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PubMed1994

Effect of contrast and adaptation on the perception of the direction and speed of drifting gratings.

Three experiments were conducted to analyse the effect of contrast and adaptation state on the ability of human observers to discriminate the motion of drifting gratings. In the first experiment, subjects judged the direction of briefly presented gratings, which slowly drifted leftward or rightward. The test gratings were enveloped in space by a raised cosine function and in time by a Gaussian. The centre of the spatial envelope was either 2 deg left or right of the fixation point. An adaptive staircase procedure was used to find the velocities, at which the observer judged the motion direction in 75% of the presentations as leftwards or rightwards, respectively. In the second experiment, subjects judged the relative speed of two simultaneously presented gratings. Stimulus contrast was varied in both experiments from 0.01 to 0.32. Discrimination threshold vs contrast functions were measured before and after adaptation to a high-contrast (0.4) grating drifting at rates between 2 and 32 Hz. In a third experiment, subjects matched, before and after adaptation, the relative speed of a test stimulus, which had a constant contrast (0.04 or 0.08) and a variable speed, to that of a reference stimulus having a variable contrast but a constant speed. The results indicate that, before adaptation, direction and speed discrimination thresholds are independent of test contrast, except when test contrast approaches the detection threshold level. Adaptation to a drifting grating increases the lower threshold of motion (LTM) and the speed discrimination threshold (delta V/V) for low test contrasts. In addition, the point of subjective stationarity (PSS) shifts towards the adapted direction and this shift is more pronounced for low test contrasts. The perceived speed of a drifting grating increases with increasing contrast level. Adaptation to a drifting grating shifts the perceived speed vs log contrast function downwards and to the right (toward higher contrast levels) and this shift is greatest for adaptation frequencies between 8 and 16 Hz. We further explored the effects of adaptation contrast (0.04, 0.4 and 0.9) and adaptation drift direction (iso- or contra-directional) on the perceived speed versus contrast function. The effect of adaptation is greatest for iso-directional drift and increases with increasing adaptation contrast. The results are discussed in terms of a contrast gain control model of adaptation.

Adaptation, Ocular↗
PubMed2000

The control of saccadic adaptation: implications for the scanning of natural visual scenes.

Accurate scanning of natural scenes depends on: (1) attentional selection of the target; (2) spatial pooling over the attended target to compute the precise landing position; and (3) adaptive modification of saccades to ensure saccadic accuracy. The present experiments studied adaptation. Adaptive modifications were induced by displacing the target during saccades. Adaptation was found to be: (1) similar for a small target point and a large target circle, despite the differences in the spatial pattern of landing position errors for each; (2) unaffected by instructions to look part way to the target, even though such instructions altered landing position error relative to the target; and (3) insensitive to symbolic cues disclosing the direction of the intra-saccadic displacement. Briefly delaying the presentation of the post-saccadic target greatly reduced adaptation. Neither corrective saccades, nor the position errors that trigger corrections, were involved in adaptation because corrective saccades rarely occurred with a large target circle even though the circle produced as much adaptation as the single point. Taken together, the results do not support the traditional notion that post-saccadic retinal position error controls adaptation. We propose that adaptation relies on a comparison of the actual post-saccadic retinal image with the post-saccadic image that would be predicted based on a representation of the planned saccade. Such a comparison: (1) is consistent with our results; (2) may be more effective than retinal position error in controlling adaptation in natural visual scenes containing large targets and backgrounds; and (3) is similar to the motion-based adaptive mechanisms associated with the VOR. Similarity between the adaptive control of saccades and adaptive control of the VOR raises the possibility that the most important role of saccadic adaptation may be the coordination of eye and head movements during shifts of gaze.

Adaptation, Physiological↗
PubMed1998

The effect of spatial frequency adaptation on the latency of spatial contrast detection.

