Colloquium 15:00-15:50 in 6627 MS
Host: Mason Porter
Paul Bressloff (University of Utah)
Spontaneous brain dynamics: from geometric visual hallucinations to ambiguous perception
Abstract. Advances in experimental imaging techniques, combined with sophisticated data analytic tools, are beginning to shed light on the intricate functional architecture of specific brain regions, and how this provides a substrate for both spontaneous and stimulus-evoked neural activity patterns. In this talk, I use the mathematical theory of continuum neural fields to explore the relationship between structure and dynamics in the primary visual cortex (V1), which is the first cortical region to process visual signals from the eyes. Neural fields model the large-scale dynamics of spatially structured networks of neurons in terms of nonlinear integrodifferential equations, whose associated integral kernels represent the spatial distribution of neuronal synaptic connections.
First, I present a neural field theory of geometric visual hallucinations, based on the assumption that the form of the eye-brain map and the network architecture of V1 determine their geometry. (With Jack Cowan and Marty Golubitsky.) Motivated by anatomical evidence, the network architecture is taken to exhibit certain symmetries rendering it invariant under the so-called shift-twist action of the Euclidean group on the product space R2 x S1. Using this symmetry, I show how the common types of geometric hallucinations arise dynamically through the spontaneous formation of neural activity patterns within the cortical network. This suggests that the cortical mechanisms that generate geometric visual hallucinations are closely related to those used to process edges and contours in normal vision, which is consistent with recent findings by experimental collaborators. I also briefly discuss extensions to other symmetry groups. (With Sam Carroll.)
Second, I describe a neural field theory of binocular rivalry waves. Binocular rivalry is the phenomenon where perception spontaneously switches back and forth between different images presented to the two eyes. The resulting fluctuations in perceptual dominance and suppression provide a basis for non-invasive studies of the human visual system and the identification of possible neural mechanisms underlying conscious visual awareness. Various imaging studies have shown that the switch in perceptual dominance propagates as a traveling wave across cortex. I derive an analytical expression for the speed of a binocular rivalry wave as a function of various neurophysiological parameters, and show how properties of the wave are consistent with the wave-like propagation of perceptual dominance observed in recent psychophysical experiments. I also highlight the important role of adaptation in providing a "symmetry breaking mechanism" that allows waves to propagate. Finally, I briefly indicate how to extend the theory to incorporate the effects of noise.
This talk requires no background knowledge in biology. The talk is intended for a general mathematics audience, and should be accessible to any advanced undergraduate or beginning graduate student. The mathematics will involve a mixture of applied PDEs, dynamical systems theory and a little group theory. So some exposure to these topics would be helpful, but not necessary.
Tea is served in the graduate lounge at 4pm
The UCLA Mathematics Colloquium is supported in part by the Larry M. Weiner Mathematics Fund.
September 27th and 28th, 2018 from 8:30am to 3:30pm
UCLA Physics & Astronomy Department, PAB 4-330 conference room
Organizer: Alex Levine
This workshop, hosted by the Bhaumik Institute of Theoretical Physics and the UCLA Center for Biological Physics, will explore the emerging connections between physics and neuroscience as part of the UCLA Julian Schwinger Centennial Celebration.
Confirmed speakers include:
The Physics of Life: How Much Can We Calculate?
William Bialek (Princeton)
Thursday, September 27th, 6:00pm, Fowler Museum, Lenart Auditorium
In the four hundred years since Galileo, the physics community has constructed a remarkably successful mathematical description of the world around us. From deep inside the atomic nucleus to the structure of the universe on the largest scales, from the flow air over the wing of an airplane to the flow of electrons in a computer chip, we can predict in detail what we see, and what will happen when we look in places we have never looked before. What are the limits to this predictive power? In particular, can we imagine a theoretical physicist’s approach to the complex and diverse phenomena of the living world? Is there something fundamentally unpredictable about life, or are we missing some deep theoretical principles that could bring the living world under the predictive umbrella of physics? Exploring this question gives us an opportunity to reflect on what we expect from our scientific theories, and on many beautiful phenomena. I hope to leave you with a deeper appreciation for the precision of life’s basic mechanisms, and with optimism about the prospects for better theories.
Light refreshments will be served at 5:30.
Co-sponsored by the Center for Biological Physics and the UCLA Mani L. Bhaumik Institute for Theoretical Physics
From Blackboard to Bedside: How Theory Helped Change the Outcome of HIV Infection
Alan Perelson, Los Alamos National Laboratory
Thursday April 6, 2017 at 6pm, UCLA Lenart Auditorium at the UCLA Fowler Museum
Abstract: Although mathematics and theoretical physics are sometimes thought of as being abstract and not of much practical use, theoretical ideas expressed mathematically changed the way we think about viral infections and their treatment. I will show how this approach lead to the introduction of combination antiretroviral therapy that has converted HIV from a death sentence to a manageable chronic disease. I will end by discussing the current state of the art efforts to cure HIV.
