The Effect Of Misleading Prior Information On The Subjective Visual Vertical

When tilted sideways participants misperceive the visual vertical assessed by means of a luminous line in otherwise complete dark- ness. A recent modeling approach (De Vrijer et al., 2009) claimed that these typical patterns of errors (known as A- and E-effects) could be explained by as- suming that participants behave in a Bayes optimal manner. In this study, we experimentally manipulate participants’ prior information about body-in-space orientation and measure the effect of this manipulation on the subjective visual vertical (SVV). Specifically, we explore the effects of veridical and misleading instructions about body tilt orientations on the SVV. We used a psychophys- ical 2AFC SVV task at roll tilt angles of 0 degrees, 16 degrees and 4 degrees CW and CCW. Participants were tilted to 4 degrees under different instruction conditions: in one condition, participants received veridical instructions as to their tilt angle, whereas in another condition, participants received the mis- leading instruction that their body position was perfectly upright. Our results indicate systematic differences between the instruction conditions at 4 degrees CW and CCW. Participants did not simply use an ego-centric reference frame in the misleading condition; instead, participants’ estimates of the SVV seem to lie between their head’s Z-axis and the estimate of the SVV as measured in the veridical condition. All participants displayed A-effects at roll tilt an- gles of 16 degrees CW and CCW. We discuss our results in the context of the Bayesian model by De Vrijer et al. (2009), and claim that this pattern of re- sults is consistent with a manipulation of precision of a prior distribution over body-in-space orientations. Furthermore, we introduce a Bayesian Generalized Linear Model for estimating parameters of participants’ psychometric function, which allows us to jointly estimate group level and individual level parameters under all experimental conditions simultaneously, rather than relying on the traditional two-step approach to obtaining group level parameter estimates.

Effects of anxiety on decision making and visual search behaviour in complex sport situations

Based on the Attentional Control Theory (ACT; Eysenck et al., 2007), performance efficiency is decreased in high-anxiety situations because worrying thoughts compete for attentional resources. A repeated-measures design (high/low state anxiety and high/low perceptual task demands) was used to test ACT explanations. Complex football situations were displayed to expert and non-expert football players in a decision making task in a controlled laboratory setting. Ratings of state anxiety and pupil diameter measures were used to check anxiety manipulations. Dependent variables were verbal response time and accuracy, mental effort ratings and visual search behavior (e.g., visual search rate). Results confirmed that an anxiety increase, indicated by higher state-anxiety ratings and larger pupil diameters, reduced processing efficiency for both groups (higher response times and mental effort ratings). Moreover, high task demands reduced the ability to shift attention between different locations for the expert group in the high anxiety condition only. Since particularly experts, who were expected to use more top-down strategies to guide visual attention under high perceptual task demands, showed less attentional shifts in the high compared to the low anxiety condition, as predicted by ACT, anxiety seems to impair the shifting function by interrupting the balance between top-down and bottom-up processes.

The quiet eye without a target: The primacy of visual information processing

Motor-performance-enhancing effects of long final fixations before movement initiation – a phenomenon called Quiet Eye (QE) – have repeatedly been demonstrated. Drawing on the information-processing framework, it is assumed that the QE supports information processing revealed by the close link between QE duration and task demands concerning, in particular, response selection and movement parameterisation. However, the question remains whether the suggested mechanism also holds for processes referring to stimulus identification. Thus, in a series of two experiments, performance in a targeting task was tested as a function of experimentally manipulated visual processing demands as well as experimentally manipulated QE durations. The results support the suggested link because a performance-enhancing QE effect was found under increased visual processing demands only: Whereas QE duration did not affect performance as long as positional information was preserved (Experiment 1), in the full vs. no target visibility comparison, QE efficiency turned out to depend on information processing time as soon as the interval falls below a certain threshold (Experiment 2). Thus, the results rather contradict alternative, e.g., posture-based explanations of QE effects and support the assumption that the crucial mechanism behind the QE phenomenon is rooted in the cognitive domain.