The effect of spatial frequency adaptation on detection response time was studied using 2-D Gabor functions as stimuli. On the basis of pilot studies, it was expected that reaction time to a given spatial frequency at a low contrast would increase following adaptation to that spatial frequency at a high contrast. Subjects were tested using 2-D Gabor functions that ranged in frequency from 25 to 24 cpd. Subjects' reaction times to the Gabor functions were measured prior to adaptation and after adaptation to a particular spatial frequency. The adapting spatial frequency was either 1, 2, 4, 8, 10, or 16 cpd. The test stimuli were 0.3, 0.5, or 0.7 log units above the unadapted threshold contrast. The subjects adapted to the high contrast test grating for 3 min (80% contrast) and reaction times were again measured in an adapt-test-readapt paradigm. The results showed the greatest increase in reaction time after adaptation when adapting and test spatial frequencies within an octave of the adapting spatial frequency also showed an increase in reaction time but to a lesser extent. Reaction times to gratings with spatial frequencies more distant from the adapting spatial frequency were not significantly affected by the adaptation. The results obtained resemble the tuning curves found for threshold data. Reaction times for stimuli at 0.5 and 0.7 log units above the unadapted threshold were affected less by adaptation than those at 0.3 log units above the unadapted threshold. These results were evaluated in terms of a shifting contrast gain mechanism which may account for both the spatial frequency specific effects of adaptation and the differences found for the different contrast test levels.

Adaptation, Ocular↗
PubMed1997

Excitatory and inhibitory response adaptation in the superior olive complex affects binaural acoustic processing.

Short-term adaptation was examined in single unit recordings from 113 superior olive neurons of anaesthetized 3- to 6-month-old Long-Evans rats. Responses to an equal intensity BF probe tone presented 1 ms after an 'adapting' BF tone were adapted by 56.3 +/- 2.6% (mean +/- S.E.) compared to responses at a 512 ms delay. The rapid decrease in discharge rate during adapting tones often approximated exponential time courses with time constants of less than 20 ms. The recovery from adaptation was exponential with time constants of 106 +/- 20.0 ms. The magnitude of adaptation and time course of recovery following monaural stimulation of binaurally excited (EE) neurons were not significantly different in both input pathways. Additionally, in 60% of EE neurons, an 'adapting' tone presented to one ear reduced subsequent responses to probe tones presented to the opposite ear. Binaural stimulation resulted in equal or greater adaptation of responses than monaural stimulation of either ear. The recovery of binaural excitatory responses generally followed a time course between recovery functions for ipsilateral and contralateral monaural stimuli. Lateral Superior Olive (LSO) neurons encode sound source location through the interaction of ipsilateral excitation and contralateral inhibition (IE). Ipsilaterally driven excitatory responses in LSO neurons exhibited the greatest magnitude of adaptation (68.5 +/- 21.1%). Adaptation of inhibition was observed in over half of IE neurons. Responses of LSO neurons to binaural BF probe stimuli were greatest immediately after a 200 ms BF 'inhibitory adapting' stimulus to the contralateral ear, and decreased with greater interstimulus delays. Responses to binaural stimulation were constant after prior binaural adaptation, when the magnitude and recovery of adaptation to monaural stimuli were similar for excitation and inhibition (8/25 IE cells). The functional significance and possible sites of adaptation processes are discussed.

Acoustic Stimulation↗
PubMed1989

Adaptation in single units in visual cortex: the tuning of aftereffects in the spatial domain.

Cat striate cortical neurons were investigated using a new method of studying adaptation aftereffects. Stimuli were sinusoidal gratings of variable contrast, spatial frequency, and drift direction and rate. A series of alternating adapting and test trials was presented while recording from single units. Control trials were completely integrated with the adapted trials in these experiments. Every cortical cell tested showed selective adaptation aftereffects. Adapting at suprathreshold contrasts invariably reduced contrast sensitivity. Significant aftereffects could be observed even when adapting at low contrasts. The spatial-frequency tuning of aftereffects varied from cell to cell. Adapting at a given spatial frequency generally resulted in a broad response reduction at test frequencies above and below the adapting frequency. Many cells lost responses predominantly at frequencies lower than the adapting frequency. The tuning of aftereffects varied with the adapting frequency. In particular, the strongest aftereffects occurred near the adapting frequency. Adapting at frequencies just above the optimum for a cell often altered the spatial-frequency tuning by shifting the peak toward lower frequencies. The fact that the tuning of aftereffects did not simply match the tuning of the cell, but depended on the adapting stimulus, implies that extrinsic mechanisms are involved in adaptation effects.

