Orthopteran DCMD neuron: a reevaluation of responses to moving objects. I. Selective responses to approaching objects.

1. The "descending contralateral movement detector" (DCMD) neuron in the locust has been challenged with a variety of moving stimuli, including scenes from a film (Star Wars), moving disks, and images generated by computer. The neuron responds well to any rapid movement. For a dark object moving along a straight path at a uniform velocity, the DCMD gives the strongest response when the object travels directly toward the eye, and the weakest when the object travels away from the eye. Instead of expressing selectivity for movements of small rather than large objects, the DCMD responds preferentially to approaching objects. 2. The neuron shows a clear selectivity for approach over recession for a variety of sizes and velocities of movement both of real objects and in simulated movements. When a disk that subtends > or = 5 degrees at the eye approaches the eye, there are two peaks in spike rate: one immediately after the start of movement; and a second that builds up during the approach. When a disk recedes from the eye, there is a single peak in response as the movement starts. There is a good correlation between spike rate and angular acceleration of the edges of the image over the eye. 3. When an object approaches from a distance sufficient for it to subtend less than one interommatidial angle at the start of its approach, there is a single peak in response. The DCMD tracks the approach, and, if the object moves at 1 m/s or faster, the spike rate increases throughout the duration of object movement. The size of the response depends on the speed of approach. 4. It is unlikely that the DCMD encodes the time to collision accurately, because the response depends on the size as well as the velocity of an approaching object. 5. Wide-field movements suppress the response to an approaching object. The suppression varies with the temporal frequency of the background pattern. 6. Over a wide range of contrasts of object against background, the DCMD gives a stronger response to approaching than to receding objects. For low contrasts, the selectivity is greater for objects that are darker than the background than for objects that are lighter.     

Modulation by a moving texture of cat area 18 neuron responses to moving bars

1. The influence of a moving texture on neuronal responses to a moving bar was tested in 103 area 18 neurons of anesthetized and paralyzed cats. The texture was a two-dimensional noise pattern, the bar moved at optimal speed, and its contrast was adjusted to yield 50% of the maximum response. 2. The moving texture exerted two different but related effects: it suppressed the response of area 18 neurons to the moving bar, and it modulated the direction selectivity of parastriate neurons. These effects were strongest when the texture moved at the same speed or faster than the bar. 3. Genuine suppressive effects of the moving texture were distinguished from lack of summation between bar and texture responses. Suppressive effects of either type were observed in 75% of the area 18 cells and occurred more frequently among C family cells, velocity tuned cells, and in layer 5 than in other groups of cells. 4. The modulation of direction selectivity was distinguished from pseudomodulation because of lack of summation of bar and texture responses. The direction selectivity of 35% of the area 18 cells was modulated by the moving texture. Six different relative direction selectivity (RDS) types were observed in area 18. 5. The neurons of which direction selectivity was modulated by the moving texture occurred predominantly in layers 2-3 and 6, suggesting that they represent a further stage of processing within area 18. 6. Many (75%) area 18 cells responded to the texture moving on its own. Most of these cells respond to isolated features ("grains") in the patterns rather than to the movement of the whole pattern. Cells responding to the movement of the whole pattern were generally C family cells, and their direction selectivity was not modulated by the moving texture. 7. These results are compared with those obtained under identical experimental conditions in area 17. Although suppressive effects are similar in both areas, RDS types are differently distributed in the two areas. 8. The possible origins of the interactions and their functional significance are discussed.     

Prefrontal responses to drug cues: a neurocognitive analysis

The construct of craving has been central to addiction research for more than 50 years. Only recently have investigators begun to apply functional neuroimaging techniques to the study of drug cue reactivity, and a small but growing number of studies implicate a distributed system of brain regions in the pathogenesis of craving. The internal consistency of this burgeoning literature has thus far been disappointing, however, leaving open the question of which brain regions contribute to craving. Here we review neuroimaging studies of cue-elicited craving in the context of a framework drawn from behavioral research indicating that perceived drug use opportunity significantly affects responses to the presentation of drug cues. Using this framework provides a way to reconcile discrepant findings among brain-imaging studies of cue-elicited craving.     