Visual avoidance in phobia: particularities in neural activity, autonomic responding, and cognitive risk evaluations.

We investigated the neural mechanisms and the autonomic and cognitive responses associated with visual avoidance behavior in spider phobia. Spider phobic and control participants imagined visiting different forest locations with the possibility of encountering spiders, snakes, or birds (neutral reference category). In each experimental trial, participants saw a picture of a forest location followed by a picture of a spider, snake, or bird, and then rated their personal risk of encountering these animals in this context, as well as their fear. The greater the visual avoidance of spiders that a phobic participant demonstrated (as measured by eye tracking), the higher were her autonomic arousal and neural activity in the amygdala, orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), and precuneus at picture onset. Visual avoidance of spiders in phobics also went hand in hand with subsequently reduced cognitive risk of encounters. Control participants, in contrast, displayed a positive relationship between gaze duration toward spiders, on the one hand, and autonomic responding, as well as OFC, ACC, and precuneus activity, on the other hand. In addition, they showed reduced encounter risk estimates when they looked longer at the animal pictures. Our data are consistent with the idea that one reason for phobics to avoid phobic information may be grounded in heightened activity in the fear circuit, which signals potential threat. Because of the absence of alternative efficient regulation strategies, visual avoidance may then function to down-regulate cognitive risk evaluations for threatening information about the phobic stimuli. Control participants, in contrast, may be characterized by a different coping style, whereby paying visual attention to potentially threatening information may help them to actively down-regulate cognitive evaluations of risk.

Effects of (un)predictable whole body vibrations on visual performance

Over recent years, it has repeatedly been shown that optimal gaze strategies enhance motor control (e.g., Foulsham, 2015). However, little is known, whether, vice versa, visual performance can be improved by optimized motor control. Consequently, in two studies, we investigated visual performance as a function of motor control strategies and task parameters, respectively. In Experiment 1, 72 participants were tested on visual acuity (Landolt) and contrast sensitivity (Grating), while standing in two different postures (upright vs. squat) on a ZEPTOR-platform that vibrated at four different frequencies (0, 4, 8, 12 Hz). After each test, perceived exertion (Borg) was assessed. Significant interactions were revealed for both tests, Landolt: F(3,213)=13.25, p<.01, ηp2=.16, Grating: F(3,213)=4.27, p<.01, ηp2=.06, elucidating a larger loss of acuity/contrast sensitivity with increasing frequencies for the upright compared with the squat posture. For perceived exertion, however, a diametrical interaction for frequency was found for acuity, F(3,213)=7.45, p<.01, ηp2=.09, and contrast sensitivity, F(3,213)=7.08, p < .01, ηp2=.09, substantiating that the impaired visual performance cannot be attributed to exertion. Consequently, the squat posture could permit better head and, hence, gaze stabilization. In Experiment 2, 64 participants performed the same tests while standing in a squat position on a ski-simulator, which vibrated with two different frequencies (2.4, 3.6 Hz) and amplitudes (50, 100 mm) in a predictable or unpredictable manner. Control strategies were identified by tracking segmental motion, which allows to derive damping characteristics. Considerable main effects were found for frequency, all F’s(1,52)>10.31, all p’s<.01, all ηp2’s>.16, as well as, in the acuity test, for predictability, F(1,52)=10.31, p<.01, ηp2=.17, and by tendency for amplitude, F(1,52)=3.53, p=.06, ηp2=.06. A significant correlation between the damping amplitude in the knee joint and the performance drop in visual acuity, r=-.97, p<.001, again points towards the importance of motor control strategies to maintain optimal visual performance.