Adaptation, Physiological↗
PubMedDate not supplied

Contrast adaptation in striate cortical neurons of the nocturnal primate bush baby (Galago crassicaudatus).

It has been argued that in order for the visual system to detect edges accurately under a range of conditions, the visual system needs to adapt to the local contrast level to preserve sensitivity (Blakemore & Campbell, 1969). Cells in the primary visual cortex of cats adapt to stimuli with low to moderate contrast. Curiously, macaque monkey neurons in primary visual cortex (V1) do not show evidence for similar adaptation. To address the question of whether this differential sensitivity in contrast adaptation might be due to phylogenetic variation between cats and primates or to specializations for visual niche (e.g. nocturnal vs. diurnal), contrast adaptation to temporally and spatially optimized gratings was examined in 30 V1 cells of three nocturnal primate bush babies (Galago crassicaudatus). A second objective was to examine the relationship between the degree of contrast adaptation and cell classification or cell location relative to cortical layers or compartments [i.e. cytochrome-oxidase (CO) blobs and interblobs]. All cells were classified (simple vs. complex) and anatomically localized relative to cortical layers and cytochrome-oxidase (CO) blob and interblob compartments. Two independent measures of contrast adaptation were used. In the first test, contrast was sequentially increased from 3-56% and then decreased. The contrast required to maintain a half-maximum response amplitude in the 30 cells tested increased an average of 0.24 (+/- 0.12) log units during the sequential decrements in contrast. For the second test, four sets of five interleaved contrasts within +/- 1 octave of a central adapting contrast (10%, 14%, 20%, and 28%, respectively) were presented. The cells produced a mean adaptation index of 0.57 (+/- 0.47) which is very similar to that exhibited by cat cortical neurons (0.54 +/- 0.41). Interestingly, cells in interblobs showed a trend toward greater adaptation than did blob cells. Moreover, cells in the supragranular layers exhibited greater adaptation than cells in the infragranular layers. No significant differences in adaptation were found to correlate with other cell classification indices. Taken together, our results suggest that contrast adaptation may be more important for maintaining sensitivity in nocturnal species (primates or cats) than in diurnal species (macaque monkeys), and that in the nocturnal bush baby, cells in cortical layers and compartments may be differentially specialized for contrast adaptation.

Adaptation, Ocular↗
PubMed2003

Adaptation to heat of cardiomyoblasts in culture protects them against heat shock: role of nitric oxide and heat shock proteins.

Dosed adaptation to environmental factors is an efficient non-drug means for increasing the resistance of organs or the body as a whole. We demonstrated earlier that nitric oxide (NO) plays an important role in adaptive defense of the organism, in particular due to activation of heat shock protein (HSP) synthesis. A key question remained open--to what extent the formation of adaptive defense depends on central mechanisms and to what extent on the intracellular mechanisms immediately responding to the adapting factor, and whether the NO-dependent activation of HSP synthesis plays a role in adaptation of isolated cells. In the present study we looked into the possibility of producing a protective effect of adaptation to heat in cell culture. A 6-day adaptation to heat limited to 17% the decrease in metabolic activity induced by heat shock in H9c2 cardiomyoblasts. The development of adaptation was associated with increased NO production. Treatment of cells with the inhibitor of NO synthase L-NNA (100 micro M) prevented the development of adaptive protection. Adaptation of cell culture enhanced synthesis of HSP70 but not HSP27. Blockade of HSP70 synthesis with quercetin (50 micro M) left unchanged the protective effect of adaptation. Inhibition of NO synthesis restricted the adaptation-induced HSP70 synthesis. Therefore, the formation of adaptation at the cell level may result from a direct action of an environmental factor without participation of neuro-humoral factors. Such adaptation involves NO-dependent mechanisms divorced from the activation of HSP70 synthesis.

Adaptation, Physiological↗
PubMed2006

Duration-dependent FMRI adaptation and distributed viewer-centered face representation in human visual cortex.

