Saccades can be aimed at the spatial location of targets flashed during pursuit

1. If an eccentric, stationary target is flashed while a subject is performing an eye movement in the dark, can this subject make a saccade to the location in space where the target briefly appeared? Different predictions result from alternative hypotheses regarding the manner in which saccade goals are determined. Retinal error being defined as the vector from the eye position at the time of the flash to the position of the target, the retinal-error hypothesis predicts that the saccade vector will be equal to the retinal-error vector. This hypothesis assumes that the oculomotor system ignores the eye displacement between target presentation and saccade. If so, the target will be missed. In contrast, the spatial-error hypothesis predicts that the eye displacement is taken into account by the brain to calculate the target's physical location to which, therefore, a correct saccade could be aimed. 2. At issue is the generality of a fundamental principle of ocular targeting. Previous studies have established that, if the movement is saccadic, eye displacement is used by the oculomotor system to calculate the target's physical location. In the case of pursuit, perceptual experiments on humans suggest that eye displacement is taken into account although its velocity is underestimated. However, in a recent study McKenzie and Lisberger reported that saccade trajectories starting during pursuit conform to the retinal error hypothesis. In other words, velocity underestimation is close to 100%. 3. Although McKenzie and Lisberger's results are very clear, they might have depended on particular experimental conditions. The issue was reinvestigated in a situation facilitating the discrimination of stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)     

Task-dependent modulation of the sensorimotor transformation for smooth pursuit eye movements

To investigate the transformation of retinal image velocity into smooth pursuit eye velocity, eye movements were measured in the presence of two moving targets. In the first experiment, the targets were identical in all respects except for direction of motion, and the monkey was not cued to attend to either target. In this experiment, smooth pursuit eye velocity elicited by two targets was the vector average of the response evoked by each target alone. In subsequent experiments, we examined the effects of stimulus and task parameters on the selectivity of pursuit. When the targets were made different colors and monkeys were cued for the color of the rewarded target, their pursuit eye movements were biased in the direction of the rewarded target, but still showed a substantial influence of the nonrewarded target (distractor). It did not matter whether the same target color was used for an entire session or whether the color was randomized from trial to trial. Reducing uncertainty about the axis of motion of the rewarded target also had little effect. However, the pattern of image motion appeared to have a substantial effect; radial image motion favored averaging, and winner-take-all pursuit was found only with nonradial image motion. We conclude that the sensorimotor interface for pursuit uses a flexible decision rule that can vary continuously from vector averaging to winner-take-all. We present a simple recurrent network model that reflects this range of behavior. The model has allowed us to identify three computational elements (selection bias, competitive inhibition, and response normalization) that should be taken into consideration in future models of smooth pursuit.     

Alloinduced suppression and cytotoxicity: two functions of a single cell

Using different experimental approaches we here show that the suppression and cytotoxicity generated during a one-way mixed lymphocyte culture (MLC) are mediated by a single cell population, in this case the cytotoxic T lymphocyte (CTL). Results of limiting-dilution analysis of cells from a 4-day MLC demonstrate the coexpression of both functions and argue against the existence of a separate suppressor cell population that regulates the in vitro alloresponse. The suppressive quality of CTL is also exemplified in cells with a clonal origin, such as cloned cytotoxic T lymphocytes and the mouse X rat hybridoma PC60. Further experiments demonstrate that this suppression is not primarily mediated through lysis of the stimulator cells, and studies in the PC60 model suggest that lysis and suppression may have different induction requirements.     

Fusional vergence hysteresis and sensorimotor connection of the two eyes

Three experiments were conducted to replicate and extend Helmholtz's observation indicating vergence hysteresis. The two stimuli were presented dichoptically to the eyes in the mirror stereoscope and moved temporalward or nasalward. Helmholtz's finding was confirmed in Experiment 1, in which the critical separations were measured for the stimuli divergently moving temporalward when fusion of their images was abruptly broken (breakaway point) and when fusion was re-established (refusion point) for the stimuli moving nasalward. In Experiment 2, in which only the stimulus for one eye moved temporalward while the stimulus for the other eye was stationary, the breakaway point of the moving stimulus was found to be linearly dependent on the position of the stationary stimulus. Experiment 3 showed that, in the asymmetric divergent tracking as in Experiment 2, the change of the perceived visual direction of the fused image was smaller than the angular magnitude of the movement of the tracking eye. These results were discussed as evidence indicating the sensory and motor connection of the two eyes.     

