Temporal Margins Research Articles

Nonuniform distribution of cell proliferation in the adult teleost retina

Teleost fish continue to grow throughout life, and their eyes enlarge correspondingly. Within the eye, the retina grows by stretching existing tissue and adding new cells. Cell addition occurs in two ways: First, all cell types except rod photoreceptors are added circumferentially at the edge of the eye where the retina meets the iris; second, rod photoreceptors are generated from a population of rod progenitor cells which divide throughout the outer nuclear layer (ONL). To determine the spatial distribution of rod progenitor cells across the teleost retina, we labeled dividing cells with an antibody to proliferating cell nuclear antigen (PCNA) throughout a 24 h period. We found a significantly higher density of dividing rod precursor cells at the nasal and temporal margins than in the central retina throughout the 24 h cycle. At night, the density of dividing cells is significantly greater at the nasal pole of the eye. The difference between cell division at the center and the margin was reduced at night when the density of cell division in the central retina increased significantly. Taken together, these data suggest that the eye grows asymmetrically, with more cells added at the nasal pole. Possible developmental causes and functional consequences of the reported distribution of cell divisions in time and location are presented.

The influence of distance to burrow on flight initiation distance in the woodchuck, Marmota monax

We used woodchucks (Marmota monax) to test predictions of a cost-benefit model of antipredator behavior that flight initiation distance would increase with distance to refuge and with predator approach velocity. We also examined the effects of distance to refuge and predator approach velocity on escape velocity and on both temporal and spatial margin of safety (expected time and distance between predator and burrow at the time of the woodchuck's arrival). The observer, assumed to be perceived as a potential predator, approached juvenile woodchucks from the direction opposite to the burrow at a slow (1.24 m/s) or fast (1.79 m/s) walking pace. When the woodchuck started to flee, the observer recorded the woodchuck's distance from the observer and from its burrow, the time spent running,.and whether the woodchuck stopped before reaching its burrow. Flight initiation distance increased consistendy with distance to the burrow over die entire observed range (0-25 m) but was not significantly affected by observer approach velocity. Escape velocity was not significandy influenced by the observer approach velocity and was approximately constant over the range of 2-25 m, but was slower for woodchucks less than 2 m from their burrows. Both temporal and spatial margins of safety increased with distance from the burrow. The temporal margin of safety increased with distance from the burrow more rapidly for slow than for fast observer approach velocity. Woodchucks fleeing from greater than 2 in usually stopped near the burrow before entering, but those from closer distances usually entered direcdy. These results support die assumption that antipredator behavior is sensitive to die costs and benefits of alternative escape decisions.

Focal suppression-burst on electrocorticography after temporal lobectomy.

Of 40 patients with cortical resections for epilepsy, three had focal suppression-burst (S-B) on postresection intraoperative electrocorticography (ECoG). Eighteen to 24 months later, two patients were seizure-free and one had rare seizures. Follow-up neuropsychological testing and MRI did not reveal unexpected postoperative abnormalities. Follow-up scalp surface EEGs did not show S-B. Although S-B on postresection ECoG suggests severe localized cortical damage, this pattern near anterior temporal lobectomy resection margins was not associated with postoperative deficits.

Postmenopausal Frontal Fibrosing Alopecia

Recession of the frontal hairline is a common event in postmenopausal women. This has been shown not to be a marker of gross androgenization, and is usually a progressive nonscarring alopecia. Six postmenopausal women, who developed a progressive frontal scarring alopecia, were studied and their clinical and laboratory data, as well as the results of scalp biopsy specimens in all six patients, were analyzed and compared with recognized forms of scarring alopecia and recently described findings in androgenetic alopecia. The six postmenopausal women developed a progressive frontal hairline recession that was associated with perifollicular erythema within the marginal hairline, producing a frontal fibrosing alopecia extending to the temporal and parietal hair margins. Scalp biopsy specimens from the frontal hair margin showed perifollicular fibrosis and lymphocytic inflammation concentrated around the isthmus and infundibular areas of the follicles. Immunophenotyping of the lymphocytes showed a dominance of activated T-helper cells. Clinical review of all six cases showed a progressive marginal alopecia without the typical multifocal areas of involvement seen in lichen planopilaris or pseudopelade. None of the patients had mucous membrane or skin lesions typical of lichen planus. Hormonal studies, in five patients, showed no elevated androgen abnormalities. Progressive frontal recession in postmenopausal women may show clinical features of a fibrosing alopecia. The histologic findings are indistinguishable from those seen in lichen planopilaris. However, the absence of associated lesions of lichen planus in all six women raises the possibility that this mode of follicular destruction represents a reaction pattern triggered by the events underlying postmenopausal frontal hairline recession.

