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Biomedical subjects

B Fischer

Publications and source records attributed to B Fischer.

At least 163 records · Page 9Linked to original sources
PubMed1997

Early detection of pneumonia in febrile neutropenic patients: use of thin-section CT.

OBJECTIVE: The purpose of this study was to evaluate the usefulness of thin-section CT for early detection of pneumonia in neutropenic patients with an unknown site of infection and normal or nonspecific findings on chest radiographs. SUBJECTS AND METHODS: Eighty-seven patients with febrile neutropenia that persisted for more than 2 days despite empiric antibiotic treatment underwent 146 prospective examinations. If findings on chest radiographs were normal (n = 126) or nonspecific (n = 20), thin-section CT (1-mm collimation, 10-mm increment) was done. If thin-section CT scans showed opacities, bronchoalveolar lavage was recommended. RESULTS: Findings on chest radiographs were nonspecific for pneumonia in 20 (14%) of 146 cases, and CT findings in those cases were suggestive of pneumonia. Microorganisms were detected in 11 of those 20 cases. Seven of the 11 cases were not optimally treated before CT diagnosis, the other four were sufficiently treated. Findings on chest radiographs and thin-section CT scans were normal in 56 (38%) of 146 cases. In 70 (48%) of 146 cases, findings on chest radiographs were normal, whereas findings on thin-section CT scans were suggestive of pneumonia. Microorganisms were detected in 30 of the 70 cases. Nineteen of 30 cases were not optimally treated before CT, whereas the other 11 cases were sufficiently treated before CT. In 22 (31%) of these 70 cases, an opacity was observed on the chest radiograph during the 7 days after the CT study. Only three (5%) of 56 pneumonias occurred during the first 7 days after thin-section CT studies with normal findings (p < .005). Additional risk factors for pneumonia occurring later that were detectable on chest radiographs were poorly defined nodules (p < .05), consolidation (p < .05), and younger age (p < .05). CONCLUSION: Thin-section CT scans show findings suggestive of pneumonia about 5 days earlier than chest radiographs show suggestive findings. When thin-section CT scans show findings suggestive of pneumonia, the probability of pneumonia being detected on chest radiographs during the 7-day follow-up is 31%, whereas the probability is only 5% when the findings on the prior thin-section CT scan were normal (p < .005). All neutropenic patients with fever of unknown origin and normal findings on chest radiographs should be examined with thin-section CT.

Antineoplastic Agents↗
PubMed1996

V+ fibronectin mRNA is increased in the brains of aged rats: effect of food restriction.

Food restriction increases life-span in rodents. With regard to the central nervous system, underfeeding has been shown to have beneficial effects on synaptic transmission in old rats. However, the molecular events underlying functional changes in the brains of food-restricted rats are largely unknown. In the present study the levels of fibronectin mRNA containing the alternatively spliced segment V (FN-V+) as well as the levels of FN mRNA containing the alternatively spliced segment EIIIB (FN-EIIIB+), were examined by RNA gel blot hybridization in the brains of 3-day-old, 24-day-old, 10-month-old, 18-month-old, 30-month-old ad libitum (AL) fed, 30-month-old food-restricted (FR), and 35-37-month-old, FR rats. The hybridization signal for the FN-EIIIB+ mRNA was relatively abundant at early postnatal stages but very few transcripts were detected in the brains of adult, AL rats. The transcripts coding for FN-V+ mRNA were moderately expressed in the brains of 3-day-old, 24-day-old, 10-month-old, and 18-month-old rats. However, the FN-V+ mRNA signal was then prominently increased (approx. 3-fold) in the brains of the 30-month-old, AL rats vs. 10-month-old, AL rats, and further increased (approx. 2-fold) in the brains of 30-month-old, FR, as compared to 30-month-old, AL rats. However, the levels of FN-V+ mRNA were slightly decreased in the brains of very old (35-37-month) FR rats vs. 30-month-old FR rats. The distribution of fibronectin messenger RNA and protein was also investigated by non-radioactive in situ hybridization and immunohistochemistry, respectively. The most prominent expression of FN-V+ messenger RNA was seen in neurons of the hippocampus, including the granule cells of the dentate gyrus, and in layers III and V of the cortex of 30-month-old, FR rats. FN immunostaining closely paralleled the distribution of FN mRNA and was confined to the neuronal cell periphery. The upregulation of fibronectin gene expression upon exposure to glucocorticoids is well documented. Prolonged food restriction, acting as a stress factor, combined with decreased plasticity of glucocorticoid regulatory responses in the aged rats could cause an increase in the levels of FN mRNA and protein in the brains of old, FR rats. Since FN has been shown to provide an adhesive substrate for extending neurites, we conclude that food restriction may potentiate synaptic plasticity, via glucocorticoid receptor binding elements of the FN gene, in the brains of old rats.