Two functional magnetic resonance imaging (fMRI) face viewpoint adaptation experiments were conducted to investigate whether fMRI adaptation in high-level visual cortex depends on the duration of adaptation and how different views of a face are represented in the human visual system. We found adaptation effects in multiple face-selective areas, which suggest a distributed, viewer-centered representation of faces in the human visual system. However, the nature of the adaptation effects was dependent on the length of adaptation. With long adaptation durations, face-selective areas along the hierarchy of the visual system gradually exhibited viewpoint-tuned adaptation. As the angular difference between the adapter and test stimulus increased, the blood oxygen level-dependent (BOLD) signal evoked by the test stimulus gradually increased as a function of the amount of 3-dimensional (3D) rotation. With short adaptation durations, however, face-selective areas in the ventral pathway, including the lateral occipital cortex and right fusiform area, exhibited viewpoint-sensitive adaptation. These areas showed an increase in the BOLD signal with a 3D rotation, but this signal increase was independent of the amount of rotation. Further, the right superior temporal sulcus showed little or very weak viewpoint adaptation with short adaptation durations. Our findings suggest that long- and short-term fMRI adaptations may reflect selective properties of different neuronal mechanisms.

Adaptation, Physiological↗
PubMed2000

Psychophysical and behavioral characteristics of olfactory adaptation.

Sensory adaptation allows organisms to reach behavioral equilibrium with the ambient environment and respond primarily to changes in stimulation. Given its functional significance, it is not surprising that adaptation in the olfactory system exhibits many of the same characteristics as adaptation in other sensory systems, including vision. Repeated or prolonged exposure to an odorant typically leads to stimulus-specific decreases in olfactory sensitivity to that odorant, but sensitivity recovers over time in the absence of further exposure. Psychophysical analysis shows that olfactory adaptation results in elevations in odor thresholds and in reduced responsiveness to suprathreshold stimulation. Further, the magnitude of the decrease and the time course of adaptation and recovery are dependent on the concentration of the odor and on the duration of exposure. It is generally agreed that olfactory adaptation can occur at multiple levels in the olfactory system and can involve both peripheral (receptor level) and more central (post-receptor) components. Evidence for peripheral and central involvement comes from studies showing that monorhinal stimulation results in adaptation in both the ipsilateral and contralateral nostril, although the degree of adaptation in the ipsilateral nostril is more profound and recovery is slower. Additional evidence for central involvement comes from studies that have found relatively small decreases in peripheral response following repeated stimulation despite substantial reductions in perceived intensity. Most psychophysical studies of adaptation, however, have not differentiated the peripheral and central processes. Although relatively few in number, studies of the parametric features of olfactory adaptation in both vertebrate (e.g. rat) and invertebrate (e.g. Drosophila, Caenorhabditis elegans) animal models appear to replicate the findings in psychophysical studies of adult humans. Despite the broad overall similarity of olfactory adaptation to adaptation in other sensory systems, olfactory adaptation exhibits some unique features. Adaptation in olfaction has been shown to be very long-lasting in some cases and may be modulated by the contribution of pre-neural events and physico-chemical properties of the odorant molecules that govern diffusion to receptor sites and post-receptor clearance.

Adaptation, Physiological↗
PubMed1999

Characteristics of simian adaptation fields produced by behavioral changes in saccade size and direction.