On the sufficiency of compound target specification of isolated vowels and vowels in /bVb/ syllables

It has been suggested [e.g., Strange et al., J. Acoust. Soc. Am. 74, 695-705 (1983); Verbrugge and Rakerd, Language Speech 29, 39-57 (1986)] that the temporal margins of vowels in consonantal contexts, consisting mainly of the rapid CV and VC transitions of CVC's, contain dynamic cues to vowel identity that are not available in isolated vowels and that may be perceptually superior in some circumstances to cues which are inherent to the vowels proper. However, this study shows that vowel-inherent formant targets and cues to vowel-inherent spectral change (measured from nucleus to offglide sections of the vowel itself) persist in the margins of /bVb/ syllables, confirming a hypothesis of Nearey and Assmann [J. Acoust. Soc. Am. 80, 1297-1308 (1986)]. Experiments were conducted to test whether listeners might be using such vowel-inherent, rather than coarticulatory information to identify the vowels. In the first experiment, perceptual tests using "hybrid silent center" syllables (i.e., syllables which contain only brief initial and final portions of the original syllable, and in which speaker identity changes from the initial to the final portion) show that listeners' error rates and confusion matrices for vowels in /bVb/ syllables are very similar to those for isolated vowels. These results suggest that listeners are using essentially the same type of information in essentially the same way to identify both kinds of stimuli. Statistical pattern recognition models confirm the relative robustness of nucleus and vocalic offglide cues and can predict reasonably well listeners' error patterns in all experimental conditions, though performance for /bVb/ syllables is somewhat worse than for isolated vowels. The second experiment involves the use of simplified synthetic stimuli, lacking consonantal transitions, which are shown to provide information that is nearly equivalent phonetically to that of the natural silent center /bVb/ syllables (from which the target measurements were extracted). Although no conclusions are drawn about other contexts, for speakers of Western Canadian English coarticulatory cues appear to play at best a minor role in the perception of vowels in /bVb/ context, while vowel-inherent factors dominate listeners' perception.

Initial Glaucomatous Optic Disk and Retinal Nerve Fiber Layer Abnormalities and Their Progression

We attempted to identify the initial glaucomatous changes of the optic disk and retinal nerve fiber layer and to analyze how these changes subsequently progressed. Of 61 eyes of 61 patients with ocular hypertension, 23 (38%) developed glaucoma during ten years of follow-up (range, five to 15 years). The initial sign of glaucomatous damage was diffuse enlargement of the optic disk cup in ten of 23 eyes or generalized thinning of the nerve fiber layer without localized changes in 12 of 23 eyes. We found localized optic disk damage in ten of 23 patients and localized retinal nerve fiber layer damage in 11 of 23 patients alone or in combination with diffuse damage. In 13 of 23 eyes, the cupping ended up in diffuse enlargement with even more profound thinning of the neural rim in the upper and lower temporal disk margins. There seems to be great variability in the appearance and progression of the initial glaucomatous optic disk and nerve fiber layer abnormalities in patients with increased intraocular pressure.

The organization of the visual hyperstriatum in the domestic chick. I. Topology and topography of the visual projection

The organization of the visual projection to the hyperstriatum, or Wulst, in the domestic chick has been investigated using extracellular recording with microelectrodes. The entire visual field of the contralateral eye projects retinotopically into the Wulst. The superior and inferior margins of the visual field are represented, respectively, in the posterior and anterior regions of the visual projection area. The projection of the nasal and temporal margins of the visual field is more complex, the superior and inferior parts of the temporal hemi-field being represented in the superficial and deep regions of the Wulst respectively, with an intervening projection of the nasal hemi-field at an intermediate depth. Visually responsive units appear to be restricted to the accessory hyperstriatum (HA) and possibly also to a narrow, medial region of the intercalated nucleus (HIS). Visual-evoked activity was never detected in the dorsal hyperstriatum (HD) or ventral hyperstriatum (HV). The organization found in the chick is discussed in relation to the previous physiological and anatomical findings of other workers in the visual Wulst of the pigeon and the owl.