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PubMed1982

An action spectrum for spatial-frequency adaptation.

The mechanism of spatial-frequency adaptation, and channel-bandwidth estimates derived from adaptation, were examined in a series of three experiments. The first two experiments measured adaptation as a function of both the frequency and modulation of the adapt stimulus. The threshold for producing adaptation at different adapt frequencies is considered to be an action spectrum whose half-amplitude bandwidth is found to lie between 1/3 and 2/3 octave. The third experiment employed a novel adaptation paradigm--varying the adapt contrast until the test grating was no longer perceptible--but the results supported those of the earlier experiments. It is concluded that adaptation is probably due to a fatigue-like mechanism, and that a sensitivity measure of adaptation (action spectrum) is probably a better representation of underlying channel tuning than is the more customary response measure.

Adaptation, Ocular↗
PubMed1986

Heterophoria: a vergence adaptive position.

Previous experiments have shown that as the adaptive change becomes more complete with prolonged wear of a prism, the adaptive decay during monocular occlusion (MO) becomes slower; at the same time, adaptation to a further prism disparity becomes faster. If phoria is an adapted position of the oculomotor system then, as with prism adaptation, it should demonstrate an adaptive decay during MO. The rate of this decay should be inversely related to the rate of adaptation to a prism. In the first part of the paper, changes in the horizontal and vertical phorias were demonstrated at distance and near during 4 hr of MO. In the second part, adaptation to various prism disparities (horizontal and vertical) was monitored. The rates of adaptation were found to be inversely related to the rates of phoria decay during MO. The phoria position is, therefore, an adapted position of the vergence system.

Accommodation, Ocular↗
PubMed2005

Predictors of psychosocial adaptation among people with spinal cord injury or disorder.

OBJECTIVE: To examine the influence of disability-related medical and psychologic variables on psychosocial adaptation to spinal cord injury or disorder (SCI/D). DESIGN: A structural equation modeling design linking 3 sets of predictive variables to an outcome measure of adaptation. SETTING: Two outpatient SCI clinics (1 veteran, 1 civilian) in Texas. PARTICIPANTS: Veterans (n=181) and civilians (n=132) with SCI/D. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The adaptation outcome was measured by 2 subscales (acknowledgment, adjustment) of the Reactions to Impairment and Disability Inventory (RIDI) and by the Quality of Life Scale. The predictive variables were measured by a demographic questionnaire, 3 subscales (intrusion, re-experiencing, hyperarousal) of the Purdue Posttraumatic Stress Disorder-Revised scale, the McMordie-Templer Death Anxiety Scale, and 3 subscales (anxiety, depression, denial) of the RIDI. RESULTS: Goodness-of-fit indices suggested that a revised model of adaptation was a moderately good fit to the data. The revised model of adaptation indicated that there were medium total effects (direct plus indirect) on psychosocial adaptation by 2 latent variables (disability severity and impact, negative affectivity) and small total effects on psychosocial adaptation by disengagement coping. The latent factor of disengagement coping had the strongest direct effect on adaptation (although not statistically significant). Disability severity and impact had medium indirect effects and negative affectivity had small indirect effects on psychosocial adaptation. All of the aforementioned effects had a negative coefficient. CONCLUSIONS: Negative emotional responses (eg, depression, anxiety) to SCI/D, disengagement-type coping (eg, disability denial, avoidance), and the severity and impact of disability were related to lower levels of adaptation to SCI/D.

Adaptation, Psychological↗
PubMed2004

Acquisition of context-specific adaptation is enhanced with rest intervals between changes in context state, suggesting a new form of motor consolidation.

We previously showed that the saccadic system could be adapted in a context-specific manner: two different adapted gains could be associated with two different context cues, with the gain state switched when the context state was switched. This was accomplished by alternating context/adaptation states several times over the course of an adaptation session, and assessing saccade gain in each context state before and after adaptation. One context cue we studied was vertical eye position; an adaptive gain increase was induced with the eyes up 10 degrees, and an adaptive gain decrease with the eyes down 10 degrees. This context cue was only partially effective: there was considerable undesired transfer of adaptation from the eyes-down condition (gain-decrease) to the eyes-up condition (gain-increase), with the result that there was little or no gain-increase adaptation. One explanation for this is that the two context/adaptation states, presented one after the other, interfered with each other. In the present study, we tested this hypothesis by interposing one-minute rest intervals between each alternation in context/adaptation state. The resulting context-specific adaptation is greatly improved (relative to the case when there are no rest intervals): both gain-increase and gain-decrease adaptations are stronger and occur more rapidly. This effect resembles that found in studies on the consolidation of motor learning, although such consolidation is believed to occur over much longer time spans (hours rather than minutes).

