Understanding what motivates participation is a central theme in the research on open source software (OSS) development. Our study contributes by revealing how the different motivations of OSS developers are interrelated, how these motivations influence participation leading to performance, and how past performance influences subsequent motivations. Drawing on theories of intrinsic and extrinsic motivation, we develop a theoretical model relating the motivations, participation, and performance of OSS developers. We evaluate our model using survey and archival data collected from a longitudinal field study of software developers in the Apache projects. Our results reveal several important findings. First, we find that developers' motivations are not independent but rather are related in complex ways. Being paid to contribute to Apache projects is positively related to developers' status motivations but negatively related to their use-value motivations. Perhaps surprisingly, we find no evidence of diminished intrinsic motivation in the presence of extrinsic motivations; rather, status motivations enhance intrinsic motivations. Second, we find that different motivations have an impact on participation in different ways. Developers' paid participation and status motivations lead to aboveaverage contribution levels, but use-value motivations lead to below-average contribution levels, and intrinsic motivations do not significantly impact average contribution levels. Third, we find that developers' contribution levels positively impact their performance rankings. Finally, our results suggest that past-performance rankings enhance developers' subsequent status motivations.

Among the identified risks and benefits of hormone-replacement therapy, the effects of treatment on cognitive function in postmenopausal women have proved difficult to define. Here we conducted a controlled, prospective analysis in a nonhuman primate model to test whether surgical menopause and estrogen replacement influence the cognitive outcome of normal aging. Sixteen aged rhesus monkeys were ovariectomized, and throughout the course of subsequent neuropsychological assessment, half received a regimen of low-dose, cyclic estradiol replacement. Hormone treatment substantially reversed the marked age-related impairment vehicle-injected monkeys exhibited on a delayed response test of spatial working memory. Modest improvement was also observed on a delayed nonmatching-to-sample recognition memory task. In contrast, ovariectomy exacerbated age-related deficits in object discrimination learning; the magnitude of this effect was equivalent among vehicle- and estrogen-treated monkeys. Together, these results demonstrate that ovarian hormone status can broadly influence normal cognitive aging in monkeys, affecting capacities mediated by multiple brain regions, including the prefrontal cortex and the medial temporal lobe memory system. The animal model established here should enable progress toward defining the neurobiological mechanisms that mediate the beneficial effects of estrogen on age-related cognitive decline in primates.

Long-term cyclic treatment with 17␤-estradiol reverses age-related impairment in ovariectomized rhesus monkeys on a test of cognitive function mediated by the prefrontal cortex (PFC). Here, we examined potential neurobiological substrates of this effect using intracellular loading and morphometric analyses to test the possibility that the cognitive benefits of hormone treatment are associated with structural plasticity in layer III pyramidal cells in PFC area 46. 17␤-Estradiol did not affect several parameters such as total dendritic length and branching. In contrast, 17␤-estradiol administration increased apical and basal dendritic spine density, and induced a shift toward smaller spines, a response linked to increased spine motility, NMDA receptor-mediated activity, and learning. These results document that, although the aged primate PFC is vulnerable in the absence of factors such as circulating estrogens, it remains responsive to long-term cyclic 17␤-estradiol treatment, and that increased dendritic spine density and altered spine morphology may contribute to the cognitive benefits of such treatment.