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PubMed1988

Factors governing the adaptation of cells in area-17 of the cat visual cortex.

Neurons in area 17 of the cat visual cortex adapt when stimulated by drifting patterns of optimal orientation, spatial frequency and temporal frequency (Ohzawa et al. 1982; Albrecht et al. 1984; Ohzawa et al. 1985). A component of this adaptation has been attributed to a contrast gain-control mechanism, rather than to neural fatigue, and results in enhanced differential sensitivity around the adapting contrast level (Ohzawa et al. 1982; Albrecht et al. 1984; Ohzawa et al. 1985). Experiments described here suggest that neural response rate, the directional selectivity of the cell, and the temporal frequency of the stimulus, are the principal determinants of adaptation, irrespective of other stimulus parameters such as contrast, velocity, or spatial frequency. The present results can nevertheless accommodate the results of previous studies of adaptation, and additionally provide scope for the resolution of apparent contradictions between results from psychophysical and neurophysiological studies of adaptation.

Adaptation, Physiological↗
PubMed1990

Nitrosoguanidine-induced adaptive repair in Pseudomonas aeruginosa.

Error-proof adaptive repair has been demonstrated in Pseudomonas aeruginosa. Cells of actively replicating wild-type Ps. aeruginosa (ATCC27853) and its auxotrophic derivative PAO 286 were subjected to stepwise adaptation (up to 1 microgram ml-1) by nitrosoguanidine (MNNG). Such cells resisted lethal and mutagenic effects of MNNG-challenge (lethal) doses more efficiently than those of nonadapted cultures. Similarly, reactivation of alkylated Pseudomonas phages was enhanced in adapted cells only. Induction of adaptive repair enzymes was sensitive to chloramphenicol (protein synthesis-inhibiting antibiotic) during adaptation treatment only. Protein extract from adapted cells showed increased levels in sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE).

Adaptation, Physiological↗
PubMed1978

A model for light adaptation: producing Weber's law with bleaching-type kinetics.

An "adaptation model" having two stages is introduced and its mathematical properties are examined. The two stages are the "adaptive process" (parameter Kb), which has bleaching-type kinetics, and the "response function" (parameters Kr and n), which incorporates response saturation. In order to study the increment threshold functions generated by the "adaptation model" the concept of a "detector" is required. It is demonstrated that without an adaptive process the compression hypothesis, in the form of the "difference equation", produces increment threshold functions which saturate and do not obey Weber's law. It is then shown that an adaptive process with bleaching-type kinetics can prevent saturation and produce Weber's law behavior provided that the "adaptive strength" of the system exceeds the "detector sensitivity".

Adaptation, Ocular↗
PubMedDate not supplied

On the mechanism and possible therapeutic application of delayed adaptation of the heart to stress situations.

Mild (not harmful) stress may initiate an adaptive mechanism, protecting the heart from harmful consequences of a more severe stress. There are at least three known types of cardiac adaptation to stress, such as: a) the gradually developing, long lasting adaptation to chronic mechanical overload, leading to cardiac hypertrophy, later to cardiomyopathy and heart failure, b) the rapidly developing adaptation to moderate stress initiated by 'preconditioning' brief coronary occlusion(s) or brief periods of rapid cardiac pacing, protecting for less than 1 h against consequences of a subsequent, severe stress, c) the later appearing, more prolonged cardio-protective adaptation, described by us in 1983, induced by various forms of more severe but not injurious stimuli, such as an optimal dose of prostacyclin or its stable analogues; or a series of brief periods of rapid pacings. This form of cardiac adaptation to stress protects for 24-48 h against consequences of a more severe stress such as: 1. myocardial ischaemia; 2. early and late postocclusion and reperfusion arrhythmias; 3. early morphologic changes secondary to ischaemia and reperfusion; 4. ischaemia induced myocardial loss of K+ and accumulation of Na+ and Ca++; 5. it may increase the tolerance to the toxic effects of cardiac glycosides. A reduced response to beta-adrenergic stimuli and a concomitant increase in activity and amount of PDE I and IV was shown by us earlier.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1986

Light and dark adaptation influences GABA receptor sites in the chick retina.

