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PubMed2001

A novel spike distance.

The discrimination between two spike trains is a fundamental problem for both experimentalists and the nervous system itself. We introduce a measure for the distance between two spike trains. The distance has a time constant as a parameter. Depending on this parameter, the distance interpolates between a coincidence detector and a rate difference counter. The dependence of the distance on noise is studied with an integrate-and-fire model. For an intermediate range of the time constants, the distance depends linearly on the noise. This property can be used to determine the intrinsic noise of a neuron.

Algorithms↗
PubMed2005

A subjective distance between stimuli: quantifying the metric structure of representations.

As subjects perceive the sensory world, different stimuli elicit a number of neural representations. Here, a subjective distance between stimuli is defined, measuring the degree of similarity between the underlying representations. As an example, the subjective distance between different locations in space is calculated from the activity of rodent's hippocampal place cells and lateral septal cells. Such a distance is compared to the real distance between locations. As the number of sampled neurons increases, the subjective distance shows a tendency to resemble the metrics of real space.

Action Potentials↗
PubMed2000

How coil-cortex distance relates to age, motor threshold, and antidepressant response to repetitive transcranial magnetic stimulation.

Repetitive transcranial magnetic stimulation (rTMS) is a tool with antidepressant potential that uses a coil placed on the scalp to produce a powerful magnetic field that directly stimulates only the outermost cortex. MRI scans were obtained in 29 depressed adults involved in an rTMS antidepressant clinical treatment. These scans were analyzed to investigate the effect of distance from coil to cortex on clinical parameters. Longer motor cortex distance, but not prefrontal distance, strongly correlated with increased motor threshold (P<0.01). Clinical antidepressant response did not correlate with either distance. The rTMS antidepressant responders, however, were significantly younger (t=-2.430, P<0.05), and there appears to be a maximum threshold of age and distance to prefrontal cortex for response.

Adult↗
PubMed1989

The acute effects of cigarette smoking on treadmill exercise distances in patients with stable intermittent claudication.

The hypothesis that smoking has an acute effect on treadmill exercise performance in patients with peripheral vascular disease was investigated in a crossover trial. Twelve patients with stable intermittent claudication who were regular smokers attended on two occasions within one week and treadmill tests were performed after 1/2, 1, 1 1/2, and 2 hours. Immediately before the second exercise test, two standard cigarettes were smoked or an unlit cigarette was "sham-smoked." Because participants could not be blinded, an attempt to control for patient bias was made. Half were told that we expected smoking to make no difference or possibly cause some improvement, and half were told that we expected it to make no difference or possibly cause some deterioration. These explanations and the order of study days were determined by balanced randomization. Suggestion had a significant influence on claudication distance immediately after smoking (p less than 0.01) but no significant effect on walking distance. Combining data from both groups assumes that no overall bias was introduced by the explanations given. Immediately after smoking, small, nonsignificant increases in claudication distance (+10%, 95% CI-7%, +27%) and walking distance (+9%, 95% CI-2%, +19%) were observed. Smoking caused a mean increase in heart rate of 9 beats per minute, which persisted for one hour, but no consistent change in blood pressure. The results show that suggestion may have a significant influence on treadmill exercise distances. Smoking is unlikely to have an important acute effect on exercise performance in claudicants.

Adult↗
PubMed1993

A botanical compound, Padma 28, increases walking distance in stable intermittent claudication.

Thirty-six patients with a median age of sixty-seven years and a median duration of intermittent claudication of five years were randomized to either active treatment with Padma 28 or placebo. The effect of treatment was quantified by measurements of systemic and peripheral systolic blood pressures and by measurements of the pain-free and the maximal walking distance on a treadmill. The ankle pressure index (ankle systolic pressure/arm systolic pressure) was calculated. The group randomized to active treatment received two tablets bid containing 340 mg of a dried herbal mixture composed according to an ancient lamaistic preparation (Padma 28). After active treatments, administered over a period of four months in a double-blinded, randomized design, the patients allocated to this group attained a significant increase in the pain-free walking distance from 52 m (20-106) to 86 m (24-164; P < 0.05) and in the maximal walking distance from 115 m (72-218) to 227 m (73- > 1,000; P < 0.05). The patient-group receiving placebo treatments did not show any significant changes in either the painfree or the maximal walking distance. The authors could not demonstrate any significant changes in the ankle pressure index either during active or during placebo treatment. In conclusion, this study has shown that treatment with Padma 28 over a period of four months significantly increased the walking distance in patients with stable, intermittent claudication of long duration.

