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 577 records · Page 32Linked to original sources
PubMed2003

GABA(A) and GABA(B) receptors mediated inhibition affect the pattern adaptation of relay cells in the dorsal lateral geniculate nucleus (LGNd) of cats.

Pattern adaptation is very important for visual function, while the mechanisms that mediate pattern adaptation, especially in the dorsal lateral geniculate nucleus (LGNd), are still unclear. Iontophoresis of the antagonists and agonists of GABA receptors were employed to separately investigate the contribution of GABA(A) and GABA(B) receptors to pattern adaptation of LGNd cells. When GABA(A) receptors were blocked by bicuculline both the response amplitude of LGNd cells and the degree of adaptation increased significantly. Many neurons showing no pattern adaptation under the normal condition became adapted to a prolonged stimulus. Moreover, the proportion of cells showing adaptation doubled (from 40 to 88%). The mean adaptation index (AI, adapted response amplitude/original response amplitude) was 0.82 during bicuculline application, compared with 0.92 under the control condition. In additional, iontophoresis of baclofen, a selective GABA(B) receptor agonist, decreased the mean response amplitude to grating stimuli to 53% of normal. Nearly half of the neurons increased their adaptation index following baclofen administration and the mean AI increased from 0.89 to 1.01. Iontophoresis of GABA(B) receptor antagonist (CGP35348) could abolish this effect, though it had no significant effect on visual response amplitude and pattern adaptation itself. Iontophoresis of another GABA(B) receptor antagonist, 2-OH-saclofen, also had no significant effect on visual response amplitude and pattern adaptation. These results suggest that both GABA(A) receptors and GABA(B) receptors modulate the pattern adaptation of LGNd cells and are involved in synaptic plasticity.

Action Potentials↗
PubMed2003

Heterogeneity of spike frequency adaptation among medium spiny neurones from the rat striatum.

The main neuronal population of the striatum is composed of the medium spiny neurones (MSNs). In fact several sub-populations of MSNs can be distinguished according to the striatal compartment (striosomes and matrix) to which they belong, their afferents and their sites of projection, their biochemical markers and their morphologies. However, these cells are generally described as an electrophysiological homogeneous population. Using brain slices from the rat and whole cell patch clamp recordings, we show that at P(15) 28% of the MSNs display a spike frequency adaptation. While the mean frequency adaptation ratio for non-adapting cells was 1.07+/-0.01 it reached 2.66+/-0.09 in adapting MSNs and the incidence of this frequency adaptation phenotype appeared to be stable during post-natal development. Single-cell RT-PCR analysis of mRNAs for mu opioid receptors, enkephalin and substance P precursors suggested that adapting MSNs are present in both striatal compartments as well as in the direct and indirect pathways of the matrix. Adapting neurones were also distinguished from non-adapting cells by a lower membrane time constant, a higher AP threshold, a reduced delay to the first spike and a higher initial firing rate. Micro-domains differing by their magnitude of adaptation could be distinguished within the spike frequency adaptation process.A subgroup of MSNs exists, showing a marked spike frequency adaptation together with other distinct properties, such as shorter delay to first spike and membrane time constant, and higher initial frequency and action potential threshold. In conclusion, when strong cortical inputs are delivered in coincidence, adapting MSNs could not only transmit faster the first AP but also exert a sort of cutoff of the transmission due to their spike frequency adaptation process.

Action Potentials↗
PubMed1991

Evidence for a common motion mechanism of luminance-modulated and contrast-modulated patterns: selective adaptation.

