Central visual persistences: II. Effects of hand and head rotations

In an earlier paper, kinesthetic effects on central visual persistences (CPs) were reported, including the ability to move these images by hand following eye closure. While all CPs could be translated anywhere within the frontal field, the present report documents a more selective influence of manual rotations on CPs in the same subjects. When common objects or figures drawn on cards were rotated (while holding one end of the object or one corner of a card between thumb and forefinger), it was found that CPs of larger objects rotated with the hand. By contrast, CPs of smaller objects, parts of objects, and textures remained stable in space as the hand rotated. It is proposed that CPs of smaller stimuli and textures are represented mainly by the ventral stream (temporal cortex) while larger CPs, which rotate, are represented mainly by the dorsal stream (parietal cortex). A second discovery was that CPs of small objects (but not of line segments or textures) could be rotated when the thumb and fingers surrounded the edges of the object. It is proposed that neuronal convergence of visual and tactile information about shape increases parietal responses to small objects, so that their CPs will rotate. Experiments with CPs offer new tools to infer visual coding differences between ventral and dorsal streams in man.

MRI of Knee Osteonecrosis in Children with Leukemia and Lymphoma: Part 2, Clinical and Imaging Patterns

OBJECTIVE

This aim of this study was to explore the relationship between MRI findings and clinical symptoms of knee osteonecrosis in children and to determine the significance of this relationship. Such information is important for early diagnosis of this frequent complication and for choosing an appropriate treatment strategy.

MATERIALS AND METHODS

Osteonecrotic lesion size and location were determined in a retrospective analysis of MR images of the knee obtained in our institution during the past 10 years. Association between MRI findings and clinical symptoms expressed by the knee scores was tested for a subgroup of our patient population who had clinical evaluation of the knees in the orthopedic clinic within 6 weeks of their MRI studies.

RESULTS

In 80% of patients, osteonecrosis was bilateral. Lesions were distributed as follows: femur and tibia, 66% of the knees; femur alone, 26%; and tibia alone, 8%. Clinical symptoms of knee osteonecrosis were associated with lesions involving the articular surface of the distal femur, large lesions, and involvement of any part of the tibia. MR images showed milder osteonecrosis in patients who were less than 10 years old at the time of primary diagnosis.

CONCLUSION

Osteonecrosis affecting the knees of children treated for leukemia and lymphoma is mostly asymptomatic. Children who are 10 years old or older have signs of more advanced osteonecrosis. Clinical symptoms often lag MRI presentation and may develop late in the course of the disease. Routine MRI evaluation is recommended for timely diagnosis of treatment-induced osteonecrosis.

Central visual persistences: I. Visual and kinesthetic interactions

Phenomena associated with 'central visual persistences' (CPs) are new to both medical and psychological literature. Five subjects have reported similar CPs: positive afterimages following brief fixation of high-contrast objects or drawings and eye closure. CPs duplicate shapes and colors of single objects, lasting for about 15 s. Unlike retinal afterimages, CPs do not move with the eyes but are stable in extrapersonal space during head or body rotations. CPs may reflect sustained neural activity in neurons of association cortex, which mediate object perception. A remarkable finding is that CPs can be moved in any direction by the (unseen) hand holding the original seen object. Moreover, a CP once formed will 'jump' into an extended hand and 'stick' in that hand as it moves about. The apparent size of a CP of a single object is determined by the size of the gap between finger and thumb, even when no object is touched. These CPs can be either magnified or minified via the grip of the extended hand. The felt orientation of the hand-held object will also determine the orientation of the CP seen in that hand. Thus, kinesthetic signals from hand and arm movements can determine perceived location, size, and orientation of CPs. A neural model based on physiological studies of premotor, temporal, parietal, and prefrontal cortices is proposed to account for these novel phenomena.

Life table methodology applied to NHANES II database for analysis of mortality associated with cholesterol/HDL ratios

This article describes the association between total cholesterol to high-density lipoprotein (HDL)-cholesterol ratios and all-cause mortality in a large cohort of Americans with nearly 17 years of follow-up. Detailed actuarial life table methodology was used. It concludes that the relationship is best described as a J-shaped curve.