Glucose-Induced Temporary Visual Recovery in Primary Open-Angle Glaucoma: A Double-Blind, Randomized Study

Purpose To investigate the effect of topical glucose on visual parameters in individuals with primary open-angle glaucoma (POAG). Design Double-blind, randomized, crossover study. Participants Nondiabetic pseudophakic patients with definite POAG were recruited; 29 eyes of 16 individuals participated in study 1. A follow-up study (study 2) included 14 eyes of 7 individuals. Intervention Eyes were randomly allocated to receive 50% glucose or saline eye drops every 5 minutes for 60 minutes. Main Outcome Measures The contrast sensitivity and best-corrected logarithm of the minimum angle of resolution (logMAR). Results The 50% glucose reached the vitreous in pseudophakic but not phakic individuals. Glucose significantly improved the mean contrast sensitivity at 12 cycles/degree compared with 0.9% saline by 0.26 log units (95% confidence interval [CI], 0.13–0.38; P < 0.001) and 0.40 log units (95% CI, 0.17–0.60; P < 0.001) in the follow-up study. The intraocular pressure, refraction, and central corneal thickness were not affected by glucose; age was not a significant predictor of the response. Conclusions Topical glucose temporarily improves psychophysical visual parameters in some individuals with POAG, suggesting that neuronal energy substrate delivery to the vitreous reservoir may recover function of “sick” retinal neurons.

Theta burst stimulation improves overt visual search in spatial neglect independently of attentional load

Visual neglect is considerably exacerbated by increases in visual attentional load. These detrimental effects of attentional load are hypothesised to be dependent on an interplay between dysfunctional inter-hemispheric inhibitory dynamics and load-related modulation of activity in cortical areas such as the posterior parietal cortex (PPC). Continuous Theta Burst Stimulation (cTBS) over the contralesional PPC reduces neglect severity. It is unknown, however, whether such positive effects also operate in the presence of the detrimental effects of heightened attentional load. Here, we examined the effects of cTBS on neglect severity in overt visual search (i.e., with eye movements), as a function of high and low visual attentional load conditions. Performance was assessed on the basis of target detection rates and eye movements, in a computerised visual search task and in two paper-pencil tasks. cTBS significantly ameliorated target detection performance, independently of attentional load. These ameliorative effects were significantly larger in the high than the low load condition, thereby equating target detection across both conditions. Eye movement analyses revealed that the improvements were mediated by a redeployment of visual fixations to the contralesional visual field. These findings represent a substantive advance, because cTBS led to an unprecedented amelioration of overt search efficiency that was independent of visual attentional load.

Ventilation/perfusion SPECT or SPECT/CT for lung function imaging in patients with pulmonary emphysema?

PURPOSE To evaluate the utility of attenuation correction (AC) of V/P SPECT images for patients with pulmonary emphysema. MATERIALS AND METHODS Twenty-one patients (mean age 67.6 years) with pulmonary emphysema who underwent V/P SPECT/CT were included. AC/non-AC V/P SPECT images were compared visually and semiquantitatively. Visual comparison of AC/non-AC images was based on a 5-point likert scale. Semiquantitative comparison assessed absolute counts per lung (aCpLu) and lung lobe (aCpLo) for AC/non-AC images using software-based analysis; percentage counts (PC = (aCpLo/aCpLu) × 100) were calculated. Correlation between AC/non-AC V/P SPECT images was analyzed using Spearman's rho correlation coefficient; differences were tested for significance with the Wilcoxon rank sum test. RESULTS Visual analysis revealed high conformity for AC and non-AC V/P SPECT images. Semiquantitative analysis of PC in AC/non-AC images had an excellent correlation and showed no significant differences in perfusion (ρ = 0.986) or ventilation (ρ = 0.979, p = 0.809) SPECT/CT images. CONCLUSION AC of V/P SPECT images for lung lobe-based function imaging in patients with pulmonary emphysema do not improve visual or semiquantitative image analysis.