Selective adaptation effects were measured with contrast-modulated patterns and sine-wave gratings in order to determine the extent to which the two patterns are processed by common mechanisms. Direction-specific adaptation effects were measured for a contrast-modulated adapting pattern and a test pattern. The contrast-modulated adapting pattern was composed of a sine-wave grating of 8 cycles deg-1 whose contrast was spatially modulated by a sinusoid of 1 cycle deg-1 at one of four levels: 100%, 60%, 30%, or 0%. The results showed that contrast-modulation thresholds for contrast-modulated gratings were raised by 0.3 to 0.5 log units following adaptation to a contrast-modulated grating moving in the same direction as the test pattern, relative to thresholds obtained following adaptation to a contrast-modulated grafting moving in the opposite direction. Cross-adaptation effects were also measured with a sine-wave adapting pattern and a contrast-modulated test pattern. The sine-wave adapting pattern was a sine-wave grating of 1 cycle deg-1 whose contrast was set to one of three levels: 16.4%, 1.25%, or 0%. The contrast-modulated test pattern was a sine-wave grating of 8 cycles deg-1 whose contrast was modulated by a sinusoid of 1 cycle deg-1. The results revealed that contrast-modulation thresholds for contrast-modulated gratings were raised by approximately 0.25 log units following adaptation to moving sine-wave gratings, relative to thresholds obtained following adaptation to a uniform field. Cross-adaptation effects were also obtained with a contrast-modulated adapting pattern and a sine-wave test pattern. The results support the view that signals generated from luminance-domain stimuli and from contrast-domain stimuli are processed by a common motion mechanism.

Adaptation, Ocular↗
PubMed1973

Salt adaptation in Bufo bufo.

1. The capacity of adaptation of toads (Bufo bufo) to environments of high salinity was studied and the relative importance of skin, kidney and urinary bladder in controlling the balance of water and salt was assessed.2. Toads were kept in NaCl solutions of 20, 50, 110, 150 and 220 mM and studied in their fourth week of adaptation. A group of animals considered as ;control' was kept in wet soil with free access to water. Plasma, ureter urine, and bladder and colon contents were analysed for sodium, potassium, chloride and osmolality, and total body sodium and water were determined. Absorption of water and (22)Na through the skin, and water flow and sodium excretion through the ureter, of intact animals was studied. Hydrosmotic water transport through the isolated urinary bladder of ;control' and adapted animals was determined. The effects of pitressin and aldosterone on the water and sodium balance are described.3. The survival rates of toads kept in saline concentrations up to 150 mM were identical to that of ;control' animals, but half of the animals kept in 220 mM died within 4 weeks.4. There is a linear correlation between the sodium concentrations and osmolality of plasma and of the external media.5. The sodium concentration in colon contents rose with rising external concentrations, up to values higher than the values in plasma.6. Sodium concentrations and osmolalities of ureter and bladder urine increased in adapted animals, the values for bladder urine becoming much higher than those for ureter urine in animals adapted to 110, 150 and 220 mM.7. Total body water, as a percentage of total weight was kept within very narrow limits, although the total body sodium increased with adaptation.8. Absorption of water through the skin for the same osmotic gradients was smaller in adapted than in ;control' animals.9. The ureteral output of water of toads adapted to 110 and 150 mM-NaCl was larger than the water absorption through the skin.10. Skin absorption of sodium was lower in animals adapted to concentrated saline solutions than in ;control' animals.11. Sodium output by the ureter was identical to skin absorption in ;control' animals adapted to 20, 50 and 110 mM-NaCl but was higher in animals adapted to 150 mM-NaCl.12. Aldosterone increased the absorption of sodium in ;control' and adapted toads, but at all dose levels absorption by control was greater than by adapted animals.13. The stimulation of water absorption by vasopressin in vivo or in isolated bladders was not modified in animals adapted to high salinities.

Adaptation, Physiological↗
PubMed1987

Spatial spread of adaptation within the cone network of turtle retina.