Acclimatization↗
PubMed2004

Prism adaptation in visually mature patients with esotropia of childhood onset.

OBJECTIVE: To investigate the role of prism adaptation in the visually mature population with esotropia onset before visual maturation. DESIGN: Retrospective, noncomparative case series. PARTICIPANTS: Eighty-five patients, 26 prism adapted for near (PAN) and 59 prism adapted for distance (PAD), were included in the study. METHODS: Patients included in this study were older than 9 years and had esotropia with an onset before age 9. Mean follow-up was 30 months (range = 6 weeks-164 months). All patients had prism adaptation and subsequent surgical correction. Surgical success was defined as peripheral fusion on the Worth 4-dot test and < or = 8(Delta) deviation at near and distance on the simultaneous prism and cover test. MAIN OUTCOME MEASURES: Response to preoperative prism adaptation and postoperative alignment and sensory results were examined. RESULTS: Twenty-six of the 85 patients had previous surgical esotropia correction. In the PAD group, 41 were responders. Seventeen of these had built their deviation > or = "0" > 10(Delta) with prism adaptation. All responders had surgery for their prism-adapted angle. Postoperatively, 34 of 41 (83%) responders and 6 of 18 (33%) nonresponders had fusion. In the PAN group, 17 were responders. Nine of these built their deviation with prisms. Postoperatively, 16 of 17 (94%) responders and builders and 1 of 9 (11%) nonresponders had successful surgery with sensory and motor fusion. CONCLUSIONS: Adults with esotropia onset before visual maturation can be prism adapted and surgically treated with a predictable outcome of sensory and motor fusion. Those prism adapted for near with response can be successfully treated with surgery for the near deviation. Prism adaptation also aids in determining those who would benefit from larger amounts of surgery.

Adaptation, Ocular↗
PubMed2004

Effect of adaptation direction on the motion VEP and perceived speed of drifting gratings.

The N200 amplitude of the motion-onset VEP evoked by a parafoveal grating of variable contrast (0.5-64%), constant speed (2 degrees/s), direction (horizontally rightward), and spatial frequency (2 cpd) was studied before and after adaptation to a stationary or drifting grating (1, 2, or 4 degrees/s rightward or leftward). These results are compared to those for the pattern-appearance VEP. Psychophysical measurements were made simultaneously of the perceived speed. While iso-directional (rightward) adaptation leads to a mean amplitude reduction of 39%, the decrease after counter-directional adaptation has a size of 20%. The post-adaptation matches of perceived speed differ in dependence on the iso-directional adapting speed and decrease on average to 98%, 85%, and 69% of the pre-adapt perceived speed after 1, 2, and 4 degrees/s adapting speeds, respectively. The perceived speed is moderately reduced (83% of the pre-adapt value) after counter-directional adaptation nearly independently of the adapting speed. A model of velocity processing is presented, which enables us to predict the trends of the experimental motion VEP and perceived speed data.

Adaptation, Physiological↗
PubMed1998

An essential role of NFkappaB in tyrosine kinase signaling of p38 MAP kinase regulation of myocardial adaptation to ischemia.