Temporal variations of dyspnea, fatigue, and lung function in chronic lung disease

Background. Research investigating symptom management in patients with chronic obstructive pulmonary disease (COPD) largely has been undertaken assuming the homeostatic construct, without regard to potential roles of circadian rhythms. Temporal relations among dyspnea, fatigue, peak expiratory flow rate (PEFR) and objective measures of activity/rest have not been reported in COPD. ^ Objectives. The specific aims of this study were to (1) explore the 24-hour patterns of dyspnea, fatigue, and PEFR in subjects with COPD; (2) examine the relations among dyspnea, fatigue, and PEFR in COPD; and (3) examine the relations among objective measures of activity/rest and dyspnea, fatigue, and PEFR in COPD. ^ Methods. The repeated-measures design involved 10 subjects with COPD who self-assessed dyspnea and fatigue by 100 mm visual analog scales, and PEFR by peak flow meter in their home 5 times a day for 8 days. Activity/rest was measured by wrist actigraphy. Single and population mean cosinor analyses and correlations were computed for dyspnea, fatigue, and PEFR; correlations were done among these variables and activity/rest. ^ Results. Circadian rhythms were documented by single cosinor analysis in 40% of the subjects for dyspnea, 60% for fatigue, and 60% for PEFR. The population cosinor analysis of PEFR yielded a significant rhythm (p < .05). The 8-day 24-hour means of dyspnea and fatigue was moderately correlated (r = .48, p < .01). Dyspnea and PEFR, and fatigue and PEFR, were weakly correlated in a negative way (r = −.11, p < .05 and r = −.15, p < .01 respectively). Weak to moderate correlations (r = .12–.34, p < .05) were demonstrated between PEFR and mean activity level measured up to 4 hours before PEFR measurement. ^ Conclusions. The findings suggest that (1) the dyspnea and fatigue experienced by COPD patients are moderately related, (2) there is a weak to modest positive relation between PEFR and activity levels, and (3) temporal variation in lung function may not affect the dyspnea and fatigue experienced by patients with COPD. Further research, examining the relations among dyspnea, fatigue, PEFR, and activity/rest is needed. Replication of this study is suggested with a larger sample size. ^

Merit function for the evaluation of color uniformity in the far field of LED spot lights

The scope of the present paper is the derivation of a merit function which predicts the visual perception of LED spot lights. The color uniformity level Usl is described by a linear regression function of the spatial color distribution in the far field. Hereby, the function is derived from four basic functions. They describe the color uniformity of spot lights through different features. The result is a reliable prediction for the perceived color uniformity in spot lights. A human factor experiment was performed to evaluate the visual preferences for colors and patterns. A perceived rank order was derived from the subjects’ answers and compared with the four basic functions. The correlation between the perceived rank order and the basic functions was calculated resulting in the definition of the merit function Usl. The application of this function is shown by a comparison of visual evaluations and measurements of LED retrofit spot lamps. The results enable a prediction of color uniformity levels of simulations and measurements concerning the visual perception. The function provides a possibility to evaluate the far field of spot lights without individual subjective judgment. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Color uniformity in spotligths - visual perception and system design

