Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ADAPTATION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,801 records · Page 100Linked to original sources
PubMed1997

Adaptive and maladaptive behaviour in children with epileptic encephalopathies: correlation with cerebral glucose metabolism.

In the childhood epileptic encephalopathies mental impairment is common and severe. Traditional cognitive assessment is difficult because of the low level of performance, autistic features, and the unpredictable effect of seizures. An alternative is to measure adaptive and maladaptive behaviour using instruments administered to the caregivers. Adults with different types of dementia have characteristic patterns of cortical glucose hypometabolism. Thirty-two children were studied using visual and semiquantitative analysis of 18fluorodeoxyglucose positron emission tomographic (PET) scans. The Vineland Scales and the Conners' Questionnaires were used to assess adaptive and maladaptive behaviour. The mean adaptive behaviour composite score was 37.3+/-15.6; all but one subject had a low adaptive level. A profile of relative strength in socialisation and weakness in daily living skills emerged. Up to two-thirds of children had abnormal behaviour patterns, particularly attention-deficit disorders and hyperactivity. Adaptive and maladaptive behaviour was not related to the presence or absence of focal cortical PET abnormalities. However, adaptive behaviour scores showed an inverse correlation with the degree of metabolic abnormality in the frontal lobes.

Adaptation, Psychological↗
PubMed2005

Distance vergence adaptation is abnormal in subjects with convergence insufficiency.

It is well known that in convergence insufficiency (CI) prism adaptation is reduced in response to base-out (BO) prisms at near. There have also been some suggestions in the literature that adaptation is reduced at other distances as well. The present data show that in CI adaptation is not only reduced in response to BO at near, but also in response to base-in (BI) at near and for both BI and BO at distance. This raises the interesting question whether distance adaptation becomes reduced because of reduced near adaptation or whether these subjects have a generally reduced horizontal adaptation mechanism.

Adaptation, Ocular↗
PubMed2005

Increasing the proportion of binocular vision makes horizontal prism adaptation complete.

In previous phoria adaptation experiments on normal subjects adaptation tends to reach only approximately 2/3 of the prism-induced phoria while clinical experience indicates that prism adaptation is usually complete. The present data show that increasing the proportion of binocular experience through the phoria-inducing prism allows adaptation to become complete. Longer periods of binocular vision give a better indication of vergence adaptation function. This is particularly important in experiments where normal and abnormal adaptive abilities are being compared.

Adaptation, Ocular↗
PubMed2005

Horizontal and vertical prism adaptation are different mechanisms.

As part of a study on subjects with convergence insufficiency (CI), their vertical and horizontal vergence adaptation was assessed and compared with age matched controls in order to investigate whether the horizontal adaptation system can be regarded as being independent of the vertical adaptation system. Using a flashed Maddox rod technique horizontal vergence adaptation was found to be reduced in CI subjects whereas no difference could be found in vertical adaptation. These results confirm that the vertical and horizontal adaptation systems can be treated as independent mechanisms.

Adaptation, Ocular↗
PubMed1985

Adaptation in family systems: a developmental perspective.

Adaptation involves a dialectic between permanence and change. At lower levels of organization, mechanisms of permanence and change are split and in opposition; at a higher level of organization, they are integrated so that change can occur while identity is preserved. Current family theory does not account for the ability of families to change while simultaneously maintaining continuity; rather, mechanisms of permanence (morphostasis) and change (morphogenesis) are treated as operating singly or sequentially. Current theory, therefore, accounts only for a lower level of adaptive functioning. Piaget's notion of "regulations" is used to supplement the description of this lower level of adapting. In addition, Piaget's notion of "operations" is used to describe a higher level of adaptive process in which permanence and change are integrated. Because adaptive functioning is tied to degree of organization, one must increase the degree of organization of a family to raise its adaptive level.

Adaptation, Psychological↗
PubMedDate not supplied

Correlation between loss of a Mg2+ conductance and an adaptation defect in a mutant of Paramecium tetraurelia.

Paramecium tetraurelia responds to chronic KCl-induced depolarization by swimming backward, but the ciliate recovers within seconds and then undergoes a prolonged adaptation period during which sensitivity to external stimuli is altered radically. We examined the role of Mg2+ in this phenomenon, prompted by finding that mutations in the eccentric-A gene both suppressed a Mg(2+)-specific conductance and prevented adaptation. Adaptation of the wild type proceeded normally when extracellular Mg2+ was varied from 0-20 mM, however, suggesting that channel-mediated Mg2+ fluxes were not involved. In seeking alternative explanations for the eccentric mutant phenotype, we ascertained that there was an osmotic component to adaptation but that K(+)-induced depolarization was the primary stimulus. We also noted that wild-type and eccentric mutant cells depolarized by equivalent amounts in KCl, suggesting that the genetic lesion must lie downstream of membrane-potential change. We also examined whether the adaptation-induced behavioral changes and, indeed, the defect in eccentric might be explained in terms of Mg2+ and Na+ efflux during behavioral testing, but experimental observations failed to support this notion. Finally, we consider the possibility that eccentric gene mutation prevents adaptation by interfering with intracellular free Mg2+ homeostasis in Paramecium.