The gain of saccadic eye movements can be altered gradually by moving targets either forward or backward during targeting saccades. If the gain of saccades to targets of only one size is adapted, the gain change generalizes or transfers only to saccades with similar vectors. In this study, we examined the spatial extent of such saccadic size adaptation, i.e., the gain adaptation field. We also attempted to adapt saccade direction by moving the target orthogonally during the targeting saccade to document the extent of a direction or cross-axis adaptation field. After adaptive gain decreases of horizontal saccades to 15 degrees target steps, >82% of the gain reduction transferred to saccades to 25 degrees horizontal target steps but only approximately 30% transferred to saccades to 5 degrees steps. For the horizontal component of oblique saccades to target steps with 15 degrees horizontal components and 10 degrees upward or downward vertical components, the transfer was similar at 51 and 60%, respectively. Thus the gain decrease adaptation field was quite asymmetric in the horizontal dimension but symmetric in the vertical dimension. Although gain increase adaptation produced a smaller gain change (13% increase for a 30% forward adapting target step) than did gain decrease adaptation (20% decrease for a 30% backward adapting target step), the spatial extent of gain transfer was quite similar. In particular, the gain increase adaptation field displayed asymmetry in the horizontal dimension (58% transfer to 25 degrees saccades but only 32% transfer to 5 degrees saccades) and symmetry in the vertical direction (50% transfer to the horizontal component of 10 degrees upward and 40% transfer to 10 degrees downward oblique saccades). When a 5 degrees vertical target movement was made to occur during a saccade to a horizontal 10 degrees target step, a vertical component gradually appeared in saccades to horizontal targets. More than 88% of the cross-axis change in the vertical component produced in 10 degrees saccades transferred to 20 degrees saccades but only 12% transferred to 4 degrees saccades. The transfer was similar to the vertical component of oblique saccades to target steps with either 10 degrees upward (46%) or 10 degrees downward (46%) vertical components. Therefore both gain and cross-axis adaptation fields have similar spatial profiles. These profiles resemble those of movement fields of neurons in the frontal eye fields and superior colliculus. How those structures might participate in the adaptation process is considered in the DISCUSSION.

Adaptation, Physiological↗
PubMed2001

Horizontal vestibuloocular reflex evoked by high-acceleration rotations in the squirrel monkey. IV. Responses after spectacle-induced adaptation.

The horizontal angular vestibuloocular reflex (VOR) evoked by sinusoidal rotations from 0.5 to 15 Hz and acceleration steps up to 3,000 degrees /s(2) to 150 degrees /s was studied in six squirrel monkeys following adaptation with x2.2 magnifying and x0.45 minimizing spectacles. For sinusoidal rotations with peak velocities of 20 degrees /s, there were significant changes in gain at all frequencies; however, the greatest gain changes occurred at the lower frequencies. The frequency- and velocity-dependent gain enhancement seen in normal monkeys was accentuated following adaptation to magnifying spectacles and diminished with adaptation to minimizing spectacles. A differential increase in gain for the steps of acceleration was noted after adaptation to the magnifying spectacles. The gain during the acceleration portion, G(A), of a step of acceleration (3,000 degrees /s(2) to 150 degrees /s) increased from preadaptation values of 1.05 +/- 0.08 to 1.96 +/- 0.16, while the gain during the velocity plateau, G(V), only increased from 0.93 +/- 0.04 to 1.36 +/- 0.08. Polynomial fits to the trajectory of the response during the acceleration step revealed a greater increase in the cubic than the linear term following adaptation with the magnifying lenses. Following adaptation to the minimizing lenses, the value of G(A) decreased to 0.61 +/- 0.08, and the value of G(V) decreased to 0.59 +/- 0.09 for the 3,000 degrees /s(2) steps of acceleration. Polynomial fits to the trajectory of the response during the acceleration step revealed that there was a significantly greater reduction in the cubic term than in the linear term following adaptation with the minimizing lenses. These findings indicate that there is greater modification of the nonlinear as compared with the linear component of the VOR with spectacle-induced adaptation. In addition, the latency to the onset of the adapted response varied with the dynamics of the stimulus. The findings were modeled with a bilateral model of the VOR containing linear and nonlinear pathways that describe the normal behavior and adaptive processes. Adaptation for the linear pathway is described by a transfer function that shows the dependence of adaptation on the frequency of the head movement. The adaptive process for the nonlinear pathway is a gain enhancement element that provides for the accentuated gain with rising head velocity and the increased cubic component of the responses to steps of acceleration. While this model is substantially different from earlier models of VOR adaptation, it accounts for the data in the present experiments and also predicts the findings observed in the earlier studies.

Acceleration↗
PubMed2001

Response adaptation of medial olivocochlear neurons is minimal.

