fMRI in the public eye

The wide dissemination and expanding applications of functional MRI have not escaped the attention of the media or discussion in the wider public arena. From the bench to the bedside, this technology has introduced substantial ethical challenges. Are the boundaries of what it can and cannot achieve being communicated to the public? Are its limitations understood? And given the complexities that are inherent to neuroscience, are current avenues for communication adequate?     

Structural and molecular biology of the eye lens membranes

Lens transparency is associated with a unique design in tissue development and architecture. The fiber plasma membrane has domains which link with the cytoskeleton, thus maintaining cell shape. Other membrane regions form processes which interlock adjacent lens fibers, and intercellular junctions contain transmembrane pores which allow passage of metabolites between cells. Much interest has recently focused on the study of lens membrane structure and function, mainly because membrane dysfunction may be associated with cataract formation. This article reviews what is known about the structure of membrane domains, about the identification of domain-specific proteins, and describes current attempts to relate these results to function. Much of the presently available data is controversial, and an attempt will be made to reconcile them in revised models and testable hypotheses.     

Multineuronal firing patterns in the signal from eye to brain

Population codes in the brain have generally been characterized by recording responses from one neuron at a time. This approach will miss codes that rely on concerted patterns of action potentials from many cells. Here we analyze visual signaling in populations of ganglion cells recorded from the isolated salamander retina. These neurons tend to fire synchronously far more frequently than expected by chance. We present an efficient algorithm to identify what groups of cells cooperate in this way. Such groups can include up to seven or more neurons and may account for more than 50% of all the spikes recorded from the retina. These firing patterns represent specific messages about the visual stimulus that differ significantly from what one would derive by single-cell analysis.     

The eye as a replicating and diverging, modular developmental unit

Sparked by new discoveries in developmental genetics, few topics have generated as much debate as eye evolution. This is somewhat surprising because the central controversy is not unique to eyes, but is a general theme of developmental genetics: evolutionarily conserved genes are deployed during the development of highly divergent morphological features. In the case of eyes, this paradox has engendered opposing camps entrenched in what has been termed a ‘scientific war’. One camp highlights conserved genetic features, concluding that eyes stem from an ancestral prototype. The opposing camp emphasizes variation, arguing that some eyes must have recruited the same genes after separate morphological origins. Here, I blur the line between these camps and suggest that eyes have often evolved by replication, perhaps through the ectopic expression of a conserved, modular regulatory cascade to produce serially homologous structures that often diverged during evolution. Therefore, morphologically diverse eyes could stem from a single ancestral prototype, yet also result from multiple morphological origins.     

Acceleration and velocity signals trigger otolithic eye movements during lateral translation

Since it is still controversial what kinds of driving signals are effective in otolith [correction of otholith] ocular responses, we attempted to compare eye movement responses between the step and sinusoidal modes of lateral translation.     

More than meets the eye: The barrier effect of the Yangtze River outflow

The Yangtze (Changjiang) River enters the East China Sea with huge annual freshwater and sediment deposits. This outflow, known as the Changjiang diluted water (CDW), causes striking ecological gradients that potentially shape coastal species’ distribution and differentiation. The CDW has long been rendered as a marine biogeographic boundary separating cold‐temperature and warm‐water faunas, but it remains unclear whether and to what extent it acts as an intraspecific barrier. Here, we synthesize published phylogeographic studies related to the CDW to address these issues. We find that the influence of the CDW on population differentiation is taxonomically variable, and even congeneric species may respond differently. In studies that claim the CDW is a phylogeographic barrier, the underlying assumptions explaining observed genetic breaks are sometimes incorrect, and some may have misinterpreted results due to conceptual confusion or insufficient geographic sampling. After excluding these studies, the remaining ones generally show shallow genetic divergence but significant population structure for coastal species across the CDW, suggesting that the CDW has not been a historically persistent barrier, but rather has acted as a filter within some species recently, probably after the last glacial maximum.     

The role of corticosteroids in the homeostasis of the eye

Three problems were studied on the human and rabbit eye: to what extent the mineralocorticoids contribute to the control of Na+ and K+ transport in the lens epithelium, how do the glucocorticoids influence the concentration of glucose in the aqueous humour and what is the effect of the pituitary-adrenal axis on the hemato-ocular barrier. Specific receptor-like proteins binding aldosterone were found in the lens epithelium. Na+ and K+ concentrations in the aqueous were influenced by both aldosterone and spironolactone administration. The aldosterone concentration in human cataracts was found to be higher in cases of cataracts complicated by arterial hypertension. In spite of some indication of anticataractogenous action of mineralocorticoids, aldosterone did not prevent the formation of cortisol-induced cataract in chick embryos. Glucose concentration in the aqueous was increased by glucocorticoid administration as well as by stimulation of their secretion by ACTH. Further, the contribution of the pituitary-adrenal axis to the breakdown of the hemato-ocular barrier was investigated by measuring the changes of the total protein content in the aqueous. ACTH1-24 caused a partial breakdown of the barrier, as well as ACTH4-10 or alpha-MSH. As the latter two peptides lack the stimulative effect on the corticoid secretion and glucocorticoids themselves fail to increase the protein content in the aqueous, the breakdown of the hemato-ocular barrier seems to be essential for ACTH-linked peptide fragments and is not mediated by corticoids.     