Adaptation, Physiological↗
PubMed1983

Time characteristics and potential dependence of early and late adaptation in the crustacean stretch receptor.

The receptor potential of the crustacean stretch receptor evoked by a ramp and hold stretch is depolarizing and consists of an initial peak followed by a static phase. The receptor current, defined as the stretch induced current change is inward and has a similar appearance. The adaptive fall of the receptor potential and receptor current occurs in two phases which can be separated by their different time characteristics. Using intracellular recordings including potential clamp an attempt has been made to fit experimental values of the adaptive fall of the potential and current response to a double exponential function. Ramp and hold stretches with a rise time of about 7-15 ms were used. The time constants were determined with the cell clamped or polarized to different holding potentials. It was found that the adaptive fall for both potential and current could be fitted reasonably well by double experimental functions with an initial fast phase and a second slow phase. For the potential response the time constant of the early adaptive fall, tau 1, varied with holding potential, having a minimum of approximately 3 ms at about -50 mV. tau 1 for the current response showed a similar variation with holding potential, although less pronounced than for the potential response. The minimum value was about 5 ms. The time constant, tau 2, of the late phase of adaptation both for the current and potential response was about 500 ms and did not vary in a systematic way with holding potential. The results are consistent with the idea that the first phase of adaptation is related to ionic mechanisms in the membrane of the receptor neuron while the second phase might be caused by mechanical factors.

Adaptation, Physiological↗
PubMed1992

Stress, coping and coping resources as correlates of adaptation in myocardial infarction patients.

A longitudinal study was conducted to examine the utility of a set of variables derived from the stress and coping literature as correlates of patients' level of psychosocial adaptation to a myocardial infarction. Forty patients participated in the study; data were collected soon after the patients' discharge from hospital and three months after the event. It was proposed that a high level of perceived stress associated with the infarct and the use of emotion-focused coping strategies would be associated with poor adaptation to the event, whereas the use of problem-focused strategies, high levels of self-efficacy and access to the appropriate personal (control beliefs, self-esteem and trait anxiety) and social (marital and family quality) coping resources were variables proposed to facilitate adaptation. There was only weak support for the proposed effects of perceived stress, and no support for the proposal that the use of problem-focused strategies would facilitate the adaptation of infarct patients. In contrast, the data provided some support for the hypothesized effects of self-efficacy and emotion-focused coping. There was also evidence to suggest that adaptation to an infarct was facilitated if subjects had internal control beliefs, high self-esteem, low trait anxiety and high-quality family relations. Contrary to expectations, marital quality was largely unrelated to the measures of adaptation.

Activities of Daily Living↗
PubMed1973

The contribution of membrane hyperpolarization to adaptation and conduction block in sensory neurones of the leech.

The factors underlying sensory adaptation and conduction block have been studied in cutaneous mechanoreceptor neurones of the leech. A touch-sensitive cell was activated by applying mechanical or electrical stimuli to its receptive field on the skin. Impulses were recorded extracellularly from its axons and intracellularly from its cell body, which is situated within the C.N.S.1. Activation of the touch cell by mechanical stimuli revealed two distinct types of adaptation with characteristically different time courses. Sustained pressure on the skin caused a brief burst of impulses at the onset of the stimulus. This rapid adaptation to pressure was restricted to the part of the receptive field that had been stimulated mechanically. A second type of adaptation developed more slowly during the course of repetitive mechanical stimulation. It persisted for many seconds after the end of a train of impulses and appeared as an increase in the threshold to mechanical stimuli not only in the region of skin that had been rubbed but throughout the receptive field of the cell.2. Impulses initiated in the cell body propagated antidromically towards the skin and also raised the threshold to touch, indicating that after-effects of impulse activity were responsible for the long-lasting threshold increase.3. Repetitive mechanical stimulation could also produce a reversible conduction block in branches of the touch cell. The block occurred in discrete regions of low safety factor such as axonal branch points both within the ganglion and in the periphery. In some experiments impulses intermittently failed to reach one axonal branch yet continued to invade a separate branch of the same cell.4. Several lines of evidence indicate that both conduction block and the slow component of adaptation are linked to a prolonged hyperpolarization that follows repetitive stimulation of the touch cell. Strophanthidin, which blocks the after-hyperpolarization in touch cells, reduced the adaptation following trains of impulses and also relieved a conduction block previously established by repetitive stimulation. Furthermore, a comparison of the effects of hyperpolarizations produced by current injection and by repetitive firing showed that most of the threshold increase in the cell body after a train of impulses could be attributed directly to the membrane hyperpolarization.5. These experiments suggest several ways in which repetitive activity can have pronounced and long-lasting effects on the performance of a highly branched sensory cell. Thus a relatively small number of impulses in a touch cell can markedly decrease its sensitivity to touch. The functional role of the conduction block observed during vigorous stimulation is not as clear because activity for many seconds or minutes is usually needed to establish a block in the larger branches of the cell.