Aged↗
PubMed1997

Impact velocities of the teeth after a sudden unloading at various initial bite forces, degrees of mouth opening, and distances of travel.

A potentially dangerous situation arises when an individual bites on hard and brittle food which suddenly breaks, since the impact velocity of the lower teeth onto the upper teeth after the food is broken can be high and may cause dental damage. The present experiments were designed to study the magnitude of the impact velocity after a sudden unloading at various initial bite forces, degrees of mouth opening, and distances of travel. Subjects were asked to perform a static biting task during which the resistance to the bite was suddenly removed. The upward mandible movement was arrested after a certain distance. The velocity of the lower teeth at impact was calculated just before the mandible came to a standstill in combinations of 4 different bite forces (100, 80, 60, and 40 N), 4 different initial degrees of mouth opening (33.5, 30.5, 27.5, and 24.5 mm), and 3 different distances of travel of the mandible (4.5, 3.0, and 1.5 mm). We found that the bite force rapidly declined after the unloading, resulting in a small impact velocity of the lower front teeth. This impact velocity largely depended on the magnitude of the initial bite force and the distance traveled; it was barely sensitive to variations in degree of initial mouth opening. The maximal velocity of the lower teeth was 0.43 m/s (at an initial bite force of 100 N). This maximum was reached after a distance of travel of about 4 mm in 12 ms. The data suggest that the rapid decline in bite force coupled with a limitation of impact velocity is due to the force-velocity properties of the active jaw muscles and is not caused by neural control.

Biomechanical Phenomena↗
PubMed1999

The intra-articular distance within the TMJ during free and loaded closing movements.

Previous studies on free opening and closing movements of the mandible have demonstrated that the opening movement traces of the condylar kinematic center (i.e., the condylar point for which the protrusive and the opening movement traces coincide) lie closer to the articular eminence than the closing traces. This indicates the presence of an intra-articular distance within the joint during free closing. Since the mandible behaves like a class III biomechanical lever, a counteracting mechanical load on the mandible during closing will press the condyle-disc complex against the articular eminence. Therefore, in this study the hypothesis was tested that the difference between opening and closing movement traces of the kinematic center is reduced when the closing movements are counteracted by a mechanical load. From 10 healthy participants, 20-second movement recordings were obtained by a six-degrees-of-freedom opto-electronic jaw movement recording system (OKAS-3D) for three types of movements: (1) free opening and closing movements, (2) free opening and loaded closing movements (i.e., the participants closed against a small or high manually applied downward-directed force to the chin), and (3) gum chewing. Off-line, the opening and closing movement traces of the kinematic center were reconstructed, and the average difference between the traces (the intra-articular distance) was calculated. The average intraarticular distance was significantly smaller during loaded closing than during free closing, whereas no significant differences were found in the intra-articular distances between the loaded situations of low and high manual loading and contralateral chewing (ANOVA and post hoc Bonferroni multiple comparisons of means test, p<0.005). In conclusion, loading of the mandible during closing movements reduces the intra-articular distance within the temporomandibular joint.

Adult↗
PubMed2006

Improving lanthanide-based resonance energy transfer detection by increasing donor-acceptor distances.

Lanthanide-based resonance energy transfer (LRET) is an established method for measuring or detecting proximity between a luminescent lanthanide (energy donor) and an organic fluorophore (energy acceptor). Because resonance energy transfer is a distance-dependent phenomenon that increases in efficiency to the 6th power of the distance between the donor and the acceptor, assay systems are often designed to minimize donor-acceptor distances. However, the authors show that because of the R(6) relationship between transfer efficiency and sensitized emission lifetime, energy transfer can be difficult to measure in a time-gated manner when the donor-acceptor distance is small relative to the Förster radius. In such systems, the advantages inherent in time-resolved, ratiometric measurements are lost but can be regained by designing the system such that the average donor-acceptor distance is increased.

Amyloid Precursor Protein Secretases↗
PubMed2004

Accurate and robust phylogeny estimation based on profile distances: a study of the Chlorophyceae (Chlorophyta).

