Study protocol of an investigation of attention and prediction error as mechanisms of action for latent inhibition of dental fear in humans.

BACKGROUND: Evidence suggests that dental anxiety and phobia are frequently the result of direct associative fear conditioning but that pre-exposure to dental stimuli prior to conditioning results in latent inhibition of fear learning. The mechanisms underlying the pre-exposure effect in humans, however, are poorly understood. Moreover, pain sensitivity has been linked to dental fear conditioning in correlational investigations and theory suggests it may moderate the latent inhibition effect, but this hypothesis has not been directly tested. These gaps in our understanding are a barrier to the development of evidence-based dental phobia prevention efforts. METHODS: Healthy volunteers between the ages of 6 and 35 years will be enrolled across two sites. Participants will complete a conditioning task in a novel virtual reality environment, allowing for control over pre-exposure and the examination of behaviour. A dental startle (a brief, pressurized puff of air to a tooth) will serve as the unconditioned stimulus. Using a within-subjects experimental design, participants will experience a pre-exposed to-be conditioned stimulus, a non-pre-exposed to-be conditioned stimulus, and a neutral control stimulus. Two hypothesized mechanisms, changes in prediction errors and attention, are expected to mediate the association between stimulus condition and fear acquisition, recall, and retention. To ascertain the involvement of pain sensitivity, this construct will be measured through self-report and the cold pressor task. DISCUSSION: Dental phobia negatively affects the dental health and overall health of individuals. This study aims to determine the mechanisms through which pre-exposure retards conditioned dental fear acquisition, recall, and retention. A randomized control trial will be used to identify these mechanisms so that they can be precisely targeted and maximally engaged in preventative efforts.

Correlations among multiple measures of functional and mechanical instability in subjects with chronic ankle instability.

CONTEXT: Although dozens of individual mechanical and functional insufficiencies have been reported in those with chronic ankle instability (CAI), no authors to date have examined the relationship of the insufficiencies to each other. Therefore, studying both the functional and mechanical insufficiencies in the same experimental design will provide valuable information. OBJECTIVE: To determine the relationships among the numerous functional and mechanical insufficiencies purported to cause CAI. DESIGN: Descriptive study with a correlational design. SETTING: Medical center and research laboratory. PATIENTS OR OTHER PARTICIPANTS: Thirty subjects with unilateral CAI (15 males and 15 females: age = 20.3 +/- 1.3 years; height = 172.5 +/- 10.7 cm; mass = 72.9 +/- 15.8 kg). MAIN OUTCOME MEASURE(S): Twenty-six measures of mechanical insufficiencies (ankle laxity and hypomobility) and functional insufficiencies (subjective level of function, static and dynamic balance, ankle and hip strength) were taken on both limbs of all subjects. Bivariate correlations using Pearson product moment coefficients were calculated between all dependent variables measured in the unstable ankles. The level of significance was set a priori at P < or = .05 for all analyses. RESULTS: A number (35) of significant bivariate correlations were identified. Most (32) of these significant relationships were found between functional instability measures ( r = .38 to .96). Three significant relationships were noted between measures of functional (balance, strength) and mechanical (laxity, hypomobility) instability ( r = .47 to .52). No significant relationships were found between the different mechanical instability measures. CONCLUSIONS: Certain measures of functional instability were significantly correlated and may be redundant. Additionally, the significant correlations between measures of functional (balance, strength) and mechanical instability (laxity, hypomobility) demonstrate that the 2 factors are not completely dichotomous and need to be examined together.

The effect of a 4-week comprehensive rehabilitation program on postural control and lower extremity function in individuals with chronic ankle instability.

STUDY DESIGN: Prospective, randomized controlled trial. OBJECTIVE: To examine the effects of a 4-week rehabilitation program for chronic ankle instability (CAI) on postural control and lower extremity function. BACKGROUND: CAI is associated with residual symptoms, performance deficits, and reinjury. Managing CAI is challenging and more evidence is needed to guide effective treatment. METHODS AND MEASURES: Subjects with unilateral CAI were randomly assigned to the rehabilitation (CAI-rehab, n=16) or control (CAI-control, n=13) group. Subjects without CAI were assigned to a healthy group (n=19). Baseline testing included the (1) center of pressure velocity (COPV), (2) star excursion balance test (SEBT), and (3) Foot and Ankle Disability index (FADI) and FADI-Sports Subscale (FADI-Sport). The CAI-rehab group completed 4 weeks of rehabilitation that addressed range of motion, strength, neuromuscular control, and functional tasks. After 4 weeks, all subjects were retested. Nonparametric analyses for group differences and between-group comparisons were performed. RESULTS: Subjects with CAI demonstrated deficits in postural control and SEBT reach tasks of the involved limb compared to the uninvolved limb and reported functional deficits of the involved limb compared to healthy subjects. Following rehabilitation, the CAI-rehab group had greater SEBT reach improvements on the involved limb than the other groups and greater improvements in FADi and FADI-Sport scores. CONCLUSIONS: These results demonstrate postural control and functional limitations exist in individuals with CAl. In addition, rehabilitation appears to improve these functional limitations. Finally, there is evidence to suggest the SEBT may be a good functional measure to monitor change after rehabilitation for CAI.

