1,720,960 research outputs found
Evidence for Long-Timescale Patterns of Synaptic Inputs in CA1 of Awake Behaving Mice
No full textRepeated sequences of neural activity are a pervasive feature of neural networks in vivo and in vitro. In the hippocampus, sequential firing of many neurons over periods of 100-300 ms reoccurs during behavior and during periods of quiescence. However, it is not known whether the hippocampus produces longer sequences of activity or whether such sequences are restricted to specific network states. Furthermore, whether long repeated patterns of activity are transmitted to single cells downstream is unclear. To answer these questions, we recorded intracellularly from hippocampal CA1 of awake, behaving male mice to examine both subthreshold activity and spiking output in single neurons. In eight of nine recordings, we discovered long (900 ms) reoccurring subthreshold fluctuations or “repeats.” Repeats generally were high-amplitude, nonoscillatory events reoccurring with 10msprecision. Using statistical controls, we determined that repeats occurred more often than would be expected from unstructured network activity (e.g., by chance). Most spikes occurred during a repeat, and when a repeat contained a spike, the spike reoccurred with precision on the order of ≤ 20 ms, showing that long repeated patterns of subthreshold activity are strongly connected to spike output. Unexpectedly, we found that repeats occurred independently of classic hippocampal network states like theta oscillations or sharp-wave ripples. Together, these results reveal surprisingly long patterns of repeated activity in the hippocampal network that occur nonstochastically, are transmitted to single downstream neurons, and strongly shape their output. This suggests that the timescale of information transmission in the hippocampal network is much longer than previously thought. Keywords: hippocampus; intracellular activity; subthreshold patternsNational Institutes of Health (U.S.) (Award 1DP1-NS-087724)National Institutes of Health (U.S.) (Award 1R01-MH-103910
Mesoscale activated states gate spiking in the awake brain
No full textThesis: Ph. D., Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2016.Cataloged from PDF version of thesis.Includes bibliographical references (pages 109-118).Neuronal action potentials ('spikes') are thought to be the fundamental units of information in the brain, hence the ability to record them and to understand their genesis is crucial to our comprehension of the biological underpinnings of our thoughts, memories, and feelings. Over the past several decades an extensive body of work has focused on the mechanisms and timescales over which neurons integrate inputs toward spike threshold. However, most of the work has been carried out in vitro or in silico, and our understanding of what underlies the generation of spike patterns in the awake brain has remained limited. Current models emphasize either seconds-scale global states shared by most neurons in a network, or the fast input integration occurring in single neurons over the few milliseconds preceding spiking, but it's not known whether these represent just the extremes of a continuum. Combining a virtual reality environment with an optimized robotic system for intracellular recordings we therefore analyzed the subthreshold dynamics leading to spiking in a variety of network and behavioral states in the hippocampus, a region known to be involved in spatial navigation, learning and memory, as well as in a model neocortical region, the primary somatosensory cortex. We discovered that the majority of spikes are in fact preceded not only by a fast, monotonic rise in voltage over a few milliseconds, consistent with fast input integration within a neuron, but also by a prolonged, gradual (tens to hundreds of ms) depolarization from baseline, which appeared to exert a gating function on subsequent inputs. Unlike the fast voltage rises, these gradual voltage rises are shared across some, but not all, neurons in the network. We propose that the gradual rises in membrane voltage constitute a novel form of activated state, intermediate both in timescale and in what proportion of neurons participate. By gating a neuron's ability to respond to subsequent inputs, these network-mediated intermediate, or mesoscale, activated states could play a key role in phenomena such as cell ensemble formation, gain modulation and selective attention.by Giovanni Talei Franzesi.Ph. D
Toward optogenetic control of neural synchrony : experimental results from the hippocampal slice model of gamma oscillations and computational modeling
No full textThesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 52-58).Ever since Hans Berger recorded the first human EEGs in humans and observed large, rhythmic 8 Hz field oscillations, neuroscientists have been intrigued by the pervasive presence of synchronized, regular patterns of the activity in the brain. A number of frequency bands, spanning from 0.1 to several hundred hertz have been described, and associated with particular functions and brain states. Not surprisingly, disruptions in such patterns have been postulated to be the mechanistic basis of a number of disorders, from schizophrenia to Parkinson's disease, to Alzheimer. Until now, however, virtually all evidence on the role of synchronous oscillations in brain functions has been merely correlative, that is, it has never been possible to selectively manipulate neural synchrony without altering other fundamental properties of the system and observing the functional outcome. This limit may now be overcome with the introduction of genetically targeted light-activeatable means of controlling neural activity, which allows spatially and temporally precise control of the activity of determined classes of neurons. Although the ultimate goal is to observe the functional, behavioral outcomes of modulating synchrony in awake animals, it's necessary first to develop such techniques in vitro, if we are to be able (given the current technological limitations) to extract useful "design principles" that can meaningfully generalize. A particularly well-studied, reliable and yet relevant in vitro model, is the hippocampal slice gamma oscillations model, so we have been focusing on those as a testbed, integrating experimental work with computational modeling. Among the previously undescribed capabilities we have gained in the process are: precisely resetting the phase of an ongoing gamma oscillation, altering its frequency, and modulating its amplitude.by Giovanni Talei Franzesi.S.M