Anticipating the effects of gravity when intercepting moving objects: differentiating up and down based on nonvisual cues

Intercepting an object requires a precise estimate of its time of arrival at the interception point (time to contact or "TTC"). It has been proposed that knowledge about gravitational acceleration can be combined with first-order, visual-field information to provide a better estimate of TTC when catching falling objects. In this experiment, we investigated the relative role of visual and nonvisual information on motor-response timing in an interceptive task. Subjects were immersed in a stereoscopic virtual environment and asked to intercept with a virtual racket a ball falling from above or rising from below. The ball moved with different initial velocities and could accelerate, decelerate, or move at a constant speed. Depending on the direction of motion, the acceleration or deceleration of the ball could therefore be congruent or not with the acceleration that would be expected due to the force of gravity acting on the ball. Although the best success rate was observed for balls moving at a constant velocity, we systematically found a cross-effect of ball direction and acceleration on success rate and response timing. Racket motion was triggered on average 25 ms earlier when the ball fell from above than when it rose from below, whatever the ball's true acceleration. As visual-flow information was the same in both cases, this shift indicates an influence of the ball's direction relative to gravity on response timing, consistent with the anticipation of the effects of gravity on the flight of the ball.     

A device to display moving objects for visual stimulation in the early development: with numerical control of a pulse motor

In order to observe oculomotor responses to moving objects in infants and the profoundly retarded, a control system of moving objects was developed. The system consists of two parts, the one is to control movement, while the other is to display stimuli. The movement control part is made of a microcomputer, a pulse motor, and a rail, which guides a stimulus carrier with slight friction. The pulse motor rotates 1.8 degrees, according to the input of one pulse. Therefore, the microcomputer can control the velocity of movement of a heavy object exactly. The microcomputer detects the position of a stimulus carrier, counting the number of pulses and receiving signals from switches attached to the rail. The stimuli displaying part controls lighting with respect to the position of a stimulus carrier. Applying this system to a profoundly retarded subject, whose DA was three months, smooth pursuit oculomotor responses at the same velocity as the stimulus were observed in EOG recordings. Measurement of duration of those responses was achieved.     

Tuning host specificity during the ontogeny of a fish ectoparasite: behavioural responses to host-induced cues

The choice between two alternative hosts, brown trout (Salmo trutta) and roach (Rutilus rutilus), and the response to visual and olfactory cues were studied in the ontogeny of Argulus coregoni. The initial preference of the smallest parasites for brighter roach changed at the age of 2 weeks, at the size of about 2 mm, for trout, a typical salmonid host. Younger argulids were attracted by a non-specific visual stimulus (white disc over dark background), and they did not respond to olfactory stimulation (fish-conditioned water). Later, the response to visual stimuli was modulated by trout-conditioned water, but not by that conditioned by roach. The primary role of vision, particularly in early ontogeny, is emphasized as an adaptation of A. coregoni to habitats in boreal latitudes, clear and running water with a sparse fish population. In sub-adult and adult parasites, vision is complimented by olfaction that enables them to choose hosts more precisely. The nature and adaptive significance of the ontogenetic shift in host choice by A. coregoni is discussed.     

Vascular and adrenocortical responses to a specific antagonist of angiotensin II.

Angiotensin II receptors in vascular smooth muscle and adrenal cortex have been characterized in the dog. The evidence was derived chiefly from experiments that assessed the ability of a structural analog of angiotensin II, [Sar1, Ile8] AII, to antagonize the effects of exogenously administered angiotensin II on arterial pressure and aldosterone secretion. [Sar1, Ile8] AII is a potent and specific blocker of the pressor response to angiotensinII; in the adrenal cortex, it is a much less effective inhibitor of aldosterone biosynthesis. These results indicate differences in the receptor sites for angiotensin II in vascular smooth muscle and adrenal cortex. Further, they raise the possibility that angiotensin II stimulates aldosterone secretion by mechanisms other than have already been proposed.     