We have recently demonstrated that myocardial adaptation to ischemia triggers a tyrosine kinase regulated signaling pathway leading to the translocation and activation of p38 MAP kinase and MAPKAP kinase 2. Since oxidative stress is developed during ischemic adaptation and since free radicals have recently been shown to function as an intracellular signaling agent leading to the activation of nuclear transcription factor, NFkappaB, we examined whether NFkappaB was involved in the ischemic adaptation process. Isolated perfused rat hearts were adapted to ischemic stress by repeated ischemia and reperfusion. Hearts were pretreated with genistein to block tyrosine kinase while SB 203580 was used to inhibit p38 MAP kinases. Ischemic adaptation was associated with the nuclear translocation and activation of NFkappaB which was significantly blocked by both genistein and SB 203580. The ischemically adapted hearts were more resistant to ischemic reperfusion injury as evidenced by better function recovery and less tissue injury during post-ischemic reperfusion. Ischemic adaptation developed oxidative stress which was reflected by increased malonaldehyde formation. A synthetic peptide containing a cell membrane-permeable motif and nuclear sequence, SN 50, which blocked nuclear translocation of NFkappaB during ischemic adaptation, significantly inhibited the beneficial effects of adaptation on functional recovery and tissue injury. In concert, SN 50 reduced the oxidative stress developed in the adapted myocardium. These results demonstrate that p38 MAP kinase might be upstream of NFkappaB which plays a role in ischemic preconditioning of heart.

Adaptation, Physiological↗
PubMed2003

Comparison of the time courses of concomitant and nonconcomitant vertical phoria adaptation.

Vertical phoria adaptation was measured before, during, and after 1 h of training with either a prism or magnifying lens. With the prism (concomitant adaptation) a single vertical disparity was presented at primary position. With the magnifier (nonconcomitant adaptation) two vertical disparities of opposite sign were presented along the vertical meridian. Following adaptation, binocular vision was prevented with an eye patch, and vertical phorias were measured periodically along the primary vertical meridian over the course of 8 h. Despite individual variation, adaptation followed approximately exponential time courses. The average time constants for the decay of concomitant and nonconcomitant adaptation were 31 and 83 min, respectively. There was no consistent relationship between the rates of acquisition and decay nor was there a strong relationship between the gains of the adaptive responses and the rates of decay although there was a general trend for the gains of the nonconcomitant responses to be higher and the rate of decay slower than the concomitant responses. The results support the notion that concomitant and nonconcomitant phoria adaptation involve different mechanisms but not the contention that adaptation to prisms is easier or more robust than adaptation to lenses.

Adaptation, Physiological↗
PubMed1996

Spatial and temporal properties of cat horizontal cells after prolonged dark adaptation.

We studied the change of spatial and temporal response properties for cat horizontal (H-) cells during prolonged dark adaptation. H-cell responses were recorded intracellularly in the optically intact, in vivo eye. Spatial and temporal properties were first measured for light-adapted H-cells, followed by a period of dark adaptation, after which the same measurements were repeated. During dark adaptation threshold sensitivity was measured at regular intervals. Stable, long lasting recordings allowed us to measure changes of sensitivity and receptive field characteristics for adaptation periods up to 45 min. Although cat H-cells showed no signs of dark suppression or light sensitization, they remained insensitive in the scotopic range, even after prolonged dark adaptation. Absolute thresholds were in the low mesopic range. The sensitization was brought about by a shift from cone to rod input, and by substantial increases of both spatial and temporal integration upon dark adaptation. The length constant in the light-adapted state was on average about 4 deg. After dark adaptation it was up to a factor of three larger, with a median ratio of 1.85. Response delays, latencies and durations for (equal amplitude) threshold flash responses substantially increased during dark adaptation.

Animals↗
PubMed1998

Motion after-effect due to binocular sum of adaptation to linear motion.

The motion after-effect (MAE) can be elicited by adapting observers to global motion of randomly distributed dots before they view a display containing dots moving in random directions, but no global motion. Experiments by others have shown that if the adaptation stimulus contains two directions of motion, the MAE points opposite to the vector sum of the adapting directions. The present study investigated whether such vector addition in the MAE could also occur if the two directions of motion were presented to separate eyes. Observers were adapted to different, but not opposite, directions of motion in the two eyes. Either the left eye, the right eye, or both eyes were tested. Observers reported the direction of perceived motion during the test. When they saw the test stimulus with both eyes, observers reported seeing motion in the direction opposite that of the vector sum of the adaptation directions. In the monocular test conditions observers reported MAE directions opposite to the corresponding monocular adaptation directions. In a second experiment we verified that subjects had interocular transfer of the MAE. Together these results are consistent with a model in which (1) addition of adaptation directions occurs at a binocular site; (2) directional adaptation occurs at a monocular site; and (3) monocular adaptation is able to change the threshold for obtaining an MAE at the binocular site, thus acting like binocular adaptation in interocular transfer of the MAE.

