Center for Philosophy of Science
“Lévy Flights of the Collective Imagination”
Carnegie Mellon University & Santa Fe Institute
Tuesday, January 22, 2019
12:05 pm, 1117 Cathedral of Learning
Abstract: We present a structured random-walk model that captures key aspects of how people communicate in groups. Our model takes the form of a correlated Lévy flight that quantifies the balance between focused discussion of an idea and long-distance leaps in semantic space. We apply our model to three cases of increasing structural complexity: philosophical texts by Aristotle, Hume, and Kant; four days of parliamentary debate during the French Revolution; and branching comment trees on the discussion website Reddit. In the philosophical and parliamentary cases, the model parameters that describe this balance converge under coarse-graining to limit regions that demonstrate the emergence of large-scale structure, a result which is robust to translation between languages. Meanwhile, we find that the political forum we consider on Reddit exhibits a debate-like pattern, while communities dedicated to the discussion of science and news show much less temporal order, and may make use of the emergent, tree-like topology of comment replies to structure their epistemic explorations. Our model allows us to quantify the ways in which social technologies such as parliamentary procedures and online commenting systems shape the joint exploration of ideas.
Please note this will now occur in 1495 Starzl BSTWR.
PhD Dissertation Defense and Final Examination
Steven Suway of the School of Medicine, Center for Neuroscience at the University of Pittsburgh and the Center for the Neural Basis of Cognition.
Neural state changes in primate motor cortex during arm movements with distinct control requirements.
10:00 AM Wednesday, January 23, 2019
1495 Starzl BSTWR
Major Advisor: Andrew B. Schwartz, PhD
Chairperson: Peter L. Strick, PhD
Robert E. Kass, PhD
Carl R. Olson, PhD
William R. Stauffer, PhD
Giuseppe Pellizzer, PhD
CMU Biological Sciences Departmental Seminar
Wednesday, January 23
Mellon Institute Conference Room (348)
Sara Aton, Ph.D.
Molecular, Cellular, and Developmental Biology
University of Michigan
Sleep-dependent memory consolidation: oscillations and ensembles
Abstract: Our laboratory is addressing how sleep contributes to two processes in the mouse brain: hippocampal long-term memory formation and visual cortex plasticity. We hypothesize that some forms of brain plasticity occur preferentially during sleep due to its unique patterns of network activity. To test this, we are using recently-developed pharmacogenetic and optogenetic tools to silence subsets of neurons involved in generating sleep-associated network oscillations. We are studying how these manipulations affect both neural and behavioral plasticity. We find that both in the hippocampus during fear memory consolidation, and in the visual cortex during consolidation of experience-dependent response changes, there are increases in network oscillations during sleep that predict subsequent plasticity. Disruption of these oscillations leads to a loss of plasticity and a failure in long-term memory formation. A correlate of memory formation is the long-term stabilization of spike-timing relationships within neuronal ensembles, which can last for several hours following learning. Manipulations which disrupt network oscillations and memory also disrupt this stabilization process, while augmentation of oscillations enhance stabilization and preserve memory. We hypothesize that sleep-associated network oscillations promote stable reactivation of neuronal ensembles, which in turn drives long-term memory storage across brain circuits.