The concept of compensation in cognitive aging: the case of prose processing in adulthood.

Although the rule of cognitive aging appears to be one of generalized decline with advancing age, much recent theoretical and empirical work has addressed a variety of potential exceptions to this rule. One mechanism through which decline might not be experienced is known as compensation. We describe a conceptualization of compensation that applies to lifespan cognitive development, in general, and the aging of prose processing skills, in particular. Our model of the forms and processes of compensation directs attention to the developing dynamics of cognitive skills and compensatory mechanisms. We outline three main approaches to research on compensation in cognitive aging: a) the logical experimental, b) on-line observation and manipulation, and c) several verbal report procedures. In summarizing our own research program, we emphasize that a) each of these approaches can render valuable information, b) each have some limitations, and c) there are potential theoretical benefits from employing more than one of them in a given study.     

Retention of "safe" blood donors. The Retrovirus Epidemiology Donor Study

BACKGROUND: There are obvious advantages to increasing donor retention. However, for reasons of blood safety, certain donors may, in fact, be more desirable to retain than others. “Safe” donors are defined as those who provided a blood donation that was negative on all laboratory screening tests and who subsequently reported no behavioral risks in response to an anonymous survey. This study identifies the most important factors affecting the intention of “safe” donors to provide another donation. STUDY DESIGN AND METHODS: An anonymous survey asking about donation history, sexual history, injecting drug use, and recent donation experience was mailed to 50,162 randomly selected allogeneic donors (including directed donors) who gave blood from April through July or from October through December 1993 at one of the five United States blood centers participating in the Retrovirus Epidemiology Donor Study. Before mailing, questionnaires were coded to designate donors with nonreactive laboratory screening tests at their most recent donation. RESULTS: A total of 34,726 donors (69%) responded, with substantially higher response among repeat donors. According to reported intentions only, the vast majority of “safe” donors indicated a high likelihood of donating again within the next 12 months. Only 3.4 percent reported a low likelihood of donating again. A comparison of those likely to return and those unlikely to return reveals significant differences in demographics and in ratings of the donation experience. A higher proportion of those unlikely to return were first-time donors, minority-group donors, and donors with less education. The highest projected loss among “safe” donors was seen for those who gave a fair to poor assessment of their treatment by blood center staff or of their physical well-being during or after donating. CONCLUSION: These data suggest that efforts to improve donors' perceptions of their donation experience, as well as attention to the physical effects of blood donation, may aid in the retention of both repeat and first-time donors.     

Computed tomography of the post-operative lumbar spine: the need for, and optimal dose of, intravenous contrast medium

Forty-five patients who had undergone previous lumbar spine surgery with symptoms and signs warranting further investigation were examined by computed tomography (CT). The findings in three separate subgroups of 15 patients were compared. The first randomly selected group underwent CT without the use of intravenous contrast medium; the second and third groups were examined both before and after the administration of contrast medium, using 16.25 g and 32.5 g iodine, respectively. In the latter two groups the CT studies were reported both before and after enhancement. In the 15 patients in the first group (no contrast medium), uncertainty as to whether disc material or fibrosis was responsible for the radiological abnormalities was expressed in the final report at six of the 20 post-surgical sites. Among the 30 patients who received contrast medium, 40 post-surgical sites were examined; at six of these sites there was no radiological cause for concern; at 16 sites there were unequivocal radiological appearances of either disc material or fibrosis. Enhancement resolved the radiological uncertainty at 13 of the remaining 18 sites, almost always by reinforcing the initial radiological opinion; this left five sites where uncertainty persisted in the final report. The larger dose of contrast medium caused the more marked enhancement of those abnormalities considered to be due to fibrosis, although enhancement was readily recognised using the lower dose. While intravenous enhancement assists radiological interpretation at those sites where diagnostic uncertainty persists after routine CT, it would seem that it is not essential in patients in whom routine CT studies show no serious abnormality or the characteristic appearances of disc material or fibrosis.     

Remodeling of B-50 (GAP-43)- and NSE-immunoreactive mucosal nerves in the intestines of rats infected with Nippostrongylus brasiliensis.

Intestinal mucosal mast cells (IMMCs) are closely apposed to nerves, which is consistent with other evidence suggesting that mast cells are innervated. Recent studies have indicated that coordinated changes in mast cell and nerve densities occur in the gut mucosa, during progressive fibrosis, but there is a lack of experimental evidence to support remodeling of intestinal nerve fibers as part of a disease process. Infection of rats with the nematode Nippostrongylus brasiliensis (Nb) results in an initial loss of stainable IMMCs, during an acute inflammatory phase, with subsequent mast cell hyperplasia. Accordingly, we employed the Nb model to look for structural neuroplasticity of intestinal mucosal nerves during inflammation. Immunocytochemical labeling of neurofilament subunits was very low in the jejunal mucosa of all animals, whereas neuron-specific enolase (NSE)-immunoreactive nerves were relatively abundant in control animals. The number of NSE-immunoreactive profiles increased approximately 2.5-fold by day 10 (d10) postinfection (p less than 0.01) and returned to near control values by d14. Immunoreactivity for B-50/GAP-43 was more extensive, labeling more than four times the number of nerves per villus, compared with NSE (p less than 0.0001). B-50 immunoreactivity decreased minimally (ca. 20%) by d7 postinfection, and then increased through control values between d10 and d21, to 30% greater than controls at d49 (p less than 0.05). Subclassification of the B-50-immunoreactive nerves according to cross-sectional area revealed a greater than twofold increase in the proportions of large fibers at d7 and d10. Subsequently, the proportions of small nerves were increased compared with controls. The fiber size changes were found to correlate with mast cell densities (r = -0.72 for large and r = 0.76 for small nerves). At d10, dilated B-50- and NSE-immunoreactive nerves predominated, and extraneuronal NSE was noted. Electron microscopy revealed that this was due to axonal dilation and degeneration. These data provide evidence for plasticity of intestinal mucosal nerve fibers during inflammation. This includes early degenerative and later regenerative phases that appear to correlate with mast cell densities. The phenotype of mucosal nerves in control animals suggests ongoing modeling of these fibers.     

Staircase bioassay: the up-and-down method

Experiments are conducted to estimate the threshold for an all-or-none response. Threshold is defined to be a point above which 50% of the subjects will respond and below which 50% of the subjects will not respond. Examples are death, death in a fixed time period, shock, fibrillation, emesis. Staircase designs, in particular up-and-down trials, produce median (ED50) estimates of given standard error with as few as one-fifth the number of subjects as the traditional designs with preset numbers of tests at each of several levels of stimulus. We discuss these estimates and their efficiency as well as procedures to estimate standard deviation and its use in designing up-and-down trails. The advantages in using several short series in factorial experiments are presented. Suggestions are given for minimizing the complications of sequential designs. Case studies indicate the efficiency of the design for various applications.