The aim of the present study was to investigate the effect of environmental conditions such as light-and-dark-adaptation on the plasticity of GABA receptor sites in the chick retina. In chicks exposed to light for 5 hr (light-adapted), specific [3H]GABA binding was increased by 35% in comparison to the binding found in chicks maintained in darkness (dark-adapted). Conversely, in the retina of chicks exposed to darkness for 5 hr, specific [3H]GABA binding was decreased by 28% with respect to that found in chicks kept in the light. Scatchard analysis of the binding data revealed that the affinity of GABA for its receptor binding site was higher in the retinas of light-adapted chicks than in those of dark-adapted chicks (Kd values of 19.20 +/- 1.23 and 27.20 +/- 1.47 nM, respectively). On the contrary, the maximal number of binding sites (Bmax) remained unchanged in light- and dark-adapted chicks (5.2 +/- 0.10 and 5.3 +/- 0.15 pmol/mg protein, respectively). These results suggest the involvement of GABA receptors in the regulation of visual function.

Animals↗
PubMedDate not supplied

Effects of adaptation to high altitude hypoxia on the contractile function and adrenoreactivity of the heart.

Effects of adaptation to mountain altitude of 3200 m on the contractile function and adrenoreactivity of the heart in rats have been investigated. It was shown that adaptation to altitude increased the contractile force and contraction and relaxation velocities of the left ventricle as compared to the controls. Simultaneously, a significant increase in cardiac response to noradrenaline developed in the course of adaptation. The increased response was accompanied by its more rapid disappearance. These changes may be explained by the increase in the activity of myocardial adenylate cyclase and phosphodiesterase. It was also shown that the decrease in cardiac function produced by cardiac denervation was less pronounced in adapted rats. This fact may be explained by increased effectiveness of cardiac autoregulatory mechanism. The comparison of these results with the data of other investigators suggests that in well adapted animals the strength of interaction between the levels of the regulatory hierarchy of the whole organism changes, i.e., the capacity of autoregulatory cell mechanisms and their reactivity to neurohumoral stimuli increase. As a result, control of the organism's reactions by higher levels of the regulatory system is more economical in adapted animals.

Adaptation, Physiological↗
PubMed1986

Effect of exercise training on the disappearance of cold adaptability in rats.

Following the transfer of cold-adapted rats to a warm environment at 25 degrees C, enhanced nonshivering thermogenesis and enlarged interscapular brown adipose tissue (BAT) decreased gradually and reached a steady state after 4 weeks of de-adaptation. Animals that were exercised in the process of de-adaptation, however, showed no decrease in enhanced nonshivering thermogenesis, but did show a decrease in BAT weight as compared with sedentarily de-adapted animals. Triiodothyronine (T3), the physiologically most active thyroid hormone, was at a higher plasma level in cold-adapted rats than in de-adapted animals with or without exercise loads. Although the resting level of T3 in running-trained rats was not higher than that in sedentary rats, some fluctuations of T3 level were observed during running.

Adaptation, Physiological↗
PubMed2000

Microvascular adaptation--regulation, coordination and function.

Microvascular networks have to adapt continuously in response to changes of the local environment in order to maintain adequate function. This adaptation involves reactions to hemodynamic and metabolic stimuli. The present study analyzes fundamental requirements for vascular adaptation by combining experimental observations in microvascular networks and mathematical simulations. Angioarchitecture and flow distribution were analyzed in microvascular networks of the rat mesentery by intravital microscopy. In addition, blood flow and oxygen distribution in these networks were simulated using a mathematical model. The model was based on experimental information on blood rheology in microvessels. In addition, the diameter adaptation of vessel segments (n = 300-1000) in the networks to different sets of stimuli was simulated. The hemodynamic analysis shows that, in the experimentally observed network architecture, average wall shear stress declines consistently with intravascular pressure (from about 100 dyn/cm2 for pressures of 70 mmHg to about 10 dyn/cm2 for pressures of 15 mmHg) indicating the importance of hemodynamic factors for vascular adaptation. However, to obtain stable adaptation of microvascular networks, additional responses to the metabolic situation and information transfer from distal to proximal vessels were needed. The metabolic stimuli maintain parallel flow pathways and adequate supply of distal tissue regions, while the hemodynamic factors optimize network structure and minimize energy expenditure.

Adaptation, Physiological↗
PubMed2006

Wide- versus specific-adaptation strategy for lucerne breeding in northern Italy.

