Efficiency of Sensorimotor Networks: Posture and Gait in Young and Older Adults.

Background/Study context: Posture and gait are complex sensorimotor functions affected by age. These difficulties are particularly apparent when performing cognitively demanding tasks. Characterizing the functional organization of brain networks involved in these associations remains a challenge because of the incompatibility of brain imagery techniques with gross body movements. The present study aimed at testing whether resting-state functional connectivity of sensorimotor networks is associated with posture and gait performance recorded offline, in young and older adults. METHODS: Young (n = 12, mean = 24.1 y/o) and older (n = 14, mean = 65.6 y/o) healthy adults were tested for stability of their posture and gait. Four hours later, anatomical and functional brain imaging data were collected with Magnetic Resonance Imaging (MRI). Bilateral precentral and postcentral gyri were used as seeds in a graph theory analysis focused on global and local efficiency. The possible association between these data and posture and gait performance was examined. RESULTS: Both samples presented similar sensorimotor graphs, but with different global and local efficiencies (small world properties). The association between the networks' graph measures and posture and gait performance also differed across groups: local efficiency was correlated with gait stability in challenging conditions in older adults, but not in young adults. CONCLUSION: This exploratory study suggests that combining analyses of functional networks and offline body movement may provide important information about motor function. In older adults, the association between graph properties of the sensorimotor network and gait performance in challenging conditions may be indicative of compensatory processes. Prospective studies involving more subjects with a larger age range are warranted.

Effect of overreaching on cognitive performance and related cardiac autonomic control.

The purpose of this study was to characterize the effect of a 2-week overload period immediately followed by a 1-week taper period on different cognitive processes including executive and nonexecutive functions, and related heart rate variability. Eleven male endurance athletes increased their usual training volume by 100% for 2 weeks, and decreased it by 50% for 1 week. A maximal graded test, a constant speed test at 85% of peak treadmill speed, and a Stroop task with the measurement of heart rate variability were performed at each period. All participants were considered as overreached. We found a moderate increase in the overall reaction time to the three conditions of the Stroop task after the overload period (816 ± 83 vs 892 ± 117 ms, P = 0.03) followed by a return to baseline after the taper period (820 ± 119 ms, P = 0.013). We found no association between cognitive performance and cardiac parasympathetic control at baseline, and no association between changes in these measures. Our findings clearly underscore the relevance of cognitive performance in the monitoring of overreaching in endurance athletes. However, contrary to our hypothesis, we did not find any relationship between executive performance and cardiac parasympathetic control.

Dietary patterns in french home-living older adults: Results from the PRAUSE study.

The aim of the present study was to provide descriptive dietary patterns of home-living older adults, and to examine their association with sociodemographic and 'diet-related' variables, and health and psychological factors. Dietary patterns were analyzed using separately cluster analysis for men (N=151,Mage=72.72, SD=8.80, range=56-97) and women (N=251, Mage=76.74, SD=9.95, range=55-97) in 402 older adults aged 55 years and over. Cluster analyses showed four distinct dietary profiles for each gender. In older men, the four distinct dietary clusters were associated with any differences in sociodemographic and 'diet-related' variables, cognitive function, and health and psychological factors. Likewise, in older women, the four distinct dietary clusters were associated with any differences in sociodemographic and 'diet-related' variables'. However in older women, results showed that the cluster 1 "high fish-fruit-vegetable" was associated with a better cognitive function, a better self-rated health and no depressive symptoms, whereas cluster 3 "moderate ready meals" was associated with cognitive decline, slight depression, and poor perceived health. Results emphasize the interest to take into consideration health and psychological factors associated with dietary patterns to better target the vulnerability of individuals and enable an effective prevention.

Assessing muscular oxygenation during incremental exercise using near-infrared spectroscopy: comparison of three different methods.

