Visuospatial Attention to Single and Multiple Objects Is Independently Impaired in Parkinson's Disease

Parkinson’s disease (PD) is associated with deficits in visuospatial attention. It is as yet unknown whether these attentional deficits begin at a perceptual level or instead reflect disruptions in oculomotor or higher-order processes. In the present study, non-demented individuals with PD and matched normal control adults (NC) participated in two tasks requiring sustained visuospatial attention, both based on a multiple object tracking paradigm. Eye tracking was used to ensure central fixation. In Experiment 1 (26 PD, 21 NC), a pair of identical red dots (one target, one distractor) rotated randomly for three seconds at varied speeds. The task was to maintain the identity of the sole target, which was labeled prior to each trial. PD were less accurate than NC overall (p = .049). When considering only trials where fixation was maintained, however, there was no significant group difference, suggesting that the deficit’s origin is closely related to oculomotor processing. To determine whether PD had additional impairment in multifocal attention, in Experiment 2 (25 PD, 15 NC), two targets were presented along with distractors at a moderate speed, along with a control condition in which dots remained stationary. PD were less accurate than NC for moving (p = 0.02) but not stationary targets. This group difference remained significant when considering only trials where fixation was maintained, suggesting the source of the PD deficit was independent from oculomotor processing. Taken together, the results implicate separate mechanisms for single vs. multiple object tracking deficits in PD.     

Gynandromorph analysis of the thoracic disc primordia inDrosophila melanogaster

Summary Cell lineage relationships observable inDrosophila gynandromorphs have been used to locate the primordia of the individual thoracic disc relative to each other in the embryo. Three observations indicate that the borders of the individual disc primordia lie very close to each other, separated by few if any non-disc cells.First, the frequency of mosaicism within each disc indicates large primordia, of similar magnitude to the distances between the centres of adjacent primordia.Second, very few XX/XO-borders cut between adjacent discs without also cutting into one or the other disc.Third, sturt distances between points on adjacent discs are often much smaller than distances measured within individual discs. The proximity of disc primordia suggests that the individual discs might share common precursor cells in the early embryo.     

Oculomotor guidance and capture by irrelevant faces

Even though it is generally agreed that face stimuli constitute a special class of stimuli, which are treated preferentially by our visual system, it remains unclear whether faces can capture attention in a stimulus-driven manner. Moreover, there is a long-standing debate regarding the mechanism underlying the preferential bias of selecting faces. Some claim that faces constitute a set of special low-level features to which our visual system is tuned; others claim that the visual system is capable of extracting the meaning of faces very rapidly, driving attentional selection. Those debates continue because many studies contain methodological peculiarities and manipulations that prevent a definitive conclusion. Here, we present a new visual search task in which observers had to make a saccade to a uniquely colored circle while completely irrelevant objects were also present in the visual field. The results indicate that faces capture and guide the eyes more than other animated objects and that our visual system is not only tuned to the low-level features that make up a face but also to its meaning.     

The existence of an insoluble Z disc scaffold in chicken skeletal muscle

Extraction of glycerinated chicken skeletal muscle with 0.6 M potassium iodide leaves a framework of insoluble components within each muscle fiber. This framework is composed primarily of planes of in-register Z discs that have been thickened by the accumulation of material on both sides of each disc during extraction. Membrane vesicles, presumably remnants of the T system, remain surrounding the Z discs. When the framework is sheared in a blender, it is preferentially cleaved between Z planes, resulting in the formation of large sheets of interconnected, closely packed Z discs in a honeycomb-like array. Cleavage occurs in regions formerly occupied by the A bands, which have been weakened by the removal of myosin. The existence and stability of these planar Z disc arrays demonstrate the presence and strength of connections between adjacent myofibrils.SDS-polyacrylamide gel electrophoresis reveals that this framework consists primarily of actin and desmin, with lesser amounts of a few proteins including α-actinin, myosin and tropomyosin. Z disc sheets and KI-extracted myofibrils provide a distinct face-on view and side view, respectively, of the Z disc. In indirect immunofluorescence, these two views have revealed that desmin is present at the periphery of each Z disc, forming a network of proteinaceous collars within the Z plane. α-Actinin is localized within each disc, giving a face-on fluorescence pattern that is complementary to that of desmin. Actin is present throughout the thickened Z plane, while myosin and tropomyosin exist only in the insoluble residue that coalesces on both faces of each disc.We conclude that desmin, perhaps in conjunction with actin, is responsible for interlinking Z discs of adjacent myofibrils, and may thus serve as a mechanical and structural integrator of muscle fibers. Its hydrophobic nature and coincident distribution with the T system suggest that it may also be responsible for mediating filament-membrane interactions and anchoring the triad to the Z disc. Its collar-like distribution suggests that it may aid in maintaining the structural integrity of the Z disc and the actin filaments inserted into it.     