Homeostasis of eye growth and the question of myopia

As with other organs, the eye's growth is regulated by homeostatic control mechanisms. Unlike other organs, the eye relies on vision as a principal input to guide growth. In this review, we consider several implications of this visual guidance. First, we compare the regulation of eye growth to that of other organs. Second, we ask how the visual system derives signals that distinguish the blur of an eye too large from one too small. Third, we ask what cascade of chemical signals constitutes this growth control system. Finally, if the match between the length and optics of the eye is under homeostatic control, why do children so commonly develop myopia, and why does the myopia not limit itself? Long-neglected studies may provide an answer to this last question.     

Landscape structure and locust swarming: a satellite's eye view

Desert locust Schistocerca gregaria outbreaks consistently start in the same places, suggesting that certain landscapes are particularly favourable for outbreaking. Outbreaks are generated by multiplication, concentration and gregarisation of locust populations. Previous research has shown how small-scale vegetation patterns in desert ecosystems influence locust gregarisation; the present study examines the effects of large-scale landscape structure on locust multiplication and concentration. NOAA/AVHRR satellite imagery was used to relate abundance and spatial distribution of resources at the landscape scale to the historical record of locust outbreaks. Threshold NDVI values were investigated to define what constitutes 'resource' for locusts. The first part of the study showed that abundance and spatial distribution of resource were not sufficient to distinguish between outbreak and non-outbreak areas in the western part of the locust distribution area. Thus, outbreak danger zones cannot be identified by landscape structure at this spatial resolution. The second analysis investigated spatio-temporal patterns of vegetation growth in two locust breeding areas with very different landscape structure; in both cases, the patterns differed significantly between outbreaking and non-outbreaking years. In Mauritania, a flat homogeneous desert landscape, both resource abundance and fragmentation were higher in outbreaking years. On the Red Sea coast, a fragmented landscape, resource spatial distribution was consistent between years, and abundance alone was a significant predictor of outbreaking. High resource abundance promotes locust multiplication, and contraction of resource into small patches increases locust concentration; these two mechanisms explain how landscape structure influences locust outbreaking.     

Evolution of eye size and shape in primates

Strepsirrhine and haplorhine primates exhibit highly derived features of the visual system that distinguish them from most other mammals. Comparative data link the evolution of these visual specializations to the sequential acquisition of nocturnal visual predation in the primate stem lineage and diurnal visual predation in the anthropoid stem lineage. However, it is unclear to what extent these shifts in primate visual ecology were accompanied by changes in eye size and shape. Here we investigate the evolution of primate eye morphology using a comparative study of a large sample of mammalian eyes. Our analysis shows that primates differ from other mammals in having large eyes relative to body size and that anthropoids exhibit unusually small corneas relative to eye size and body size. The large eyes of basal primates probably evolved to improve visual acuity while maintaining high sensitivity in a nocturnal context. The reduced corneal sizes of anthropoids reflect reductions in the size of the dioptric apparatus as a means of increasing posterior nodal distance to improve visual acuity. These data support the conclusion that the origin of anthropoids was associated with a change in eye shape to improve visual acuity in the context of a diurnal predatory habitus.     

