Figure-Ground Segregation at Contours: a Neural Mechanism in the Visual Cortex of the Alert Monkey

An important task of vision is the segregation of figure and ground in situations of spatial occlusion. Psychophysical evidence suggests that the depth order at contours is defined early in visual processing. We have analysed this process in the visual cortex of the alert monkey. The animals were trained on a visual fixation task which reinforced foveal viewing. During periods of active visual fixation, we recorded the responses of single neurons in striate and prestriate cortex (areas V1, V2, and V3/V3A). The stimuli mimicked situations of spatial occlusion, usually a uniform light (or dark) rectangle overlaying a grating texture of opposite contrast. The direction of figure and ground at the borders of these rectangles was defined by the direction of the terminating grating lines (occlusion cues). Neuronal responses were analysed with respect to figure-ground direction and contrast polarity at such contours. Striate neurons often failed to respond to such stimuli, or were selective for contrast polarity; others were non-selective. Some neurons preferred a certain combination of figure-ground direction and contrast polarity. These neurons were rare both in striate and prestriate cortex. The majority of neurons signalled figure-ground direction independent of contrast polarity. These neurons were only found in prestriate cortex. We explain these responses in terms of a model which also explains neuronal signals of illusory contours. These results suggest that occlusion cues are used at an early level of processing to segregate figure and ground at contours.     

Comparison of a neutralization enzyme immunoassay and an enzyme-linked immunosorbent assay for evaluation of immune status of children vaccinated for mumps.

A 50% neutralization enzyme immunoassay (N50-EIA) was compared with an indirect enzyme-linked immunosorbent assay (ELISA) for determining mumps virus antibodies in three consecutive serum samples from 138 children vaccinated with a live mumps vaccine at the age (in years) of 1.5. By the N50-EIA, most (132 of 138) preserum samples did not show neutralizing activity. Eight to 12 weeks after vaccination, 17 of the children were still negative, but only 7 remained so after 2.5 years, resulting in a seroconversion rate of 125 of 132 (95%). Over the same period, the neutralization geometric mean titer rose from 3.6 to 9.9. By an indirect ELISA, 128 of 138 preserum samples were found negative. The early and late postvaccination sera of 8 children were ELISA negative, resulting in a seroconversion rate of 120 of 128 (94%). Only two children remained seronegative by both methods. Seven of the late postvaccination serum samples yielded noncorresponding results, reflecting 95% correlation between both methods. Due to cross-reactivity with parainfluenza viruses, the ELISA proved to be less specific, but on the other hand, it showed a greater sensitivity than the N50-EIA.     

Sumatriptan nasal spray in the acute treatment of migraine in adolescents and children

About 4-10% of children and adolescents suffer from migraine. In the last few years, several studies have been performed to assess the efficacy and safety of triptans for the acute treatment of migraine in children and adolescents. Only sumatriptan nasal spray has been approved for the treatment of acute migraine with or without aura in adolescents aged 12-17 years in Europe. This review describes the results of the studies with sumatriptan nasal spray that have been performed in children and adolescents, including a study performed in the Netherlands.     

Purification of specific precipitinogen and extraction of endotoxin from Haemophilus influenzae.

After purifying a Haemophilus influenzae precipitinogen from endotoxic activity by means of ultracentrifugation, column chromatography (Sepharose 6B) and ion exchange chromatography (DEAE Sephadex A25) a fraction was obtained which still contained a specific precipitinogen that was virtually free of endotoxin. Furthermore, during the chromatographic procedures fractions with a high and a low molecular weight endotoxic activity were found. The limulus lysate test was more sensitive in the high molecular weight fractions and the LD50 in mice in the low molecular weight fractions with endotoxic activity.     