Action Potentials↗
PubMed1975

Rushton's paradox: rod dark adaptation after flash photolysis.

1. Rod dark adaptations after a photoregenerating flash and quantum-equivalent 30 sec bleach are found to be in exact agreement, while the measured rhodopsin regenerations are grossly different. This finding confirms and clarifies "Rushton's paradox', the failure of the Dowling-Rushton equation (linking log sensitivity linearly with unregenerated rhodopsin) to account for human rod dark adaptation after flash photolysis. 2. The hypothesis that the agreement between rod dark adaptation curves after a photoregenerating flash and after a quantum-equivalent 30 sec bleach is coincidental is rejected on the basic of two classes of experiments. 3. Rod "bleaching' adaptation is demonstrated to be entirely determined by the number of rhodopsin molecules which absorb at least one quantum in a temporal period T, whose range includes the time interval 600 musec less than or equal T less than or equal 30 sec. This generalization obtains over the entire scotopic energy range (congruent to 3 log units) where rod dark adaptations has been studied. 4. Thus, the state of "bleaching' adaptation is determined by some by-product of the normal chain of events in scotopic excitation. About this by-product three important deductions are made: (i) its production is a monotonic function of the initial effective quantum absorptions; (ii) its production occurs before the metarhodopsin I leads to to metarhodopsin II dark reaction; (iii) it cannot be any photoproduct of the rhodopsin cycle.

Dark Adaptation↗
PubMed1979

Dark-adaptation of the aspartate-isolated rod receptor potential of the frog retina: threshold measurements.

1. The dark-adaptation of the aspartate-isolated rod receptor potential of the isolated and perfused frog retina has been measured after bleaching about 5-10% of the rhodopsin. The fraction bleached (DeltaR) and the decay of rhodopsin photoproducts were determined using alternating measurements with a photometric technique (Donner & Hemilä, 1975).2. The dark-adaptation time course of the log threshold elevation is exponential, log I(t)/I(0) = W exp (-t/tau)+P, where W is the extrapolated value for log I(t)/I(0)-P at t = 0 and P is log I(t)/I(0) for t = infinity. When DeltaR increases from 2 to 10% W increases from ca. 2.6 to ca. 5. The time constant tau is about 13 min at 9 degrees C and 7 min at 14 degrees C (DeltaR = 5-10%).3. When the bleaching period is extended, keeping the amount bleached (Ixt) constant, dark-adaptation is completed earlier.4. The time course of dark-adaptation and the decay of the photoproduct ;retinal' are similar, as is also their dependence on temperature (Q(10) approximately 3).5. The permanent log threshold rise P is approximately proportional to DeltaR after small bleaches; when more than about 10% is bleached the slope of the curve P(DeltaR) decreases. P is considerably larger (about 2.5-fold) for the same fraction bleached in experiments at 14 degrees C as compared to experiments at 9 degrees C.6. A comparison with previously obtained corresponding values for dark-adaptation after small bleaches at the ganglion cell level shows a close agreement between the time constants for the dark-adaptation curve, its range and the dependence of threshold on the fraction of rhodopsin bleached.

Animals↗
PubMed1983

Compensatory eye movements during active and passive head movements: fast adaptation to changes in visual magnification.

