Dubious decision evidence and criterion flexibility in recognition memory.

When old-new recognition judgments must be based on ambiguous memory evidence, a proper criterion for responding "old" can substantially improve accuracy, but participants are typically suboptimal in their placement of decision criteria. Various accounts of suboptimal criterion placement have been proposed. The most parsimonious, however, is that subjects simply over-rely on memory evidence - however faulty - as a basis for decisions. We tested this account with a novel recognition paradigm in which old-new discrimination was minimal and critical errors were avoided by adopting highly liberal or conservative biases. In Experiment 1, criterion shifts were necessary to adapt to changing target probabilities or, in a "security patrol" scenario, to avoid either letting dangerous people go free (misses) or harming innocent people (false alarms). Experiment 2 added a condition in which financial incentives drove criterion shifts. Critical errors were frequent, similar across sources of motivation, and only moderately reduced by feedback. In Experiment 3, critical errors were only modestly reduced in a version of the security patrol with no study phase. These findings indicate that participants use even transparently non-probative information as an alternative to heavy reliance on a decision rule, a strategy that precludes optimal criterion placement

Sacagawea and Son: The Visual Construction of America’s Maternal Feminine

Through an analysis of public statues commemorating Sacagawea, I argue that her maternal body has come to symbolize the American frontier and the “birth” of a new nation. Her “willingness” to guide Lewis and Clark on America’s most sacred mission into the wilderness has served to sanctify the “civilized” settlement of the fecund “native” land she represents, as does her giving up of her young son to Clark, a self-sacrificial act in keeping with the mythic construct of the maternal feminine, which in this case enables historical realities concerning race, genocide, appropriation, displacement, slavery, and sexual abuse to be submerged

Network constraints on learnability of probabilistic motor sequences

Human learners are adept at grasping the complex relationships underlying incoming sequential input. In the present work, we formalize complex relationships as graph structures derived from temporal associations in motor sequences. Next, we explore the extent to which learners are sensitive to key variations in the topological properties inherent to those graph structures. Participants performed a probabilistic motor sequence task in which the order of button presses was determined by the traversal of graphs with modular, lattice-like, or random organization. Graph nodes each represented a unique button press and edges represented a transition between button presses. Results indicate that learning, indexed here by participants' response times, was strongly mediated by the graph's meso-scale organization, with modular graphs being associated with shorter response times than random and lattice graphs. Moreover, variations in a node's number of connections (degree) and a node's role in mediating long-distance communication (betweenness centrality) impacted graph learning, even after accounting for level of practice on that node. These results demonstrate that the graph architecture underlying temporal sequences of stimuli fundamentally constrains learning, and moreover that tools from network science provide a valuable framework for assessing how learners encode complex, temporally structured information.Comment: 29 pages, 4 figure

Functional brain network architecture supporting the learning of social networks in humans

Most humans have the good fortune to live their lives embedded in richly structured social groups. Yet, it remains unclear how humans acquire knowledge about these social structures to successfully navigate social relationships. Here we address this knowledge gap with an interdisciplinary neuroimaging study drawing on recent advances in network science and statistical learning. Specifically, we collected BOLD MRI data while participants learned the community structure of both social and non-social networks, in order to examine whether the learning of these two types of networks was differentially associated with functional brain network topology. From the behavioral data in both tasks, we found that learners were sensitive to the community structure of the networks, as evidenced by a slower reaction time on trials transitioning between clusters than on trials transitioning within a cluster. From the neuroimaging data collected during the social network learning task, we observed that the functional connectivity of the hippocampus and temporoparietal junction was significantly greater when transitioning between clusters than when transitioning within a cluster. Furthermore, temporoparietal regions of the default mode were more strongly connected to hippocampus, somatomotor, and visual regions during the social task than during the non-social task. Collectively, our results identify neurophysiological underpinnings of social versus non-social network learning, extending our knowledge about the impact of social context on learning processes. More broadly, this work offers an empirical approach to study the learning of social network structures, which could be fruitfully extended to other participant populations, various graph architectures, and a diversity of social contexts in future studies

Controllability of structural brain networks.