Mania and dysregulation in goal pursuit: a review

This paper reviews evidence for deficits in goal regulation in bipolar disorder. A series of authors have described mania as related to higher accomplishment, elevated achievement motivation, and ambitious goal setting. These characteristics appear to be evident outside of episodes, and to some extent, among family members of people with a history of mania. In addition, people with a history of mania demonstrate intense mood reactivity, particularly in response to success and reward. During positive moods, they appear to experience robust increases in confidence. These increases in confidence, coupled with a background of ambitious goals, are believed to promote excessive pursuit of goals. This excessive goal engagement is hypothesized to contribute to manic symptoms after an initial life success.     

Saccades to sounds: effects of tracking illusory visual stimuli

Somers, Jeffrey T.,Vallabh E. Das,Louis F. Dell'Osso, andR. John Leigh.Saccades to Sounds: Effects of Tracking Illusory Visual Stimuli. J. Neurophysiol. 84: 96-101, 2000. In 10 normal human subjects, we studied the accuracy ofmemory-guided saccades made to the remembered locations of visual targets and sounds. During the time of stimulus presentation, subjectswere smoothly tracking a projected laser spot that was movinghorizontally across a tangent screen, sinusoidally ±15° at 0.25 Hz.In one set of experiments, the laser spot moved across a 40° × 28°random dot display that moved synchronously in the vertical plane; thisinduced a strong illusion that the trajectory of the laser spot wasdiagonal (variant of Duncker illusion). In control experiments, thelaser spot moved across the same display, which was stationary. Thevisual targets and speakers were at six locations (range ±15°) inthe horizontal plane. Saccades made to the remembered locations oftargets presented during background motion (illusion) weresignificantly (P < 0.05) more inaccurate than withthe background stationary (control) in 9 of 10 subjects for lights andin 6 of 10 subjects for sounds. As a group, the median change in errorsdue to the Duncker illusion was ~2.5 times greater for visualcompared with acoustic targets (P < 0.001). Thesefindings are consistent with electrophysiological studies which haveshown that neurons in the primate lateral intraparietal area (LIP) mayrespond to both visual and auditory targets and these neurons are alsoinfluenced by the Duncker illusion during programming of memory-guided saccades.

     

Twenty-five years of renal transplantation from: a single center a risk factor analysis for short- and long-term outcomes

Summary Between 1966 and 1991 a total of 1000 renal transplants were performed in Erlangen-Nuremberg. Patients were operated upon in Erlangen and transferred immediately 25 km to Nuremberg for their postoperative and immunosuppressive care. Despite these considerable logistical obstacles, the 10-year graft survival rate in 785 consecutive transplants performed between 1980 and 1990 was 44%, while patient survival was 84%. Mismatch at the HLA-DR locus, preformed antibodies, multiple transplants, and kidneys from donors aged 10 years or younger or over 60 years were risk factors for decreased graft survival. An immunosuppressive regimen of cyclosporine and methylprednisolone resulted in better graft survival than did azothioprine and methylprednisolone, or reduced-dose cyclosporine, azathioprine, and methylprednisolone. The cyclosporine and methylprednisolone regimen had a better patient survival than azathioprine and methylprednisolone. A hazard analysis demonstrated a particular risk of late rejection between the 70th and 90th months, after transplantation. Our data indicate that favorable transplant results can be obtained despite major logistical disadvantages. Very close cooperation between referring centers, transplant surgeons, and nephrologists is indispensable for success.This paper is dedicated to the memory of Prof. Ulrich Gessler, a thoughtful clinician, a dedicated teacher, and a valued friend See Appendix

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An erratum to this article is available at .     