Sensory gain control (amplification) as a mechanism of selective attention: electrophysiological and neuroimaging evidence.

Both physiological and behavioral studies have suggested that stimulus-driven neural activity in the sensory pathways can be modulated in amplitude during selective attention. Recordings of event-related brain potentials indicate that such sensory gain control or amplification processes play an important role in visual-spatial attention. Combined event-related brain potential and neuroimaging experiments provide strong evidence that attentional gain control operates at an early stage of visual processing in extrastriate cortical areas. These data support early selection theories of attention and provide a basis for distinguishing between separate mechanisms of attentional suppression (of unattended inputs) and attentional facilitation (of attended inputs).     

Saliency changes appearance

Numerous studies have suggested that the deployment of attention is linked to saliency. In contrast, very little is known about how salient objects are perceived. To probe the perception of salient elements, observers compared two horizontally aligned stimuli in an array of eight elements. One of them was salient because of its orientation or direction of motion. We observed that the perceived luminance contrast or color saturation of the salient element increased: the salient stimulus looked even more salient. We explored the possibility that changes in appearance were caused by attention. We chose an event-related potential indexing attentional selection, the N2pc, to answer this question. The absence of an N2pc to the salient object provides preliminary evidence against involuntary attentional capture by the salient element. We suggest that signals from a master saliency map flow back into individual feature maps. These signals boost the perceived feature contrast of salient objects, even on perceptual dimensions different from the one that initially defined saliency.     

Freely flying bees discriminate between stationary and moving objects: performance and possible mechanisms

Summary Freely flying honeybees are innately attracted to moving objects, as revealed by their spontaneous preference for a moving disc over an identical, but stationary disc. We have exploited this spontaneous preference to explore the visual cues by which a bee, which is herself in motion, recognizes a moving object. We find that the moving disc is not detected on the basis that it produces a more rapidly moving image on the retina. The relevant cue might therefore be the motion of the disc relative to the visual surround. We have attempted to test this hypothesis by artificially rotating the structured environment, together with the moving disc, around the bee. Under these conditions, the image of the stationary disc rather than that of the actually moving disc is in motion relative to the surround. We find that rotation of the surround disrupts the bee's capacity not only to distinguish a moving object from a stationary one, but also to discriminate stationary objects at different ranges. Possible interpretations of these results are discussed.     

Behavioral discrimination of water motions caused by moving objects.

We tested whether goldfish, Carassius auratus, discriminate hydrodynamic stimuli caused by moving objects. Blindfolded goldfish responded to a passing object with changes in inter-gill-movement intervals. To learn whether goldfish can discriminate water motions caused by different moving objects we habituated them to a certain object stimulus. If the stimulus was altered, e.g., by altering speed, direction of motion, or size or shape of the object, fish again showed a temporary suspension of breathing when the object passed by. If animals failed to respond to an altered stimulus, we paired this stimulus with a weak electric shock during training. Goldfish discriminated object motion direction. In addition, in two choice experiments goldfish discriminated water motions caused by objects which moved with different speeds (e.g., 5 cm s(-1) versus 6 cm s(-1)), or by objects which differed in size (e.g., 1 cm x 1 cm versus 1.4 cm x 1.4 cm cross section), or shape (e.g., a round versus a triangular object). If object size and/or shape was varied quasi-randomly such that the faster moving object not always caused the greatest water velocities, fish still discriminated object speed.     