1. The spatial characteristics of adaptation were studied in the red-sensitive cones of the snapping turtle retina using intracellular microelectrodes. Light responses elicited with slit-shaped test and adapting stimuli revealed that test response amplitudes and adaptation decline similarly with distance from the impaled cone. The spatial spread of adaptation and the light response cannot be accounted for by scattered light and must therefore result from electrical coupling between cones. 2. The reduction in the amplitude of the test response correlated strongly with the magnitude of the sustained hyperpolarization induced by the adapting fields. This dependence of adaptation on membrane potential was independent of the spatial configuration of the adapting field. 3. The time courses of flash responses were monotonically related to the membrane potential induced by adapting stimuli and were also independent of adapting field configuration. 4. Adapting slits imaged on the cone receptive field centres uniformly depressed sensitivity without altering the shape of the field or its exponential fall-off. Since the membrane potential evoked by the adapting slit falls off exponentially, the invariance of receptive field shape implies that the spread of adaptation cannot be attributed solely to voltage-dependent desensitization of the transduction apparatus in the cones. Therefore a substantial part of the membrane potential dependency of adaptation probably results from a shunting of signals across the plasma membrane of the cone. 5. Full field backgrounds depressed sensitivity but did not alter the receptive field profiles. On the model of electrical coupling proposed by Lamb & Simon (1976), this suggests that to the extent that the voltage-dependent desensitization results from an increased conductance and hence an increased shunt of the signals at the plasma membrane, there must be a concomitant increase in the conductance of the electrical pathways linking cones to one another.

Action Potentials↗
PubMed1985

Effect of food restriction on cold adaptability of rats.

To determine the role of the nutritional state in nonshivering thermogenesis during cold adaptation, cold adaptability was compared between cold-adapted (5 degrees C for 4-5 weeks) rats fed ad libitum and cold-adapted rats pair fed with warm controls having the same food intake. Cold-adapted pair-fed rats suffered a significant loss in body weight during cold exposure. However, brown adipose tissue (BAT) in both cold-adapted ad libitum fed and cold-adapted pair-fed rats was enlarged to the same extent as compared with that in control rats. Fat-free dry matter in BAT also increased in cold-adapted ad libitum fed and cold-adapted pair-fed rats to the same extent. Cold tolerance as assessed by the change in the colonic temperature at -5 degrees C was improved relative to control rats and was the same for cold-adapted ad libitum fed and cold-adapted pair-fed rats. Nonshivering thermogenesis as estimated by the noradrenaline-induced increase in oxygen consumption was significantly greater in the cold-exposed rats and there was no significant difference between cold-adapted ad libitum fed and cold-adapted pair-fed rats. These results suggest that an improved cold tolerance by means of nonshivering thermogenesis in brown adipose tissue is closely related to the low temperature itself but not the increased food intake which occurred in the cold.

Adaptation, Physiological↗
PubMed2005

Vibratory adaptation of cutaneous mechanoreceptive afferents.

The objective of this study was to investigate the effects of extended suprathreshold vibratory stimulation on the sensitivity of slowly adapting type 1 (SA1), rapidly adapting (RA), and Pacinian (PC) afferents. To that end, an algorithm was developed to track afferent absolute (I0) and entrainment (I1) thresholds as they change over time. We recorded afferent responses to periliminal vibratory test stimuli, which were interleaved with intense vibratory conditioning stimuli during the adaptation period of each experimental run. From these measurements, the algorithm allowed us to infer changes in the afferents' sensitivity. We investigated the stimulus parameters that affect adaptation by assessing the degree to which adaptation depends on the amplitude and frequency of the adapting stimulus. For all three afferent types, I0 and I1 increased with increasing adaptation frequency and amplitude. The degree of adaptation seems to be independent of the firing rate evoked in the afferent by the conditioning stimulus. In the analysis, we distinguished between additive adaptation (in which I0 and I1 shift equally) and multiplicative effects (in which the ratio I1/I0 remains constant). RA threshold shifts are almost perfectly additive. SA1 threshold shifts are close to additive and far from multiplicative (I1 threshold shifts are twice the I0 shifts). PC shifts are more difficult to classify. We used an integrate-and-fire model to study the possible neural mechanisms. A change in transducer gain predicts a multiplicative change in I0 and I1 and is thus ruled out as a mechanism underlying SA1 and RA adaptation. A change in the resting action potential threshold predicts equal, additive change in I0 and I1 and thus accounts well for RA adaptation. A change in the degree of refractoriness during the relative refractory period predicts an additional change in I1 such as that observed for SA1 fibers. We infer that adaptation is caused by an increase in spiking thresholds produced by ion flow through transducer channels in the receptor membrane. In a companion paper, we describe the time-course of vibratory adaptation and recovery for SA1, RA, and PC fibers.

