SD of the cycle duration intervals (r=-0.91, P<0.001). The mean beat frequency and the SD of cycle duration intervals of the highest-frequency electrode were 8.8+/-2.0 Hz and 17+/-11 ms. In 3 cases, a region with regular activation throughout the recording was identified (SD of the cycle duration interval, 6.0+/-0.7 ms). Two of these sites and 67% of all sites with low local cycle duration variability were intramural. They occurred within regions with a high dominant frequency as determined by fast Fourier transform of the unipolar electrogram. Regions with the highest frequency of activation during VF were always associated with a low local cycle duration variability and usually intramural in this chronic infarct model. In a minority of cases, a region of stable, rapid, and very regular activation could be identified. These findings support the hypothesis that relatively stable periodic sources form a component of the mechanism of VF in this model.

Patterns of interarticulator phasing and their relation to linguistic structure.

Work by Tuller and Kelso [J. Acoust. Soc. Am. 76, 1030-1036 (1984)] and Kelso et al. [J. Phon. 14, 29-59 (1986)] has demonstrated stable relations between jaw and lip movements in (bV#CVb) utterances across rate and stress conditions. Specifically, the onset of lip movement toward the intervocalic consonant was found to be constant with respect to the vowel-to-vowel jaw cycle in both time and relative phasing. An attempt was made to replicate and extend this work by investigating interarticulator phase relations for utterances having a broader range of linguistic organization: In addition to rate and stress, syllable structure (open versus closed syllables) and identity of the intervocalic consonant (/p/ vs /m/) were manipulated. Results showed that the upper lip's lowering onset varied systematically with respect to the jaw vowel cycle as a function of both rate and stress. In addition, syllable structure and consonant identity influenced the relation of lip and jaw gestures. There was a general tendency for any condition that shortened the first vowel to produce earlier onsets of the upper lip relative to the jaw. However, the within-condition jaw cycle duration variability did not correlate with the within-condition variability in phase. Thus it seems that stable interarticulator phase relations maintain not only the integrity of phonological structure, as suggested by Kelso et al., but structural integrity at other levels of linguistic organization as well.

Inter and intratrial variation in cat locomotor behavior

Four cats were trained to locomote on a treadmill at a variety of speeds. The cats were then filmed at weekly intervals for three weeks; additionally, one of the cats was filmed 35 days prior to the first weekly filming. The films were used to characterize the variation exhibited by the cats in total cycle and swing/stance durations, and in footfall patterns both across the weekly trials and within them, and across speeds. The intertrial comparison indicated the existence of a “training effect” (i.e., a consistent change in gait subsequent to continued training) for only one cat; the cat showed notable reductions in cycle duration at all speeds over time. The intertrial comparison also indicated that a limb (especially a forelimb) could exhibit slightly different (but internally consistent) footfall patterns during different trials. Furthermore, the variation in one forelimb's pattern was usually associated with corresponding, but reciprocal, variation in the other forelimb's pattern. The analysis comparing variation in cycle duration across speeds indicated generally more variability at slow speeds relative to fast speeds. However, maximum or near maximum variability in cycle duration as well as in footfall pattern often occurred at an intermediate speed near the walk-trot transition. The data also demonstrated that both swing and stance durations could be modified at all speeds, although individual cats may consistently modify one more than the other. Additionally, swing duration appeared to be the primary variable during galloping. These results are discussed in terms of their implications for comparative studies of cat locomotor behavior subsequent to surgically induced lesions, and in terms of achieving a better understanding of cat locomotion and its neural control.

A tomographic comparison of the temporomandibular joint in the hypo- and hyperdivergent patient

Introduction: The notion that chewing cycle shape and cycle dynamics differ between subjects with and without malocclusion is largely based on qualitative studies that combined various types of malocclusion. The purpose of this prospective study was to determine whether chewing cycle kinematics of untreated young adults with deepbite malocclusion differ from those with normal occlusion. Methods: Twenty-three deepbite subjects (>50% overbite) and 24 controls with normal occlusion chewed gum (right side only) while their jaw movements were recorded at 100 Hz by using an optoelectric jaw tracking system. Results: Differences in cycle duration between deepbite and control subjects were small and not significant (P >.05). The deepbite subjects showed significantly (P <.05) less maximum inferior excursion (7.7 vs 9.0 mm) and significantly greater maximum posterior excursion (5.1 vs 4.0 mm) than subjects with normal occlusion. In addition, the deepbite subjects had significantly smaller maximum vertical velocities than subjects with normal occlusion (49.2 vs 60.8 mm per second). Deepbite subjects also showed significantly (P <.05) less cycle-to-cycle variability in maximum velocities and excursions to the balancing side but significantly (P <.05) greater variability in cycle duration and maximum posterior excursions. Conclusions: A deepbite malocclusion alters the shape of chewing cycles and the consistency of chewing cycle kinematics.