Relationship of cholesterol content to spatial distribution and age of disc membranes in retinal rod outer segments

The initial events of visual transduction occur on disc membranes which are sequestered within the photoreceptor outer segment. In rod cells, the discs are stacked in the outer segment. Discs are formed at the base of the rod outer segment (ROS) from evaginations of the plasma membrane. As new discs form, older discs move toward the apical tip of the rod, from which they are eventually shed and subsequently phagocytosed by the adjacent pigment epithelium. Thus, disc membranes within a given rod cell are not of uniform age. We have recently shown that disc membranes are not homogeneous with respect to cholesterol content (Boesze-Battaglia, K., Hennessey, T., and Albert, A. D. (1989) J. Biol. Chem. 264, 8151-8155). In the present study, freshly isolated bovine retinas were incubated with [3H]leucine for 4 h in order to allow sufficient time for the radiolabeled proteins to become incorporated into the basal-most (newest) discs. Osmotically intact discs were then isolated. After the addition of digitonin, the discs were fractionated based on cholesterol content, and radioactivity (indicative of newly synthesized protein) was measured. Discs which exhibited high cholesterol content also exhibited high radio-activity. These results demonstrate that the cholesterol heterogeneity of ROS disc membranes is related to the age, and thus the position, of the discs in the ROS.     

The neurobiology of selective attention.

Research in the field of selective visual attention has recently seen substantial progress in several areas. Neuroimaging and electrical recording results have indicated that selective attention amplifies neural activity in prestriate areas concerned with basic visual processing. Imaging and cellular studies are delineating the networks of anatomical areas that serve as the source of attentional modulation and have suggested that these networks are anatomically distinct from the sites of the resulting amplifications. Cognitive studies of visual search have explored the role of these amplified computations in the integration of visual features into objects. Attentional effects in normal subjects, and their disruption following brain injury, have revealed the mental representations upon which attention operates.     

Fate map of the eye-antennal imaginal disc in the stalk-eyed fly <Emphasis Type="Italic">Cyrtodiopsis dalmanni</Emphasis>

Hypercephaly, in the form of lateral extensions of the head capsule, is observed in several families of Diptera. A particularly extreme form is found in diopsid stalk-eyed flies, in which both eyes and antennae are laterally displaced at the end of eyestalks. We have studied the developmental basis of this exaggerated morphology in Cyrtodiopsis dalmanni. Diopsid eye-antennal imaginal discs are divided into anterior and posterior portions, which are joined by a narrow "disc-stalk" of intervening tissue. We established a fate map for this disc by cutting it into fragments and culturing them in vivo by injecting them into host larvae. The adult eye and dorsal head capsule structures, including the eyestalk and the ocelli, are derived from the posterior portion of the disc, while ventral adult structures such as the antenna and the palpus are derived from the anterior portion of the disc. Thus both posterior and anterior disc portions give rise to structures that are widely separated in the adult head. Moreover, structures that are adjacent in the adult are derived from different regions of the disc. These results confirm and extend previous conclusions about regional identity in diopsid eye-antennal discs that were based on the analysis of molecular markers.     

Sexual homologies and intercalation between parts of the male and female genital discs of Drosophila melanogaster.

To compare the homologies in distribution of positional values within the male and female genital discs, bilaterally symmetrical (horizontally cut) fragments were isolated and combined by mixing them together with tungsten needles. The combinations were then cultured in adult hosts before transfer to larvae for metamorphosis. Fragments that showed no regeneration when cultured intact or when mixed with identical fragments could be induced to regenerate by mixing them with different parts of the same disc. Fragments that showed occasional regeneration in controls were induced to regenerate at higher frequencies in such mixtures. Regeneration could also be induced or increased in frequency by mixing with certain fragments of the genital disc of the opposite sex. It is argued that the extra cases of regeneration in the mixed combinations are due to intercalation between the two components in the combination, and a detailed model is presented to account for the results. It is suggested that the male and female genital discs begin development with identical arrays of positional information, but that different parts of the field grow in the two sexes. The part which does not grow might be retained in the disc to provide a continuous field of positional information, although it would not produce any adult derivatives.     