Response adaptation is a general characteristic of neurons. A number of studies have investigated the adaptation characteristics of auditory-nerve fibers, which send information to the brain about sound stimuli. However, there have been no previous adaptation studies of olivocochlear neurons, which provide efferent fibers to hair cells and auditory nerve dendrites in the auditory periphery. To study adaptation in efferent fibers, responses of single olivocochlear neurons were recorded to characteristic-frequency tones and noise, using anesthetized guinea pigs. To measure short-term adaptation, stimuli of 500 ms duration were presented, and the responses were displayed as peristimulus time histograms. These histograms showed regular peaks, indicating a "chopping" pattern of response. The rate during each chopping period as well as the general trend of the histogram could be well fit by an equation that expresses the firing rate as a sum of 1) a short-term adaptive rate that decays exponentially with time and 2) a constant steady-state rate. For the adaptation in medial olivocochlear (MOC) neurons, the average exponential time constant was 47 ms, which is roughly similar to that for short-term adaptation in auditory-nerve fibers. The amount of adaptation (expressed as a percentage decrease of onset firing rate), however, was substantially less in MOC neurons (average 31%) than in auditory-nerve fibers (average 63%). To test for adaptation over longer periods, we used noise and tones of 10 s duration. After the short-term adaptation, the responses of MOC neurons were almost completely sustained (average long-term adaptation 3%). However, in the same preparations, significant long-term adaptation was present in auditory-nerve fibers. These results indicate that the MOC response adaptation is minimal compared with that of auditory-nerve fibers. Such sustained responses may enable the MOC system to produce sustained effects in the periphery, supporting a role for this efferent system during ongoing stimuli of long duration.

Acoustic Stimulation↗
PubMed2002

[Professional adaptation of nurses as a factor influencing the efficiency of medical care for hospitalised patients].

Adaptation is defined as a specific kind of human accommodation to a particular environment. Such definition allows to describe professional adaptation as a process which prepares an employee to work effectively in a given position. Professional adaptation may comprise an employee's adaptation for professional work as well as his working community. An employee learns to perform his professional as well as social duties in a new workplace. Professional adaptation is one of the components of management in employment policy which influences the effectiveness of operation of the health care system. In the present study the author tries to answer the following questions. What are the factors influencing the course of nurses' professional adaptation? How do nurses evaluate the course of their professional adaptation? Do nurses think that the process of professional adaptation influences the effectiveness of medical operations performed by nurses with regard to hospitalised patients? The research included 120 section nurses employed for the first time in maintenance departments of different hospitals (not including clinical hospitals). The research was conducted in the autumn of 2000 in the whole country. A questionnaire for section nurses was employed. As a result of the analysis of the data obtained in the research the posed questions (among other things) were answered. The investigated nurses positively assess the course of professional adaptation which they underwent at the beginning of their professional careers. Among the factors influencing the course of professional adaptation the following were named among others: adaptation programme, choice of adaptation tutor, organisation of the working process and allocation of tasks during adaptation, the relations in the group, the equipment in departments. According to the investigated nurses correct course, properly prepared and realised professional adaptation programme helps to reduce professional difficulties and is conductive to improve the quality and effectiveness of medical care for hospitalised patients.

Adaptation, Psychological↗
PubMed1983

On the ionic mechanisms of adaptation in an isolated mechanoreceptor --an electrophysiological study.

The ionic mechanisms of adaptation of the receptor potential, especially the early adaptation, was studied in an isolated mechanoreceptor, the slowly adapting crustacean stretch receptor, with electrophysiological methods including potential clamp technique. This receptor has frequently been used as a model to demonstrate general principles for the generation of signals in sensory receptors. The receptor potential is depolarizing and consists of an initial peak followed by a static phase in response to a ramp and hold stretch with a high rate of rise. The receptor current, defined as the stretch induced current, is inward and has a similar appearance. The adaptive fall of the receptor potential and receptor current occurs in two phases, an initial rapid fall from the peak (early adaptation) followed by a slow decline during the static phase (late adaptation). The two phases could be characterized by different time constants. By polarizing the cell to various steady potentials before stretch it was shown that the time constant of the early adaptive fall of the receptor potential varied with potential and had a minimum close to resting membrane potential. The time course of the late adaptive fall appeared to be independent of holding potential. These results suggest that ionic mechanisms play an important role during early adaptation, whereas late adaptation probably is governed by mechanical factors. Prolonged exposure to K+-free solutions or injection of TEA caused nearly complete abolition of the early adaptive fall of the receptor potential, making the response almost rectangular in shape. The outward current associated with a positive potential step was considerably reduced after injection of TEA. Intracellular injection of Ca2+ or exposure to isotonic Ca2+-saline decreased the amplitude of the static phase of the receptor potential, whereas injection of EGTA caused an increase in amplitude. Ion substitution experiments indicated that Ca2+ might enter the neuron through the transducer channels opened by stretch. It is concluded that the major cause of the early adaptive fall of the receptor potential is an outward K+ current activated by the stretch-induced depolarization. The effects of varied intra- and extracellular Ca2+ concentration suggest that a part of the K+ current might be activated by Ca2+ influx. Another possibility is that intracellular Ca2+ contributes to adaptation by inactivation of the transducer channels. The present results demonstrate a possible mechanism for adaptation in sensory receptors. A potential activated outward K+ current enhances the fall of the receptor potential from the initial peak.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMedDate not supplied