Action Potentials↗
PubMed1996

Short-term adaptation of electrically induced saccades in monkey superior colliculus.

1. This study focuses on the neural mechanisms underlying short-term adaptation of saccadic eye movements in the rhesus monkey. Involuntary saccades of various amplitudes and directions (E-saccades) were elicited in complete darkness by electrical stimulation (< or = 50 microA) in the deeper layers of the superior colliculus (SC) at 30 different sites in two monkeys. E-saccades at a given site could be adapted by presenting a visual target at a small distance from the expected end point immediately after their occurrence. The monkeys were trained to null the ensuing error signal by making the appropriate correction saccade to the visual target in many successive trials (E-adap paradigm). By properly adjusting the location of the visual target relative to the end point of the E-saccade, the latter could be modified in amplitude as well as in direction. 2. E-saccade modifications were highly significant, always in the intended direction, and occurred only if a postsaccadic visual error signal was created. These changes were plastic and required a subsequent E-adap series with an opposite error signal to cancel them. Their time course, both during the adaptation and the readaptation period, indicated that the modification was a slow and gradual process, as has been observed earlier in classical visual adaptation experiments. 3. Postadaptation tests, assessing whether the adaptation of E-saccades was also noticeable in normal visually guided saccades (V-saccades), showed incomplete adaptation transfer that was significant in most cases. A similar result, significant in all cases, was obtained with an extended version of the E-adap paradigm in which movement planning on the basis of target selection was possible. In this case, a presaccadic visual target was presented at the expected end point of the E-saccade, which was evoked just before the monkey would make a voluntary saccade itself (VE-adap). 4. In another series of experiments, V-saccades, which were matched to the optimal saccade vector of the particular collicular site under investigation, were adapted with the classical intrasaccadic target shift paradigm (V-adap). In agreement with earlier findings, this V-adaptation showed no transfer to the E-saccades. This result was obtained even in trials in which movement planning on the basis of target selection was possible (VE-test). 5. Our experiments have shown that saccades of collicular origin can be adapted and that presaccadic target selection is not crucial for this process. Both results are nicely in line with an existing model featuring a downstream adaptive corrector with access to SC inputs. This scheme, however, does not explain why the degree of saccadic adaptation, achieved by applying any of the three adaptation paradigms (E-adap, EV-adap, or V-adap), was never equally expressed in V- and E-saccades. Arguments for extending the model by adding a cortical input from the frontal eye fields to the adaptive corrector are discussed.

Adaptation, Physiological↗
PubMed1999

Contrast adaptation and infomax in visual cortical neurons.

In the primary visual cortex (V1) the contrast response function of many neurons saturates at high contrast and adapts depending on the visual stimulus. We propose that both effects - contrast saturation and adaptation - can be explained by a fast and a slow component in the synaptic dynamics. In our model the saturation is an effect of fast synaptic depression with a recovery time constant of about 200 ms. Fast synaptic depression leads to a contrast response function with a high gain for only a limited range of contrast values. Furthermore, we propose that slow adaptation of the transmitter release probability at the geniculocortical synapses is the underlying neural mechanism that accounts for contrast adaptation on a time scale of about 7 sec. For the functional role of contrast adaptation we make the hypothesis that it serves to achieve the best visual cortical representation of the geniculate input. This representation should maximize the mutual information between the cortical activity and the geniculocortical input by increasing the release probability in a low contrast environment. We derive an adaptation rule for the transmitter release probability based on this infomax principle. We show that changes in the transmitter release probability may compensate for changes in the variance of the geniculate inputs - an essential requirement for contrast adaptation. Also, we suggest that increasing the release probability in a low contrast environment is beneficial for signal extraction, because neurons remain sensitive only to an increase in the presynaptic activity if it is synchronous and, therefore, likely to be stimulus related. Our hypotheses are tested in numerical simulations of a network of integrate-and-fire neurons for one column of V1 using fast synaptic depression and slow synaptic adaptation. The simulations show that changing the synaptic release probability of the geniculocortical synapses is a better model for contrast adaptation than the adaptation of the synaptic weights: only in the case of changing the transmitter release probability does our model reproduce the experimental finding that the average membrane potential (DC component) adapts much more strongly than the stimulus modulated component (F1 component). In the case of changing the synaptic weights, however, the average membrane potential (DC) as well as the stimulus modulated component (F1 component) would adapt. Furthermore, changing the release probability at the recurrent cortical synapses cannot account for contrast adaptation, but could be responsible for establishing oscillatory activity often observed in recordings from visual cortical cells.