Changes in mouse intervertebral-disc proteoglycan synthesis with age. Hereditary kyphoscoliosis is associated with elevated synthesis.

Mice with hereditary kyphoscoliosis (ky/ky) develop intervertebral-disc degeneration at the cervico-thoracic junction. Disc proteoglycans were investigated to determine whether changes in synthesis or structure were associated with this. Elevated 35S-proteoglycan synthesis was found in one or more cervico-thoracic discs in 80-day-old ky/ky mice. The hydrodynamic size and aggregation properties of ky/ky-mouse disc 35S-proteoglycans extracted with 4 M-guanidinium chloride were normal. Increased proportions of small 35S-proteoglycans were extracted with 0.5 M-guanidinium chloride from discs of normal and ky/ky mice with increasing age.     

Is regeneration inDrosophila the result of epimorphic regulation?

Summary It has been known for many years that when a wing disc ofDrosophila is bisected, and the fragments cultured in adult females, regulation occurs and either a complete disc is regenerated or the fragment is duplicated. We have investigated how this regeneration process occurs. To establish which cells contribute to the regenerate, and thus determine if regeneration is the result of epimorphic regulation, fragments of discs, after culture in an adult for one to five days, were exposed to³H-thymidine to label replicating cells. Imaginal discs, both whole and as regenerating fragments, undergo some DNA replication which is distributed throughout the disc, but cut discs frequently show clusters of labelled cells around the wound, indicating that regeneration is probably epimorphic.     

Domain-Specific Control of Selective Attention

Previous research has shown that loading information on working memory affects selective attention. However, whether the load effect on selective attention is domain-general or domain-specific remains unresolved. The domain-general effect refers to the findings that load in one content (e.g. phonological) domain in working memory influences processing in another content (e.g., visuospatial) domain. Attentional control supervises selection regardless of information domain. The domain-specific effect refers to the constraint of influence only when maintenance and processing operate in the same domain. Selective attention operates in a specific content domain. This study is designed to resolve this controversy. Across three experiments, we manipulated the type of representation maintained in working memory and the type of representation upon which the participants must exert control to resolve conflict and select a target into the focus of attention. In Experiments 1a and 1b, participants maintained digits and nonverbalized objects, respectively, in working memory while selecting a target in a letter array. In Experiment 2, we presented auditory digits with a letter flanker task to exclude the involvement of resource competition within the same input modality. In Experiments 3a and 3b, we replaced the letter flanker task with an object flanker task while manipulating the memory load on object and digit representation, respectively. The results consistently showed that memory load modulated distractibility only when the stimuli of the two tasks were represented in the same domain. The magnitude of distractor interference was larger under high load than under low load, reflecting a lower efficacy of information prioritization. When the stimuli of the two tasks were represented in different domains, memory load did not modulate distractibility. Control of processing priority in selective attention demands domain-specific resources.     

Attentive mechanisms in visual search

Selective attention can be employed to a restricted region in space or to specific objects. Many properties of this attentional window or spotlight are not well understood. In the present study, we examined the question whether the putative shape of the attentional spotlight can be determined by endogenous cueing within a visual search paradigm. Participants searched for a target among distractors, which were arranged within a vertical or horizontal rectangle. The shape of this rectangle was cued endogenously in a valid or invalid way. Response times (RTs) to correct identification of target orientation were recorded. In Experiment 1, the difference between valid and invalid RTs demonstrated that cueing resulted in elongated attentional areas. This was true only for a group of experienced psychophysical participants, whereas a group of inexperienced participants were not able to use cueing in this way. In Experiment 2, the line motion illusion was used to examine the spatial properties of the attended area. The results confirmed for both experienced and inexperienced participants that attention was confined to the cued elongated area only. We present converging evidence for an attentional spotlight whose shape can be adjusted flexibly by appropriate endogenous cueing.     