La iluminación con diodos emisores de luz (LED) está reemplazando cada vez en mayor medida a las fuentes de luz tradicionales. La iluminación LED ofrece ventajas en eficiencia, consumo de energía, diseño, tamaño y calidad de la luz. Durante más de 50 años, los investigadores han estado trabajando en mejoras LED. Su principal relevancia para la iluminación está aumentando rápidamente. Esta tesis se centra en un campo de aplicación importante, como son los focos. Se utilizan para enfocar la luz en áreas definidas, en objetos sobresalientes en condiciones profesionales. Esta iluminación de alto rendimiento requiere una calidad de luz definida, que incluya temperaturas ajustables de color correlacionadas (CCT), de alto índice de reproducción cromática (CRI), altas eficiencias, y colores vivos y brillantes. En el paquete LED varios chips de diferentes colores (rojo, azul, fósforo convertido) se combinan para cumplir con la distribución de energía espectral con alto CRI. Para colimar la luz en los puntos concretos deseados con un ángulo de emisión determinado, se utilizan blancos sintonizables y diversos colores de luz y ópticas secundarias. La combinación de una fuente LED de varios colores con elementos ópticos puede causar falta de homogeneidad cromática en la distribución espacial y angular de la luz, que debe resolverse en el diseño óptico. Sin embargo, no hay necesidad de uniformidad perfecta en el punto de luz debido al umbral en la percepción visual del ojo humano. Por lo tanto, se requiere una descripción matemática del nivel de uniformidad del color con respecto a la percepción visual. Esta tesis está organizada en siete capítulos. Después de un capítulo inicial que presenta la motivación que ha guiado la investigación de esta tesis, en el capítulo 2 se presentan los fundamentos científicos de la uniformidad del color en luces concentradas, como son: el espacio de color aplicado CIELAB, la percepción visual del color, los fundamentos de diseño de focos respecto a los motores de luz y ópticas no formadoras de imágenes, y los últimos avances en la evaluación de la uniformidad del color en el campo de los focos. El capítulo 3 desarrolla diferentes métodos para la descripción matemática de la distribución espacial del color en un área definida, como son la diferencia de color máxima, la desviación media del color, el gradiente de la distribución espacial de color, así como la suavidad radial y axial. Cada función se refiere a los diferentes factores que influyen en la visión, los cuales necesitan un tratamiento distinto que el de los datos que se tendrán en cuenta, además de funciones de ponderación que pre- y post-procesan los datos simulados o medidos para la reducción del ruido, la luminancia de corte, la aplicación de la ponderación de luminancia, la función de sensibilidad de contraste, y la función de distribución acumulativa. En el capítulo 4, se obtiene la función de mérito Usl para la estimación de la uniformidad del color percibida en focos. Se basó en los resultados de dos conjuntos de experimentos con factor humano realizados para evaluar la percepción visual de los sujetos de los patrones de focos típicos. El primer experimento con factor humano dio lugar al orden de importancia percibida de los focos. El orden de rango percibido se utilizó para correlacionar las descripciones matemáticas de las funciones básicas y la función ponderada sobre la distribución espacial del color, que condujo a la función Usl. El segundo experimento con factor humano probó la percepción de los focos bajo condiciones ambientales diversas, con el objetivo de proporcionar una escala absoluta para Usl, para poder así sustituir la opinión subjetiva personal de los individuos por una función de mérito estandarizada. La validación de la función Usl se presenta en relación con el alcance de la aplicación y condiciones, así como las limitaciones y restricciones que se realizan en el capítulo 5. Se compararon los datos medidos y simulados de varios sistemas ópticos. Se discuten los campos de aplicación , así como validaciones y restricciones de la función. El capítulo 6 presenta el diseño del sistema de focos y su optimización. Una evaluación muestra el análisis de sistemas basados en el reflector y la lente TIR. Los sistemas ópticos simulados se comparan en la uniformidad del color Usl, sensibilidad a las sombras coloreadas, eficiencia e intensidad luminosa máxima. Se ha comprobado que no hay un sistema único que obtenga los mejores resultados