Using continuous-wave near-infrared spectroscopy (NIRS), this study compared three different methods, namely the slope method (SM), the amplitude method (AM), and the area under the curve (AUC) method to determine the variations of intramuscular oxygenation level as a function of workload. Ten right-handed subjects (22+/-4 years) performed one isometric contraction at each of three different workloads (30 %, 50 % and 90 % of maximal voluntary strength) during a period of twenty seconds. Changes in oxyhemoglobin (delta[HbO(2)]) and deoxyhemoglobin (delta[HHb]) concentrations in the superficial flexor of fingers were recorded using continuous-wave NIRS. The results showed a strong consistency between the three methods, with standardized Cronbach alphas of 0.87 for delta[HHb] and 0.95 for delta[HbO(2)]. No significant differences between the three methods were observed concerning delta[HHb] as a function of workload. However, only the SM showed sufficient sensitivity to detect a significant decrease in delta[HbO(2)] between 30 % and 50 % of workload (p<0.01). Among these three methods, the SM appeared to be the only method that was well adapted and sensitive enough to determine slight changes in delta[HbO(2)]. Theoretical and methodological implications of these results are discussed.

Dietary patterns in French home-living older adults: Results from the PRAUSE study.

The aim of the present study was to provide descriptive dietary patterns of home-living older adults, and to examine their association with sociodemographic and 'diet-related' variables, and health and psychological factors. Dietary patterns were analyzed using separately cluster analysis for men (N=151,Mage=72.72, SD=8.80, range=56-97) and women (N=251, Mage=76.74, SD=9.95, range=55-97) in 402 older adults aged 55 years and over. Cluster analyses showed four distinct dietary profiles for each gender. In older men, the four distinct dietary clusters were associated with any differences in sociodemographic and diet-related variables, cognitive function, and health and psychological factors. Likewise, in older women, the four distinct dietary clusters were associated with any differences in sociodemographic and 'diet-related' variables'. However in older women, results showed that the cluster 1 "high fish-fruit-vegetable" was associated with a better cognitive function, a better self-rated health and no depressive symptoms, whereas cluster 3 "moderate ready meals" was associated with cognitive decline, slight depression, and poor perceived health. Results emphasize the interest to take into consideration health and psychological factors associated with dietary patterns to better target the vulnerability of individuals and enable an effective prevention.

[Change in effects of motor preparation due to priming as a function of the amount of practice]. / Evolution des effets d'une préparation motrice induite par amorçage en fonction de la quantité de pratique.

The goal of the present experiment is to assess the effects of motor preparation on reaction time (RT) as a function of practice. We used a priming procedure to induce different levels of motor preparation. In reaction to a visual signal, the 16 participants had to respond with a flexion or an extension of the right or left wrist. Each participant performed 6120 successful trials divided into 34 experimental series. The first analysis of RT as a function of the type of cue (valid, neutral, or invalid) suggested that the time needed (a) to inhibit the prepared response and (b) to program the required one, remains stable throughout practice. A second analysis on the amount of information to be processed according to type of cue (0.42, 2.00, and 3.58 bits) indicated that central processing speed did not vary with practice. Indeed, only RT for the 0 bit condition decreased during the first 720 trials, suggesting that only the peripheral processes were influenced in early learning.

Study of anticipatory postural adjustments in an air pistol-shooting task.

A segmental teleokinetic movement performed from an upright standing position is usually preceded by a sequence of postural movements having the goal of counteracting the imbalance which will be caused by the forthcoming movement. This study had two aims, (1) to verify whether the postural component was programmed in the same way as that of the teleokinetic component and (2) to verify whether the postural component was specific to the direction and speed of the movement. 12 participants performed a pistol-shooting task involving a rapid arm-raising movement. Three directions, two time deadlines, and three types of cue were manipulated. This study showed that the postural component was sensitive to the cue effects, the characteristics of anticipatory postural adjustments were specific to the direction of the movement, and the characteristics of the postural muscle EMG burst were the same whether the participants programmed or deprogrammed and reprogrammed their movements for a given direction. The speed parameter did not seem to have any significant influence on the characteristics of the anticipatory postural adjustments.

Effects of a prolonged run on simple reaction time of well trained runners.