Rotational eye and head movements were recorded with great precision with scleral and cranial search coils in a rotating magnetic field. Compensatory eye movements were recorded in light and darkness during active as well as passive head movements in the frequency range 0.33-1.33 Hz. From the recorded, nominal gaze movements the effective gaze was reconstructed taking into account magnification or reduction factors of corrective spectacles. Effective gain was calculated as the ratio between the velocities of the effective corrective eye movements and the head movements. In the light, effective gain of compensatory eye movements during active head motion was mostly between 0.97 and 1.03. It was never precisely unity and differed systematically between subjects and between the two eyes of each subject. During passive head motion in the light, gain was lower by about 3% than during active motion. During active head movement in the dark, gain was mostly between 0.92 and 1.00; values were about 5% lower than during active motion in the light. During passive head movement in the dark, gain was about 13% lower than during active motion, and the variability of the oculomotor response increased. Adaptation of these base-line conditions was induced by fitting the subjects with magnifying or reducing spectacles for periods of 40 min to 24 h. The largest required change in amplitude of eye movements was 36%. When active head movements were made, the amplitude of compensatory eye movements in the light as well as in the dark adjusted rapidly. Most of the adaptation of the vestibulo-ocular reflex in the dark was completed in about 30 min. This rate is much faster than that found in previous experiments requiring larger adaptive changes. Differential adaptation to unequal demands for the two eyes proved to be very hard or impossible. In a mild conflict situation the system adjusted to an intermediate level, distributing the error symmetrically between the eyes. When the discrepancy was large, the adaptive process of both eyes was controlled by the one eye which provided the most meaningful information. It is concluded that the system generating compensatory eye movements performs best during active rather than passive head movements, and that adaptation to moderate changes in optimal gain are made very rapidly.

Adaptation, Ocular↗
PubMed1983

Effects of extracellular calcium and of light adaptation on the response to dim light in honey bee drone photoreceptors.

Light responses in honey bee drone photoreceptors were recorded with intracellular micro-electrodes in superfused slices of retina. The effects of changes in extracellular calcium on the size and the shape of the response to dim light were studied and compared with the effects of light adaptation. Dim light stimuli were used so that the amplitude of the response was linearly related to the number of the photons absorbed, the effects of voltage-dependent mechanisms were negligible and no detectable light adaptation was produced by the stimulus. Lowering the extracellular calcium concentration increased the amplitude and the duration of the response. Raising the extracellular calcium concentration produced the opposite effects. Changing the extracellular calcium concentration modified the response without altering either the linearity of the intensity--response relation or the resting membrane potential in the dark. Light adaptation decreased the amplitude and the duration of the response in a manner that could be quantitatively simulated, in the same photoreceptors, by an increase in the extracellular calcium concentration. Changing the extracellular calcium concentration, or light-adapting the preparation, modified the response without altering its early depolarizing phase. Lowering external calcium either did not affect, or slightly increased, the maximum rate of the light-induced depolarization; raising external calcium, or light-adapting the preparation, either did not affect, or slightly decreased, the maximum rate of the light-induced depolarization. The experimental data can be quantitatively described by a mathematical model with the basic assumption that calcium acts in the process of light adaptation by decreasing the mean open time of the light-activated channels.

Adaptation, Ocular↗
PubMed1991

Incorporation of chelator into guinea-pig rods shows that calcium mediates mammalian photoreceptor light adaptation.

1. The effects of steady light on the sensitivity and kinetics of the photocurrent response were studied in the rod photoreceptors of the guinea-pig, using suction pipette recordings of circulating current. 2. The sensitivity of the flash response decreased with increasing background intensity according to Weber's law. Ultimately for the brightest backgrounds saturation ensued. The recovery phase of the flash response was accelerated by steady light, while the early rising phase was little affected. 3. These results indicate that guinea-pig rods adapt to light in much the same way as do the rods and cones of lower vertebrates. 4. The role of cytoplasmic calcium concentration in this adaptation was studied by incorporation of the calcium chelator bis(o-aminophenoxy)ethane- N,N,N',N'-tetraacetic acid (BAPTA) into the rod cytoplasm. Superfusion with a solution containing the membrane-permeant acetoxymethyl ester resulted in progressive changes in the response to light. 5. BAPTA incorporation retarded the falling phase of the flash response, thereby increasing receptor sensitivity, but did not affect the early rising phase of the response. BAPTA also slowed the adaptation of the response to steady illumination. 6. These results indicate that cytoplasmic calcium concentration plays a similar role in the light adaptation of guinea-pig rods to that in the adaptation of the rods and cones of lower vertebrates. Calcium therefore appears to act as the messenger of light adaptation in mammalian rods.

Action Potentials↗
PubMed2004

Uncoupling protein and ATP/ADP carrier increase mitochondrial proton conductance after cold adaptation of king penguins.