The functions of the proprioceptors of the eye muscles

This article sets out to present a fairly comprehensive review of our knowledge about the functions of the receptors that have been found in the extraocular muscles--the six muscles that move each eye of vertebrates in its orbit--of all the animals in which they have been sought, including Man. Since their discovery at the beginning of the 20th century these receptors have, at various times, been credited with important roles in the control of eye movement and the construction of extrapersonal space and have also been denied any function whatsoever. Experiments intended to study the actions of eye muscle receptors and, even more so, opinions (and indeed polemic) derived from these observations have been influenced by the changing fashions and beliefs about the more general question of how limb position and movement is detected by the brain and which signals contribute to those aspects of this that are perceived (kinaesthesis). But the conclusions drawn from studies on the eye have also influenced beliefs about the mechanisms of kinaesthesis and, arguably, this influence has been even larger than that in the converse direction. Experimental evidence accumulated over rather more than a century is set out and discussed. It supports the view that, at the beginning of the 21st century, there are excellent grounds for believing that the receptors in the extraocular muscles are indeed proprioceptors, that is to say that the signals that they send into the brain are used to provide information about the position and movement of the eye in the orbit. It seems that this information is important in the control of eye movements of at least some types, and in the determination by the brain of the direction of gaze and the relationship of the organism to its environment. In addition, signals from these receptors in the eye muscles are seen to be necessary for the development of normal mechanisms of visual analysis in the mammalian visual cortex and for both the development and maintenance of normal visuomotor behaviour. Man is among those vertebrates to whose brains eye muscle proprioceptive signals provide information apparently used in normal sensorimotor functions; these include various aspects of perception, and of the control of eye movement. It is possible that abnormalities of the eye muscle proprioceptors and their signals may play a part in the genesis of some types of human squint (strabismus); conversely studies of patients with squint in the course of their surgical or pharmacological treatment have yielded much interesting evidence about the central actions of the proprioceptive signals from the extraocular muscles. The results of experiments on the eye have played a large part in the historical controversy, now in at least its third century, about the origin of signals that inform the brain about movement of parts of the body. Some of these results, and more of the interpretations of them, now need to be critically re-examined. The re-examination in the light of recent experiments that is presented here does not support many of the conclusions confidently drawn in the past and leads to both new insights and fresh questions about the roles of information from motor signals flowing out of the brain and that from signals from the peripheral receptors flowing into it. There remain many lacunae in our knowledge and filling some of these will, it is contended, be essential to advance our understanding further. It is argued that such understanding of eye muscle proprioception is a necessary part of the understanding of the physiology and pathophysiology of eye movement control and that it is also essential to an account of how organisms, including Man, build and maintain knowledge of their relationship to the external visual world. The eye would seem to provide a uniquely favourable system in which to study the way in which information derived within the brain about motor actions may interact with signals flowing in from peripheral receptors. The review is constructed in relatively independent sections that deal with particular topics. It ends with a fairly brief piece in which the author sets out some personal views about what has been achieved recently and what most immediately needs to be done. It also suggests some lines of study that appear to the author to be important for the future.     

Vision as oculomotor reward: cognitive contributions to the dynamic control of saccadic eye movements

Humans and other primates are equipped with a foveated visual system. As a consequence, we reorient our fovea to objects and targets in the visual field that are conspicuous or that we consider relevant or worth looking at. These reorientations are achieved by means of saccadic eye movements. Where we saccade to depends on various low-level factors such as a targets’ luminance but also crucially on high-level factors like the expected reward or a targets’ relevance for perception and subsequent behavior. Here, we review recent findings how the control of saccadic eye movements is influenced by higher-level cognitive processes. We first describe the pathways by which cognitive contributions can influence the neural oculomotor circuit. Second, we summarize what saccade parameters reveal about cognitive mechanisms, particularly saccade latencies, saccade kinematics and changes in saccade gain. Finally, we review findings on what renders a saccade target valuable, as reflected in oculomotor behavior. We emphasize that foveal vision of the target after the saccade can constitute an internal reward for the visual system and that this is reflected in oculomotor dynamics that serve to quickly and accurately provide detailed foveal vision of relevant targets in the visual field.     

Visual cortical responses to the input from the amblyopic eye are suppressed during binocular viewing

Amblyopia is a visual disorder caused by an anomalous early visual experience. It has been suggested that suppression of the visual input from the weaker eye might be a primary underlying mechanism of the amblyopic syndrome. However, it is still an unresolved question to what extent neural responses to the visual information coming from the amblyopic eye are suppressed during binocular viewing. To address this question we measured event-related potentials (ERP) to foveal face stimuli in amblyopic patients, both in monocular and binocular viewing conditions. The results revealed no difference in the amplitude and latency of early components of the ERP responses between the binocular and fellow eye stimulation. On the other hand, early ERP components were reduced and delayed in the case of monocular stimulation of the amblyopic eye as compared to the fellow eye stimulation or to binocular viewing. The magnitude of the amblyopic effect measured on the ERP amplitudes was comparable to that found on the fMRI responses in the fusiform face area using the same face stimuli and task conditions. Our findings showing that the amblyopic effects present on the early ERP components in the case of monocular stimulation are not manifested in the ERP responses during binocular viewing suggest that input from the amblyopic eye is completely suppressed already at the earliest stages of visual cortical processing when stimuli are viewed by both eyes.     

Improvement of design of a surgical interface using an eye tracking device

Background

Surgical interfaces are used for helping surgeons in interpretation and quantification of the patient information, and for the presentation of an integrated workflow where all available data are combined to enable optimal treatments. Human factors research provides a systematic approach to design user interfaces with safety, accuracy, satisfaction and comfort. One of the human factors research called user-centered design approach is used to develop a surgical interface for kidney tumor cryoablation. An eye tracking device is used to obtain the best configuration of the developed surgical interface.

