Visual Working Memory Load-Related Changes in Neural Activity and Functional Connectivity

BACKGROUND: Visual working memory (VWM) helps us store visual information to prepare for subsequent behavior. The neuronal mechanisms for sustaining coherent visual information and the mechanisms for limited VWM capacity have remained uncharacterized. Although numerous studies have utilized behavioral accuracy, neural activity, and connectivity to explore the mechanism of VWM retention, little is known about the load-related changes in functional connectivity for hemi-field VWM retention. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we recorded electroencephalography (EEG) from 14 normal young adults while they performed a bilateral visual field memory task. Subjects had more rapid and accurate responses to the left visual field (LVF) memory condition. The difference in mean amplitude between the ipsilateral and contralateral event-related potential (ERP) at parietal-occipital electrodes in retention interval period was obtained with six different memory loads. Functional connectivity between 128 scalp regions was measured by EEG phase synchronization in the theta- (4-8 Hz), alpha- (8-12 Hz), beta- (12-32 Hz), and gamma- (32-40 Hz) frequency bands. The resulting matrices were converted to graphs, and mean degree, clustering coefficient and shortest path length was computed as a function of memory load. The results showed that brain networks of theta-, alpha-, beta-, and gamma- frequency bands were load-dependent and visual-field dependent. The networks of theta- and alpha- bands phase synchrony were most predominant in retention period for right visual field (RVF) WM than for LVF WM. Furthermore, only for RVF memory condition, brain network density of theta-band during the retention interval were linked to the delay of behavior reaction time, and the topological property of alpha-band network was negative correlation with behavior accuracy. CONCLUSIONS/SIGNIFICANCE: We suggest that the differences in theta- and alpha- bands between LVF and RVF conditions in functional connectivity and topological properties during retention period may result in the decline of behavioral performance in RVF task

Abnormal cognition, sleep, EEG and brain metabolism in a novel knock-in Alzheimer mouse, PLB1

Peer reviewedPublisher PD

Effects of quartz particle size on hydrogarnet formation during autoclaving at 180°C in the CaO-Al<inf>2</inf>O<inf>3</inf>-SiO<inf>2</inf>-H<inf>2</inf>O system

The effects of quartz particle size on the nature of hydration products in unstirred, autoclaved metakaolin-lime-quartz slurries with Ca/(Al + Si) and Al/(Al + Si) ratios of 0.80 and 0.13 were investigated. While hydrogarnet invariably appeared before 11 Å tobermorite when using either fine or coarse quartz, its formation was more prominent in the presence of coarse quartz. The breakdown of hydrogarnet and the formation of 11 Å tobermorite were delayed in the presence of coarse quartz, suggesting that when using aluminous additives under autoclaving conditions, quartz fineness is a deciding factor. The amount of hydrogarnet formed during autoclaving followed by its breakdown is significant in relation to the formation of 11 Å tobermorite. © 1998 Elsevier Science Ltd

Effects of quartz particle size and kaolin on hydrogarnet formation during autoclaving

The effects of quartz particle size on the formation of hydrogarnet in unstirred, autoclaved kaolin-lime-quartz slurries with Ca/(Al + Si) and Al/(Al + Si) ratios of 0.8 and 0.13 were investigated. The initial lime-kaolin reaction was retarded only when fine quartz was used. The slower release of silicate anions from coarse quartz prolonged the stability of hydrogarnet while retarding the formation of 11Å tobermorite. Both the type of aluminous source and the extent of release of silicate anion from the silica source influence the formations of hydrogarnet and 11 Å tobermorite as well as the stability of the hydrogarnet. The interdependency between aluminous and siliceous sources is evident. © 1998 Elsevier Science Ltd

Autoclaved cement-quartz pastes: The effects on chemical and physical properties when using ground quartz with different surface areas part II: Results of accelerated carbonation

Previously saturated and oven dried, autoclaved cement-quartz prisms, made with quartz of varying fineness, were exposed to carbon dioxide for 24 hours. The extent of carbonation and drying shrinkage, as well as the degree of cracking were found to increase with increasing surface area of quartz. The binder became progressively more like SiO2-gel in character. Thermal analysis revealed both low- and high-temperature decarbonation steps, the mass loss increasing, in both decarbonation steps, with the surface area of quartz used. Difficulties encountered in interpreting the results, attributed to a multiplicity of factors involved, are highlighted. © 1997 Elsevier Science Ltd

DTA-TGA of unstirred autoclaved metakaolin-lime-quartz slurries. The formation of hydrogarnet

DTA-TGA was used to monitor the evolution of hydration products in unstirred autoclaved metakaolin-lime-quartz slurries with reaction time. Hydrogarnet was always one of the first phases formed at all metakaolin additions and invariably appeared before 11 Å tobermorite. These findings explain apparent inconsistencies in the literature because the continued existence of hydrogarnet depends on such factors as reaction time and bulk composition. DTA-TGA indicated that the lime-quartz reaction was retarded and inferred differences in the precursor silicate anion structure of calcium silicate hydrates with increasing metakaolin addition. © 1998 Elsevier Science B.V