This study is aimed at comparing wide- versus specific-adaptation strategies for lucerne in northern Italy on the basis of actual dry matter yield gains over 12 harvests from phenotypic selection, assessing the value of specific genetic bases and selecting environments for the contrasting subregion A (no drought stress/sandy-loam soil) and subregion C (summer drought stress/silty-clay soil). A second aim is to investigate the adaptive responses of five sets of 18 half-sib progenies. The following selected populations were evaluated along with five cultivars: GW-SW, GA-SA, GA-SC, GC-SC and GC-SA (where GW, GA and GC are the genetic bases for wide adaptation, subregions A and C; SW, SA and SC are the selection environments for wide adaptation, subregions A and C). The selection and test environments were four artificial environments created by the factorial combination of two drought stress levels by two soil types. Two environments represented the subregions A and C whereas the combination of the other two environments represented the intermediate subregion B. Genotype x environment interaction (P < or = 0.001) due to both environmental factors and implying cross-over interaction between the contrasting subregions occurred for the populations and the five selections. Specific genetic bases (GA and GC) implied gains in their target subregions of 5.2% for subregion A and 2.9% for subregion C compared with the widely adapted one (GW). The gain of SA ('no stress/sandy-loam soil') over SC ('stress/silty-clay soil') decreased from subregion A (10.6%) through subregion C (1.7%) but exhibited an advantage per se across environments of 5.4%. The best specific selections (GA-SA for subregions A and B; GC-SA for subregion C) implied higher yields of 9.8% in subregion A and 6.5% in subregion C, and over twofold greater selection efficiency across the region, relative to GW-SW. Half-sib progeny x artificial environment interaction (P < or = 0.05) occurred in three sets of progenies whose parents belonged to cultivars with different or similar adaptation.

Adaptation, Biological↗
PubMed2002

Context-specific adaptation of the gain of the oculomotor response to lateral translation using roll and pitch head tilts as contexts.

Previous studies established that vestibular and oculomotor behaviors can have two adapted states (e.g., gain) simultaneously, and that a context cue (e.g., vertical eye position) can switch between the two states. The present study examined this phenomenon of context-specific adaptation for the oculomotor response to interaural translation (which we term "linear vestibulo-ocular reflex" or LVOR even though it may have extravestibular components). Subjects sat upright on a linear sled and were translated at 0.7 Hz and 0.3 gpeak acceleration while a visual-vestibular mismatch paradigm was used to adaptively increase (x2) or decrease (x0) the gain of the LVOR. In each experimental session, gain increase was asked for in one context, and gain decrease in another context. Testing in darkness with steps and sines before and after adaptation, in each context, assessed the extent to which the context itself could recall the gain state that was imposed in that context during adaptation. Two different contexts were used: head pitch (26 degrees forward and backward) and head roll (26 degrees or 45 degrees, right and left). Head roll tilt worked well as a context cue: with the head rolled to the right the LVOR could be made to have a higher gain than with the head rolled to the left. Head pitch tilt was less effective as a context cue. This suggests that the more closely related a context cue is to the response being adapted, the more effective it is.

Adaptation, Psychological↗
PubMed2002

Cross-axis adaptation of torsional components in the yaw-axis vestibulo-ocular reflex.

The three pairs of semicircular canals within the labyrinth are not perfectly aligned with the pulling directions of the six extraocular muscles. Therefore, for a given head movement, the vestibulo-ocular reflex (VOR) depends upon central neural mechanisms that couple the canals to the muscles with the appropriate functional gains in order to generate a response that rotates the eye the correct amount and around the correct axis. A consequence of these neural connections is a cross-axis adaptive capability, which can be stimulated experimentally when head rotation is around one axis and visual motion about another. From this visual-vestibular conflict the brain infers that the slow-phase eye movement is rotating around the wrong axis. We explored the capability of human cross-axis adaptation, using a short-term training paradigm, to determine if torsional eye movements could be elicited by yaw (horizontal) head rotation (where torsion is normally inappropriate). We applied yaw sinusoidal head rotation (+/-10 degrees, 0.33 Hz) and measured eye movement responses in the dark, and before and after adaptation. The adaptation paradigm lasted 45-60 min, and consisted of the identical head motion, coupled with a moving visual scene that required one of several types of eye movements: (1) torsion alone (-Roll); (2) horizontal/torsional, head right/CW torsion (Yaw-Roll); (3) horizontal/torsional, head right/CCW torsion (Yaw+Roll); (4) horizontal, vertical, torsional combined (Yaw+Pitch-Roll); and (5) horizontal and vertical together (Yaw+Pitch). The largest and most significant changes in torsional amplitude occurred in the Yaw-Roll and Yaw+Roll conditions. We conclude that short-term, cross-axis adaptation of torsion is possible but constrained by the complexity of the adaptation task: smaller torsional components are produced if more than one cross-coupling component is required. In contrast, vertical cross-axis components can be easily trained to occur with yaw head movements.