Methods

Surgical interface for kidney tumor cryoablation has been developed considering the four phases of user-centered design approach, which are analysis, design, implementation and deployment. Possible configurations of the surgical interface, which comprise various combinations of menu-based command controls, visual display of multi-modal medical images, 2D and 3D models of the surgical environment, graphical or tabulated information, visual alerts, etc., has been developed. Experiments of a simulated cryoablation of a tumor task have been performed with surgeons to evaluate the proposed surgical interface. Fixation durations and number of fixations at informative regions of the surgical interface have been analyzed, and these data are used to modify the surgical interface.

Results

Eye movement data has shown that participants concentrated their attention on informative regions more when the number of displayed Computer Tomography (CT) images has been reduced. Additionally, the time required to complete the kidney tumor cryoablation task by the participants had been decreased with the reduced number of CT images. Furthermore, the fixation durations obtained after the revision of the surgical interface are very close to what is observed in visual search and natural scene perception studies suggesting more efficient and comfortable interaction with the surgical interface. The National Aeronautics and Space Administration Task Load Index (NASA-TLX) and Short Post-Assessment Situational Awareness (SPASA) questionnaire results have shown that overall mental workload of surgeons related with surgical interface has been low as it has been aimed, and overall situational awareness scores of surgeons have been considerably high.

Conclusions

This preliminary study highlights the improvement of a developed surgical interface using eye tracking technology to obtain the best SI configuration. The results presented here reveal that visual surgical interface design prepared according to eye movement characteristics may lead to improved usability.

     

Nonstereospecific biosynthesis of 11-cis-retinal in the eye

[3H]-all-trans-Retinol injected intraocularly into rats is processed to [3H]-11-cis-retinal, the visually active retinoid that binds to opsin. After 18 h, virtually all (93%) of the radioactive retinals recovered were in the form of 11-cis-retinal. At earlier times, however, both all-trans- and 13-cis-retinals, the latter being a nonphysiological isomer, were formed. Both of these isomers disappeared concomitant with the formation of 11-cis-retinal. The rise and fall of 13-cis-retinal suggest that this isomer can be converted into 11-cis-retinal either directly or indirectly in vivo and, hence, that the biosynthesis of the latter is nonstereospecific. This hypothesis was verified by showing that in double-labeling experiments [14C]-13-cis-retinol was converted into 11-cis-retinal nearly as well (approximately 70%) as [3H]-all-trans-retinol. These studies show that the biosynthesis of 11-cis-retinal can be nonstereospecific and, hence, that the process may be chemically rather than enzymatically mediated in vivo. In contrast, double-labeling studies with [14C]-9-cis-retinol and [3H]-all-trans-retinol showed that very little, if any, of the 9-cis isomer was processed to 11-cis-retinal in vivo although it did form isorhodopsin. This is consistent with what is known about the relative chemical stabilities of 9-cis-retinoids from model studies. The isomerization of 9-cis-retinoids is much slower than that of their all-trans, 13-cis, or 11-cis congeners. These results are discussed in terms of a possible mechanism for the biosynthesis of 11-cis-retinal in vivo and suggest that the isomerization event need not necessarily be enzyme mediated.     

Coming to terms with Ox‐eye Daisy (Leucanthemum vulgare) in Kosciuszko National Park,New South Wales

Australia's mountain vegetation is under pressure from a range of threats, not least being weed invasion. Can a program to control the introduced Ox‐eye Daisy succeed and what can be learned to assist management of this weed in other natural areas?     

Perspectives on eye development

The lens of the vertebrate eye was the classic model used to demonstrate the concepts of inductive interactions controlling development. However, it is in the Drosophila model that the greatest progress in understanding molecular mechanisms of eye development have most recently been made. This progress can be attributed to the power of molecular genetics, an approach that was once confined to simpler systems like worms and flies, but is now becoming possible in vertebrates. Thus, the use of transgenic and knock-out gene technology, coupled with the availability of new positional cloning methods, has recently initiated a surge of progress in the mouse genetic model and has also led to the identification of genes involved in human inherited disorders. In addition, gene transfer techniques have opened up opportunities for progress using chick, Xenopus, and other classic developmental systems. Finally, a new vertebrate genetic model, zebrafish, appears very promising for molecular studies. As a result of the opportunities presented by these new approaches, eye development has come into the limelight, hence the timeliness of this focus issue of Developmental Genetics. In this introductory review, we discuss three areas of current work arising through the use of these newer genetic approaches, and pertinent to research articles presented herein. We also touch on related studies reported at the first Keystone Meeting on Ocular Cell and Molecular Biology, recently held in Tamarron Springs, Colorado, January 7–12, 1997. Dev. Genet. 20:175–185, 1997. © 1997 Wiley-Liss, Inc.