Adaptation, Ocular↗
PubMed2001

Patterns of transfer of adaptation among body segments.

Two experiments were conducted in order to determine the patterns of transfer of visuomotor adaptation between arm and head pointing. An altered gain of display of pointing movements was used to induce a conflict between visual and somatosensory representations. Two subject groups participated in Experiment 1: group 1 adapted shoulder pointing movements, and group 2 adapted wrist pointing movements to a 0.5 gain of display. Following the adaptation regimen, subjects performed a transfer test in which the shoulder group performed wrist movements and the wrist group performed shoulder movements. The results demonstrated that both groups displayed typical adaptation curves, initially undershooting the target followed by a return to baseline performance. Transfer tests revealed that both groups had high transfer of the acquired adaptation to the other joint. Experiment 2 followed a similar design except that group 1 adapted head pointing movements and group 2 adapted arm pointing movements. The arm adaptation had high transfer to head pointing while the head adaptation had very little transfer to arm pointing. These results imply that, while the arm segments may share a common target representation for goal-directed actions, individual but functionally dependent target representations may exist for the control of head and arm movements.

Adaptation, Physiological↗
PubMed1992

Adaptation of aimed arm movements to sensorimotor discordance: evidence for direction-independent gain control.

Human subjects pointed, without sight of their arm, at visual targets presented on a mirror-viewed monitor screen. During the adaptation period of each experiment, the position of the pointing fingertip was continuously recorded and displayed on the screen along with the targets. This visual feedback was not always veridical; rather, it was manipulated to require a gradual modification of the pointing response gain throughout the adaptation period. No visual feedback at all was available during the pre- and postadaptation periods of each experiment. The adaptive effect was determined as difference between pre- and postadaptation gains. In Expt. A, visual feedback during the adaptation period prescribed a gradual reduction of the horizontal response gain without specifying the gain for other directions; the adaptive effect was found to generalize uniformly to all movement directions. Expt. B1 prescribed a reduction of the horizontal, and an unchanged vertical gain component: in spite of this differential requirement, the adaptive effect was again uniform for all directions. Expt. B2 prescribed a reduction of the horizontal, and an increase of the vertical gain component: we found a reduced gain for all directions, with a mild direction-dependence in the magnitude of the adaptive effect. In a modified version of Expt. B2, no intermanual transfer of the adaptive effect was found. Expt. C1-3 prescribed gain reduction for target directions within 15, 30, or 45 degrees around the horizontal, and gain increase for all other directions: we found little or no adaptive effects under such conditions. From the above findings, we concluded that the adapted system controls movement gain largely independent of movement direction. This mechanism responds readily to requirements for gain reduction, but not gain increase. No evidence for an organization of the arm motor system in direction-selective channels was found, in contrast to findings on the saccadic control system in a paradigm similar to our Expt. A8. This discrepancy supports the view that arm and eye movements are controlled by distinct mechanisms.

Adaptation, Psychological↗
PubMed2002

Dynamics of metal adaptation in riverine chironomids.

The ability of the non-biting midge Chironomus riparius to survive and reproduce in metal polluted lowland rivers facilitates the opportunity to study micro-evolutionary processes in situ. However, due to larval drift, adapted midge populations are subject to regular immigration of non-adapted specimens from clean upstream river reaches. To examine the influence of non-adapted genes in adapted midge populations on the level of metal adaptation, an upstream and downstream chironomid population were crossbred on eight separate occasions in the laboratory to mimic gene flow. Several life-history characteristics, indicating adaptation to metals, were followed seasonally in the parental strains as well as in the reciprocal crossings. Such crossings were done over a 14-month period and maternal effects were found to be absent, indicating a major genetic component for the increased metal tolerance in the exposed midge populations. Furthermore, results confirmed the presence of adaptation to metals in exposed chironomids. However, a rapid loss of metal adaptation in the first generation hybrid offspring was clearly demonstrated. Consequently, the large temporal variation in metal adaptation in midge populations from the river can be explained by the earlier reported seasonal variations in selection pressure and immigration rates from non-adapted sub-populations.

Adaptation, Physiological↗
PubMed2004

Adaptation changes the direction tuning of macaque MT neurons.

