Synaptic potentiation facilitates memory-like attractor dynamics in cultured in vitro hippocampal networks

Collective rhythmic dynamics from neurons is vital for cognitive functions such as memory formation but how neurons self-organize to produce such activity is not well understood. Attractor-based models have been successfully implemented as a theoretical framework for memory storage in networks of neurons. Activity-dependent modification of synaptic transmission is thought to be the physiological basis of learning and memory. The goal of this study is to demonstrate that using a pharmacological perturbation on in vitro networks of hippocampal neurons that has been shown to increase synaptic strength follows the dynamical postulates theorized by attractor models. We use a grid of extracellular electrodes to study changes in network activity after this perturbation and show that there is a persistent increase in overall spiking and bursting activity after treatment. This increase in activity appears to recruit more "errant" spikes into bursts. Lastly, phase plots indicate a conserved activity pattern suggesting that the network is operating in a stable dynamical state

Probing Ultrafast Dynamics of Bacterial Reaction Centers Using Two-Dimensional Electronic Spectroscopy

In the initial steps of photosynthesis, solar energy is converted to stable charge separated states with high efficiency. Understanding the relationship between structure and function in the photosynthetic reaction centers where these conversion steps take place could guide the development of more efficient artificial light harvesting systems. Reaction centers are complicated pigment-protein complexes with multiple spectrally overlapped absorption bands, making interpretation of spectroscopic data challenging. The sub-picosecond time scales involved in the energy transfer and charge separation processes present another challenge. Two-dimensional electronic spectroscopy (2DES) has proven to be a powerful tool for disentangling features in spectrally congested systems like reaction centers by resolving the optical response with respect to excitation and detection frequencies. 2DES also obtains the excitation frequency dependence without sacrificing time resolution, which is necessary to resolve energy transfer processes in reaction centers occurring on time scales faster than 100fs. We perform 2DES on bacterial reaction centers (BRCs) from the purple bacterium Rhodobacter capsulatus, using a degenerate optical parametric amplifier producing 12fs pulses with bandwidth spanning the broad near-IR absorption bands of the BRC. The 2D spectra are analyzed using several global analysis methods to extract the underlying energy transfer and charge separation kinetics, and we compare the results to published transient absorption studies on BRCs. Commonly used 2DES global analysis techniques proved inadequate for resolving specific branched and parallel reaction mechanisms. We developed an improved 2D kinetic fitting approach which employs a common set of basis spectra for all excitation frequencies, and uses information from the linear absorption spectrum and BRC structure to model the excitation frequency dependence of the 2D spectrum. Using the improved fitting method, we show that the entire time-dependent 2D spectrum is well-represented by a sequential reaction scheme with a single charge-separation pathway. We tested several proposed alternative reaction schemes involving branched charge separation pathways, and did not find compelling evidence from our data that favors a particular branched model. Based on this analysis, we conclude that our data supports the simpler, single pathway charge separation model.PHDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138758/1/aniedrin_1.pd

Up Close: From English to e-commerce

Kathryn Petralia \u2792 uses her liberal arts and sciences education to conquer the fintech worl

Oxygen uptake by the benthal sludge of a waste stabilization pond

This thesis describes the laboratory evaluation of the benthal sludge oxygen uptake of a 6.7 acre waste stabilization pond which has served a city of 2,400 population for a period of seven years. Special emphasis is directed toward the explanation of laboratory techniques developed for this study to measure the oxygen uptake rate. The effects on oxygen consumption of temperature, nature of sludge, initial oxygen tension, and sludge consolidation are discussed. Benthal sludge samples were taken from three locations in the pond. Oxygen consumption studies were conducted in a specially designed plastic cylinder which included a novel magnetic mixing system. BOD dilution water was employed as the supernatant over the sludge. Tests were run at 10, 22, and 35 degrees centigrade. Oxygen uptake was measured using an automatic oxygen analyzer and recorded on a continuous recorder. The data were converted to mg O₂ uptake per minute per square meter of sludge surface area. At the conclusion of each test, the supernatant was withdrawn and analyzed for COD, pH, alkalanity [sic], and suspended solids. Additional oxygen consumption tests were performed on the unsettled and settled supernatants in order to evaluate the oxygen uptakes exerted by the dissolved and suspended organic materials apart from the sludge phase. Results obtained from this study indicated that the oxygen uptake bore a definite relationship with volatile solids suspended from the sludge phase. The supernatant which was siphoned off during the mixing showed an oxygen consumption rate approaching that of the supernatant-sludge system. Temperature was also observed to have a significant effect on the oxygen uptake rate. At 35 degrees centigrade the dissolved oxygen in the test chamber was exhausted within a few minutes, while at 10 degrees centigrade the same sample took several days to deplete completely the oxygen content. The effects of the oxygen tension and the sludge compaction on the oxygen uptake were also evaluated. Neither oxygen tension or sludge compaction could be shown to have a significant effect on the rate of oxygen consumption --Abstract, Pages ii-iii

Dialing in the Numbers

Professional bike racing team seeks Furman\u27s assistance in medical testing

After the Aisle: Message on a Notecard

Mark Allen \u2790 and Susan Crowell \u2791 stay grounded in their written word

Saying Yes

Aneesh Borah \u2718 found his voice at Furman