Contributing factors to chronic ankle instability.

BACKGROUND: The development of repetitive ankle sprains and persistent symptoms after initial ankle sprain has been termed chronic ankle instability (CAI). There is no clear indication of which measures are most important in discriminating between individuals with and without CAI. METHODS: Thirty subjects with unilateral CAI and controls had measures of ankle laxity and hypomobility, static and dynamic balance, ankle and hip strength, lower extremity alignments, and flexibility taken on both limbs. RESULTS: Based on comparisons of CAI ankles and side-matched limbs in controls, the measures significantly predictive of CAI were increased inversion laxity (r(2) change = 0.203), increased anterior laxity (r(2) change = 0.11), more missed balance trials (r(2) change = 0.094), and lower plantarflexion to dorsiflexion peak torque (r(2) change = 0.052). Symmetry indices comparing the side-to-side differences of each measure also were calculated for each dependent variable and compared between groups. The measures significantly predictive of CAI were decreased anterior reach (r(2) change = 0.185), decreased plantarflexion peak torque (r(2) change = 0.099), decreased posterior medial reach (r(2) change = 0.094), and increased inversion laxity (r(2) change = 0.041). CONCLUSIONS: The results of this study elucidate the specific measures that best discriminate between individuals with and without CAI. Both mechanical (anterior and inversion laxity) and functional (strength, dynamic balance) insufficiencies significantly contribute to the etiology of CAI. Prevention of CAI may be possible with proper initial management of the acute injury with rehabilitation aimed at those factors that best discriminate between individuals with and without CAI.

Deficits in time-to-boundary measures of postural control with chronic ankle instability.

Our purpose was to examine postural control in single leg stance in subjects with and without unilateral chronic ankle instability (CAI) using traditional center of pressure (COP)-based and time-to-boundary (TTB) measures. Fifteen physically active females with self-reported unilateral chronic ankle instability (CAI) and nine healthy female controls performed three 10-s trials of eyes open single limb quiet standing on a force plate on both their legs. The traditional measures were mean COP velocity, standard deviation of COP, range of COP, and percent of available range utilized. The TTB measures were absolute minimum TTB, mean of the minimum TTB samples, and standard deviation of the minimum TTB samples. All measures were calculated in both the mediolateral (ML) and anteroposterior (AP) directions. A 2x2 group (CAI, control) by side (involved, uninvolved) design was utilized. The CAI group had significantly lower scores for five of the six TTB measures compared to the control group, however only one (AP COP velocity) of the eight traditional measures was different between groups. The TTB measures appear to detect postural control deficits related to CAI that traditional measures do not.

Time-to-boundary measures of postural control during single leg quiet standing.

A novel approach to quantifying postural stability in single leg stance is assessment of time-to-boundary (TTB) of center of pressure (COP) excursions. TTB measures estimate the time required for the COP to reach the boundary of the base of support if it were to continue on its instantaneous trajectory and velocity, thus quantifying the spatiotemporal characteristics of postural control. Our purposes were to examine: (a) the intrasession reliability of TTB and traditional COP-based measures of postural control, and (b) the correlations between these measures. Twenty-four young women completed three 10-second trials of single-limb quiet standing on each limb. Traditional measures included mean velocity, standard deviation, and range of mediolateral (ML) and anterior-posterior (AP) COP excursions. TTB variables were the absolute minimum, mean of minimum samples, and standard deviation of minimum samples in the ML and AP directions. The intrasession reliability of TTB measures was comparable to traditional COP based measures. Correlations between TTB and traditional COP based measures were weaker than those within each category of measures, indicating that TTB measures capture different aspects of postural control than traditional measures. TTB measures provide a unique method of assessing spatiotemporal characteristics of postural control during single limb stance.

Simplifying the star excursion balance test: analyses of subjects with and without chronic ankle instability.