Fetal alcohol syndrome in Alaska, 1977 through 1992: an administrative prevalence derived from multiple data sources

OBJECTIVES

The prevalence and characteristics of fetal alcohol syndrome cases and the usefulness of various data sources in surveillance were examined in Alaska to guide prevention and future surveillance efforts.

METHODS

Sixteen data sources in Alaska were used to identify children with fetal alcohol syndrome. Medical charts were reviewed to verify cases, and records were reviewed to provide descriptive data.

RESULTS

Fetal alcohol syndrome rates varied markedly by birth year and race, with the highest prevalence (4.1 per 1000 live births) found among Alaska Natives born between 1985 and 1988. Screening and referral programs to diagnostic clinics identified 70% of all recorded cases. The intervention program for children 0 to 3 years of age detected 29% of age-appropriate cases, and Medicaid data identified 11% of all cases; birth certificates detected only 9% of the age-appropriate cases.

CONCLUSIONS

Our findings indicate a high prevalence of fetal alcohol syndrome in Alaska and illustrate that reliance on any one data source would lead to underestimates of the extent of fetal alcohol syndrome in a population.

The contribution of reinfection to gonorrhea incidence in Alaska, 1983 to 1987

Gonorrhea case reports to the Alaska Department of Health and Social Services were used to study the contribution of reinfection to rates of gonorrhea infection in Alaska. The case reports of 13,910 infections among 11,132 persons who had laboratory-proven gonorrhea between 1983 and 1987 were examined. Among 1,886 persons who had multiple infections, the average number of infections per person was 2.5 (range = 2-11). These persons accounted for 33.5% of all infections and 16.9% of all patients with gonorrhea from 1983 to 1987. Compared to persons with one infection, those having multiple infections were more likely to be Alaska Natives (relative risk = 1.8, 95% confidence interval = 1.6-1.9) and less than 21 years of age (relative risk = 1.3, 95% confidence interval = 1.2-1.4). There was no difference in risk between men and women. Two thirds of the reinfections occurred within 12 months of the initial infection. If gonorrhea incidence were calculated based on the number of people infected rather than as a "case rate," the mean annual rate (per 100,000) from 1983 to 1987 decreased from 1,644 to 1,228 (a 25.3% decrease) for Alaska Natives and from 316 to 267 (a 15.5% decrease) for non-Natives. Reporting gonorrhea incidence rates by number of persons infected rather than by total number of cases more accurately measures gonorrhea morbidity in a population and will allow prevention efforts to be directed to those persons who contribute the most to perpetuating the disease.

Interocular transfer of visual discriminations in goldfish after selective commissure lesions

Goldfish with transections of the intertectal commissure learned but failed to transfer interocularly a simple visually cued avoidance task in a shuttle box, whereas posterior commissure lesions had no effect on this simple transfer task. However, fish with tectal commissure lesions could show normal interocular transfer of a shape discrimination, once discrimination pretraining with color cues had been carried out with each eye separately. Lesions of anterior commissure had no effect on either shape or color transfer, but fish with intended cuts of the postoptic commissures showed striking deficits of interocular transfer. As with comparable studies in the pigeon, it is concluded that postoptic, but not tectal, commissures are required for interocular transfer in the goldfish.

Focal attention in the frog: behavioral and physiological correlates

The prey-catching response of frogs toward small moving objects can be facilitated by small movements of the same stimulus a few seconds earlier, even though initial movements seldom trigger the feeding response. This focal attention phenomenon may be related to the observation that one class of tectal unit continues to discharge for a few seconds following a brief stimulus motion. Together with anatomical data of other investigators, results of the present study suggest that self-exciting neural loops within the tectum mediate this type of selective attention.

Two visual systems in the frog

After unilateral removal of the optic tectum in frogs, the cut optic tract regenerates to the remaining ipsilateral tectum. Although the orienting movementselicited by moving objects (food or threats) are now directed mirror-symmetrically to normal responses, these frogs correctly localize stationary objects as barriers. Apparently, thalamic and tectal visual mechanisms can operate independently.

Disinhibition of tectal neurons by pretectal lesions in the frog

The rapid habituation of many neurons in the frog optic tectum to moving spots is presumed to underlie the behavioral habituation of the frog to repeated movement of prey objects. The "disinhibited" feeding of frogs after pretectal lesions is paralleled by the consistent failure of tectal neurons to ignore moving buglike stimuli.