Pattern adaptation and cross-orientation interactions in the primary visual cortex.

The responsiveness of neurons in the primary visual cortex (V1) is substantially reduced after a few seconds of visual stimulation with an effective pattern. This phenomenon, called pattern adaptation, is uniquely cortical and is the likely substrate of a variety of perceptual after-effects. While adaptation to a given pattern reduces the responses of V1 neurons to all subsequently viewed test patterns, this reduction shows some specificity, being strongest when the adapting and test patterns are identical. This specificity may indicate that adaptation affects the interaction between groups of neurons that are jointly activated by the adapting stimulus. We investigated this possibility by studying the effects of adaptation to visual patterns containing one or both of two orientations--the preferred orientation for a cell, and the orientation orthogonal to it. Because neurons in the primary visual cortex are sharply tuned for orientation, stimulation with orthogonal orientations excites two largely distinct populations of neurons. With intracellular recordings of the membrane potential of cat V1 neurons, we found that adaptation to the orthogonal orientation alone does not evoke the hyperpolarization that is typical of adaptation to the preferred orientation. With extracellular recordings of the firing rate of macaque V1 neurons, we found that the responses were not reduced by adaptation to the orthogonal orientation alone nearly as much as by adaptation to the preferred orientation. In the macaque we also studied the effects of adaptation to plaids containing both the preferred and the orthogonal orientations. We found that adaptation to these stimuli could modify the interactions between orientations. It increased the amount of cross-orientation suppression displayed by some cells, even turning some cells that showed cross-orientation facilitation when adapted to a blank stimulus into cells that show cross-orientation suppression. This result suggests that pattern adaptation can affect the interaction between the groups of neurons tuned to the orthogonal orientations, either by increasing their mutual inhibition or by decreasing their mutual excitation.

Animals↗
PubMed1999

Cerebellar subjects show impaired adaptation of anticipatory EMG during catching.

We evaluated the role of the cerebellum in adapting anticipatory muscle activity during a multijointed catching task. Individuals with and without cerebellar damage caught a series of balls of different weights dropped from above. In Experiment 1 (light-heavy-light), each subject was required to catch light balls (baseline phase), heavy balls (adaptation phase), and then light balls again (postadaptation phase). Subjects were not told when the balls would be switched, and they were required to keep their hand within a vertical spatial "window" during the catch. During the series of trials, we measured three-dimensional (3-D) position and electromyogram (EMG) from the catching arm. We modeled the adaptation process using an exponential decay function; this model allowed us to dissociate adaptation from performance variability. Results from the position data show that cerebellar subjects did not adapt or adapted very slowly to the changed ball weight when compared with the control subjects. The cerebellar group required an average of 30.9 +/- 8.7 trials (mean +/- SE) to progress approximately two-thirds of the way through the adaptation compared with 1.7 +/- 0.2 trials for the control group. Only control subjects showed a negative aftereffect indicating storage of the adaptation. No difference in performance variability existed between the two groups. EMG data show that control subjects increased their anticipatory muscle activity in the flexor muscles of the arm to control the momentum of the ball at impact. Cerebellar subjects were unable to differentially increase the anticipatory muscle activity across three joints to perform the task successfully. In Experiment 2 (heavy-light-heavy), we tested to see whether the rate of adaptation changed when adapting to a light ball versus a heavy ball. Subjects caught the heavy balls (baseline phase), the light balls (adaptation phase), and then heavy balls again (postadaptation phase). Comparison of rates of adaptation between Experiment 1 and Experiment 2 showed that the rate of adaptation was unchanged whether adapting to a light ball or a heavy ball. Given these findings, we conclude that the cerebellum is important in generating the appropriate anticipatory muscle activity across multiple muscles and modifying it in response to changing demands though trial-and-error practice.

