The information content of spontaneous retinal waves.
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Spontaneous neural activity that is present in the mammalian retina before the onset of vision is required for the refinement of retinotopy in the lateral geniculate nucleus and superior colliculus. This paper explores the information content of this retinal activity, with the goal of determining constraints on the nature of the developmental mechanisms that use it. Through information-theoretic analysis of multielectrode and calcium-imaging experiments, we show that the spontaneous retinal activity present early in development provides information about the relative positions of retinal ganglion cells and can, in principle, be used at retinogeniculate and retinocollicular synapses to refine retinotopy. Remarkably, we find that most retinotopic information provided by retinal waves exists on relatively coarse time scales, suggesting that developmental mechanisms must be sensitive to timing differences from 100 msec up to 2 sec to make optimal use of it. In fact, a simple Hebbian-type learning rule with a correlation window on the order of seconds is able to extract the bulk of the available information. These findings are consistent with bursts of action potentials (rather than single spikes) being the unit of information used during development and suggest new experimental approaches for studying developmental plasticity of the retinogeniculate and retinocollicular synapses. More generally, these results demonstrate how the properties of neuronal systems can be inferred from the statistics of their input. (+info)
Persistent primary enuresis: a urodynamic assessment.
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Videocystourethrography with synchronous pressure and flow-rate recordings has been carried out on 50 patients referred for the investigation of persistent primary enuresis. Urodynamic studies showed nocturnal enuresis to be associated mainly with normal detrusor function and nocturnal plus diurnal enuresis mainly with abnormal detrusor function. Evidence is presented which suggests that these two distinct types of enuresis occur de novo and do not overlap. Out of 18 of formerly enuretic male patients nine with abnormal detrusor function showed persistent nocturnal plus diurnal symptoms. (+info)
A microcantilever device to assess the effect of force on the lifetime of selectin-carbohydrate bonds.
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A microcantilever technique was used to apply force to receptor-ligand molecules involved in leukocyte rolling on blood vessel walls. E-selectin was adsorbed onto 3-microm-diameter, 4-mm-long glass fibers, and the selectin ligand, sialyl Lewis(x), was coupled to latex microspheres. After binding, the microsphere and bound fiber were retracted using a computerized loading protocol that combines hydrodynamic and Hookean forces on the fiber to produce a range of force loading rates (force/time), r(f). From the distribution of forces at failure, the average force was determined and plotted as a function of ln r(f). The slope and intercept of the plot yield the unstressed reverse reaction rate, k(r)(o), and a parameter that describes the force dependence of reverse reaction rates, r(o). The ligand was titrated so adhesion occurred in approximately 30% of tests, implying that >80% of adhesive events involve single bonds. Monte Carlo simulations show that this level of multiple bonding has little effect on parameter estimation. The estimates are r(o) = 0.048 and 0.016 nm and k(r)(o) = 0.72 and 2.2 s(-1) for loading rates in the ranges 200-1000 and 1000-5000 pN s(-1), respectively. Levenberg-Marquardt fitting across all values of r(f) gives r(o) = 0.034 nm and k(r)(o) = 0.82 s(-1). The values of these parameters are in the range required for rolling, as suggested by adhesive dynamics simulations. (+info)
Coordinated righting behaviour in locusts.
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A locust placed upside down on a flat surface uses a predictable sequence of leg movements to right itself. To analyse this behaviour, we made use of a naturally occurring state of quiescence (thanatosis) to position locusts in a standardised upside-down position from which they spontaneously right themselves. Locusts grasped around the pronotum enter a state of thanatosis during which the limbs can be manipulated into particular postures, where they remain, and the animal can be placed upside down on the ground. When released, thanatosis lasts 4-456 s (mean 73 s) before the animal suddenly becomes active again and rights itself within a further 600 ms. Thanatosis is characterised by very low levels of leg motor activity. During righting, one hind leg provides most of the downward force against the ground that rolls the body around a longitudinal axis towards the other side. The driving force is produced by femoral levation (relative to the body) at the trochanter and by tibial extension. As the animal rolls over, the hind leg on the other side is also levated at the trochanter, so that it does not obstruct the movement. The forelegs and middle legs are not required for successful righting but they can help initially to tip the locust to one side, and at the end of the movement they help stop the roll as the animal turns upright. Individual locusts have a preferred righting direction but can, nevertheless, roll to either side. Locusts falling upside down through the air use both passive and active mechanisms to right themselves before they land. Without active movements, falling locusts tend to rotate into an upright position, but most locusts extend their hind leg tibiae and/or spread their wings, which increases the success of mid-air righting from 28 to 49 % when falling from 30 cm. The rapid and reliable righting behaviour of locusts reduces the time spent in a vulnerable upside-down position. Their narrow body geometry, large hind legs, which can generate substantial dorsally directed force, and the particular patterns of coordinated movements of the legs on both sides of the body are the key features that permit locusts to right themselves effectively. The reliability of autonomous multi-legged robots may be enhanced by incorporating these features into their design. (+info)
Reliability of measurements obtained with the Timed "Up & Go" test in people with Parkinson disease.