The morphogenesis of bacterial microcolonies
Nicholas Desprat, PhD
Laboratoire de Physique Statistique, Assistant Professor, Department of Physics
Monday January 9, 2017, 11:00am - 12:00pm, 5101 Engineering V
Abstract: Biofilms are bacterial communities that are spatially structured and differentiate depending on environmental conditions. During biofilm formation, bacteria attached to a surface use cell-cell contacts to convey signals required for the coordination of biofilm morphogenesis. A critical ill-understood question is how bacteria can maintain both substrate adhesions and cell-cell contacts while elongating for division. Here, we developed time-resolved methods to measure substrate adhesion at single cell level during the formation of E. coli and P. aeruginosa microcolonies. We show that adhesion is polar and dynamic. Since adhesion maturates over one generation, bacteria can efficiently reattach while the microcolony grows. We developed a quantitative model for microcolony morphogenesis based on the dynamics of microscopic adhesive links. We show that polar adhesion generates round microcolonies which enhance cell to cell interactions. Our results evidence how subcellular features of the adhesion dynamics build the organization of bacterial communities at upper scale.
Self-assembly from atoms to life: A workshop presented by the UCLA Center for Biological Physics and the Institute for Complex Adaptive Matter in honor of Bill Gelbart’s 70th Birthday
October 3-5, 2016, Mesoamerican Centre for Theoretical Physics in Tuxtla Gutiérrez, Chiapas, Mexico
Marriott Tuxtla Gutierrez Hotel website
William ("Bill") Gelbart is Distinguished Professor of Chemistry and Biochemistry at the University of California, Los Angeles. He was trained as a physical chemical theorist, obtaining his BS at Harvard University in 1967 and his PhD at the University of Chicago in 1970.
The Mesoamerican Centre for Theoretical Physics (MCTP) was created from the collaboration between ICTP and the Autonomous University of Chiapas (UNACH) to establish a regional headquarters of the ICTP in Central America, the Caribbean and Mexico.
We hope to see you there in October.
Public lecture: Size Matters: Hydrodynamics and the problem of Multicellularity
Albert J. Libchaber, The Rockefeller University
CNSI Auditorium October 30, 2014 6:00pm
Coffee and dessert reception following the lecture
One of the great evolutionary challenges in the history of life is multi-cellularity: individual cells joining together to form more complex beings. Size and complexity offer clear advantages, but also present new problems involving the transport of nutrients into the organism. Some microbes can band together to create collectives, bridging the gap between the single cell lifestyle and true multi-cellularity. Such bacterial “superorganisms” have evolved structures remarkably similar to the cilia in our airways that they use to drive the flows necessary to feed the collective. We discuss this fascinating emergent behavior and examine the insights it provides for both hydrodynamics and the evolution of multi-cellularity.
Born in Paris, Dr. Libchaber received his undergraduate degree in mathematics and his Ph.D. in physics from the École Normale Supérieure at the University of Paris. He held physics faculty positions at the University of Chicago and Princeton before coming to Rockefeller in 1994. In 1999 Dr. Libchaber was awarded the Prix des Trois Physiciens from the Foundation of France. He received both the Wolf Foundation Prize in Physics and a John D. and Catherine T. MacArthur Foundation Fellowship. He is a member of the French Academy of Sciences, the American Academy of Arts and Sciences and the National Academy of Sciences.
Visit with Dr. Christoph F. Schmidt
Professor of Physics, Georg-August-Universität, Göttingen
April 22, 2014
Center for Biological Physics Laboratory
Please alevinechem.ucla.edu (contact the CBP director) to meet with him.
Dr. Schmidt's research interests include:
Motor proteins: physical principles of biological force generation, transport processes, "collective machines", mitotic spindle. Optical tweezers, single-molecule fluorescence.
DNA enzymes: replication, transcription, or packing of DNA, single-molecule experiments to investigate the dynamics of enzymes performing these functions.
Cytoskeletal polymers and cells: semiflexible proteins, non-proteinaceous soft matter model systems, in vitro and in living cells, functional principles of the cytoskeleton, cell division, cell locomotion, cell growth and mechanosensing. Microrheology, laser interferometry.
Protein shells, membranes and viruses: elastic properties of protein assemblies, sheets to tubes (microtubules) and capsids (viruses). Atomic force microscopy.