Aging↗
PubMed1996

[Alzheimer disease: involvement of the complement system in cell death. Gene expression of C1q and C3 in the frontal cortex of patients with Alzheimer disease and control probands].

Patients with Alzheimer's disease are found to have inflammatory changes in the vicinity of plaques and fibrils, and involvement of the complement system has been confirmed by immunocytochemical studies. In order to confirm these findings on the genetic plane, the prevalence of mRNAs for C1q and C3 complement components were investigated in our laboratory. We were able to show that the hybridization signals for complement C1q-mRNA on Northern blots of deceased Alzheimer patients were about 3.5 times as pronounced as in the case of control persons. In contrast to earlier reports, no difference in the expression of complement C3-mRNA in the brains of decreased Alzheimer patients and control persons was established. On the other hand, with the aid of non-radioactive in situ hybridization with digoxigenin-labelled riboprobes, it has been shown that complement C1q- and C3-mRNA is closely associated with the neurons.

Aged↗
PubMed1996

A phase III randomized prospective trial of external beam radiotherapy, mitomycin C, carmustine, and 6-mercaptopurine for the treatment of adults with anaplastic glioma of the brain. CNS Cancer Consortium.

PURPOSE: This study was designed to evaluate strategies to overcome the resistance of anaplastic gliomas of the brain to external beam radiotherapy (ERT) plus carmustine (BCNU). Patients were > or = 15 years of age, had a histologic diagnosis of malignant glioma, and a Karnofsky performance status (KPS) > or = 60%. METHODS AND MATERIALS: In Randomization 1, patients were assigned to receive either ERT alone (61.2 Gy) or ERT plus mitomycin C (Mito, IV 12.5 mg/m(2)) during the first and fourth week of ERT. After this treatment, patients went on to Randomization 2, where they were assigned to receive either BCNU (i.v. 200 mg/m(2)) given at 6-week intervals or 6-mercaptopurine (6- MP, 750 mg/m(2) IV daily for 3 days every six weeks), with BCNU given on the third day of the 6-MP treatment. Three hundred twenty-seven patients underwent Randomization 1. One hundred sixty-four received ERT alone, and 163 received ERT + Mito [average 52.7 years; 63% male; 69% glioblastoma multiforme (GBM); 66% had a resection; 56% KPS > or = 90%]. Step-wise analysis of survival from Randomization 1 or 2 indicates that survival was significantly diminished by: (a) age > or = 45 years (b) KPS < 90%; (c) GBM/gliosarcoma histology; (d) stereotactic biopsy as opposed to open biopsy or resection. Median survival from Randomization 1 in both arms (ERT + Mito) was 10.8 months. Median survival from Randomization 2 was 9.3 months for BCNU/6MP vs. 11.4 months for the BCNU group (p = 0.35). Carmustine/6-MP showed a possible survival benefit for histologies other than GBM/GS. Two hundred and thirty-three patients underwent Randomization 2. The proportion of patients in the ERT group who terminated study prior to Randomization 2 was significantly less in the ERT group than in the ERT + Mito group (20 vs. 37%, p < 0.001). CONCLUSIONS: (a) The addition of Mito to ERT had no impact on survival; (b) patients treated with ERT + Mito were at greater risk of terminating therapy prior to Randomization 2; (c) there was not a significant survival benefit to the addition of 6-MP to BCNU.

Adult↗
PubMed1996

Expression and functional characterization of a melatonin-sensitive receptor in Xenopus oocytes.

Melatonin (MEL) plays a central role in the regulation of seasonal cycles and in the control of circadian rhythms in mammals. Functional MEL-sensitive receptors were expressed in Xenopus laevis oocytes following injection of poly (A)+ RNA from rat brain. Administration of 0.1-100 micromol/l MEL to voltage-clamped oocytes (holding potential: -70 mV) elicited oscillatory inward currents (reversal potential: -24 mV) which could be blocked by 9-anthracenecarboxylic acid and caffeine. After preincubation with pertussis toxin (PTX) the MEL response disappeared. The expressed MEL-sensitive receptor probably activates Ca(2+)-dependent chloride currents via a PTX-sensitive G protein and the phosphoinositol pathway.

