Working Memory Load Modulates Neuronal Coupling

There is a severe limitation in the number of items that can be held in working memory. However, the neurophysiological limits remain unknown. We asked whether the capacity limit might be explained by differences in neuronal coupling. We developed a theoretical model based on Predictive Coding and used it to analyze Cross Spectral Density data from the prefrontal cortex (PFC), frontal eye fields (FEF), and lateral intraparietal area (LIP). Monkeys performed a change detection task. The number of objects that had to be remembered (memory load) was varied (1–3 objects in the same visual hemifield). Changes in memory load changed the connectivity in the PFC–FEF–LIP network. Feedback (top-down) coupling broke down when the number of objects exceeded cognitive capacity. Thus, impaired behavioral performance coincided with a break-down of Prediction signals. This provides new insights into the neuronal underpinnings of cognitive capacity and how coupling in a distributed working memory network is affected by memory load

Configuration Factors for Exchange of Radiant Energy Between Axisymmetrical Sections of Cylinders, Cones, and Hemispheres and Their Bases

Radiation-interchange configuration factors are derived for axisymmetrical sections of cylinders, cones, and hemispheres radiating internally to annular and circular sections of their bases and to other axisymmetrical sections. The general procedure of obtaining configuration factors is outlined and the results are presented in the form of equations, tables, and figures

Comparison of frontal and parietal cortices in the control of visual attention

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 178-186).The ability to switch between tasks reflects a fundamental part of our intelligence. A foundation of this ability lies in perceiving and processing information pertinent to the situation at hand. It is our capacity to attend to specific objects and, more importantly, our ability to switch our attention from object to object, that supports complex cognitive behavior. Therefore, by understanding the neural mechanisms involved in directing attention we hope to better understand cognition. Previous work investigating the ability to control attention has suggested that attention is influenced from two sources -- attention can either be driven from external sources in an bottom-up, exogenous manner or directed internally in an top-down, endogenous manner.This project will utilize two different forms of visual search in order to emphasize these two different types of attentional control. Both the prefrontal and parietal regions are implicated as the source of this control. In order to investigate their relative roles we recorded simultaneously from both parietal cortex (specifically, the lateral intraparietal cortex) and prefrontal cortex (specifically, the frontal eye fields and dorsolateral prefrontal cortex). We address four main questions. First, we contrast the respective roles of frontal and parietal cortex in the direction of attention when it is under either top-down or bottom-up control. We use the timing of attention signals between frontal and parietal cortex to establish that frontal cortex directs top-down attention back into parietal cortex, while bottom-up attention is reflected first in parietal cortex, flowing forward to frontal cortex. Secondly, we investigated the role of synchrony and the inter-areal relationships underlying top-down and bottom-up control of attention. Our results suggest synchrony between areas shifts as the task shifts, likely aiding in the selection of the network best suited to the current task. Third, we compare the neural mechanisms between internal and external control of attention.(cont) Finally, we investigate the neural correlates of the putative parallel and serial mechanisms underlying visual search, finding support for the existence of a serial search and for the role of the frontal eye fields in the direction of spatial attention.by Timothy J. Buschman.Ph.D

Intrinsic neuronal dynamics predict distinct functional roles during working memory

Working memory (WM) is characterized by the ability to maintain stable representations over time; however, neural activity associated with WM maintenance can be highly dynamic. We explore whether complex population coding dynamics during WM relate to the intrinsic temporal properties of single neurons in lateral prefrontal cortex (lPFC), the frontal eye fields (FEF), and lateral intraparietal cortex (LIP) of two monkeys (Macaca mulatta). We find that cells with short timescales carry memory information relatively early during memory encoding in lPFC; whereas long-timescale cells play a greater role later during processing, dominating coding in the delay period. We also observe a link between functional connectivity at rest and the intrinsic timescale in FEF and LIP. Our results indicate that individual differences in the temporal processing capacity predict complex neuronal dynamics during WM, ranging from rapid dynamic encoding of stimuli to slower, but stable, maintenance of mnemonic information.Biotechnology and Biological Sciences Research Council (Great Britain) (BB/M010732/1)United States. Office of Naval Research (N00014-14-1-0681)National Institute of Mental Health (U.S.) (R00MH092715)National Institute of Mental Health (U.S.) (R37MH087027)Massachusetts Institute of Technology. Picower Innovation FundUnited States. Office of Naval Research. Multidisciplinary University Research Initiative (grant N00014-16-1-2832)National Institute for Health Research (Great Britain). Wellcome Trust (203139/Z/16/Z

Gamma and Beta Bursts Underlie Working Memory

Working memory is thought to result from sustained neuron spiking. However, computational models suggest complex dynamics with discrete oscillatory bursts. We analyzed local field potential (LFP) and spiking from the prefrontal cortex (PFC) of monkeys performing a working memory task. There were brief bursts of narrow-band gamma oscillations (45–100 Hz), varied in time and frequency, accompanying encoding and re-activation of sensory information. They appeared at a minority of recording sites associated with spiking reflecting the to-be-remembered items. Beta oscillations (20–35 Hz) also occurred in brief, variable bursts but reflected a default state interrupted by encoding and decoding. Only activity of neurons reflecting encoding/decoding correlated with changes in gamma burst rate. Thus, gamma bursts could gate access to, and prevent sensory interference with, working memory. This supports the hypothesis that working memory is manifested by discrete oscillatory dynamics and spiking, not sustained activity.National Institute of Mental Health (U.S.) (Grant 5R01MH091174-05)National Institute of Mental Health (U.S.) (Grant 5R37MH087027-07

Materiality in information environments: Objects, spaces, and bodies in three outpatient hemodialysis facilities

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152032/1/asi24277.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152032/2/asi24277_am.pd

Epithelial-to-mesenchymal transition drives a pro-metastatic Golgi compaction process through scaffolding protein PAQR11

Tumor cells gain metastatic capacity through a Golgi phosphoprotein 3-dependent (GOLPH3-dependent) Golgi membrane dispersal process that drives the budding and transport of secretory vesicles. Whether Golgi dispersal underlies the prometastatic vesicular trafficking that is associated with epithelial-to-mesenchymal transition (EMT) remains unclear. Here, we have shown that, rather than causing Golgi dispersal, EMT led to the formation of compact Golgi organelles with improved ribbon linking and cisternal stacking. Ectopic expression of the EMT-activating transcription factor ZEB1 stimulated Golgi compaction and relieved microRNA-mediated repression of the Golgi scaffolding protein PAQR11. Depletion of PAQR11 dispersed Golgi organelles and impaired anterograde vesicle transport to the plasma membrane as well as retrograde vesicle tethering to the Golgi. The N-terminal scaffolding domain of PAQR11 was associated with key regulators of Golgi compaction and vesicle transport in pull-down assays and was required to reconstitute Golgi compaction in PAQR11-deficient tumor cells. Finally, high PAQR11 levels were correlated with EMT and shorter survival in human cancers, and PAQR11 was found to be essential for tumor cell migration and metastasis in EMT-driven lung adenocarcinoma models. We conclude that EMT initiates a PAQR11-mediated Golgi compaction process that drives metastasis