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BACKGROUND AND PURPOSE: The Timed "Up & Go" Test (TUG) is used to measure the ability of patients to perform sequential locomotor tasks that incorporate walking and turning. This study investigated the retest reliability, interrater reliability, and sensitivity of scores obtained with the TUG in detecting changes in mobility in subjects with idiopathic Parkinson disease (PD). SUBJECTS: The performance of 12 people with PD was compared with that of 12 age-matched comparison subjects without PD. METHODS: The subjects with PD completed 5 trials of the TUG after withdrawal of levodopa for 12 hours ("off" phase of the medication cycle) as well as an additional 5 trials 1 hour after levodopa was administered ("on" phase of the medication cycle). They were scored on the Modified Webster Scale at both sessions. The comparison subjects also performed 5 TUG trials. All trials were videotaped and timed by 2 experienced raters. The videotape was later rated by 3 experienced clinicians and 3 inexperienced clinicians. RESULTS: For the subjects with PD, within-session performance was highly consistent, with correlations (r) ranging from.80 to.98 for the "off" phase and from.73 to.99 for the "on" phase. The performance of the comparison subjects across the 5 trials was also highly consistent (r=.90-.97). Comparisons showed differences between trials 1 and 2 on the TUG for both groups. Removal of data for trial 1 (the practice trial) further enhanced retest reliability. There was close agreement in TUG scores among raters despite different levels of experience (intraclass correlation coefficient [3,1]=.87-.99). Mean TUG scores were different between the "on" and "off" phases of the levodopa cycle and between subjects with PD and comparison subjects during the "on" phase. CONCLUSION AND DISCUSSION: Retest reliability and interrater reliability of the TUG measurements were high, and the measurements reflected changes in performance according to levodopa use. The TUG can also be used to detect differences in performance between people with PD and elderly people without PD. (+info)
An evaluation of the impact of training Honduran health care providers in interpersonal communication.
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OBJECTIVE: To evaluate the impact of interpersonal communication (IPC) training on practice and patient satisfaction and to determine the acceptability of this training to providers in a developing country. DESIGN: The study used a pre-post design with treatment and control groups. Data collection methods included interaction analysis of audio-taped clinical encounters, patient exit interviews, and a self-administered questionnaire for health providers. STUDY PARTICIPANTS: Interaction analysis was based on an experimental group of 24 doctors and a control group of eight with multiple observations for each provider). Exit interviews were carried out with 220 pre-test patients and 218 post-test patients. All 87 health providers who received training responded to the self-administered questionnaire. INTERVENTION: A brief in-service training programme on interpersonal communications was presented in three half-day sessions; these focused on overall socio-emotional communication, problem solving skills and counselling. MAIN OUTCOME MEASURES AND RESULTS: The IPC intervention was associated with more communication by trained providers (mean scores of 136.6 versus 94.4; P = 0.001), more positive talk (15.93 versus 7.99; P = 0.001), less negative talk (0.11 versus 0.59; P = 0.018), more emotional talk (15.7 versus 5.5; P = 0.021), and more medical counselling (17.3 versus 11.3; P = 0.026). Patients responded by communicating more (mean scores of 113.8 versus 79.6; P = 0.011) and disclosing more medical information (54.7 versus 41.7; P = 0.002). Patient satisfaction ratings were higher for providers who had received the training and providers reported training to be relevant and useful. CONCLUSIONS: Further validation of IPC skills and simplification of assessment methods are needed if IPC is to be an area for routine monitoring and quality improvement. (+info)
A study of helical and planar waves on sea urchin sperm flagella, with a theory of how they are generated.
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When the spermatozoon of Echinus esculentus swims in sea water containing methyl cellulose (viscosity 1.5--4 Pa s), its flagellum may generate either a helical or a planar waveform, each type being stable. The helical wave, which is dextral, is complicated by the concurrent passage of miniature waves along it. These miniature waves have a pulsatile origin in the neck region of the spermatozoon. Our videotape analysis indicates that there are two pulses of mechanical activity for each true cycle of the helical wave. (The true helical frequency was obtained from the apparent wave frequency and the roll frequency of the sperm head, the latter being detectable in some sperm when lit stroboscopically.) The planar wave has a meander shape. During the propagation of planar waves, the sliding displacements are adjustable in either direction; moribund flagella can undergo unrestricted sliding. The planar waves are, in fact, exactly planar only at interfaces. Otherwise, there tend to be torsions in the interbend segments between planar bends. Mechanical stimulation of the flagellum can cause a sudden transition from the helical to the planar waveform. To account for the two modes of beating, we advance the hypothesis that circumferential linkages yield beyond a threshold strain. Whether this yield point is exceeded, we suggest, depends upon the balance between the active shear force and the external viscosity (among other factors). We propose that a subthreshold force originates in one array and then triggers the other dynein arrays circumferentially, but unidirectionally, around the base of the flagellum; whereas a suprathreshold force provokes bi-directional circumferential triggering. These may be the two patterns of activation that result in helical and planar waveforms, respectively. The transition from helical to planar bending may result from an increment in the force produced by the dynein motors. The pulsatile origin of the helical wave resembles behaviour described previously for spermatozoa of Ciona intestinalis and of the quail Coturnix coturnix. (+info)
A technology to measure multiple driving behaviors without self-report or participant reactivity.
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An in-vehicle information system (IVIS) was used to videotape drivers (N = 61) without their knowledge while driving 22 miles in normal traffic. The drivers were told that they were participating in a study of direction following and map reading. Two data-coding procedures were used to analyze videotapes. Safety-related behaviors were counted during consecutive 15-s intervals of a driving trial, and the occurrence of certain safety-related behaviors was assessed under critical conditions. These two methods of data coding were assessed for practicality, reliability, and sensitivity. Interobserver agreement for the five different driving behaviors ranged from 85% to 95%. Within-subject variability in safe driving was more pronounced among younger drivers and decreased as a function of age. Contrary to previous research that has relied on self-reports, driver risk taking did not vary significantly as a function of gender. These results are used to illustrate the capabilities of the technology introduced here to design and evaluate behavior-analytic interventions to increase safe driving. (+info)