Adult↗
PubMed2026

Cerebellar iTBS enhances gait adaptation by modulating cortical sensorimotor network dynamics: a randomized controlled trial.

Gait adaptation enables individuals to maintain locomotor stability under persistent perturbations. Although the cerebellum is critical for sensory prediction error-based (SPE) adaptation, how cerebellar neuromodulation reshapes cortical sensorimotor networks to enhance gait adaptation remains unclear. This study investigated the behavioral effects and underlying cortical neurodynamic mechanisms of cerebellar intermittent theta-burst stimulation (iTBS) on gait adaptation. Thirty-two healthy adults received either active or sham cerebellar iTBS. Participants performed a split-belt treadmill adaptation task before and after intervention. Cortical responsiveness was evaluated using TMS-evoked EEG over primary motor cortex (M1), while resting-state EEG was analyzed to assess spectral power and directional functional connectivity. Compared to sham, cerebellar iTBS significantly enhanced gait adaptation, evidenced by a faster adaptation rate (p = 0.035) and enhanced Early Adaptation SLS (p = 0.011), without altering initial perturbation responses or post-adaptation outcomes. The iTBS increased TMS-evoked α (p = 0.031) and γ (p = 0.022) power in M1, while the α power was correlated with faster adaptation (r = 0.526, p = 0.002). Furthermore, iTBS strengthened PPC-to-M1 directed connectivity in the β (p = 0.025) and γ (p = 0.013) bands. Enhanced parieto-motor directionality were positively associated with adaptation rate (β: r = 0.515, p = 0.003; γ: r = 0.463, p = 0.009). These findings suggest that cerebellar iTBS facilitates gait adaptation by modulating cortical responsiveness and directional sensorimotor network connectivity, providing multi-level neurodynamic evidence for the cerebello-cortical modulation during gait adaptation and offering a strong physiological rationale for targeted neuromodulation in gait rehabilitation strategies.

Humans↗
PubMed1993

The latency of the cat vestibulo-ocular reflex before and after short- and long-term adaptation.

Latencies of normal and adapted feline vestibulo-ocular reflex (VOR) were studied in five cats by applying +/- 20 degrees/s horizontal head velocity steps (4000 degrees/s2 acceleration) and measuring the elicited horizontal or vertical reflex eye responses. Normal VOR latency was 13.0 ms +/- 1.9 SD. Short-term adaptation was then accomplished by using 2 h of paired horizontal sinusoidal vestibular stimulation and phase-synchronized vertical optokinetic stimulation (cross-axis adaptation). For long-term adaptation, cats wore x 0.25 or x 2.2 magnifying lenses for 4 days. The cats were passively rotated for 2 h/day and allowed to walk freely in the laboratory or their cages for the remainder of the time. The latency of the early (primary) adaptive response was 15.2 ms +/- 5.2 SD for cross-axis adaptation and 12.5 ms +/- 3.9 SD for lens adaptation. This short-latency response appeared within 30 min after beginning the adaptation procedure and diminished in magnitude overnight. A late (secondary) adaptive response with latency of 76.8 ms +/- 7.0 SD for cross-axis adaptation and 68.1 ms +/- 8.8 SD for lens adaptation appeared after approximately 2 h of adaptation. It had a more gradual increase in magnitude than the primary response and did not diminish in magnitude overnight. These data suggest that brainstem VOR pathways are a site of learning for adaptive VOR modification, since the primary latency is short and has a similar latency to that of the normal VOR.

Adaptation, Physiological↗