Prolonged exposure to a stimulus, called 'adaptation', reduces cortical responsiveness. Adaptation has been studied extensively in primary visual cortex (V1), where responsivity is usually reduced most when the adapting and test stimuli are well matched. Theories about the functional benefits of adaptation have relied on this specificity, but the resultant changes in neuronal tuning are of the wrong type to account for well-documented perceptual aftereffects. Here we have used moving sinusoidal gratings to study the effect of adaptation on the direction tuning of neurons in area MT in macaques. Responsivity in MT is maintained best in the adapted direction and is strongly reduced for nearby directions. Consequently, adaptation in the preferred direction reduces the direction-tuning bandwidth, whereas adaptation at near-preferred directions causes tuning to shift toward the adapted direction. This previously unknown effect of adaptation is consistent with perceptual aftereffects and indicates that different cortical regions may adjust to constant sensory input in distinct ways.

Action Potentials↗
PubMed1989

Extrarenal potassium adaptation: the role of aldosterone.

1. Prior adaptation to a high potassium (HK) diet reduces the increment in plasma potassium after nephrectomy and acute potassium loading. Previous work has suggested that this 'extrarenal potassium adaptation' is due to direct stimulation of cellular potassium uptake by chronic hyperaldosteronism. 2. In contrast, we have shown that when dietary potassium is withdrawn from HK rats, large urinary potassium losses persist, resulting in 'paradoxical potassium depletion'. This potassium depletion facilitates cellular potassium uptake and is, at least in part, responsible for extrarenal potassium adaptation. 3. To try to reconcile these observations, we explored further the role of aldosterone in extrarenal potassium adaptation. When dietary potassium was withdrawn from chronically adrenalectomized HK rats, paradoxical potassium depletion was markedly blunted and extrarenal potassium adaptation could not be demonstrated. Similarly, urinary potassium losses and potassium depletion were reduced when acute adrenalectomy was performed concomitantly with dietary potassium withdrawal. 4. We were unable to confirm previous studies showing extrarenal potassium adaptation in the absence of potassium depletion. Thus, extrarenal potassium adaptation did not occur after pretreatment with chronic high-dose mineralocorticoid, after prior adaptation to a sodium-free diet, or after prior adaptation to an extremely HK diet in the absence of dietary potassium withdrawal. 5. We conclude that chronic hyperaldosteronism is important in extrarenal potassium adaptation, but probably not via direct enhancement of cellular potassium uptake. Rather, in HK animals, hyperaldosteronism magnifies urinary potassium losses during fasting and thus promotes potassium depletion, which in turn facilitates the uptake of an acute potassium load.

Adaptation, Physiological↗
PubMed1999

Symptoms of depression are important to psychological adaptation and metabolic control in children with diabetes mellitus.

AIMS: Sixty-two children (37 girls, 25 boys) between 9 and 18 years of age were enrolled to investigate: (1) the relationship between adaptation to diabetes mellitus (DM) and psychological functioning; (2) if adaptation or psychological functioning was related to metabolic control; and (3) if the patients' ability to cope with diabetes as assessed by physicians, was correlated to adaptation or psychological functioning. METHODS: Psychological functioning was measured by three general psychological instruments for depressive symptoms, self-esteem and fear. Diabetes adaptation was evaluated by questionnaires and coping with diabetes by an assessment of the physicians. Metabolic control was expressed by the individual HbA1c measured during the last year. RESULTS: Adaptation to diabetes correlated to psychological functioning (depression, P<0.001; self-esteem, P<0.01; and fear, P<0.01). Multiple regression analyses showed that metabolic control was predicted by adaptation (P=0.0013) with monitoring of diabetes as the only significant aspect of the adaptation (P < or = 0.0001). In turn, adaptation was predicted by symptoms of depression and metabolic control (P<0.0001). In support of this observation, a depressed (n = 9) and a non depressed (n= 53) group showed significant differences in metabolic control (P < or = 0.01), adaptation (P < or = 0.001) and self-esteem (P < or = 0.001). The only significant variable for the physicians assessment was metabolic control, which explained 35 % of the variance (P < 0.001). CONCLUSIONS: The major conclusion is that symptoms of depression affect both adaptation and metabolic control. It should be of concern to identify patients with depressive symptoms, offer treatment for their emotional difficulties and increase the support for taking care of their diabetes.