Animals↗
PubMed1996

Electrophysiological effects of catheter ablation of inferior vena cava-tricuspid annulus isthmus in common atrial flutter.

BACKGROUND: The electrophysiological mechanisms for successful catheter ablation of atrial flutter (AFI) targeting the inferior vena cava-tricuspid annulus (IVC-TA) isthmus have not been determined. METHODS AND RESULTS: Twenty patients with common AFI were studied. All had inducible common AFI, and 8 of them had both common and reverse AFI. Right atrial (RA) activation sequences were investigated during pacing from sites proximal (low lateral RA) and distal (proximal coronary sinus) to the IVC-TA isthmus both during entrainment of common or reverse AFI and during pacing in sinus rhythm. This was repeated after ablation. During pacing in sinus rhythm from the low lateral RA, the septum was activated by caudocranial and craniocaudal wave fronts. Similarly, during pacing from the proximal coronary sinus, the lateral RA was activated by two wave fronts. Catheter ablation of the IVC-TA isthmus induced dramatic changes in mapping due to the loss of caudocranial wave front in all but 1 patient. The septum and the lateral RA were activated by a single craniocaudal front as during entrainment of reverse or common AFI, respectively. After a follow-up of 8 +/- 2 months, common or reverse AFI occurred in 4 patients. Two had no or only unidirectional changes in the isthmus conduction induced by ablation. The other 2 had a late recovery of conduction. CONCLUSIONS: The present study provides evidence that the mechanism of successful AFI ablation targeting the IVC-TA isthmus is local bidirectional conduction block. This change can be used as a new and complementary electrophysiological end point for the procedure. AFI recurrences are associated with failure to achieve a permanent block.

Aged↗
PubMed1996

Novel animal model for studying the molecular mechanisms of bacterial adhesion to bone-implanted metallic devices: role of fibronectin in Staphylococcus aureus adhesion.

Infection around metallic implants is a rare but severe complication of orthopaedic surgery. A novel animal model mimicking conditions of internal fixation devices was developed to evaluate the role of host proteins adsorbed on metallic devices in promoting adhesion and colonization of the material surfaces by Staphylococcus aureus. Small plates made of pure titanium were either fixed (three screws per plate) onto the iliac bones of guinea pigs or implanted into their subcutaneous space as controls. Five to 6 weeks after surgery, the plates and screws were removed from the previously killed animals, carefully rinsed in buffer, and tested in an in vitro assay of S. aureus adhesion to metallic surfaces. To evaluate the role of fibronectin in staphylococcal adhesion to explanted plates and screws, a mutant of S. aureus that is specifically defictive in fibronectin adhesion due to decreased expression of the fibronectin adhesin was compared with its isogenic parental strain. A significant reduction in adhesion of the fibronectin adhesin-defective mutant compared with the parental strain occurred on both the subcutaneously implanted and bone-implanted metallic plates. The results of this specific biological assay suggest that fibronectin is present on bone-implanted metallic devices and promotes attachment of S. aureus to their surfaces. This novel experimental model should help, to characterize several parameters of bacterial adhesion to metallic orthopaedic devices and to develop novel anti-adhesive strategies for preventing such infections.

Animals↗
PubMed1996

Folding of lysozyme.

Due to the detailed knowledge of the three-dimensional structure, chemistry and catalytic mechanism of hen egg white lysozyme, this enzyme has become a major model for the analysis of the folding pathway of globular proteins. Unfolding and folding of lysozyme are reversible processes. Unfolding is a highly cooperative event; under physiological conditions only the native and the unfolded states are stable. Folding of lysozyme involves both a cooperative and a parallel pathway. The complexities in the folding pathway arise from the collapsed state which is formed within a burst-phase in the first milliseconds of folding. In a second, fast folding phase, major parts of the secondary structures both in the alpha-domain and the beta-domain are formed. During the slow folding phase, formation of secondary structure is completed and native tertiary structure is formed in less than 1 second. Folding of reduced lysozyme combines both secondary and tertiary structure organization, as well as formation of four disulphide bonds. Analysis of formation of disulphide bonds showed that there exists a restricted search of structures in the formation of the native conformation and a nucleation in the folding pathway. The transition from a two-disulphide bond intermediate to a three-disulphide bond form appears to be the rate-limiting step in this pathway. Native-like catalytic properties depend on the correct generation of all four disulphide bonds. Folding of both denatured and denatured/reduced lysozyme is characterized by transient folding species possessing structural properties of the molten globule state: high content of secondary structure, no tertiary fold, and the appearance of hydrophobic structures.