Adaptation, Physiological↗
PubMed1993

Alternating prism exposure causes dual adaptation and generalization to a novel displacement.

In two experiments, we examined the hypothesis that repeatedly adapting and readapting to two mutually conflicting sensory environments fosters the development of a separate adaptation to each situation (dual adaptation) as well as an increased ability to adapt to a novel displacement (adaptive generalization). In the preliminary study, subjects alternated between adapting their visuomotor coordination to 30-diopter prismatic displacement and readapting to normal vision. Dual adaptation was observed by the end of 10 alternation cycles. However, an unconfounded test of adaptive generalization was prevented by an unexpected prism-adaptive shift in preexposure baselines for the dual-adapted subjects. In the primary experiment, the subjects adapted and readapted to opposite 15-diopter displacements for a total of 12 cycles. Both dual adaptation and adaptive generalization to a 30-diopter displacement were obtained. These findings may be understood in terms of serial reversal learning and "learning to learn."

Adaptation, Psychological↗
PubMed1992

Phenomenon of the adaptive stabilization of structures and protection of the heart.

OBJECTIVE: To study the role of heat shock proteins in the mechanism of adaptive stabilization of structures. DESIGN: Double-blind randomized trial. ANIMALS: Wistar male rats weighting between 250 and 300 g. INTERVENTIONS: Adaptation to restraint stress. Animals were heparinized and anesthetized with nembutal. Experiments on isolated heart included ischemia, reperfusion, adrenergic damage and heat shock. Biochemical investigations studied calcium transport from sarcoplasmic reticulum and mitochondria, and cytofluorimetrical analysis of DNA using the O'Farrell method. MAIN RESULTS: In reperfusion, the contraction amplitude of the hearts from adapted animals was 8.8 times higher than control. This acceleration of the contractile function recovery was due to a more rapid disappearance of the contracture. The duration of ventricular tachycardia and fibrillation was 246 +/- 16 s in control and 119 +/- 12 s in adaptation (P < 0.001). The creatine kinase release was 719 +/- 34 mU/min/g wet weight in control and 302 +/- 120 mU/min/g wet weight in adaptation (P < 0.05). In adaptation, the heat shock-induced contraction amplitude was 2.4 times higher than control and the enzyme yield was practically absent. Adaptation reduced the duration of atrioventricular blockade from 385 to 233 s per group and decreased the number of extrasystoles by 6.5 times. The calcium leakage from intracellular stores during storage proceeded slower in adaptation than in control. During storage of mitochondria at 4 degrees C, oxygen consumption fell much slower in adaptation than in control. As a result, the capacity of mitochondria (isolated from hearts of adapted animals stored for two days) to consume oxygen was 50% higher than in controls; in controls, almost one-half of nuclei were already damaged at one-chain DNA concentration of 50 micrograms/mL, while this phenomenon was 5.5 times less pronounced in adaptation. Adaptation resulted in the accumulation of five polypeptides (molecular weight 72 kDa and pl from 6.3 to 5.7). CONCLUSIONS: The mechanism providing adaptive increase of the heart resistance is apparent both at the central level and at the level of heart cells, and is accompanied by accumulation of inducible polypeptides.

Adaptation, Physiological↗
PubMedDate not supplied

Conflicts of thermal adaptation and fever--a cybernetic approach based on physiological experiments.