BACKGROUND: In phylogenetic analysis we face the problem that several subclade topologies are known or easily inferred and well supported by bootstrap analysis, but basal branching patterns cannot be unambiguously estimated by the usual methods (maximum parsimony (MP), neighbor-joining (NJ), or maximum likelihood (ML)), nor are they well supported. We represent each subclade by a sequence profile and estimate evolutionary distances between profiles to obtain a matrix of distances between subclades. RESULTS: Our estimator of profile distances generalizes the maximum likelihood estimator of sequence distances. The basal branching pattern can be estimated by any distance-based method, such as neighbor-joining. Our method (profile neighbor-joining, PNJ) then inherits the accuracy and robustness of profiles and the time efficiency of neighbor-joining. CONCLUSIONS: Phylogenetic analysis of Chlorophyceae with traditional methods (MP, NJ, ML and MrBayes) reveals seven well supported subclades, but the methods disagree on the basal branching pattern. The tree reconstructed by our method is better supported and can be confirmed by known morphological characters. Moreover the accuracy is significantly improved as shown by parametric bootstrap.

Animals↗
PubMed2005

Are long-distance migrants constrained in their evolutionary response to environmental change? Causes of variation in the timing of autumn migration in a blackcap (S. atricapilla) and two garden warbler (Sylvia borin) populations.

Long-distance migratory birds often show little phenotypic variation in the timing of life-history events like breeding, molt, or migration. It has been hypothesized that this could result from low levels of heritable variation. If this were true, the adaptability of long-distance migratory birds would be limited, which would explain the vulnerability of this group of birds to environmental changes. The amount of phenotypic, environmental, and genetic variation in the onset of autumn migratory activity was assessed in two garden warbler (Sylvia borin) populations differing in breeding phenology and the length of the breeding season with the aim of investigating the effects of selection on the adaptability of long-distance migrants. High heritabilities and additive genetic variance components for the timing of autumn migration were found in both populations. Although genetic variation in the mountain population was lower than in the lowlands, this difference was not statistically significant. Moreover, no evidence was found for reduced levels of genetic variation in the garden warbler as compared to its sister species, the blackcap (S. atricapilla). Environmental variation, however, was markedly reduced in the garden warbler, suggesting that low levels of phenotypic variation typically found in long-distance migrants may be a consequence of environmental canalization of migratory traits. The buffering of environmental variation may be an adaptive response to strong stabilizing selection on the timing of migration. High environmental canalization of migration phenology in long-distance migrants could potentially explain low rates of immediate phenotypic change in response to environmental change.

Animal Migration↗
PubMed1985

Altered neuroendocrine regulation of gonadotropin secretion in women distance runners.

We tested the hypothesis that the neuroendocrine control of gonadotropin secretion is altered in certain women distance runners with secondary amenorrhea. To this end, we quantitated the frequency and amplitude of spontaneous pulsatile LH secretion during a 24-h interval in nine such women. The ability of the pituitary gland to release LH normally was assessed by administration of graded bolus doses of GnRH during the subsequent 8 h. Compared to normally menstruating women, six of nine amenorrheic distance runners had a distinct reduction in spontaneous LH pulse frequency, with one, three, six, five, four, or two pulses per 24 h (normal, 8-15 pulses/24 h). This reduction in LH pulse frequency occurred without any significant alterations in plasma concentrations of estradiol and free testosterone or 24-h integrated serum concentrations of LH, FSH, or PRL. Moreover, in long-distance runners, the capacity of the pituitary gland to release LH was normal or accentuated in response to exogenous pulses of GnRH. In the six women athletes with diminished spontaneous LH pulsatility, acute ovarian responsiveness also was normal, since serum estradiol concentrations increased normally in response to the GnRH-induced LH pulses. Although long-distance runners had significantly lower estimated percent body fat compared to control women, specific changes in pulsatile gonadotropin release did not correlate with degree of body leanness. In summary, certain long-distance runners with secondary amenorrhea or severe oligomenorrhea have unambiguously decreased spontaneous LH pulse frequency with intact pituitary responsiveness to GnRH. This neuroendocrine disturbance may be relevant to exercise-associated amenorrhea, since pulsatile LH release is a prerequisite for cyclic ovarian function. We speculate that such alterations in pulsatile LH release in exercising women reflect an adaptive response of the hypothalamic pulse generator controlling the intermittent GnRH signal to the pituitary gland. The basis for amenorrhea in the remaining runners who have normal pulsatile properties of LH release is not known.

Adolescent↗
PubMed2004

Functional magnetic resonance imaging-integrated neuronavigation: correlation between lesion-to-motor cortex distance and outcome.