High-flow transcranial bypass for prevention of brain ischemia

In patients in whom the internal carotid artery has to be occluded because of the presence of an intracranial giant aneurysm or an infiltrating skull base tumour and in patients with brain ischaemia, whose internal carotid artery has been occluded spontaneously on the basis of atherosclerosis, a transcranial bypass can be created. Since the beginning of the seventies 'low-flow bypasses' are made in which a branch of the superficial temporal artery is connected with a cortical branch of the middle cerebral artery. Because of the small calibre of the blood vessels involved the desired effect on the brain circulation is limited. Thanks to the nonocclusive Excimer laser-assisted anastomosing technique, developed by Tulleken et al. in the last fifteen years, it is now possible to create a high-flow bypass in a safe way. A donor vessel, e.g. the V. saphena magna, is connected at one end to the external carotid artery and at the other to the intracranial part of the internal carotid artery beyond the pathological lesion. The mean flow through the bypass was 140 ml/min in about 90 patients. For example, in three patients, a woman aged 45 with rightsided progressive ophthalmoplegia due to a giant aneurysm, a woman aged 31 years with an aneurysm in the right middle ear and a man with a chemodectoma at the base of the skull, a transcranial high-flow bypass was created nonocclusively, after which the internal carotid artery was closed without any problems.     

Scanning Electron Microscopic Evaluation of Nonocclusive Excimer Laser-Assisted Anastomosis in Rabbits

Summary  Background. The nonocclusive Excimer laser-assisted bypass technique has been described in previous studies and proved to be a promising bypass operation in vascular brain surgery. Little is known about the morphological regeneration process of the laser-assisted anastomosis in time.  By way of a scanning electron microscopic study we examined the way in which the anastomosis site created by the nonocclusive Excimer laser-assisted anastomosis technique becomes endothelialized.  Methods. In 14 rabbits the internal jugular vein was placed in a loop on the abdominal aorta. The distal anastomosis was made using the nonocclusive Excimer laser-assisted technique. The proximal anastomosis was made either laser-assisted or conventional end-to-side. After clipping of the aorta between the two anastomoses sites the vein served as a bypass. To evaluate the endothelialization at the laser-assisted anastomosis site in time, a scanning electron microscopic study was performed.  Results. In the first hours after the bypass operation a new intimal surface is formed by fibrin and activated platelets. Some leukocytes are seen during the first days. The endothelialization process of the laser-assisted anastomosis site begins one day after the operation. The gradual endothelialization process evolved along two lines. First, endothelial cells grow from the side of the aorta to the bypass. Second, after one day solitary (blood-borne) endothelial cells deposit on the laser edge and the sutures, covering the platelet aggregates.  Conclusions. The endothelialization of the Excimer laser-assisted anastomosis is more or less completed 9 days after the operation. The edge created by the laser becomes smoother after a few days and is gone for the most part after 9 days.     

Branching Pattern of the Cerebral Arterial Tree

Quantitative data on branching patterns of the human cerebral arterial tree are lacking in the 1.0–0.1 mm radius range. We aimed to collect quantitative data in this range, and to study if the cerebral artery tree complies with the principle of minimal work (Law of Murray). To enable easy quantification of branching patterns a semi-automatic method was employed to measure 1,294 bifurcations and 2,031 segments on 7 T-MRI scans of two corrosion casts embedded in a gel. Additionally, to measure segments with a radius smaller than 0.1 mm, 9.4 T-MRI was used on a small cast section to characterize 1,147 bifurcations and 1,150 segments. Besides MRI, traditional methods were employed. Seven hundred thirty-three bifurcations were manually measured on a corrosion cast and 1,808 bifurcations and 1,799 segment lengths were manually measured on a fresh dissected cerebral arterial tree. Data showed a large variation in branching pattern parameters (asymmetry-ratio, area-ratio, length-radius-ratio, tapering). Part of the variation may be explained by the variation in measurement techniques, number of measurements and location of measurement in the vascular tree. This study confirms that the cerebral arterial tree complies with the principle of minimum work. These data are essential in the future development of more accurate mathematical blood flow models. Anat Rec, 302:1434–1446, 2019. © 2018 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.     

A novel HLA-A24 (A*2420) allele identified in the Atayal tribe of Taiwan

The Taiwan indigenous population groups are classified into different tribes according their linguistic classification and cultural anthropology. One of the tribes, the Atayal, showed a high frequency of A24 alleles by SSOP analysis. High-resolution sequencing based typing identified a A*2402 variant "A*2420" which was found in 6 unrelated individuals. High-resolution typing is required to identify HLA polymorphism in the Taiwanese minority groups.