Adaptation, Psychological↗
PubMed2005

A low-flow adaptation phase improves shear-stress resistance of artificially seeded endothelial cells.

INTRODUCTION: The purpose of this study was to evaluate the effect of different adaptation phases on the shear-stress resistance of endothelial cells seeded artificially onto vascular prostheses and biological heart valves. MATERIAL AND METHODS: Human endothelial cells (EC), fibroblasts (FB), and smooth muscle cells (SMC) were isolated from vena saphena magna pieces and expanded in culture. Group A: 15 polyurethane vascular grafts (20 mm diameter) were seeded with FB and SMC (53 +/- 1.2 million cells), followed by EC seeding (39 +/- 0.9 million cells). Group B: eight stentless porcine valves (Freestyle, Medtronic, USA) were seeded with FB (68 +/- 1.5 million cells) and EC (42 +/- 1.1 million cells). Shear-stress testing was done under pulsatile flow (pulse rate: 80 pulses/min.). Adaptation phase: flow was set to 0.9 +/- 0.3 l/min (systolic pressure: 40 - 50 mm Hg). High flow was 3.2 +/- 0.6 l/min. (systolic pressure: 140 - 160 mm Hg) and lasted over four hours in all groups. The vascular grafts were divided into three groups (n = 5 each): group 1 (high flow immediately), group 2 (adaptation phase of 15 minutes), and group 3 (adaptation phase of 30 minutes). The valves either were given high flow immediately (n = 4) or had an adaptation phase of 30 minutes (n = 4). Specimens were obtained after cell seeding, before, and after perfusion. RESULTS: A confluent EC layer was achieved on all grafts. After perfusion without adaptation, large defects within the cell layer were found. No FB and SMC were seen at the bottom of these defects. In group B, the defects were largest on the ventricular surface of the leaflets. After an adaptation phase of 15 minutes in group A, only a few defects within the EC layer were detected with a still confluent FB and SMC. After a 30-minute adaptation phase defects within the EC layer were very rare and no interruption of the underlying FB and SMC layer was seen. Immunohistochemical staining for factor VIII and CD31 proved the EC to be viable and staining for collagen IV and laminin revealed the formation of a basement membrane. After perfusion, the specimen also stained positive for eNOS. CONCLUSION: An adaptation phase of 30 minutes proved to be sufficient to allow artificially seeded endothelial cells to adapt to shear stress. The formation of a basement membrane was of great importance for the maintenance of a confluent EC layer.

Adaptation, Physiological↗
PubMed1999

Properties of rat cone-mediated electroretinograms during light adaptation.

PURPOSE: Our aim was to better understand how to isolate the cone-mediated response in rats. Therefore, we studied the difference of ERGs in the course of light adaptation between 2 and 20 Hz stimulus frequencies. METHODS: A total of 90 rats divided into 18 different groups were used following overnight dark adaptation. ERGs were recorded against 3 different adapting field luminances (1.15, 1. 50 or 1.75 log cd/m(2)) with a combination of 3 stimulus flash intensities (0.86, 1.30 or 2.03 log cd sec/m( 2)). The responses were obtained at 2 minute intervals for 25 minutes of light adaptation. RESULTS: The response of the rat cone ERG was large despite the small number of cones. The mean amplitude increased systematically from the dark-adapted value requiring more than 15 minutes to reach an asymptote at 2 Hz stimulation, but only 10 minutes at 20 Hz stimulation. The 2 Hz adaptation curves had biphasic pattern compared to the monophasic 20 Hz curve. This second increase in the amplitude at 2 Hz appeared at around 7-8 minutes as a function of adaptation time. This tendency was most evident when using a low adapting field luminance with a high flash intensity. CONCLUSIONS: Our results suggest that the rods intrude much more during light adaptation at 2 Hz stimulation in rodents than in humans. Therefore, 20 Hz flicker stimulation can better isolate more the cone-mediated function than 2 Hz stimulation during the course of light adaptation in rats. Furthermore, the functional characteristics of the cone in rats may be different from that in humans.

Adaptation, Ocular↗