Repeated context-specific actions disrupt feedforward adjustments in motor commands in younger and older adults.

The flexibility of the motor system to adjust a planned action before or during the execution of the movement in response to sensory information is critical for preventing errors in motor control. As individuals age, this function declines, leading to an increased incidence of motor errors. Although sensory processing and cognitive decline are known contributors to this impairment, here, we test the hypothesis that repetition of context-specific planned actions interferes with the adjustment of feedforward motor commands. Younger and older participants were instructed to grasp and lift a T-shaped object with a concealed, off-sided center of mass and minimize its roll through anticipatory force control, relying predominantly on predictive model-driven planning (i.e., sensorimotor memories) developed through repeated lifts. We selectively manipulate the number of trial repeats with the center of mass on one side before switching it to the other side of the T-shaped object. The results showed that increasing the number of repetitions improved performance in manipulating an object with a given center of mass but led to increased errors when the object's center of mass was switched. This deleterious effect of repetition on feedforward motor adjustment was observed in younger and older adults. Critically, we show these effects on an internal model-driven motor planning task that relies predominantly on sensorimotor memory, with no differences in sensory inputs from the repetition manipulation. The findings indicate that feedforward motor adjustments are hampered by repetitive stereotyped planning and execution of motor behavior.NEW & NOTEWORTHY Adjusting planned actions in response to sensory stimuli degrades with age contributing to increased incidence of errors ranging from clumsy spills to catastrophic falls. Multiple factors likely contribute to age-related motor inflexibility, including sensory- and cognition-supporting system declines. Here, we present compelling evidence for repetition to disrupt feedforward adjusting of motor commands in younger and older adults, which suggests increases in stereotypy as a deleterious potentiator of motor control errors.

Chaotic markers in dynamic diffraction.

In a dynamic far-field diffraction experiment, we calculate the largest Lyapunov exponent of a time series obtained from the optical fluctuations in a dynamic diffraction pattern. The time series is used to characterize the locomotory predictability of an oversampled microscopic species. We use a live nematode, Caenorhabditis elegans, as a model organism to demonstrate our method. The time series is derived from the intensity at one point in the diffraction pattern. This single time series displays chaotic markers in the locomotion of the Caenorhabditis elegans by reconstructing the multidimensional phase space. The average largest Lyapunov exponent (base e) associated with the dynamic diffraction of 10 adult wildtype (N2) Caenorhabditis elegans is 1.27±0.03s-1.

Fourier-Based Diffraction Analysis of Live Caenorhabditis elegans.

This manuscript describes how to classify nematodes using temporal far-field diffraction signatures. A single C. elegans is suspended in a water column inside an optical cuvette. A 632 nm continuous wave HeNe laser is directed through the cuvette using front surface mirrors. A significant distance of at least 20-30 cm traveled after the light passes through the cuvette ensures a useful far-field (Fraunhofer) diffraction pattern. The diffraction pattern changes in real time as the nematode swims within the laser beam. The photodiode is placed off-center in the diffraction pattern. The voltage signal from the photodiode is observed in real time and recorded using a digital oscilloscope. This process is repeated for 139 wild type and 108 "roller" C. elegans. Wild type worms exhibit a rapid oscillation pattern in solution. The "roller" worms have a mutation in a key component of the cuticle that interferes with smooth locomotion. Time intervals that are not free of saturation and inactivity are discarded. It is practical to divide each average by its maximum to compare relative intensities. The signal for each worm is Fourier transformed so that the frequency pattern for each worm emerges. The signal for each type of worm is averaged. The averaged Fourier spectra for the wild type and the "roller" C. elegans are distinctly different and reveal that the dynamic worm shapes of the two different worm strains can be distinguished using Fourier analysis. The Fourier spectra of each worm strain match an approximate model using two different binary worm shapes that correspond to locomotory moments. The envelope of the averaged frequency distribution for actual and modeled worms confirms the model matches the data. This method can serve as a baseline for Fourier analysis for many microscopic species, as every microorganism will have its unique Fourier spectrum.

Optimal control of type 1 diabetes mellitus in youth receiving intensive treatment.

OBJECTIVE: To investigate the impact of factors that might interfere with optimal glycemic control in youth with type 1 diabetes mellitus (T1DM) in the current era of intensive management, including the interplay of race/ethnicity and socioeconomic status (SES) on HbA1c levels. STUDY DESIGN: This study comprised a database review of all patients under age 18 years with T1DM for at least 6 months duration. Sex, age, race/ethnicity, duration of diabetes, mode of insulin administration (pump vs injection), body mass index, SES, and HbA1c level were recorded at each patient's most recent visit between January and September 2003. RESULTS: Mean HbA1c level for the 455 patients was 7.6% +/- 1.4%; only 31% of patients failed to meet the therapeutic goal of < 8.0%. Multiple linear regression analysis identified female sex (P = .02), older age (P = .001), longer duration of diabetes (P < .001), injection therapy (P < .001), and lower SES (P = .001) as significantly associated with higher HbA1c level. After adjustment for SES, race/ethnicity was not a determinant of HbA1c level. CONCLUSIONS: Low SES had a greater association with poor metabolic control than did race/ethnicity, which was not associated with differences in HbA1c level after controlling for SES. Most children were able to attain glycemic targets at least as good as the Diabetes Control and Complications Trial recommendations in a large clinical practice.