Cold adaptation aims primarily at a better economy, i.e., preservation of energy often at the cost of a lower mean body temperature during cold stress, whereas heat adaptation whether achieved by exposure to a hot environment or by endogenous heat produced by muscle exercise, often brings about a higher efficiency of control, i.e., a lower mean body temperature during heat stress, at the cost of a higher water loss. While cold adaptation is beneficial in a cold environment, it may constitute a detrimental factor for exposure to a hot environment, mainly because of morphological adaptation. Heat adaptation may be maladaptive for cold exposure, mainly because of functional adaptation. Heat adaptation clearly is best suited to avoid higher body temperatures in fever, no matter which environmental conditions prevail. On the other hand, cold adaptation is detrimental for coping with fever in hot environment. Yet, in the cold, preceding cold adaptation may, because of reduced metabolic heat production, result in lower febrile increase of body temperature. Apparently controversial effects and results may be analyzed in the framework of a cybernetic approach to the main mechanisms of thermal adaptation and fever. Morphological adaptations alter the properties of the heat transfer characteristics of the body ("passive system"), whereas functional adaptation and fever concern the subsystems of control, namely sensors, integrative centers and effectors. In a closed control-loop the two types of adaptation have totally different consequences. It is shown that the experimental results are consistent with the predictions of such an approach.

Acclimatization↗
PubMed1991

Simulated bipolar cells in fovea of human retina. III. Effects of chromatic adaptation in bipolar cell spectral responses.

Effects of chromatic adaptation on C-type bipolar cells (BC) in human retinal fovea are studied. Adaptation of the r-g channel is linear for both central fovea and parafovea. Adaptation of the parafovea bl-y channel, on the other hand, is nonlinear, which is accounted for by the slower adaptation rate of blue-sensitive cones with white light intensity as compared to rates of red- and green-sensitive cones. Achromatic adaptation of red- and green-center BCs produces uniform response decreases but without unique yellow loci shifts. Achromatic adaptation of blue-center BCs, on the other hand, does cause shifts of the unique green locus. Shifts of the crossover points for the BC response spectra occur with chromatic adaptation; the unique yellow loci shifts to shorter wavelengths with adapting wavelengths shorter than 550 nm and longer wave-lengths with longer adapting wavelengths than 550 nm. Chromatic adaptation is sufficient to explain the Bezold-Brüke effects; but to fully account for these shifts a novel hypothesis is proposed. For the green and red spectrum regions Bezold-Brücke shifts are due to r-g channel chromatic adaptation, while for the blue spectrum region bl-y channel chromatic adaptation accounts for Bezold-Brücke shifts. The two channels function independently in an either/or manner. The bl-y channel, besides having a unique green locus at 517.7 nm, has a crossover point at about 670 nm. Chromatic adaptation of the bl-y channel produces shifts of the unique red locus, which may account for extraspectral hue shifts.

Acclimatization↗
PubMed1995

Spike frequency adaptation studied in hypoglossal motoneurons of the rat.

1. We studied spike frequency adaptation of motoneuron discharge in the rat hypoglossal nucleus using a brain stem slice preparation. The characteristics of adaptation in response to long (60 s) injected current steps were qualitatively similar to those observed previously in cat hindlimb motoneurons. The discharge rate typically exhibited a rapid initial decline, characterized by a linear frequency-time relation, followed by a gradual exponential decline that continued for the duration of current injection. However, a more systematic, quantitative analysis of the data revealed that there were often three distinct phases of the adaptation rather than two. 2. The three phases of adaptation (initial, early, and late) were present in at least one 60-s trial of repetitive firing in all but a small number of motoneurons. Initial adaptation was limited to the first few spikes except in a few trials (7%) in which there was no initial adaptation. The time course of the subsequent decline in rate could be adequately described by a single-exponential function in about half of the trials (48%). In the remaining trials this subsequent decline in frequency was better described as the sum of two exponential functions: an early phase, lasting < 2 s, and a late phase, which lasted for the duration of the discharge period. 3. The magnitude of initial adaptation was correlated with the initial firing frequency (i.e., the reciprocal of the 1st interspike interval). The magnitudes of the early and late phases of adaptation were correlated with the firing frequency reached at the end of initial adaptation. Neither the magnitudes nor the time courses of the three phases were correlated with other membrane properties such as input resistance, rheobase, or repetitive firing threshold. 4. The slope of the frequency-current (f-I) curve was steeper in the initial phase (first 2-5 spikes) than in either the early (< 2 s) or late (> 2 s) phases of adaptation as previously reported by other investigators. In the absence of early adaptation, a steady state for the f-I slope was reached by 0.7-1 s, the time typically reported in studies of repetitive discharge. However, when early adaptation was present (50% of the trials), a steady-state value for the f-I slope was not reached until the cell had discharged for > 1 s. 5. To characterize the time course of firing rate recovery from the adaptive processes, the current was turned off for periods of < or = 10 s during the course of a 60-s trial.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2005