A novel polymeric microelectrode array for highly parallel, long-term neuronal culture and stimulation
Get PDFThesis (M. Eng.)--Harvard-MIT Division of Health Sciences and Technology, 2008.Includes bibliographical references (leaves 51-56).Cell-based high-throughput screening is emerging as a disruptive technology in drug discovery; however, massively parallel electrical assaying of neurons and cardiomyocites has until now been prohibitively expensive. To address this limitation, we developed a scalable, all-organic 3D microelectrode array technology. The cheap, disposable arrays would be integrated into a fixed stimulation and imaging setup, potentially amenable to automated handling and data analysis. A combination of activity-dependent plasticity, made possible by independent control of up to 64 stimulating electrodes, and, eventually, of substrate chemical patterning would be employed to constrain the neuronal culture network connectivity. In order to ensure longterm survival of the cultures, a bottom feeder layer of glial cells would be grown. In addition to high-throughput screening application, the polymeric microelectrode arrays and integrated stimulation systems were designed to allow the long-term study of synaptic plasticity, combining excellent long-term culture capabilities with a unique ability to independently control each electrode stimulation pattern. The resulting activity could be monitored optically, e,g, with calcium or voltage sensitive dyes, and the images could be stored and processed (possibly even in real time) within the same environment (LabView) as the stimulator. To fabricate the polymeric microelectrode array, we prepare a multilayered mask substrate, by reversibly bonding together two sheets of implant-grade polydimethylsiloxane (PDMS) sheets, with or without a glass coverslip between them. Thanks to PDMS self-adhesive properties the various layers are held together stably but reversibly. The mask is then laser-patterned, using either a standard CO2 laser or a 193 nm excimer laser.(cont.) The mask can then be adhered onto a glassy carbon or ITO electrode, and polypyrrole, doped with either hyaluronic acid or sodium dodecylbenzesulfonic acid, can be electrodeposited through it. Finally, the construct is removed from the deposition bath and the upper, sacrificial mask layer carefully peeled away. This fabrication method allows exquisite control overall 3D electrode geometry, is suitable to produce structures between one and several hundred micrometers in diameter, either filled or tubular, and scales extremely well, so that, for example, 384 by 64 electrodes arrays can be patterned in just a few minutes and grown in the same time as a single array.by Giovanni Talei Franzesi.M.Eng
Design of a novel ACL prosthesis
No full textThesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (p. 17-19).Injuries to the anterior cruciate ligament (ACL) are extremely common (approximately 100,000 every year in the US) and result in greatly reduced mobility; although several surgical procedures have been devised to address this condition, they are far from being completely satisfactory. The golden standard is currently represented by tendon autografts which, however, result in considerable donor site morbidity. An ideal solution would be to use effective, off-the-shelf permanent prostheses: however, all such devices proposed to date have proved highly disappointing, because of poor long term stability and biocompatibility, and unphysiological mechanical behavior. To address both concerns a novel prosthetic device has been developed, employing crimped NiTi superelastic wire bundles. To achieve near-physiological mechanical behavior, the fiber geometry resembles (on a much larger scale) that of the collagen fibrils that naturally make up the ligament, using as a starting point the Comninou-Yannas crimped-fiber model.(cont.) NiTi (a superelastic alloy of titanium and nickel) has been tested and employed in a variety of biomedical settings and its excellent wear and biocompatibility characteristics make it a superior candidate for this application; the relevant literature has been reviewed and assessed. A detailed design for such prosthesis has been proposed, and a proof-of-principle model of the fiber geometry built and tested. The results obtained to date are encouraging and further testing, with a NiTi prototype should be carried out to validate our proposed design.by Giovanni Talei Franzesi.S.B
Automated whole-cell patch-clamp electrophysiology of neurons in vivo
Get PDFWhole-cell patch-clamp electrophysiology of neurons is a gold-standard technique for high-fidelity analysis of the biophysical mechanisms of neural computation and pathology, but it requires great skill to perform. We have developed a robot that automatically performs patch clamping in vivo, algorithmically detecting cells by analyzing the temporal sequence of electrode impedance changes. We demonstrate good yield, throughput and quality of automated intracellular recording in mouse cortex and hippocampus.National Institutes of Health (U.S.) (NIH EUREKA Award program (1R01NS075421))National Institutes of Health (U.S.) ((NIH) Director′s New Innovator Award (DP2OD002002)National Science Foundation (U.S.) ((NSF) CAREER award (CBET 1053233))New York Stem Cell Foundation (Robertson Neuroscience Award)Dr. Gerald Burnett and Marjorie BurnettNational Science Foundation (U.S.) (grant CISE 1110947)National Science Foundation (U.S.) (grant EHR 0965945)American Heart Association (10GRNT4430029
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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