Cognitive function is driven by dynamic interactions between large-scale neural circuits or networks, enabling behaviour. However, fundamental principles constraining these dynamic network processes have remained elusive. Here we use tools from control and network theories to offer a mechanistic explanation for how the brain moves between cognitive states drawn from the network organization of white matter microstructure. Our results suggest that densely connected areas, particularly in the default mode system, facilitate the movement of the brain to many easily reachable states. Weakly connected areas, particularly in cognitive control systems, facilitate the movement of the brain to difficult-to-reach states. Areas located on the boundary between network communities, particularly in attentional control systems, facilitate the integration or segregation of diverse cognitive systems. Our results suggest that structural network differences between cognitive circuits dictate their distinct roles in controlling trajectories of brain network function

Charakterisierung des Guaninnukleotid-Austauschfaktors p63RhoGEF als neuen Mediator der Galphaq/11-induzierten RhoA-Aktivierung

Monomere GTPasen der Rho-Familie spielen als zentrale Mediatoren eine entscheidende Rolle bei der Regulation multipler zellulärer Prozesse, wie der Reorganisation des Aktin-Zytoskeletts, der Genexpression, Proliferation, Migration und Apoptose. Bis heute ist jedoch nur wenig über die unmittelbar beteiligten akzessorischen Proteine und Signalübertragungswege bekannt. Ziel dieser Arbeit war es daher, die Funktion des neu identifizierten, Galphaq/11-spezifischen Guaninnukleotid-Austauschfaktors (GEF) p63RhoGEF näher zu charakterisieren, zu untersuchen ob er an der RhoA-Aktivierung in kardialen Primärzellen der Ratte beteiligt ist und welche Bedeutung er bei der Entwicklung einer zellulären Hypertrophie in isolierten Kardiomyozyten hat. Zunächst wurden die biochemischen Eigenschaften von p63RhoGEF im Vergleich zum Leukemia-associated RhoGEF (LARG), das ebenfalls als Gq/11-reguliert beschrieben war, analysiert. Für beide GEFs konnte die Aktivierung über Galphaq/11-Proteine bestätigt werden, wobei unterschiedliche Mechanismen dieser Aktivierung zu Grunde liegen. Während für die Aktivierung von LARG, zusäztlich zur Bereitstellung von aktiviertem Galphaq/11, ein direkter Kontakt des GEFs mit dem Agonist-gebunden Gq/11PCR benötigt wird, ist für die Stimulation von p63RhoGEF eine direkte Interaktion mit aktivierten Proteinen der Galphaq/11-Familie ausreichend. Wie durch Analyse der Kristallstruktur von p63RhoGEF und Punktmutationen gezeigt, umfasst dabei die Kernregion der Bindung den C-terminalen Bereich der PH-Domäne („PH-Extension“) und wird zusätzlich durch einzelne Aminosäuren innerhalb der DH- und der PH-Domäne stabilisiert. Vergleichbare Charakteristika zeigen auch die beiden p63RhoGEF-Homologe Kalirin/Duet und Trio, so dass die drei GEFs zu einer neuen Dbl-Unterfamilie zusammengefasst werden können, die sich entwicklungsbiologisch von einem schon in Invertebraten (z.B. Unc73 in C.elegans) vorhanden Vetreter dieser Familie ableiten. Die Stimulation isolierter Kardiomyozyten der neonatalen Ratte (NRCM) mit Phenylephrin (PE) und Endothelin-1 (ET-1) induzierte eine partiell über Galphaq/11-vermittelte Aktivierung von RhoA. Im Gegensatz zu PE, führte dabei die ET-1-induzierte RhoA-Aktivierung zur Stressfaserbildung und dem Aufbau sarkomerer Strukturen, wobei der Galphaq/11-abhängige Anteil über p63RhoGEF vermittelt wurde. Klassische Hypertrophie-Indikatoren (verstärkte Proteinsynthese, Expression von Markerproteinen) zeigten keine Abhängigkeit von p63RhoGEF bzw. RhoA, sondern wurden über den Galphaq/11-Effektor PLCß sowie die monomere GTPase Rac1 reguliert. Die Stimulation von isolierten kardialen Fibroblasten mit Angiotensin II induzierte eine RhoA-Aktivierung, die selektiv über den Angiotensin II–Rezeptoren-Typ I - Galphaq/11 - p63RhoGEF-Signalweg erfolgte. Die Daten belegen eine Galphaq/11-p63RhoGEF-vermittelte RhoA-Aktivierung sowohl in Kardiomyozyten als auch in kardialen Fibroblasten. Da Angiotensin II ein wichtiger Mediator der pathologischen Fibrose im Herzen ist, könnte dieser Signalweg von pathophysiologischer Bedeutung sein