Persistence of benefits of continuous subcutaneous insulin infusion in very young children with type 1 diabetes: a follow-up report.

OBJECTIVE: Use of continuous subcutaneous insulin infusion (CSII) has increased dramatically in recent years, and pump therapy has been shown to be a safe and effective alternative to multiple daily injections in adults and older pediatric patients with type 1 diabetes. Its use in very young children, however, has been limited, although this group might be expected to benefit the most from CSII. The objective of this study was to analyze the CSII efficacy and safety data in very young children with type 1 diabetes from our Diabetes Clinic database. METHODS: Glycosylated hemoglobin (HbA1c), severe hypoglycemia (SH), and ketoacidosis (DKA) in the year before CSII were compared with corresponding values during pump treatment in all children who started CSII before age 7. RESULTS: Sixty-five children (mean age: 4.5 y at CSII initiation; range: 1.4-6.9 years; 28 girls; 3 black, 1 Hispanic) were analyzed for >162 patient-years of follow-up. Mean HbA(1c) (7.4 +/- 1.0 prepump) decreased to 7.0 +/- 0.9 after 12 months of CSII and continued to improve even after 4 years on CSII. The rate of SH was reduced by 53% (from 78 to 37/100 patient-years). Children who received daytime care from paid caregivers (n = 26) experienced significant reductions in HbA1c and hypoglycemia frequency. There were no episodes of DKA requiring emergency treatment in the year before CSII and 4 episodes (4 per 100 patient-years) after transition to pump. CONCLUSIONS: CSII is a durable and effective means of optimizing glycemic control in very young patients with type 1 diabetes and may be superior to multiple daily injections in minimizing the risk of severe hypoglycemia in this age group. Employment of paid caregivers does not preclude safe and effective use of CSII.

A randomized, prospective trial comparing the efficacy of continuous subcutaneous insulin infusion with multiple daily injections using insulin glargine.

OBJECTIVE: The efficacy of the insulin analogs now available for multiple daily injection (MDI) and continuous subcutaneous insulin infusion (CSII) therapy in type 1 diabetes has not yet been established in pediatric patients. Our principal aim in this short-term study was to compare the efficacy of CSII to MDI with glargine in lowering HbA(1c) levels in children and adolescents with type 1 diabetes. RESEARCH DESIGN AND METHODS: Thirty-two youth with type 1 diabetes (age 8-21 years) were randomly assigned to receive either MDI treatment with once-daily glargine and premeal/snack insulin aspart or CSII with insulin aspart. Dose titration in both groups was based on home self-monitored blood glucose measurements and monthly HbA(1c). HbA(1c), total daily insulin dose (TDD), self-monitored blood glucose readings, and adverse events were compared after 16 weeks of therapy. RESULTS: While there was no significant change in the glargine group (HbA(1c) 8.2% at baseline vs. 8.1% at 16 weeks), youth randomized to CSII had a sharp reduction in HbA(1c) levels, from 8.1 to 7.2% after 16 weeks of therapy (P < 0.02 vs. baseline and <0.05 vs. glargine group). TDD was unchanged in the glargine group, but significantly dropped with CSII (1.4 units/kg at baseline vs. 0.9 units/kg at 16 weeks, P < 0.01). Both groups had similar basal doses and insulin-to-carbohydrate ratios. Fasting self-monitored blood glucose was similar in both groups, but lunch, dinner, and bedtime readings were significantly lower in the CSII group (P < 0.01). CONCLUSIONS: Lower HbA(1c) and premeal glucose levels were more achievable in this short-term study with CSII than with glargine-based MDI treatment. CSII is an efficacious treatment to improve metabolic control in youth with type 1 diabetes.

Insulin pump therapy in pediatrics: a therapeutic alternative to safely lower HbA1c levels across all age groups.

OBJECTIVE: To examine the efficacy and safety of using continuous subcutaneous insulin infusion (CSII) therapy in a large group of patients 18 months to 18 yr from a single pediatric diabetes program. RESEARCH DESIGN AND METHODS: All patients < or = 18 yr of age starting on CSII from 1 January 1997 to 31 March 2000 at the Yale Children's Diabetes Program were included. Clinical data were collected prospectively before and during pump treatment. HbA1c was the primary efficacy outcome and rates of diabetes-related adverse events were the primary safety measures. RESULTS: One hundred and sixty-one children ranging in age from 18 months to 18 yr received CSII for an average of 32 +/- 9 months when data collection was closed on 31 October 2001, including 26 preschoolers (< 7 yr), 76 school-agers (7-11 yr) and 59 adolescents (12-18 yr). Mean HbA1c levels were 7.1% in the preschoolers, 7.8% in the school-agers and 8.1% in the adolescents prior to the start of CSII. There was a significant and consistent reduction in mean HbA1c levels after 12 months of CSII (to 6.5% in preschoolers, 7.3% in school-agers and 7.4% in adolescents, p < 0.02 vs. prepump) that was maintained at the most recent visit. Improved diabetes control was achieved with CSII without increasing daily insulin doses and in association with a decrease in the frequency of severe hypoglycemic events (p < 0.05 vs. prepump, all three age groups combined). CONCLUSIONS: CSII is an effective alternative to injection therapy in a large pediatric diabetes clinic setting. Even very young patients can utilize CSII to safely lower HbA1c levels.