Early plasma protein and mineral changes after surgery: a two stage process.

Sequential changes in albumin, transferrin, alpha 1-acid glycoprotein, C reactive protein, fibrinogen, copper, iron, and zinc in plasma up to 24 h after hysterectomy were measured. No increases in the concentrations of the acute phase proteins alpha 1-acid glycoprotein, C reactive protein, and fibrinogen were observed until 6 h after the skin incision. These increases were preceded by significant falls at 2-4 h, and this was shown also by albumin, transferrin, iron, zinc, and copper. The ratios of iron and zinc to their binding proteins, transferrin and albumin, did not decrease until 4-6 h and their concentrations remained low for at least 24 h. These patterns suggest that at least two mechanisms operate after trauma. The early fall in the concentrations of the proteins in plasma is consistent with a prompt increase in microvascular permeability. The later decrease in binding of the metals iron and zinc to their transport proteins and the increase in concentrations of the acute phase proteins could be initiated by a common mediator.     

Electrophysiological analysis of a sensorimotor integration task

The present experiment aimed at investigating electrophysiologic changes observed as beta band asymmetry, by Quantitative Electroencephalography (qEEG), when individuals performed a reaching motor task (catching a ball in free fall). The sample was composed of 23 healthy individuals, of both sexes, with ages varying between 25 and 40 years old. All the subjects were right handed. A two-way ANOVA was applied for the statistical analysis, to verify the interaction between task moment (i.e., 2 s before and 2 s after ball's fall) and electrode (i.e., frontal, central and temporal regions). The first analysis compared electrodes placed over the somatosensory cortex. Central sites (C3–C4) were compared with temporal regions (T3–T4). The results showed a main effect for moment and position. The second analysis was focused over the premotor cortex, which was represented by the electrodes placed on the frontal sites (F3–F4 versus F7–F8), and a main effect was observed for position. Taken together, these results show a pattern of asymmetry in the somatosensory cortex, associated with a preparatory mechanism when individuals have to catch an object during free fall. With respect to task moment, after the ball's fall, the asymmetry was reduced. Moreover, the difference in asymmetry between the observed regions were related to a supposed specialization of areas (i.e., temporal and central). The temporal region was associated with cognitive processes involved in the motor action (i.e., explicit knowledge). On the other hand, the central sites were related to the motor control mechanisms per se (i.e., implicit knowledge). The premotor cortex, represented by two frontal regions (i.e., F3–F4 versus F7–F8), showed a decrease on neural activity in the contralateral hemisphere (i.e., to the right hand). This result is in agreement with other experiments suggesting a participation of the frontal cortex in the planning of the apprehension task. This sensorimotor paradigm may contribute to the repertoire of tasks used to study clinical conditions such as depression, alzheimer and Parkinson diseases.     

Inactivation and stimulation of the frontal pursuit area change pursuit metrics without affecting pursuit target selection

The frontal pursuit area (FPA) lies posterior to the frontal eye fields in the frontal cortex and contains neurons that are directionally selective for pursuit eye movements. Lesions of the FPA (alternately called "FEFsem") cause deficits in pursuit acceleration and velocity, which are largest for movements directed toward the lesioned side. Conversely, stimulation of the FPA evokes pursuit from fixation and increases the gain of the pursuit response. On the basis of these properties, it has been hypothesized that the FPA could underlie the selection of pursuit direction. To test this possibility, we manipulated FPA activity and measured the effect on target selection behavior in rhesus monkeys. First, we unilaterally inactivated the FPA with the GABA agonist muscimol. We then measured the monkeys' performance on a pursuit-choice task. Second, we applied microstimulation unilaterally to the FPA during pursuit initiation while monkeys performed the same pursuit-choice task. Both of these manipulations produced significant effects on pursuit metrics; the inactivation decreased pursuit velocity and acceleration, and microstimulation evoked pursuit directly. Despite these changes, both manipulations failed to significantly alter choice behavior. These results show that FPA activity is not necessary for pursuit target selection.