Adaptation, Physiological↗
PubMed2002

Transfer of sensorimotor adaptation between different movement categories.

It is well known that sensorimotor adaptation will transfer from the practiced to the unpracticed arm, which has been taken as evidence that adaptation is located in the brain before the divergence point for left and right arm control. We now explore whether adaptation will transfer between different movement categories as well. Subjects were exposed to a 60-deg visual rotation first in a tracking and then in a pointing task, or vice versa. We found a substantial transfer of adaptation between tasks, but its magnitude was larger from pointing to tracking than from tracking to pointing. This benefit of pointing persisted when the use of cognitive strategies was minimized by a concurrent, attention-demanding task, but it was lost when pointing amplitudes were very small. We conclude that adaptation is located in the brain before the divergence point for different movement categories, and that movements with a large ballistic component facilitate adaptation transfer.

Adaptation, Physiological↗
PubMed2003

Functional significance of stiffness in adaptation of multijoint arm movements to stable and unstable dynamics.

This study compared the mechanisms of adaptation to stable and unstable dynamics from the perspective of changes in joint mechanics. Subjects were instructed to make point to point movements in force fields generated by a robotic manipulandum which interacted with the arm in either a stable or an unstable manner. After subjects adjusted to the initial disturbing effects of the force fields they were able to produce normal straight movements to the target. In the case of the stable interaction, subjects modified the joint torques in order to appropriately compensate for the force field. No change in joint torque or endpoint force was required or observed in the case of the unstable interaction. After adaptation, the endpoint stiffness of the arm was measured by applying displacements to the hand in eight different directions midway through the movements. This was compared to the stiffness measured similarly during movements in a null force field. After adaptation, the endpoint stiffness under both the stable and unstable dynamics was modified relative to the null field. Adaptation to unstable dynamics was achieved by selective modification of endpoint stiffness in the direction of the instability. To investigate whether the change in endpoint stiffness could be accounted for by change in joint torque or endpoint force, we estimated the change in stiffness on each trial based on the change in joint torque relative to the null field. For stable dynamics the change in endpoint stiffness was accurately predicted. However, for unstable dynamics the change in endpoint stiffness could not be reproduced. In fact, the predicted endpoint stiffness was similar to that in the null force field. Thus, the change in endpoint stiffness seen after adaptation to stable dynamics was directly related to changes in net joint torque necessary to compensate for the dynamics in contrast to adaptation to unstable dynamics, where a selective change in endpoint stiffness occurred without any modification of net joint torque.

Adaptation, Physiological↗
PubMed2004

Components of sensorimotor adaptation in young and elderly subjects.

Previous studies have found that sensorimotor adaptation to visual distortions is degraded in seniors compared with younger subjects, whereas after-effects on removal of the distortion are age-independent. The latter finding was interpreted as evidence that adaptive recalibration is not affected by old age, and that the observed degradation is therefore due to impairment of strategic control. However, after-effects are not a reliable measure of recalibration, because they can be artificially inflated by perseveration, a characteristic symptom in old age. The present work therefore introduces a test of recalibration which is insensitive to perseveration. Twelve young and twelve old subjects executed center-out pointing movements while visual feedback about their fingertip was either veridical (baseline), 60-deg rotated (adaptation), or absent (after-effect). They also executed tracking movements toward an unpredictably moving object before and after the pointing task. Seniors adapted less than younger subjects but their after-effects were not degraded. More importantly, transfer of adaptation from a pointing to a tracking task was not degraded in seniors. The latter outcome documents, in a more compelling fashion than previous work, that recalibration in the elderly is not impaired, and that the observed deficit of adaptation is therefore most probably because of impaired strategic control. This conclusion is supported by two additional findings: compared with young subjects our seniors performed less well on a cognitive screening test and acquired no explicit knowledge about the nature of the imposed visual distortion.

Adaptation, Physiological↗
PubMed2005

Relationship between sensorimotor adaptation and cognitive functions in younger and older subjects.