en todas las categorías, y que una excelente uniformidad de color se pudo alcanzar por la conjunción de dos sistemas diferentes. Finalmente, el capítulo 7 presenta el resumen de esta tesis y la perspectiva para investigar otros aspectos. ABSTRACT Illumination with light-emitting diodes (LED) is more and more replacing traditional light sources. They provide advantages in efficiency, energy consumption, design, size and light quality. For more than 50 years, researchers have been working on LED improvements. Their main relevance for illumination is rapidly increasing. This thesis is focused on one important field of application which are spotlights. They are used to focus light on defined areas, outstanding objects in professional conditions. This high performance illumination required a defined light quality including tunable correlated color temperatures (CCT), high color rendering index (CRI), high efficiencies and bright, vivid colors. Several differently colored chips (red, blue, phosphor converted) in the LED package are combined to meet spectral power distribution with high CRI, tunable white and several light colors and secondary optics are used to collimate the light into the desired narrow spots with defined angle of emission. The combination of multi-color LED source and optical elements may cause chromatic inhomogeneities in spatial and angular light distribution which needs to solved at the optical design. However, there is no need for perfect uniformity in the spot light due to threshold in visual perception of human eye. Therefore, a mathematical description of color uniformity level with regard to visual perception is required. This thesis is organized seven seven chapters. After an initial one presenting the motivation that has guided the research of this thesis, Chapter 2 introduces the scientific basics of color uniformity in spot lights including: the applied color space CIELAB, the visual color perception, the spotlight design fundamentals with regards to light engines and nonimaging optics, and the state of the art for the evaluation of color uniformity in the far field of spotlights. Chapter 3 develops different methods for mathematical description of spatial color distribution in a defined area, which are the maximum color difference, the average color deviation, the gradient of spatial color distribution as well as the radial and axial smoothness. Each function refers to different visual influencing factors, and they need different handling of data be taken into account, along with weighting functions which pre- and post-process the simulated or measured data for noise reduction, luminance cutoff, the implementation of luminance weighting, contrast sensitivity function, and cumulative distribution function. In chapter 4, the merit function Usl for the estimation of the perceived color uniformity in spotlights is derived. It was based on the results of two sets of human factor experiments performed to evaluate the visual perception of typical spotlight patterns by subjects. The first human factor experiment resulted in the perceived rank order of the spotlights. The perceived rank order was used to correlate the mathematical descriptions of basic functions and weighted function concerning the spatial color distribution, which lead to the Usl function. The second human factor experiment tested the perception of spotlights under varied environmental conditions, with to objective to provide an absolute scale for Usl, so the subjective personal opinion of individuals could be replaced by a standardized merit function. The validation of the Usl function is presented concerning the application range and conditions as well as limitations and restrictions in carried out in chapter 5. Measured and simulated data of various optical several systems were compared. Fields of applications are discussed as well as validations and restrictions of the function. Chapter 6 presents spotlight system design and their optimization. An evaluation shows the analysis of reflector-based and TIR lens systems. The simulated optical systems are compared in color uniformity Usl , sensitivity to colored shadows, efficiency, and peak luminous intensity. It has been found that no single system which performed best in all categories, and that excellent color uniformity could be reached by two different system assemblies. Finally, chapter 7 summarizes the conclusions of the present thesis and an outlook for further investigation topics.