An Evening in the Lab: The Physics of Hearing
5:00 p.m. - Reception, Physics & Astronomy 3rd Floor Patio
6:00 p.m. - Lecture, Room 1-434A Physics and Astronomy Building
Followed by Lab Tours
Dolores Bozovic received her Ph.D. in Physics from Harvard University in 2001 for her work with Professor Michael Tinkham on the electron transport in carbon nanotubes. She then switched her focus from traditional condensed matter physics to biological physics during her postdoctoral studies at Rockefeller University (2001-2005), working in a sensory neuroscience laboratory under the direction of Professor Hudspeth. During that time, she explored the physics of hearing, particularly with respect to elucidating the role of nonlinear and active (molecular motor driven) mechanics underlying the ear’s remarkable performance.
She joined the UCLA physics department in the fall of 2005. Today, she is an Associate Professor in the Department of Physics and Astronomy and the California NanoSystems Institute. The Bozovic lab focuses on problems at the interface between physics and sensory neuroscience. In particular, they study how auditory and vestibular systems perform mechanical sensing down to the nanometer level. They also have the ability to simultaneously monitor the electrical response of these cells, and thus study the transduction of mechanics to neural impulses.
Click the image at right to view the 2014 Evening in the Lab brochure.
To submit your reservation please respond by email to jcaulfieldsupport.ucla.edu (subject: Reservation%3A%20An%20Evening%20at%20the%20Lab) (Jennifer Caulfield) or phone (310) 206-5621.
Special Lecture: Visualizing the Neuronal Orchestra: Imaging the Dynamics of Large-scale Neural Ensembles in Freely Behaving Mice
Mark Schnitzer (Stanford University)
Tuesday, May 28, 2013, 5:30pm
Physics & Astronomy Building 1-434A
Co-sponsored by the Center for Biological Physics and the UCLA Division of Physical Sciences
Abstract: The human brain consists of more than 100 billion neurons, a significant fraction of which are active simultaneously. Understanding how populations of individual neurons and glia contribute to animal behavior and brain disease has been a longstanding challenge—partly due to lack of appropriate brain imaging technology for visualizing cellular properties in awake, behaving animals. Using a miniaturized, integrated fluorescence microscope, which allows time-lapse imaging, Schnitzer’s team was able to image the cellular dynamics in the brains of freely behaving mice to observe how individual cells' coding properties evolve over weeks.
By performing calcium-imaging in freely behaving mice as they repeatedly explored a familiar environment, Schnitzer’s team tracked the activity of thousands of individual neurons that represent the spatial location of the mice, a.k.a. place cells. Further, they were able to image the activity of these same neurons over weeks. These data have revealed that spatial coding is highly dynamic, for on each day the neural representation of this environment involved a unique subset of neurons, yet the ensemble representation of space across weeks was accurate. This study illustrates the types of time-lapse studies on memory, ensemble neural dynamics, and coding that will now be possible in multiple brain regions of freely behaving rodents.
An Evening in the Lab: The Physics of Viruses
Professor William Gelbart and Robijn Bruinsma, January 2013
Center for Biological Physics Labpratory
Professors Gelbart and Bruinsma will present an overview of viruses, how physics plays an essential role in understanding their properties, and a report from the current research frontier in the field.
We will learn about the underlying physical processes that make viruses excellent geometers -- exploring the Platonic solids and related shapes. We will ask questions related to how genes pack into a virus and what this teaches us about the mechanics of life’s information storage molecules, RNA and DNA.
After the lecture, please join us for light refreshments. At that time we will break up into smaller groups to tour some of the world class microscopy facilities in the California Nanosystems Institute (CNSI) in the floors below you now.
These facilities, along with X-ray scattering experiments, provide new windows on the structure and mechanics of viruses.
Gene Surfing and Survival of the Luckiest
June 13, 2012 at 6:30 PM, reception to follow
Physics & Astronomy Building Auditorium PAB 1425, UCLA
David R. Nelson Lyman Laboratory of Physics
Population waves have played a crucial role in evolutionary history, as in the "out of Africa" hypothesis for human ancestry. Population geneticists and physicists are now developing methods for understanding how mutations, number fluctuations and selective advantages play out in such situations. Once the behavior of pioneer organisms at frontiers is understood, genetic markers can be used to infer information about growth, ancestral population size and colonization pathways. Neutral mutations optimally positioned at the front of a growing population wave can increase their abundance by "surfing" on the population wave. Experimental and theoretical studies of this effect will be presented, using bacteria and yeast as model systems.
He has given this as a public lecture at the Aspen center for physics. Click the poster image for an enlargement.
A brief biosketch of David Nelson
Education and Appointments:
1975 Ph.D., Cornell
1975-1978 Junior Fellow, Harvard Society of Fellows
1978- Professor of Physics, Harvard
1992-2005 Mallinckrodt Professor of Physics, Harvard
2005- Solomon Professor of Biophysics, Harvard
1984-1989 MacArthur Fellow
1993-1994 Guggenheim Fellow
1994 - Member, National Academy of Sciences
2003 Bardeen Prize for research in superconductivity
2004 Oliver Buckley Prize for soft condensed matter physics