Animals↗
PubMed1996

Comparison of N-Glycan Pattern of Recombinant Human Coagulation Factors II and IX Expressed in Chinese Hamster Ovary (CHO) and African Green Monkey (Vero) Cells.

The N-glycan patterns of recombinant human coagulation factors II (rF-II) and IX (rF-IX), derived from both transfected Chinese hamster ovary (CHO) cells and African green monkay (Vero) cells produced at industrial scale, were analyzed by binding to carbohydrate-specific lectins and were compared with the glycan structure of human plasma-derived coagulation factors. Human plasma-derived coagulation factors II (hpF-II) and IX (hpF-IX) exhibited complex-type glycan structures with carbohydrate chains capped with alpha(2-6)-sialic acid. Terminal galactose-beta(1-4)-N-acetylglucosamine units were detected in hpF-IX. Both CHO cell-derived rF-II and rF-IX exhibited complex-type glycosylation and contained alpha(2-3)-sialic acid in addition to terminal galactose-beta(1-4)-N-acetylglucosamine. Vero cell-derived rF-IX exhibited a complex-type glycan structure similar to that of CHO cell-derived rF-IX. In contrast, rF-II produced by Vero cells exhibited a glycan microheterogeneity composed of hybrid-type glycosylation containing "high-mannose" structures and complex-type glycosylation containing alpha(2-3)-sialic acid. Galactose-beta(1-4)-N-acetylglucosamine structures and a low concentration of alpha(2-6)-sialic acid were detected in both microheterogeneity fractions of Vero cell-derived rF-II. Although different in their carbohydrate structures, coagulation factors II and IX obtained recombinantly from both transformed CHO cells and Vero cells exhibited coagulation activities comparable with the plasma-derived proteins.

Journal Article↗
PubMed1996

Effects of procues on error rate and reaction times of antisaccades in human subjects.

In a gap paradigm, where the saccadic reaction times are usually short, the number of express saccades can be further increased and their latency decreased when a valid transient peripheral cue is given 100 ms before target occurrence. In the present study we measured the saccadic reaction times of seven human subjects who had been instructed to make antisaccades (saccades to the side opposite to stimulus presentation) in the gap paradigm. In the first experiment, we presented a 100% valid cue with 100 ms cue lead time. To explore whether the cue reduced the reaction times of the antisaccades, the cue was always presented on the opposite side to where the stimulus occurred (stimulus direction was randomized between 4 degrees to the left and right), and it was thus indicated in each trial to which side the antisaccade was required (procue). In the second set of experiments the cue was consistently presented on either the left or the right side in two different blocks; it was thus noninformative with respect to the direction of the antisaccade. In the first experiment, a significant increase in mean reaction times of correct antisaccades and a considerable increase in erratic prosaccades to the stimulus were obtained compared with a control session with no cue. In the two experimental blocks with noninformative cues, the reaction times of correct antisaccades were decreased when cue and stimulus were on at the same side, while large numbers of erratic prosaccades were again obtained when cue and stimulus were presented on opposite sides. These results suggest that the orienting mechanism elicited by a transient peripheral cue relates to the command and to the decision to make a pro- versus an antisaccade. Since the subjects reported that they could not prevent, or, moreover, in some cases did not even realize that they were making erratic prosaccades, we conclude that this orienting mechanism occurs automatically, being largely beyond voluntary control.

Attention↗
PubMed1996

Visualisation of intracranial aneurysms by transcranial duplex sonography.

We examined 72 patients with 89 angiographically confirmed intracranial aneurysms, using transcranial colour-coded duplex sonography (TCCD) to determine the location and size of the aneurysm. The patients were admitted for coil embolisation of their aneurysm following subarachnoid haemorrhage or because of a cranial nerve palsy. Using a 2/2.25 MHz transducer, 42 aneurysms (47%) were seen satisfactorily through the temporal bone window or foramen magnum. In 24 cases (27%) image quality was insufficient as a result of a poor bone window, of the aneurysm having a diameter of less than 6 mm or of its being in an unfavorable location. In 23 other cases (26%) it was not possible to detect the aneurysm. Thrombosed structures could be demonstrated using TCCD in 8 of 12 giant intracavernous or basilar artery aneurysms, and in 15 of 19 aneurysms treated by platinum coil embolisation. TCCD offers a noninvasive method for monitoring progressive intra-aneurysmal thrombosis following coil embolisation and for follow-up of patients with untreatable fusiform aneurysms, should this be required. Detection of small aneurysms is limited by spatial resolution and insonation angles.

