Representation of memory for order of mental operations in cognitive tasks

Journal ArticleRecent research shows that people learning a cognitive task acquire a memory for the order of operations applied, independent of the data to which those operations were applied. We designed two experiments to show how this sequence memory is represented. Experiment 1 compared predictions based on 3 possible sequence representation methods: composition, dyad transition, and associative chain. Latency and error results from a simple sequential task supported the associative chain representation. The associative links between operations presumably enhance performance by priming subsequent operations but do not operate in an all-or-none fashion. Experiment 2 explored whether transfer items that matched the first 2 rules and first 3 elements of a training item could bias participants toward executing a composed production learned during training. Latency and undetected error results were consistent with an associative chain representation but not with additional predictions made by the composition representation. These two experiments support the representation of operation sequences in memory as an associative chain

Absolute Proper Motion of the Fornax Dwarf Spheroidal Galaxy from Photographic and HST WFPC2 Data

We have measured the absolute proper motion of the Fornax dwarf spheroidal galaxy from a combination of photographic plate material and HST WFPC2 data that provide a time baseline of up to 50 years. The extragalactic reference frame consists of 8 QSO images and 48 galaxies. The absolute proper motion is mu_alpha cos(delta) = 0.59 +-0.16 mas/yr and mu_delta = -0.15 +- 0.16 mas/yr. The corresponding orbit of Fornax is polar, with an eccentricity of 0.27, and a radial period of 4.5 Gyr. Fornax's current location is near pericenter. The direction of the motion of Fornax supports the notion that Fornax belongs to the Fornax-LeoI-LeoII-Sculptor-Sextans stream as hypothesized by Lynden-Bell (1976, 1982) and Majewski (1994). According to our orbit determination, Fornax crossed the Magellanic plane \~190 Myr ago, a time that coincides with the termination of the star-formation process in Fornax. We propose that ram-pressure stripping due to the passage of Fornax through a gaseous medium denser than the typical intragalactic medium left behind from the LMC may have caused the end of star formation in Fornax. The excess, anomalous clouds within the South Galactic pole region of the Magellanic Stream whose origin has long been debated in the literature as constituents of either the Magellanic Stream or of the extragalactic Sculptor group, are found to lie along the orbit of Fornax. We speculate that these clouds are stripped material from Fornax as the dwarf crossed the Magellanic Clouds' orbit.Comment: Accepted for publication in Astronomical Journal. The version with high resolution figures can be found at ftp://pegasus.astro.yale.edu/pub/dana/paper

Investigating Miniature Electrodynamic Tethers and Interaction with the Low Earth Orbit Plasma

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106509/1/AIAA2013-5391.pd

Investigating Miniaturized Electrodynamic Tethers for Picosatellites and Femtosatellites

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143110/1/1.A33629.pd

Development of a Modeling Capability for Energy Harvesting Modules in Electrodynamic Tether Systems

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90615/1/AIAA-2011-7323-271.pd

Toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the developing male Wistar(Han) rat II: chronic dosing causes developmental delay

We have investigated whether fetal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes defects in the male reproductive system of the rat, using chronically exposed rats to ensure continuous exposure of the fetus. 5-6 week old rats were exposed to control diet, or diet containing TCDD, to attain an average dose of 2.4, 8 and 46 ng TCDD kg-1 day-1 for twelve weeks, whereupon the rats were mated, and allowed to litter; rats were switched to control diet after parturition. Male offspring were allowed to develop until kills on PND70 (25 per group), or PND120 (all remaining animals). Offspring from the high dose group showed an increase in total litter loss, and the number of animals alive on post-natal day (PND) 4 in the high dose group was ~26% less than control. The high and medium dose offspring showed decreased weights at various ages. Balano-preputial separation was significantly delayed in all three dose groups, compared to control. There were no significant effects of maternal treatment when the offspring were subjected to a functional observational battery, or learning tests, with the exception that the high dose group showed a deficit in motor activity. 20 rats per group were mated to females, and there were no significant effects of maternal treatment on the fertility of these rats, nor on the F1 or F2 sex ratio. Sperm parameters at PND70 and 120 showed no significant effect of maternal treatment, with the exception that there was an increase in the proportion of abnormal sperm in the high dose group at PND70; this is associated with the developmental delay in puberty in this dose group. There were no remarkable findings of maternal treatment on organ weights, with the exception that testis weights were reduced by ~10% at PND70 (but not PND120), and although the experiment was sufficiently powered to detect small changes, ventral prostate weight was not reduced. There were no significant effects of maternal treatment upon histopathological comparison of high dose and control group organs. These data confirm that developmental exposure to TCDD shows no potent effect on adult sperm parameters or accessory sexual organs, but show that delay in BPS occurs after exposure to low doses of TCDD, and this is dependent upon whether TCDD is administered acutely or chronically

