Normal volunteers, aged 30 to 99 years, were studied with MRI. Age was related to estimated volumes of: gray matter, white matter, and CSF of the cerebrum and cerebellum; gray matter, white matter, white matter abnormality, and CSF within each cerebral lobe; and gray matter of eight subcortical structures. The results were: 1) Age-related losses in the hippocampus were significantly accelerated relative to gray matter losses elsewhere in the brain. 2) Among the cerebral lobes, the frontal lobes were disproportionately affected by cortical volume loss and increased white matter abnormality. 3) Loss of cerebral and cerebellar white matter occurred later than, but was ultimately greater than, loss of gray matter. It is estimated that between the ages of 30 and 90 volume loss averages 14% in the cerebral cortex, 35% in the hippocampus, and 26% in the cerebral white matter. Separate analyses were conducted in which genetic risk associated with the Apolipoprotein E ⑀4 allele was either overrepresented or underrepresented among elderly participants. Accelerated loss of hippocampal volume was observed with both analyses and thus does not appear to be due to the presence of at-risk subjects. MR signal alterations in the tissues of older individuals pose challenges to the validity of current methods of tissue segmentation, and should be considered in the interpretation of the results.

The migrating slug of the cellular slime mould, Dictyostelium discoideum is capable of directed movement. A rather large literature on how this simple group of amoebae move and orient is briefly summarized, All the amoebae in the slug move, and their internal direction is controlled by chemotaxis, by relay waves of cAMP that start at the anterior tip. This moving mass of amoebae can be oriented by directional light, as well as heat and chemical gradients. Such external factors could orient by shifting the position of the cAMP pulse pacemaker in the tip, or by making the cells move faster or slower on one side of the anterior portion of the slug, or a combination of the two.

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A great deal of research exists in the use of multimedia communications in online classrooms as a means of furthering student engagement. However, little research exists that examines the perceptions of students when such technologies are used. Additionally, it is unclear that students are likely to engage in the use of such technologies when available. This research explores the perceptions of 69 students taking both online and hybrid undergraduate project management courses. Specifically, the study seeks to explore how students experienced the use of multimedia by their instructor and classmates in both online announcements and discussions, as well as whether these same students used or would be likely to use multimedia for similar communications. Finally, student perceptions of social presence, the degree to which one is perceived as a real person in computer-mediated communication (Gunawardena, 1995), are examined. The results of the study indicate that while students overwhelming enjoy the instructor's use of multimedia communication, they are unlikely to engage in using these technologies themselves. A discussion of these results and recommendations for further research complete this paper.

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