The aim of the present study was to examine the effect of increased arousal induced by a prolonged exercise at ventilatory threshold simple reaction time performance performed during a running task. 11 well trained triathletes completed two testing sessions within a 2-wk. period. The first session was a protocol of VO2 max determination conducted on a treadmill. This protocol was used to assess the velocity associated with ventilatory threshold (vVvt). The second session was a 90-min. running test performed at vVvt. This last session was composed of five submaximal treadmill runs (10-min. long, 0% grade) separated by four overground runs (10-min.). Before, during each treadmill run, and after exercise, subjects performed three blocks of 20 simple reaction time. Furthermore, at the end of each overground run, perceived exertion (RPE) was recorded. Analysis showed a significant impairment in Simple RT performance during the first treadmill run only. After this first run a significant effect of exercise duration on Simple RT was observed. After 40-min. of exercise a significant improvement in reaction time during exercise was recorded, Furthermore, when Simple RT was recorded at rest, there was no difference pre-exercise and postexercise. These results suggest that a simple cognitive performance could be improved during exercise, despite the negative effect of the dual task. This improvement in reaction time could be explained mainly by an increase in arousal induced by a prolonged exercise.

Age differences in using precued information to preprogram interception of a ball.

The present experiment examined the development of programming interception of a ball's movement across three groups of children ages 6, 8, and 10 years, who were compared with adults. In an interception task we manipulated the subjects' preparation by using Rosenbaum's 1980 precuing procedure. Two levels of precued information were used concerning the effector specified (right or left arm) and the direction of the arm projection (outside or inside). We focused particularly on RT and response errors. Analysis indicated RT decreased across the age groups and errors decreased mainly in the nonprecued condition. A critical period in improvement might be at age 8 as children use precue information to program their movements as efficiently as adults. The duration of effector programming was similar for children and adults but was more precise for the older subjects. For children as well as for adults, the specification of direction occurs after movement initiation and not before.

Influence of physical exercise on simple reaction time: effect of physical fitness.

The influence of physical fitness and energy expenditure on a simple reaction time task performed during exercise was investigated. Two groups of 10 subjects were used, one was composed of trained middle-distance runners and one of students who had no regular physical training. The subjects performed a simple reaction time task while pedalling on a cycloergometer at different relative power output corresponding to 20, 40, 60, and 80% of their own maximal aerobic power and immediately after exercise. During exercise, the results showed a decrease in cognitive performance for both groups whereas no significant effect was found after exercise. A significant effect of physical fitness on simple reaction time was noted during exercise. The data are interpreted in terms of optimization of performance focusing particularly on the relations between energy cost of the physical task and attentional demand.

Local muscular fatigue and attentional processes in a fencing task.

Study of the effects of brief exercise on mental processes by Tomporowski and Ellis (1986) has shown that moderate muscular tension improves cognitive performance while low or high tension does not. Improvements in performance induced by exercise are commonly associated with increase in arousal, while impairments are generally attributed to the effects of muscular or central fatigue. To test two hypotheses, that (1) submaximal muscular exercise would decrease premotor time and increase would increase the attentional and preparatory effects observed in premotor time 9 men, aged 20 to 30 years, performed an isometric test at 50% of their maximum voluntary contraction between blocks of a 3-choice reaction-time fencing task. Analysis showed (1) physical exercise did not improve postexercise premotor time, (2) muscular fatigue induced by isometric contractions did not increase motor time, (3) there was no effect of exercise on attentional and preparatory processes involved in the postexercise choice-RT task. The invalidation of hypotheses was mainly explained by disparity in directional effects across subjects and by use of an exercise that was not really fatiguing.

Perceptual factors contribute to akinesia in Parkinson's disease.