We investigated whether deficits of adaptive improvement in seniors are related to an age-dependent decay of the brain's executive functions. Younger and older subjects completed a battery of cognitive tests, and preformed aimed arm movements before and during exposure to rotated visual feedback. In accordance with previous work, we found that adaptive improvement during exposure was degraded in seniors, while the transfer of adaptation to a new motor task was not. This pattern of findings confirms that strategic control but not sensorimotor recalibration is affected by old age. Using multiple linear regression (MLR) to extract separate executive components from our test battery, we found that basic response speed and decision-making, but not the inhibition of prepotent responses or mental flexibility, were degraded in our older subjects. Again using MLR, we found that degraded adaptive improvement in our seniors was partly related to the decay of basic response speed and decision-making, and partly to age-dependent phenomena not addressed by our cognitive-test battery. Finally, we observed that interindividual variability of cognition and adaptive improvement was larger in old than in young subjects, which could explain why some previous studies found degraded adaptation in seniors while others did not.

Adaptation, Physiological↗
PubMed2005

Two waves of a long-lasting aftereffect of prism adaptation measured over 7 days.

Prism adaptation is a useful paradigm to study the integration and reorganization of various sensory modalities involved in sensory-motor tasks. By prolonging the prismatic aftereffect and well-timed observation, we aimed to dissociate the components and mechanisms involved in human prism adaptation by their differential decay and development time courses. Here, we show that a single session of prism adaptation training, combining small increments of prism strength below the subjects' awareness threshold, during a pointing task with a free walk session with total prism exposure duration of 75 min, generated a surprisingly long-lasting aftereffect. The aftereffect was measured by the magnitude of the proprioceptive shift (assessed by straight-ahead pointing in the dark) for 7 days. An aftereffect was observed, which lasted for more than 6 days, by a single prism adaptation session. The aftereffect did not decay gradually. Unlike previous descriptions, the aftereffect showed two separate time-courses of decay and increase. After a significant initial decay within 6 h, the aftereffect increased again from 1 day up to 3 days. The novel decay and delayed development profile of this adaptation aftereffect suggests two separate underlying neural mechanisms with different time scales. Our experimental paradigms promise to reveal directly the temporal characteristics of early versus late long-term neural plasticity in complex human adaptive behavior.

Adaptation, Physiological↗
PubMed2001

Cross-axis adaptation of the translational vestibulo-ocular reflex.

The adaptive plasticity of the translational vestibulo-ocular reflex (VOR) was investigated in rhesus monkeys after 2-h exposure to either vertical or torsional optic flow stimulation accompanied by lateral translation stimuli (0.5 Hz). Because of the inherent ambiguity in the otolith system for the detection of gravitoinertial accelerations, we hypothesized that cross-axis adaptation of the translational VOR during lateral motion would be preferentially selective for a torsional optic flow stimulus that would mimic a roll tilt movement. However, we found that both vertical and torsional adaptation was possible. Furthermore, there was no significant preference for whether the torsional adaptation was in phase or out of phase with the apparent tilt induced by the motion stimulus. These results suggest that, at least at 0.5 Hz, there seems to be no preferential, visually induced adaptive capacity of the otolith system for tilt/translation reinterpretation during motion. Like the rotational VOR, translational VOR appears to exhibit a general form of cross-axis adaptation that operates for different directions of optic flow stimulation.

Adaptation, Physiological↗
PubMed2002

Dark adaptation in age-related macular degeneration: relationship to the fellow eye.

BACKGROUND: Abnormalities of dark adaptation have been documented in patients with age-related macular degeneration (AMD), but the relationship with the various forms of this disorder has not been studied systematically. METHODS: Dark-adapted retinal sensitivities and kinetics of dark adaptation were studied using a Humphrey visual field analyzer adapted for these purposes in patients over 64 years of age. One eye per patient was studied. Study eyes had a normal visual acuity and macular drusen only. The fellow eye was categorized as follows: group I, pigment epithelial detachments and tears of the retinal pigment epithelium (RPE); group II, choroidal neovascularization; and group III, drusen only. The results of psychophysical tests of the study eyes (group I and II and one eye of group III patients) were compared with one another and with older patients without evidence of AMD (group IV). RESULTS: Retinal sensitivity was found to be most consistently abnormal nearest the fovea. The time course of dark adaptation was prolonged beyond 45 min in 10/11 patients (91%) in group I, 6/10 patients (60%) in group II, and 6/10 (60%) in group III and 1/11 (9%) in group IV. CONCLUSION: In a high proportion of patients with visual loss from AMD in one eye, the fellow eye shows abnormal dark adaptation. These changes appear to be most pronounced in patients with detachments of the RPE in the fellow eye.

Aged↗