OBJECTIVE: The integration of functional magnetic resonance imaging (fMRI) data into neuronavigation is a new concept for surgery adjacent to the motor cortex. However, the clinical value remains to be defined. In this study, we investigated the correlation between the lesion-to-fMRI activation distance and the occurrence of a new postoperative deficit. METHODS: fMRI-integrated "functional" neuronavigation was used for surgery around the motor strip in 54 patients. During standardized paradigms for hand, foot, and tongue movements, echo-planar imaging T2* blood oxygen level-dependent sequences were acquired and processed with BrainVoyager 2000 software (Brain Innovation, Maastricht, The Netherlands). Neuronavigation was performed with the VectorVision(2) system (BrainLAB, Heimstetten, Germany). For outcome analysis, patient age, histological findings, size of lesion, distance to the fMRI areas, preoperative and postoperative Karnofsky index, postoperative motor deficit, and type of resection were analyzed. RESULTS: In 45 patients, a gross total resection (>95%) was performed, and for 9 lesions (low-grade glioma, 4; glioblastoma, 5), a subtotal resection (80-95%) was achieved. The neurological outcome improved in 16 patients (29.6%), was unchanged in 29 patients (53.7%), and deteriorated in 9 patients (16.7%). Significant predictors of a new neurological deficit were a lesion-to-activation distance of less than 5 mm (P < 0.01) and incomplete resection (P < 0.05). CONCLUSION: fMRI-integrated neuronavigation is a useful concept to assess the risk of a new motor deficit after surgery. Our data suggest that a lesion-to-activation distance of less than 5 mm is associated with a higher risk of neurological deterioration. Within a 10-mm range, cortical stimulation should be performed. For a lesion-to-activation distance of more than 10 mm, a complete resection can be achieved safely. The visualization of fiber tracks is desirable to complete the representation of the motor system.

Adult↗
PubMed2005

Effect of food quality, distance and height on thoracic temperature in the stingless bee Melipona panamica.

Stingless bees (Apidae, Meliponini) can recruit nestmates to good food sources. We present the first data showing that recruiting meliponine foragers at feeders and inside nests regulate their thoracic temperature according to net food profitability. Using infrared thermography, we found that Melipona panamica foragers elevated their thoracic temperature at profitable food sources (higher sucrose concentration, closer to the nest). At food sources, there is an increase of approximately 0.9 degrees C in thoracic temperature (Tth) per 1 mol l(-1) increase in sucrose concentration (at 20 m distance from nest: 1 mol l(-1) sucrose concentration, Tth=36.6+/-0.8 degrees C, T(a)=31.3+/-0.5 degrees C; 2.5 mol l(-1) sucrose concentration, Tth=36.9+/-0.6 degrees C, Ta=29.9+/-0.2 degrees C). Inside the nest, the difference between thoracic temperature Tth and ambient air temperature Ta (DeltaTnest) decreases by 0.4 degrees C with each 100 m increase in feeder-to-nest distance and increases by 0.1 degrees C per 1 mol l(-1) increase in sucrose concentration. The Tth of returning foragers was significantly higher at all tested sucrose concentrations (1.0-2.5 mol l(-1) sucrose concentration) and distances (25-437 m) as compared to Ta (at 2.5 mol l(-1) sucrose concentration: 25 m distance from nest, intranidal Tth=30.2+/-1.3 degrees C, Ta=24.8+/-0.7 degrees C; 437 m distance from nest, intranidal Tth=28.6+/-1.7 degrees C, Tnest=25.4+/-1.4 degrees C). For highly profitable food sources (2.5 mol l(-1) sucrose concentration and < or =100 m from the nest), forager Tth was slightly higher than that of randomly chosen control bees inside the nest.

Animal Communication↗
PubMed2000

Lateral optic flow does not influence distance estimation in the desert ant Cataglyphis fortis.

The present account answers the question of whether desert ants (Cataglyphis fortis) gauge the distance they have travelled by using self-induced lateral optic-flow parameters, as has been described for bees. The ants were trained to run to a distant food source within a channel whose walls were covered with black-and-white gratings. From the food source, they were transferred to test channels of double or half the training width, and the distance they travelled before searching for home and their walking speeds were recorded. Since the animals experience different motion parallax cues when walking in the broader or narrower channels, the optic-flow hypothesis predicted that the ants would walk faster and further in the broader channels, but more slowly and less far in the narrower channels. In contrast to this expectation, neither the walking speeds nor the searching distances depended on the width or height of the channels or on the pattern wavelengths. Even when ventral-field visual cues were excluded by covering the eyes with light-tight paint, the ants were not influenced by lateral optic flow-field cues. Hence, walking desert ants do not depend on self-induced visual flow-field cues in gauging the distance they have travelled, as do flying honeybees, but can measure locomotor distance exclusively by idiothetic means.