Aneurysm, Ruptured↗
PubMed1996

[High resolution computed tomography of the lung in neutropenic patients with fever].

PURPOSE: To determine the sensitivity and clinical impact of high-resolution CT (HRCT) of the lung in febrile neutropenic patients under antibiotic therapy. MATERIAL AND METHODS: Chest X-ray and HRCT were prospectively performed to exclude pneumonia in 34 patients (53 examinations) suffering from febrile neutropenia following antitumor therapy. Diagnosis was confirmed by bronchoalveolar lavage or sputum cultures. RESULTS: Chest X-ray showed pneumonia in 13/53 examinations, in 12/13 a micro-organism was found. HRCT demonstrated pneumonia in 39/53, in 31/39 a micro-organism was found. All cases with positive cultures showed suspicious HRCT findings. Changes in antibiotic treatment resulted in findings suspicious for pneumonia and evidence of a new or a just treated micro-organism (chest X-ray 8/53, HRCT 31/53); the search for the source of fever was escalated in cases without evidence of micro-organisms and without suspicion of pneumonia findings 14/53. CONCLUSION: HRCT of the lung exhibits a higher sensitivity than conventional radiographs. Findings resulted in relevant therapeutic consequences. Hence, HRCT is indicated in neutropenic patients with fever and inconspicuous chest X-ray.

Adolescent↗
PubMed1996

Identification of potent P2Y-purinoceptor agonists that are derivatives of adenosine 5'-monophosphate.

1. A series of chain-extended 2-thioether derivatives of adenosine monophosphate were synthesized and tested as agonists for activation of the phospholipase C-linked P2Y-purinoceptor of turkey erythrocyte membranes, the adenylyl cyclase-linked P2Y-purinoceptor of C6 rat glioma cells, and the cloned human P2U-receptor stably expressed in 1321N1 human astrocytoma cells. 2. Although adenosine monophosphate itself was not an agonist in the two P2Y-purinoceptor test systems, eleven different 2-thioether-substituted adenosine monophosphate analogues were full agonists. The most potent of these agonists, 2-hexylthio AMP, exhibited an EC50 value of 0.2 nM for activation of the C6 cell receptor. This potency was 16,000 fold greater than that of ATP and was only 10 fold less than the potency of 2-hexylthio ATP in the same system. 2-hexylthio adenosine was inactive. 3. Monophosphate analogues that were the most potent activators of the C6 cell P2Y-purinoceptor were also the most potent activators of the turkey erythrocyte P2Y-purinoceptor. However, agonists were in general more potent at the C6 cell receptor, and potency differences varied between 10 fold and 300 fold between the two receptors. 4. Although 2-thioether derivatives of adenosine monophosphate were potent P2Y-purinoceptor agonists no effect of these analogues on the human P2U-purinoceptor were observed. 5. These results support the view that a single monophosphate is sufficient and necessary for full agonist activity at P2Y-purinoceptors, and provide insight for strategies for development of novel P2Y-purinoceptor agonists of high potency and selectivity.

Adenosine Monophosphate↗
PubMed1996

Radiofrequency catheter ablation of common atrial flutter in 200 patients.

