The control of global brain dynamics: opposing actions of frontoparietal control and default mode networks on attention

Understanding how dynamic changes in brain activity control behavior is a major challenge of cognitive neuroscience. Here, we consider the brain as a complex dynamic system and define two measures of brain dynamics: the synchrony of brain activity, measured by the spatial coherence of the BOLD signal across regions of the brain; and metastability, which we define as the extent to which synchrony varies over time. We investigate the relationship among brain network activity, metastability, and cognitive state in humans, testing the hypothesis that global metastability is “tuned” by network interactions. We study the following two conditions: (1) an attentionally demanding choice reaction time task (CRT); and (2) an unconstrained “rest” state. Functional MRI demonstrated increased synchrony, and decreased metastability was associated with increased activity within the frontoparietal control/dorsal attention network (FPCN/DAN) activity and decreased default mode network (DMN) activity during the CRT compared with rest. Using a computational model of neural dynamics that is constrained by white matter structure to test whether simulated changes in FPCN/DAN and DMN activity produce similar effects, we demonstate that activation of the FPCN/DAN increases global synchrony and decreases metastability. DMN activation had the opposite effects. These results suggest that the balance of activity in the FPCN/DAN and DMN might control global metastability, providing a mechanistic explanation of how attentional state is shifted between an unfocused/exploratory mode characterized by high metastability, and a focused/constrained mode characterized by low metastability

Tubular free by cyclic groups act freely on CAT(0) cube complexes

AbstractWe identify when a tubular group (the fundamental group of a ûnite graph of groups with ℤ2 vertex and ℤ edge groups) is free by cyclic and show, using Wise’s equitable sets criterion, that every tubular free by cyclic group acts freely on a CAT(0) cube complex.</jats:p

Iceland’s bourgeoning cruise industry: An economic opportunity or a local threat?

The cruise industry is the fastest growing component of mass tourism and is as a key contributor to overtourism. The cruise industry is having a very significant impact on the country of Iceland, as cruises take people to some of the country’s most remote areas. In Iceland, the increase has been even more dramatic, with cruise ship arrivals increasing by over 91% (between 2015 and 2019) in Iceland’s small northern town of Akureyri and its surrounding ports. This paper is critical of the expansion of cruise tourism in Iceland despite the potential economic impacts of cruise ship tourism. Scholars argue is the need to consider economic gains alongside environmental costs and social consequences that disrupt communities. This in perspective paper considers current economic, environmental and social impacts of cruise ship arrivals in Iceland before outlining some recommendations that align with environmentally friendly practices for policy makers to consider going forward. The triple bottom line framework is widely considered in tourism planning, and this paper seeks to connect the economic, social and environmental dimensions of tourism in a sustainable way to look at the present situation in Iceland and address policy considerations going forward

The effect of delayed auditory feedback on activity in the temporal lobe while speaking: A Positron Emission Tomography study

Purpose: Delayed auditory feedback is a technique that can improve fluency in stutterers, while disrupting fluency in many non-stuttering individuals. The aim of this study was to determine the neural basis for the detection of and compensation for such a delay, and the effects of increases in the delay duration. Method: Positron emission tomography (PET) was used to image regional cerebral blood flow changes, an index of neural activity, and assessed the influence of increasing amounts of delay. Results: Delayed auditory feedback led to increased activation in the bilateral superior temporal lobes, extending into posterior-medial auditory areas. Similar peaks in the temporal lobe were sensitive to increases in the amount of delay. A single peak in the temporal parietal junction responded to the amount of delay but not to the presence of a delay (relative to no delay). Conclusions: This study permitted distinctions to be made between the neural response to hearing one's voice at a delay, and the neural activity that correlates with this delay. Notably all the peaks showed some influence of the amount of delay. This result confirms a role for the posterior, sensori-motor ‘how’ system in the production of speech under conditions of delayed auditory feedback

Separable subsets of GFERF negatively curved groups

A word hyperbolic group G is called GFERF if every quasiconvex subgroup coincides with the intersection of finite index subgroups containing it. We show that in any such group, the product of finitely many quasiconvex subgroups is closed in the profinite topology on G

The Puck Stops Here: Evolving Social Norms of Helmet Usage in the National Hockey League

Since the mid 1960s, the use of safety helmets in the National Hockey League (NHL) went from virtually nil to almost universal adoption. Despite horrific injuries sustained by players early in the history of the sport, widespread helmet adoption did not take place immediately. Using the NHL as an example, this paper examines the process of emerging norms in a social group, considering peer influence and exogenous policy impacts. The historical circumstances surrounding the NHL helmet usage policy changes are presented, along with a brief survey of the social science modeling of cultural norms. The study presents a peer-influence model in which players helmet usage decisions are influenced by their immediate social network and an exogenous mandate requiring helmet usage for new players. Model results are compared to actual NHL helmet usage trends based on data extracted by review of NHL game footage. The results show eventual dominance of helmet usage, but without the wide fluctuations in the actual historical adoption trends. The study is of interest to policy makers comparing interventionist strategies versus social network based approaches for influencing cultural norms of behavior

The Impact of Dispersion on Amplitude and Frequency Noise in a Yb-fiber Laser Comb

We describe a Yb-fiber based laser comb, with a focus on the relationship between net-cavity dispersion and the frequency noise on the comb. While tuning the net cavity dispersion from anomalous to normal, we measure the amplitude noise (RIN), offset frequency (f_CEO) linewidth, and the resulting frequency noise spectrum on f_CEO. We find that the laser operating at zero net-cavity dispersion has many advantages, including an approximately 100x reduction in free-running f_CEO linewidth and frequency noise power spectral density between laser operation at normal and zero dispersion. In this latter regime, we demonstrate a phase-locked f_CEO beat with low residual noise

Paper Session III-B - Life Support Research & Development for the Department of Energy Space Exploration Initiative

Long-term, manned space missions of the future will require an approach to life support systems in which most of the waste materials must be processed and recycled and/or local resources are utilized. The requirement for a reliable life support system has been recognized as an important component of the Space Exploration Initiative, and the Department of Energy (DOE), in conjunction with the National Aeronautics and Space Agency, is organizing a program in support of the development of this type of technology. It is quite likely that bioprocesses will be important components of the integrated system, and this will be the primary area of research and development (R&D) within the DOE national laboratories. Microbial, enzymatic, and thermochemical processing of wastes will be investigated in the initial research studies. Other research areas of interest include water and air purification by plants, microbial detection systems, biophotochemical CO2 recycle, tissue cultures for food, single-cell protein, bioadsorbents for pollutant removal, and several others. The resulting innovative technology developed for space exploration could also serve as the basis for new approaches for the processing and recycle of waste materials on Earth