Bidirectional, experience-dependent regulation of N-methyl-d-aspartate receptor subunit composition in the rat visual cortex during postnatal development

In the visual cortex, as elsewhere, N-methyl-d-aspartate receptors (NMDARs) play a critical role in triggering long-term, experience-dependent synaptic plasticity. Modifications of NMDAR subunit composition alter receptor function, and could have a large impact on the properties of synaptic plasticity. We have used immunoblot analysis to investigate the effects of age and visual experience on the expression of different NMDAR subunits in synaptoneurosomes prepared from rat visual cortices. NMDARs at birth are comprised of NR2B and NR1 subunits, and, over the first 5 postnatal weeks, there is a progressive inclusion of the NR2A subunit. Dark rearing from birth attenuates the developmental increase in NR2A. Levels of NR2A increase rapidly (in <2 hr) when dark-reared animals are exposed to light, and decrease gradually over the course of 3 to 4 days when animals are deprived of light. These data reveal that NMDAR subunit composition in the visual cortex is remarkably dynamic and bidirectionally regulated by sensory experience. We propose that NMDAR subunit regulation is a mechanism for experience-dependent modulation of synaptic plasticity in the visual cortex, and serves to maintain synaptic strength within an optimal dynamic range.

Pattern of neuronal activity associated with conscious and unconscious processing of visual signals

Following striate cortex damage in monkeys and humans there can be residual function mediated by parallel visual pathways. In humans this can sometimes be associated with a “feeling” that something has happened, especially with rapid movement or abrupt onset. For less transient events, discriminative performance may still be well above chance even when the subject reports no conscious awareness of the stimulus. In a previous study we examined parameters that yield good residual visual performance in the “blind” hemifield of a subject with unilateral damage to the primary visual cortex. With appropriate parameters we demonstrated good discriminative performance, both with and without conscious awareness of a visual event. These observations raise the possibility of imaging the brain activity generated in the “aware” and the “unaware” modes, with matched levels of discrimination performance, and hence of revealing patterns of brain activation associated with visual awareness. The intact hemifield also allows a comparison with normal vision. Here we report the results of a functional magnetic resonance imaging study on the same subject carried out under aware and unaware stimulus conditions. The results point to a shift in the pattern of activity from neocortex in the aware mode, to subcortical structures in the unaware mode. In the aware mode prestriate and dorsolateral prefrontal cortices (area 46) are active. In the unaware mode the superior colliculus is active, together with medial and orbital prefrontal cortical sites.

Perturbed dentate gyrus function in serotonin 5-HT2C receptor mutant mice

Serotonin systems have been implicated in the regulation of hippocampal function. Serotonin 5-HT2C receptors are widely expressed throughout the hippocampal formation, and these receptors have been proposed to modulate synaptic plasticity in the visual cortex. To assess the contribution of 5-HT2C receptors to the serotonergic regulation of hippocampal function, mice with a targeted 5-HT2C-receptor gene mutation were examined. An examination of long-term potentiation at each of four principal regions of the hippocampal formation revealed a selective impairment restricted to medial perforant path–dentate gyrus synapses of mutant mice. This deficit was accompanied by abnormal performance in behavioral assays associated with dentate gyrus function. 5-HT2C receptor mutants exhibited abnormal performance in the Morris water maze assay of spatial learning and reduced aversion to a novel environment. These deficits were selective and were not associated with a generalized learning deficit or with an impairment in the discrimination of spatial context. These results indicate that a genetic perturbation of serotonin receptor function can modulate dentate gyrus plasticity and that plasticity in this structure may contribute to neural mechanisms underlying hippocampus-dependent behaviors.

N-methyl-d-aspartate receptor activation and visual activity induce elongation factor-2 phosphorylation in amphibian tecta: A role for N-methyl-d-aspartate receptors in controlling protein synthesis

N-methyl-d-aspartate receptor (NMDAR) activation has been implicated in forms of synaptic plasticity involving long-term changes in neuronal structure, function, or protein expression. Transcriptional alterations have been correlated with NMDAR-mediated synaptic plasticity, but the problem of rapidly targeting new proteins to particular synapses is unsolved. One potential solution is synapse-specific protein translation, which is suggested by dendritic localization of numerous transcripts and subsynaptic polyribosomes. We report here a mechanism by which NMDAR activation at synapses may control this protein synthetic machinery. In intact tadpole tecta, NMDAR activation leads to phosphorylation of a subset of proteins, one of which we now identify as the eukaryotic translation elongation factor 2 (eEF2). Phosphorylation of eEF2 halts protein synthesis and may prepare cells to translate a new set of mRNAs. We show that NMDAR activation-induced eEF2 phosphorylation is widespread in tadpole tecta. In contrast, in adult tecta, where synaptic plasticity is reduced, this phosphorylation is restricted to short dendritic regions that process binocular information. Biochemical and anatomical evidence shows that this NMDAR activation-induced eEF2 phosphorylation is localized to subsynaptic sites. Moreover, eEF2 phosphorylation is induced by visual stimulation, and NMDAR blockade before stimulation eliminates this effect. Thus, NMDAR activation, which is known to mediate synaptic changes in the developing frog, could produce local postsynaptic alterations in protein synthesis by inducing eEF2 phosphorylation.