INTRODUCTION: The purpose of this study was to evaluate the efficacy and safety of radiofrequency (RF) catheter ablation of common atrial flutter and to determine the optimum target sites in a large series of patients. Three different approaches were used to target the ablation site. The first used a combined anatomic and electrophysiologic approach, whereas the second and the third approaches relied primarily on anatomic guidelines to target the critical area in the atrial flutter reentrant circuit located in the low right atrium. BACKGROUND: Recent studies report the efficacy of RF current application in the low right atrial region to interrupt and prevent recurrences of common atrial flutter using either anatomic or electrophysiologic targets. However, larger groups of patients are required to confirm the efficacy of this technique and to specify the target sites. METHODS AND RESULTS: Two hundred consecutive patients with drug-resistant common atrial flutter were studied. In the first 50 patients, target sites were localized using both anatomic landmarks and electrophysiologic parameters. The anatomic landmarks were area 1 between the tricuspid valve and inferior vena cava orifice; area 2 between the tricuspid valve and coronary sinus ostium; and area 3 between the inferior vena and coronary sinus. The electrophysiologic criterion was to ablate when there was an atrial electrogram occurring during the plateau phase (preceding F wave). The first targeted area was that giving the more stable catheter position. In the following 30 patients, we assessed the effect of RF energy application in a single line to area 1 in the first 10 patients, area 2 in the next 10, and area 3 in the last 10 patients. In the last 120 patients, RF energy was applied only in area 1 using repeated applications. RF energy of 12 to 30 W, or that achieving a temperature of 70 degrees C, was applied for 60 to 90 seconds at each site. The endpoint of the ablation procedure was interruption and noninducibility of common atrial flutter in the first 110 patients and additional isthmal block in 48 of the last 90 patients. Overall, atrial flutter was interrupted and rendered noninducible after a single session in 191 (95%) patients and could not be interrupted in 9 (4.5%) patients. The mean number of RF applications was 12 +/- 8. After a mean follow-up of 24 +/- 9 months, recurrences occurred in 31 (15.5%) patients, 26 of whom underwent a successful second or third session without further recurrences of atrial flutter. Atrial fibrillation not documented before the ablation was detected in 11 patients. On a retrospective analysis of the final successful site in the first group of 50 patients, the location was in area 1 in 39% of patients; area 2 in 36% of patients, and area 3 in 25% of patients. Atrial electrograms recorded at these sites showed a single spike pattern in 46% of patients, and double spike pattern (28%) or fractioned electrogram in 26% patients. When lines of RF lesions were placed at several sites, they produced a success rate of 70%, 40%, and 10% at areas 1, 2, and 3 respectively. In the last series of 120 patients, the procedure was successful in 119 patients: 92% of whom were successfully treated only by a linear lesion between the tricuspid annulus isthmus and the inferior vena cava, and the other 8% by additional applications near the coronary sinus ostium. No complications were observed. CONCLUSIONS: RF catheter ablation of atrial flutter can be done with a high success rate and is safe. The highest success rate is achieved with RF energy applied in the isthmus between the inferior vena cava orifice and the tricuspid valve. However, 15.5% of patients need multiple sessions to achieve success because of recurrence of flutter. Further follow-up is needed to evaluate the long-term effects of this procedure.

Adult↗
PubMed1996

Human express saccade makers are impaired at suppressing visually evoked saccades.

1. We report the oculomotor behavior of human subjects who produce unusually high numbers (> 30%) of express saccades (latency range 85-135 ms) in the overlap saccade task, where express saccades are usually absent or small in number (< 15%). We refer to these subjects as "express saccade makers" (ES makers). 2. We tested the hypothesis that ES makers have difficulties in maintaining fixation and in suppressing unwanted saccades to a suddenly appearing peripheral target by comparing the performances of 10 ES makers and 10 control subjects in gap and overlap antisaccade tasks and in a memory-guided saccade task. 3. The ES makers produced between 35% and 95% incorrect saccades toward the stimulus (prosaccades) in the antisaccade tasks, compared with control subjects, who produced < 20%. Their correct antisaccades appeared to be normal. 4. We further tested the ability of ES makers to maintain fixation and to avoid reflexive saccades to the onset of a target in the memory-guided saccade task. ES makers tended to glance to the briefly presented cue in many trials (4 of them in 50-80% of the trials) instead of delaying the saccade until fixation point offset. Most of the inappropriate saccades had latencies in the range of express saccades. 5. These results can be associated with the finding of fixation related neurons in different cortical and subcortical brain regions (e.g., inferior-parietal and frontal cortex, basal ganglia, superior colliculus). The unusual number of express saccades made by the ES makers in the standard overlap and gap tasks, and their unwanted short-latency reflexive saccades to the target in the memory-guided saccade task, are reminiscent of the performance in these tasks of monkeys whose collicular fixation neurons were chemically deactivated. The collicular fixation neurons are probably the final common pathway in the control of active fixation, and are in mutual inhibitory relationship with the saccade cells. 6. The decreased saccadic control observed in the ES makers suggests that saccade execution in humans is also gated by a fixation system. These ES makers may have reduced voluntarily control over saccade generation as a result of a defect or poor development of their fixation system.

Adolescent↗