STUDY DESIGN: Case control study. OBJECTIVES: The objectives of this study are: (1) to perform factor analyses on data from the 8 components of the star excursion balance test (SEBT) in subjects with and without chronic ankle instability (CAI) in an effort to reduce the number of components of the SEBT, (2) to assess the relationships between performance of the different reach directions using correlation analyses, and (3) to determine which components of the SEBT are most affected by CAI. BACKGROUND: The SEBT is a series of 8 lower-extremity-reaching tasks purported to be useful in identifying lower extremity functional deficits. METHODS AND MEASURES: Forty-eight young adults with unilateral CAI (22 males, 26 females; mean +/- SD age, 20.9 +/- 3.2 years; mean +/- SD height, 173.6 +/- 11.1 cm; mean +/- SD mass, 80.1 +/- 22.1 kg) and 39 controls (23 males, 16 females; mean +/- SD age, 20.7 +/- 2.4 years; mean +/- SD height, 174.1 +/- 12.9 cm; mean +/- SD mass, 75.1 +/- 18.6 kg) performed 3 trials of the 8 tasks with each of their limbs. Separate exploratory factor analyses were performed on data for involved limbs of the CAI group, uninvolved limbs of the CAI and control groups, and both limbs of the CAI and control groups. Pearson product moment correlations were calculated to identify the relationships between the different reach directions. A series of eight 2 x 2 analyses of variance were calculated to determine the influence of group (CAI, control) and side (involved, uninvolved) on performance of the 8 tasks. RESULTS: For all 3 factor analyses, only 1 factor in each analysis produced an eigenvalue greater than 1 and the posteromedial reach score was the most strongly correlated task with the computed factor (alpha > .90), although all 8 tasks produced alpha scores greater than .67. Bivariate correlations between specific reach directions ranged from .40 to .91. Subjects with CAI reached significantly less on the anteromedial, medial, and posteromedial directions when balancing on their involved limbs compared to their uninvolved limbs and the side-matched limbs of controls. CONCLUSIONS: The posteromedial component of the SEBT is highly representative of the performance of all 8 components of the test in limbs with and without CAI. There is considerable redundancy in the 8 tasks. The anteromedial, medial, and posteromedial reach tasks may be used clinically to test for functional deficits related to CAI in lieu of testing all 8 tasks. There is a need for a hypothesis-driven study to confirm the results of this exploratory study.

Neuromuscular performance and knee laxity do not change across the menstrual cycle in female athletes.

Female athletes incur anterior cruciate ligament ruptures at a rate at least twice that of male athletes. Hypothesized factors for the increased injury risk in females include biomechanical, neuromuscular, and hormonal differences between genders. A wealth of literature exists examining these potential predispositions individually, but the interactions between these factors have not been examined extensively. Our purpose was to investigate changes in neuromuscular control and laxity at the knee across the menstrual cycle of healthy females. Fourteen female collegiate athletes with normal, documented ovulatory menstrual cycles, confirmed ovulation, and no history of serious knee injury participated. The presence and timing of ovulation was determined during a screening cycle with ovulation detection kits and during an experimental cycle with collection of daily urine samples and subsequent analysis of urinary estrone-3-glucuronide (E3G) and pregnanediol-3-glucoronide (PdG), which correlate with circulating estrogen and progesterone. Each subject had measures of knee neuromuscular performance and laxity once during the mid-follicular, ovulatory, and mid-luteal stages of her menstrual cycle. The test battery included assessments of knee flexion and extension peak torque, passive knee joint position sense, and postural control in single leg stance. Knee joint laxity was measured with an arthrometer. Analyses of variance revealed that E3G and PdG levels were significantly different across the three testing sessions, but there were no significant differences in the measures of strength, joint position sense, postural control, or laxity. No significant correlations were found between changes in E3G or PdG levels and changes in the performance and laxity measures between sessions. These results suggest that neuromuscular control and knee joint laxity do not change substantially across the menstrual cycle of females despite varying estrogen and progesterone levels.

Expression of PEG11 and PEG11AS transcripts in normal and callipyge sheep.

BACKGROUND: The callipyge mutation is located within an imprinted gene cluster on ovine chromosome 18. The callipyge trait exhibits polar overdominant inheritance due to the fact that only heterozygotes inheriting a mutant paternal allele (paternal heterozygotes) have a phenotype of muscle hypertrophy, reduced fat and a more compact skeleton. The mutation is a single A to G transition in an intergenic region that results in the increased expression of several genes within the imprinted cluster without changing their parent-of-origin allele-specific expression. RESULTS: There was a significant effect of genotype (p < 0.0001) on the transcript abundance of DLK1, PEG11, and MEG8 in the muscles of lambs with the callipyge allele. DLK1 and PEG11 transcript levels were elevated in the hypertrophied muscles of paternal heterozygous animals relative to animals of the other three genotypes. The PEG11 locus produces a single 6.5 kb transcript and two smaller antisense strand transcripts, referred to as PEG11AS, in skeletal muscle. PEG11AS transcripts were detectable over a 5.5 kb region beginning 1.2 kb upstream of the PEG11 start codon and spanning the entire open reading frame. Analysis of PEG11 expression by quantitative PCR shows a 200-fold induction in the hypertrophied muscles of paternal heterozygous animals and a 13-fold induction in homozygous callipyge animals. PEG11 transcripts were 14-fold more abundant than PEG11AS transcripts in the gluteus medius of paternal heterozygous animals. PEG11AS transcripts were expressed at higher levels than PEG11 transcripts in the gluteus medius of animals of the other three genotypes. CONCLUSIONS: The effect of the callipyge mutation has been to alter the expression of DLK1, GTL2, PEG11 and MEG8 in the hypertrophied skeletal muscles. Transcript abundance of DLK1 and PEG11 was highest in paternal heterozygous animals and exhibited polar overdominant gene expression patterns; therefore, both genes are candidates for causing skeletal muscle hypertrophy. There was unique relationship of PEG11 and PEG11AS transcript abundance in the paternal heterozygous animals that suggests a RNA interference mechanism may have a role in PEG11 gene regulation and polar overdominance in callipyge sheep.