Context-specific adaptation of saccade gain is enhanced with rest intervals between changes in context state.

Dual-state adaptation of motor responses has been known for some time. A more recent development is a form of dual-state adaptation known as "context-specific adaptation," which was explored through the use of saccade gain adaptation. In this model, two different adapted saccade gains are associated with two different states of a context cue, and the gain switches between the two adapted states when the context cue changes state. Such adaptation is imposed by alternating context/adaptation states over the course of an adaptation session. Here, vertical eye position as a context cue for adaptation of horizontal saccade gain is used: gain increase is induced with the eyes up 10 degrees, and gain decrease with the eyes down 10 degrees. This context cue is not very effective: there is interference between context/adaptation conditions such that gain-decrease adaptation with eyes down transfers to the eyes-up (gain-increase) context. It was hypothesized that the juxtaposition in time of the alternating adaptation states exacerbated this interference. In order to test this, one-minute rest breaks were inserted between each change in context/adaptation state. The resulting context-specific adaptation improved dramatically: gain-increase and gain-decrease adaptations were more rapid and more complete. This resembles consolidation of motor learning, which, however, occurs over much longer time spans (hours rather than minutes). Thus, the results may reflect the operation of a novel "short-term" motor consolidation process.

Acclimatization↗
PubMed1973

Adaptation in the ventral eye of Limulus is functionally independent of the photochemical cycle, membrane potential, and membrane resistance.

The early receptor potential (ERP), membrane potential, membrane resistance, and sensitivity were measured during light and/or dark adaptation in the ventral eye of Limulus. After a bright flash, the ERP amplitude recovered with a time constant of 100 ms, whereas the sensitivity recovered with an initial time constant of 20 s. When a strong adapting light was turned off, the recovery of membrane potential and of membrane resistance had time-courses similar to each other, and both recovered more rapidly than the sensitivity. The receptor depolarization was compared during dark adaptation after strong illumination and during light adaptation with weaker illumination; at equal sensitivities the cell was more depolarized during light adaptation than during dark adaptation. Finally, the waveforms of responses to flashes were compared during dark adaptation after strong illumination and during light adaptation with weaker illumination. At equal sensitivities (equal amplitude responses for identical flashes), the responses during light adaptation had faster time-courses than the responses during dark adaptation. Thus neither the photochemical cycle nor the membrane potential nor the membrane resistance is related to sensitivity changes during dark adaptation in the photoreceptors of the ventral eye. By elimination, these results imply that there are (unknown) intermediate process(es) responsible for adaptation interposed between the photochemical cycle and the electrical properties of the photoreceptor.

Action Potentials↗
PubMed2026

Pathogen local adaptation shapes Pierce's disease of grapevines outcomes under field conditions.