Distribution of responses to visual cues for movement in precentral cortex of awake primates

Unit recordings were made from areas 4 and 6 of monkeys after they were trained to align a cursor over a vertical target line on a video screen by control of a manipulandum with wrist flexion or extension movement. The appearance of the cursor and line on the screen was the visual cue for movement. Responses were observed 150 (±40) msec after cue presentation. The responses were found only in the forelimb area of precentral cortex, which was most immediately involved in the control of the task, and the majority of them were uncorrelated with either the specific details of the visual cue, or with the direction of the subsequent wrist movement.     

Central and peripheral psychophysiological responses to trauma-related cues in subclinical posttraumatic stress disorder: a pilot study

This study examined verbal-subjective, peripheral and central physiological responses of motor vehicle accident (MVA) survivors with subclinical posttraumatic stress disorder (PTSD), without PTSD symptoms as well as healthy controls. Seven persons of each group were exposed to positive, neutral, accident-related and negative, non-accident-related slides. The verbal-subjective ratings of the slides did not differ between the groups. In contrast to the verbal ratings of the trauma-related materials, the behavioral and physiological responses showed a remarkable dissociation from these reports. The startle responses were enhanced to accident-related slides only in the PTSD group and MVA survivors with PTSD had a significantly lower response to the neutral slides than MVA survivors without PTSD. P200 was lower to positive, neutral and negative slides in the PTSD group compared to both other groups. The late positive complex showed no group-related effects. The data suggest that traumatized persons with PTSD show exaggerated emotional responses to trauma-related stimuli and reduced cognitive responses to several types of stimuli that may interfere with the extinction of the emotional trauma memory.     

Immune responses to lipoteichoic acid: comparison of antibody responses in rabbits and mice. Part II

Humoral immune responses to lipoteichoic acid (LTA) as a surface antigen of Lactobacillus fermentum were assessed in rabbits and mice. Intravenous injection of rabbits with whole bacteria was effective, over a wide range of doses (10(4) to 10(10) cells), in eliciting antibodies to LTA. In mice, significant levels of anti-LTA antibodies were induced only following intraperitoneal injection of 10(8) to 10(9) L. fermentum cells. Rabbit antibodies to LTA were predominantly of the IgM class and were specific for the polyglycerol phosphate and carbohydrate moieties of the LTA. In contrast, both IgM and IgG anti-LTA antibodies were produced in the mouse, and antibody specificity was restricted to the polyglycerol phosphate sequence.     

Improved colorimetric assay for detecting influenza B virus neutralizing antibody responses to vaccination and infection.

An automated neutralization test for influenza B virus is described in which antibody titers are determined according to the release of neutral red from infected or uninfected cells of the Madin-Darby canine kidney line. Endpoints are determined in a standard enzyme-linked immunosorbent assay reader. The test requires no expensive immunologic reagents and was used to evaluate responses to both vaccination and natural infection against influenza B virus. Overall responses to vaccination were comparable with those obtained by hemagglutination inhibition, using Tween-ether-split influenza B/Ann Arbor/1/86 virus as the antigen (the HI-TE test). The sensitivities of neutralization responses compared with those obtained by the HI-TE test for two vaccines were 88 and 89%; the specificities were lower at 61 and 60%, respectively. Responses to vaccination, measured by hemagglutination inhibition, were significantly higher with split virus compared with whole virus. However, seroconversion by both the HI-TE and neutralization tests was observed in 5 of 10 individuals from whom virus was detected by either culture of nasal or throat washings or the presence of antigen from immunofluorescence in cells from nasal washings.     