Alpha beta TCRs differ in the degree of their specificity for the positively selecting MHC/peptide ligand

We have tested the peptide specificity of positive selection using three transgenic alphabetaTCRs, originally selected on class II MHC (A(b)) covalently bound with one peptide Ealpha (52-68) (Ep). The transgenic TCR specific for the cytochrome c-derived (43-58) peptide was selected on A(b) bound with different arrays of endogenous peptides or the analogue of Ep covalently bound to A(b), but not on the original A(b)Ep complex. In contrast, transgenic TCRs specific for two different analogues of the Ep peptide and A(b) did not mature as CD4(+) T cells in various thymic environments, including the A(b)EpIi(-) mice. These results show that TCRs can be promiscuous or specific for the selecting MHC/peptide complex, and suggest that in mice described in this study transgenic expression of the TCR changes the original requirements for the positively selecting MHC/peptide complex. Future studies will determine whether the latter phenomenon is general or specific for this system.     

Protein synthesis and accumulation in Drosophila melanogaster imaginal discs: Identification of a protein with a nonrandom spatial distribution

Proteins from Drosophila imaginal discs and disc fragments were analyzed on two-dimensional electrophoretic gels following labeling in vitro with [³⁵S]methionine. The protein synthetic pattern in autoradiograms is very complex and parallels the pattern of protein accumulation visualized in silver-stained gels. We find no reproducible qualitative differences in the proteins synthesized or accumulated by different disc types. Additionally, analysis of the proteins synthesized by different fragments of wing and haltere discs has resulted in the identification of a polypeptide which is synthesized preferentially in homologous regions of these two imaginal discs. Scanning densitometry of our autoradiograms corroborates these findings. This protein, therefore, has some of the properties one would predict for a molecule involved in the imaginal disc positional information system.     

Osseointegration of preformed polymethylmethacrylate craniofacial prostheses coated with bone marrow-impregnated poly (DL-lactic-co-glycolic acid) foam.

Osseointegration of bone marrow-PLGA-coated, preformed polymethylmethacrylate cranioplasties offers the possibility of reducing: operative time, periimplant seroma and infection, metallic fixation, and periprosthetic resorption following surgical skull remodeling. These alloplastic materials are FDA-approved but previously have not been used together to promote cranioplasty incorporation. The objective of this study was to determine whether the use of PLGA foam coating improves host osseointegration of preformed, textured, polymethylmethacrylate prosthetic cranioplasties. A critical-sized cranial defect was created in two groups of 10 and one group of three rabbits. The defect was filled with either a textured, preformed polymethylmethacrylate disc or a textured, preformed polymethylmethacrylate disc coated with poly (DL-lactic-co-glycolic acid). Both implants were immersed in autologous bone marrow for 20 minutes before implantation. Half of each group of 10 were killed at 3 weeks, and the remainder at 6 weeks. A third group of three rabbits with excised periosteum was evaluated at 6 weeks. Histologic analysis of the discs determined relative amounts of cancellous bone formation adjacent to the prostheses. Woven trabecular bone was present at each host bone to implant perimeter interface at 3 weeks, with fine fibrous capsular formation around the implants. Thicker, lamellar trabeculae were present at 6 weeks with an increased fibrous layer surrounding both types of implants. Bone formed on the superficial and deep implant surfaces in a noncontiguous fashion. Two of five measures showed that total bone formation was significantly greater in the PLGA-coated implants. Polymethylmethacrylate discs coated with bone marrow-impregnated PLGA foam demonstrate increased bone formation at 3 and 6 weeks as compared with non-coated preformed polymethylmethacrylate discs. Only implants with preserved periosteum showed bone formation away from the host-implant interface (centrally) on the superficial surface at 6 weeks.