Electrodynamic Tethers for Energy Harvesting and Propulsion on Space Platforms

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83661/1/AIAA-2010-8844-783.pd

Infection with Chlamydia Pneumoniae Alters Calcium-associated Gene Regulation and Processes in Neuronal Cells and Monocytes: Implications for Alzheimer’s Disease

Background: First proposed by Khachaturian in 1994, the calcium hypothesis postulates that sustained disturbance of intracellular calcium is the leading cause of neurodegenerative disorders. Studies showing alteration in calcium signaling in both sporadic and familial Alzheimer’s disease (AD) support this hypothesis. Intracellular calcium signaling is tightly regulated in time, intensity, and space, and is responsible for a variety of neuronal functions. Calcium influx from the extracellular environment modulates calcium levels, as do intracellular stores in the endoplasmic reticulum. The focus of this study was to test various calcium related genes in both monocytes and neuronal cells. Previous studies have shown that cells infected with Chlamydia pneumoniae (Cpn) exhibit altered protein processing, such as amyloid and tau modification, consistent with those found in AD. We expect to see significant alterations in calcium genes, as well as their protein products in Cpn infected cells. Every calcium gene has a unique function in the cell. Determining which genes are up or down regulated following infection may provide insight into how the neurodegeneration process observed in AD is initiated by Cpn infections

Chlamydophila (Chlamydia) pneumoniae promotes Ab 1-42 amyloid processing in Neuronal Cells: A Pathogenic Trigger for Alzheimer\u27s Disease

Background: Previously, our laboratory identified Chlamydophila (Chlamydia) pneumoniae (Cpn) in autopsied sporadic AD brains. Furthermore, we have developed a BALB/c mouse model that demonstrated infection-induced amyloid plaques similar to those found in AD, and demonstrated that Cpn infection of neuronal cells inhibited apoptotic pathways of cell death. Hypothesis: Our current studies address whether infection with Cpn in neuronal cells triggers abnormal cleavage of the beta amyloid precursor protein (bAPP) into Ab1-42, thereby contributing to amyloid plaque formation characteristic of the pathology identified in AD. Materials and Methods: Human neuroblastoma cells were infected with the respiratory strain AR39 Cpn in vitro, then amyloid processing was analyzed and quantitated using immunocytochemistry, Western blotting and ELISA assays. Results: Cpn was shown to infect neuronal cells and induce intracellular amyloid processing. Cpn infection yielded cytoplasmic labeling of Ab 1-42 that was increased relative to uninfected cells. The ELISA assay revealed that in neuronal cell lysates, Ab 1-42 in the infected cells was increased 3 to 16-fold over the uninfected cells, from 24 to 72hr post infection. Western blot analysis confirmed an increase in Ab 1-42 in the infected neuronal cell lysates. Conclusions: These data suggest that infection of neuronal cells with Chlamydophila (Chlamydia) pneumoniae alters the processing of bAPP, thereby producing Ab1-42. Therefore, these studies and previous research reported by our laboratory support the implication of Cpn as a pathogenic agent in perpetuating the hallmark amyloid plaque formations observed in AD. This concept holds major therapeutic considerations for future studies.https://digitalcommons.pcom.edu/posters/1004/thumbnail.jp