Differential motivational responses to food and pleasurable cues in anorexia and bulimia nervosa: a startle reflex paradigm

BACKGROUND: Abnormal perceptions of food and shape underpin the cognitive behavioural model of eating disorders (EDs). The aim of this study was to investigate motivational processing of disorder-specific and standard emotional cues in anorexia (AN) and bulimia nervosa (BN) using startle eyeblink modulation (SEM). SEM was used because it is sensitive to motivational states of approach (appetitive response) and withdrawal (aversive response), which are independent of conscious intentional control. METHOD: Acoustically elicited SEM and subjective anxiety ratings were measured in 30 female patients with an ED (n=15 AN, n=15 BN) and 30 female control subjects while they viewed ED-relevant stimuli (food, female bodies) and standardized emotional pictures. RESULTS: BN subjects showed an appetitive response (startle inhibition) to food relative to neutral cues that differed significantly from AN subjects. By contrast, self-reports indicated significantly increased anxiety related to food cues across both ED groups. To female body picture (relative to neutral) cues, no significant between-group differences were found for SEM. ED subjects unexpectedly showed an aversive response (startle potentiation) to positive cues, in contrast to controls, who showed the established startle attenuation. CONCLUSIONS: These preliminary results suggest that BN patients demonstrated an exaggerated appetitive response to food but not to standardized positive cues, whereas SEM in AN patients points to a generalized failure to activate the appetitive motivational system. Differences in motivational salience to food cues are in line with distinctions between AN and BN in eating behaviour and food consumption and support differential treatment requirements.     

Connective tissue responses to some heavy metals. II. Lead: histology and ultrastructure.

Lead loaded ion exchange resin beads implanted into the loose connective tissue of the rat pinna induced local lesions which differed widely from those of the control (sodium loaded) beads (Ellender & Ham 1987). These lesions were characterized by changes in the granulation tissue and the approximating connective tissue. Granulation tissue contained mononuclear phagocytes in various guises, and some cells with intranuclear inclusion bodies. The matrix of the granulation tissue contained collagen fibrils having a wide range of diameters suggestive of altered collagen biosynthesis. Foci of collagen mineralization occurred in zones of combined trauma and lead impregnation. Once mineralized they became enveloped by giant cells and epithelioid cells. Lead in damaged tissues is thought to modify the protective mechanism of calcification inhibition and the biosynthesis of the matrix.     

Postural responses to simulated moving environments are not invariant for the direction of gaze

Summary Postural responses were measured for observers instructed to maintain an erect position when viewing a visual scene, which simulated motion of the observer relative to a corridor with texture on the walls. Both the direction and amplitude of the postural responses appeared to depend on the fixation direction of the observer. This result indicates that postural responses are not invariant with respect to fixation direction. Our results suggest that not one of the frequently suggested features in the optical flow in particular is used to maintain posture but rather that a combination of several optical flow components, that have been suggested in the literature, is relevant.     

Neurophysiological responses to face, facial regions and objects in adults with Asperger's syndrome: an ERP investigation.

Face processing differences have been observed between AS and control subjects at the behavioural and neurological levels. The purpose of the present study was to investigate the neurophysiological basis of processing faces and facial features (eyes and mouths) in adults with AS relative to age- and gender-matched typically-developing controls. These results were compared with ERPs generated to objects in both groups to determine if any differences were specific to facial stimuli. Although both groups elicited earlier N170 latencies to faces than to face parts and to eyes relative to mouths, adults with AS exhibited delayed N170 latencies to faces and face parts relative to controls. This difference was not observed to objects. Together these findings suggest that adults with AS may be slower to process facial information.     

Infant hand-use preferences for grasping objects contributes to the development of a hand-use preference for manipulating objects

Twenty-five infants, divided into three approximately equal groups according to their hand-use preference for reaching for and grasping objects (right, left, or no-preference), were videotaped at 7 and 11 months while involved in a semiplay activity in which they were presented with 26 toys (20-40 s for each presentation). Unimanual manipulation activity was coded, and the increase or decrease in preferred hand use across the two ages was analyzed. Infants with a right preference for reaching showed an increase in right-hand use for unimanual manipulatory actions from 7 to 11 months. Infants with a left preference for reaching showed an increase in left-hand use whereas infants with no preference for reaching showed a modest increase in the use of the right hand. These results support a modified progressive lateralization theory, which posits that a hand-use preference for reaching for and grasping objects will concatenate during development into a hand-use preference for manipulating objects.