Animals↗
PubMed2003

Validity of 10 electronic pedometers for measuring steps, distance, and energy cost.

PURPOSE: This study examined the effects of walking speed on the accuracy and reliability of 10 pedometers: Yamasa Skeletone (SK), Sportline 330 (SL330) and 345 (SL345), Omron (OM), Yamax Digiwalker SW-701 (DW), Kenz Lifecorder (KZ), New Lifestyles 2000 (NL), Oregon Scientific (OR), Freestyle Pacer Pro (FR), and Walk4Life LS 2525 (WL). METHODS: Ten subjects (33 +/- 12 yr) walked on a treadmill at various speeds (54, 67, 80, 94, and 107 m x min-1) for 5-min stages. Simultaneously, an investigator determined steps by a hand counter and energy expenditure (kcal) by indirect calorimetry. Each brand was measured on the right and left sides. RESULTS: Correlation coefficients between right and left sides exceeded 0.81 for all pedometers except OR (0.76) and SL345 (0.57). Most pedometers underestimated steps at 54 m x min-1, but accuracy for step counting improved at faster speeds. At 80 m x min-1 and above, six models (SK, OM, DW, KZ, NL, and WL) gave mean values that were within +/- 1% of actual steps. Six pedometers displayed the distance traveled. Most of them estimated mean distance to within +/- 10% at 80 m x min-1 but overestimated distance at slower speeds and underestimated distance at faster speeds. Eight pedometers displayed kilocalories, but except for KZ and NL, it is unclear whether this should reflect net or gross kilocalories. If one assumes they display net kilocalories, the general trend was an overestimation of kilocalories at every speed. If one assumes they display gross kilocalorie, then seven of the eight pedometers were accurate to within +/-30% at all speeds. CONCLUSION: In general, pedometers are most accurate for assessing steps, less accurate for assessing distance, and even less accurate for assessing kilocalories.

Adult↗
PubMed1978

Stereotype content and social distance: changing views of homosexuality.

This project examined effects of stereotype content and uniformity on social distance regarding homosexuals. Administration of an adjective checklist and social distance scale to 538 undergraduates resulted in identification of "traits" that change social distance. Those traits that positively correlated with distance at or beyond the .05 level were: "cowardly," "sly," "suspicious," "shrewd," "stupid," "impulsive," and "ignorant." Traits that correlated with reduced distance ("sensitive," individualistic," "intelligent," "honest," "imaginative," "neat," "reserved," "alert," "kind" "faithful," "courteous," "sophisticated," and "artistic") were more uniform. Both clusters of negative and positive traits were moderately intercorrelated within and suggest that they each represent underlying dimensions. It is suggested that sterotypes about homosexuals are changing in a more positive direction.

Attitude↗
PubMed2004

Three Mahalanobis distances and their role in assessing unidimensionality.

Unidimensionality is the hallmark psychometric feature of a well-constructed measurement scale. However, in determining the degree to which a set of items form a unidimensional scale, aberrant item response patterns may distort our investigations. For example, aberrant response patterns may adversely impact interitem covariances which, in turn, can distort estimates of a scale's dimensionality and reliability. In this study, we investigate and compare the utility of three Mahalanobis distance (M-distance) measures in identifying and downweighting aberrant item response patterns. Our findings indicated that a residual-based M-distance measure had the best properties. Specifically, response patterns having greater residual-based M-distances were responsible for observed violations of unidimensionality. When these response patterns were properly downweighted according to this M-distance, the data fitted a one-factor model better and scale reliability increased. The procedures are illustrated using three real data sets.

Humans↗
PubMed2002

Two class minimax distance transform correlation filter.

A new correlation filter formulation (that we refer to as the minimax distance transform correlation filter (MDTCF) is presented that minimizes the average squared distance from the filtered desired (or true-) class training images to a filtered reference image while maximizing the mean squared distance of the filtered undesired (or false-) class training images to this filtered reference image. This approach increases the separation between the false-class correlation outputs and the true-class correlation outputs. Classification can be performned using the squared distance of a filtered test image to the chosen filtered reference image. We show that the previously introduced distance classifier correlation filter (DCCF) is similar to a special case of MDTCF. We also examine the differences between the DCCF and the MDTCF, and show that MDTCF can offer increased discrimination performance. Also, MDTCF performance is evaluated on two different face databases.

Journal Article↗