Parkinson's disease (PD) patients have longer reaction time (RT) than age-matched control subjects. During the last decades, conflicting results have been reported regarding the source of this deficit. Here, we addressed the possibility that experimental inconsistencies originated in the composite nature of RT responses. To investigate this idea, we examined the effect of PD on different processes that compose RT responses. Three variables were manipulated: the signal quality, the stimulus-response compatibility and the foreperiod duration. These variables have been shown to affect, respectively, the ability to extract the relevant features of the stimulus (perceptual stage), the intentional selection of the motor response (cognitive stage) and the implementation of the muscle command (motor stage). Sixteen PD patients were tested on and off-medication and compared with an age and gender-matched control group. Results indicated that degrading the legibility of the response stimulus affected the latency of simple key-press movements more dramatically in the off-medication PD group than in the control population. The stimulus-response compatibility and the foreperiod duration had similar effects in the two groups. Interestingly, the response slowing associated with the degradation of the stimulus was the same whether the patients were on or off dopaminergic medication. This suggests that the high-level perceptual deficits observed in the present study do not have a dopaminergic origin.

A methodology and an instrument for the temperature-controlled optimization of crystal growth.

A method and a device for the promotion of crystal growth by keeping the crystallization solution metastable during the growth process are described. This is achieved by controlled temperature variation of the crystallization solution using parameters determined in situ during the growth process. The technique finds application in the growth of large high-quality crystals for neutron crystallography. Thus, it has been applied to grow large crystals of several proteins of interest such as human gamma-crystallin E, PA-IIL lectin from Pseudomonas aeruginosa, yeast inorganic pyrophosphatase, urate oxidase from Aspergillus flavus and human carbonic anhydrase II.

Age-related differences in the preparatory processes of motor programming.

This article investigates the mechanisms underlying the age-related differences in information processing in the production of motor responses, especially the development of feedforward mechanisms. No age-related differences have emerged from developmental studies aiming at analyzing motor programming. Nevertheless, age effects have seldom been studied in function of motor preparation. The aim of the present experiment was (1) to study age differences in motor preparation, and (2) to validate the early maturation of movement parameters specification. Two conditions were used (1) no advanced information on the movement to be made was given to the subject (neutral prime), and (2) advanced information on which direction should be followed was provided to the subject, allowing him to prepare a response based on a prime (primed condition). Four age groups were studied 6, 8, 10 and 22 years. Our results showed mainly an early maturation of the programming processes. More specifically, (1) beyond 6 years of age, children are capable of using the information provided by the prime to prepare their movement in advance, (2) costs and benefits of pre-programming do not vary significantly with age, (3) deprogramming-reprogramming of effector and direction is quite similar across the four age groups.

Single and choice reaction time during prolonged exercise in trained subjects: influence of carbohydrate availability.

The aim of the present study was to examine the effects of prolonged exercise at the ventilatory threshold and carbohydrate ingestion on single (SRT) and choice (CRT) reaction time. Eight well-trained triathletes completed three testing sessions within a 3-week period. Maximal oxygen uptake was determined in the first test, whereas the second and the third sessions were composed of a 100-min run (treadmill 15 min, overground 70 min, treadmill 15 min) performed at the velocity associated with the ventilatory threshold. During these submaximal tests, the subjects ingested (in random order) 8 ml x kg(-1) body weight of either a placebo (Pl) or 5.5% carbohydrate (CHO) solution prior to the first submaximal run and 2 ml x kg(-1) body weight every 15 min after that. The cognitive tasks were performed before and after exercise for CRT, and before, during each submaximal run and after exercise for SRT. Furthermore, at the end of each submaximal test subjects were asked to report their rating of perceived exertion (RPE). Results showed a significant positive effect of CHO ingestion on RPE and CRT performance at the end of exercise, while no effect of exercise duration was found in the Pl condition. After a 100-min run, during the CHO condition, CRT mean (SD) group values decreased from 688.5 (51) ms to 654 (63) ms, while during the Pl condition, RPE mean group values increased from 11 (2) to 16 (1.02) and CRT mean values remained stable [688 (104) ms vs 676 (73.4) ms, P > 0.05]. No similar effect was observed for SRT. These results suggest that CHO-electrolyte ingestion during a 100-min run results in an improvement in the complex cognitive performance measured at the end of that run.