Climate change is broadly expected to increase the range of many plant diseases, yet the current status of local thermal adaptation in many pathogens is poorly understood. Xylella fastidiosa (Xf) is a global bacterial plant pathogen that causes Pierce's disease (PD) of grapevines and infects over 700 other host plant species, impacting both agricultural and natural ecosystems. In a common garden experiment with 477 vines in the field, we compared PD outcomes from a local (colder climate in CA) vs non-local (warmer climate in CA) bacterial strain in 13 Mediterranean grapevine varieties over 3 years. Relative to the local strain, there was 77% lower overwinter survival in the non-local strain from a warmer climate, strongly indicating local adaptation in these CA Xf populations. Host genotype also had a significant effect on pathogen winter survival, and grapevine varieties differed in PD susceptibility. Additionally, we assessed in planta evolution of the two pathogen strains over 3 years by whole-genome sequencing 58 field-derived isolates. There were convergent loss-of-function mutations in genes encoding minor Type IV pilin (T4P) proteins, which control twitching motility and other virulence phenotypes, suggesting rapid adaptive evolution. Our results suggest local adaptation to cold temperatures in a bacterial plant pathogen and a possible role for minor Type IV pilins in thermal adaptation. These findings demonstrate the urgent need to incorporate X. fastidiosa evolution and local thermal adaptation into global models of PD spread. Differentiating pathotypes with distinct thermal adaptations will improve disease forecasting and inform quarantine decisions.IMPORTANCEForecasting the movement of plant pathogens is a critical issue under global warming to effectively manage future plant disease outbreaks. Yet, current plant pathogen local thermal adaptation is often unaccounted for, especially in bacterial pathogens. Our study examines local adaptation to temperature in a bacterial plant pathogen, Xylella fastidiosa, that causes disease in grapevines in addition to infecting 700 other plant species. In a large-scale field experiment across 13 grapevine varieties, we demonstrate local adaptation in pathogen winter survival in distinct Xylella fastidiosa strains. Additionally, we found evidence of adaptive evolution in just 3 years, as we observed convergent mutations after resequencing strains that evolved in the field. Our results suggest that X. fastidiosa populations-even within a small geographic area-have distinct adaptations to winter temperatures and may exhibit differential responses to warming winters.

Type IV pili↗
PubMed2006

The role of kinematic redundancy in adaptation of reaching.

Although important differences exist between learning a new motor skill and adapting a well-learned skill to new environmental constraints, studies of force field adaptation have been used frequently in recent years to identify processes underlying learning. Most of these studies have been of reaching tasks that were each hand position was specified by a unique combination of joint angles. At the same time, evidence has been provided from a variety of tasks that the central nervous system takes advantage of the redundancy available to it when planning and executing functional movements. The current study attempted to determine whether a change in the use of joint motion redundancy is associated with the adaptation process. Both experimental and control subjects performed 160 trials of reaching in each of four adaptation phases, while holding the handle of a robot manipulandum. During the first and last adaptation phases, the robot motors were turned off. During phases 2 and 3 the motors produced a velocity-dependent force field to which experimental subjects had to adapt to regain relatively straight line hand movements during reaching to a target, while the motors remained off for the control group. The uncontrolled manifold (UCM) method was used to partition the variance of planar clavicle-scapular, shoulder, elbow and wrist joint movements into two orthogonal components, one (V(UCM)) that reflected combinations of joint angles that were equivalent with respect to achieving the average hand path and another (V(ORT)) that took the hand away from its average path. There was no change in either variance component for the control group performing 640 non-perturbed reaches across four 'pseudo-adaptation' phases. The experimental group showed adaptation to reaching in the force field that was accompanied initially by an increase in both components of variance, followed by a smaller decrease of V(UCM) than V(ORT) during 320 practice reaches in the force field. After initial re-adaptation to reaching to the null field, V(UCM) was higher in experimental than in control subjects after performing a comparable number of reaches. V(UCM) was also larger in the experimental group after re-adaptation when compared to the 160 null field reaching trials performed prior to initial force field introduction. The results suggest that the central nervous system makes use of kinematic redundancy, or flexibility of motor patterns, to adapt reaching performance to unusual force fields, a fact that has implications for the hypothesis that motor adaptation requires learning of formal models of limb and environmental dynamics.

Adaptation, Physiological↗