Juvenile king penguins develop adaptive thermogenesis after repeated immersion in cold water. However, the mechanisms of such metabolic adaptation in birds are unknown, as they lack brown adipose tissue and uncoupling protein-1 (UCP1), which mediate adaptive non-shivering thermogenesis in mammals. We used three different groups of juvenile king penguins to investigate the mitochondrial basis of avian adaptive thermogenesis in vitro. Skeletal muscle mitochondria isolated from penguins that had never been immersed in cold water showed no superoxide-stimulated proton conductance, indicating no functional avian UCP. Skeletal muscle mitochondria from penguins that had been either experimentally immersed or naturally adapted to cold water did possess functional avian UCP, demonstrated by a superoxide-stimulated, GDP-inhibitable proton conductance across their inner membrane. This was associated with a markedly greater abundance of avian UCP mRNA. In the presence (but not the absence) of fatty acids, these mitochondria also showed a greater adenine nucleotide translocase-catalysed proton conductance than those from never-immersed penguins. This was due to an increase in the amount of adenine nucleotide translocase. Therefore, adaptive thermogenesis in juvenile king penguins is linked to two separate mechanisms of uncoupling of oxidative phosphorylation in skeletal muscle mitochondria: increased proton transport activity of avian UCP (dependent on superoxide and inhibited by GDP) and increased proton transport activity of the adenine nucleotide translocase (dependent on fatty acids and inhibited by carboxyatractylate).

Adaptation, Physiological↗
PubMed2004

Mechanism of spike frequency adaptation in substantia gelatinosa neurones of rat.

Using tight-seal recordings from rat spinal cord slices, intracellular labelling and computer simulation, we analysed the mechanisms of spike frequency adaptation in substantia gelatinosa (SG) neurones. Adapting-firing neurones (AFNs) generated short bursts of spikes during sustained depolarization and were mostly found in lateral SG. The firing pattern and the shape of single spikes did not change after substitution of Ca2+ with Co2+, Mg2+ or Cd2+ indicating that Ca2+-dependent conductances do not contribute to adapting firing. Transient KA current was small and completely inactivated at resting potential suggesting that adapting firing was mainly generated by voltage-gated Na+ and delayed-rectifier K+ (KDR) currents. Although these currents were similar to those previously described in tonic-firing neurones (TFNs), we found that Na+ and KDR currents were smaller in AFNs. Discharge pattern in TFNs could be reversibly converted into that typical of AFNs in the presence of tetrodotoxin but not tetraethylammonium, suggesting that lower Na+ conductance is more critical for the appearance of firing adaptation. Intracellularly labelled AFNs showed specific morphological features and preserved long extensively branching axons, indicating that smaller Na+ conductance could not result from the axon cut. Computer simulation has further revealed that down-regulation of Na+ conductance represents an effective mechanism for the induction of firing adaptation. It is suggested that the cell-specific regulation of Na+ channel expression can be an important factor underlying the diversity of firing patterns in SG neurones.

Action Potentials↗
PubMed2005

An analysis of the impact of auditory-nerve adaptation on behavioral measures of temporal integration in cochlear implant recipients.

The objective of this study was to determine the impact that auditory-nerve adaptation has on behavioral measures of temporal integration in Nucleus 24 cochlear implant recipients. It was expected that, because the auditory nerve serves as the input to central temporal integrator, a large degree of auditory-nerve adaptation would reduce the amount of temporal integration. Neural adaptation was measured by tracking amplitude changes of the electrically evoked compound action potential (ECAP) in response to 1000-pps biphasic pulse trains of varying durations. Temporal integration was measured at both suprathreshold and threshold levels by an adaptive procedure. Although varying degrees of neural adaptation and temporal integration were observed across individuals, results of this investigation revealed no correlation between the degree of neural adaptation and psychophysical measures of temporal integration.

Acoustic Stimulation↗
PubMed1982

Transient complex and pure tone pitch changes by adaptation.

The effect of pitch adaptation by a complex stimulus was examined in two experiments. In experiment 1, a monaural complex tone pitch change was measured after ipsilateral or contralateral complex stimulus adaptation. While ipsilateral adaptation resulted in pitch changes away from the pitch of the adapting stimulus, no pitch occurred for contralateral adaptation. The precision of pitch matching was reduced by both ipsilateral and contralateral adaptation. Experiment 2 examined whether the complex tone pitch changes in experiment 1 could be accounted for by pitch changes induced in the pure tone components. Results indicated that changes induced in the pure tone components were too small to account for the complex tone shift magnitudes found in experiment 1. These results support a degree of independence of complex tone pitch from the pitches of the pure tone components. Results also supported pitch extractor specialization for a particular ear of stimulus presentation.

Adaptation, Physiological↗

Refine your search to explore more results.