Transverse Target Moments of SIDIS Vector Meson Production at HERMES

The on-going analysis of the transverse target ( A UT ) moments of the non-collinear cross section for SIDIS dihadron production at Hermes is discussed. These moments access the transversity ( h 1 ), pretzelocity ( h _ 1T ), and Sivers ( f _ 1T ) distribution functions convoluted with the unpolarized ( D 1 ) and Collins ( H 1 ) dihadron fragmentation functions. This measurement allows greater insight into the flavor decomposition and factorization of these functions. Additionally, the results will test the Lund/Artru fragmentation model, which predicts a sign change in the Collins function between pseudo-scalar mesons and certain partial waves of vector mesons. In preparation for this analysis, a new Monte Carlo generator has been written, and non-collinear fragmentation functions have been computed in a spectator model. Additionally, an alternate partial wave expansion is presented, providing a complementary interpretation of the fragmentation functions and allowing computation of the next-to-leading twist cross section.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90826/1/1742-6596_295_1_012044.pd

The intrinsic value of HFO features as a biomarker of epileptic activity

High frequency oscillations (HFOs) are a promising biomarker of epileptic brain tissue and activity. HFOs additionally serve as a prototypical example of challenges in the analysis of discrete events in high-temporal resolution, intracranial EEG data. Two primary challenges are 1) dimensionality reduction, and 2) assessing feasibility of classification. Dimensionality reduction assumes that the data lie on a manifold with dimension less than that of the feature space. However, previous HFO analyses have assumed a linear manifold, global across time, space (i.e. recording electrode/channel), and individual patients. Instead, we assess both a) whether linear methods are appropriate and b) the consistency of the manifold across time, space, and patients. We also estimate bounds on the Bayes classification error to quantify the distinction between two classes of HFOs (those occurring during seizures and those occurring due to other processes). This analysis provides the foundation for future clinical use of HFO features and buides the analysis for other discrete events, such as individual action potentials or multi-unit activity.Comment: 5 pages, 5 figure

Transverse Target Moments of Dihadron Production in Semi-inclusive Deep Inelastic Scattering at HERMES.

Pseudo-scalar meson production in semi-inclusive deep inelastic scattering (SIDIS) at HERMES has provided essential information towards the understanding of the transverse momentum dependent structure of the proton. SIDIS dihadron (hadron pair) production also provides access to the structure of the proton and is complimentary to that provided by pseudo-scalars production, as the same parton distribution functions are involved. For example, while pion and kaon final states allow access to flavor combinations of the Sivers distribution function, SIDIS $phi$ meson production (included in the $K^+K^-$ dihadron sample) allows direct access to the Sivers function for the strange quarks. The Sivers function for strange quarks is also related to the orbital angular momentum of the gluons. In the SIDIS cross section, the distribution functions are integrated with fragmentation functions for the respective final states. These fragmentation functions yield information regarding the quark hadronization process. Of particular interest, the Lund/Artru model of fragmentation makes specific predictions regarding the relation between results for dihadron and pseudo-scalar meson production for certain transverse momentum dependent moments. This dissertation presents the first transverse momentum dependent (non-collinear) analysis of the transverse target moments in SIDIS dihadron production, extracting results from the 2002-2005 HERMES data set for $pi^+pi^0$, $pi^+pi^-$, $pi^-pi^0$ and $K^+K^-$ dihadrons. A new transverse momentum dependent Monte Carlo generator, TMDGen, is also introduced. Additionally, several theoretical developments have been completed, including a new partial wave analysis of the fragmentation functions, computation of the next-to-leading twist dihadron cross section, and the first model calculation for transverse momentum dependent dihadron fragmentation functions.Ph.D.PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/86394/1/sgliske_1.pd

Preictal variability of high‐frequency oscillation rates in refractory epilepsy

ObjectiveHigh‐frequency oscillations (HFOs) have shown promising utility in the spatial localization of the seizure onset zone for patients with focal refractory epilepsy. Comparatively few studies have addressed potential temporal variations in HFOs, or their role in the preictal period. Here, we introduce a novel evaluation of the instantaneous HFO rate through interictal and peri‐ictal epochs to assess their usefulness in identifying imminent seizure onset.MethodsUtilizing an automated HFO detector, we analyzed intracranial electroencephalographic data from 30 patients with refractory epilepsy undergoing long‐term presurgical evaluation. We evaluated HFO rates both as a 30‐minute average and as a continuous function of time and used nonparametric statistical methods to compare individual and population‐level differences in rate during peri‐ictal and interictal periods.ResultsMean HFO rate was significantly higher for all epochs in seizure onset zone channels versus other channels. Across the 30 patients of our cohort, we found no statistically significant differences in mean HFO rate during preictal and interictal epochs. For continuous HFO rates in seizure onset zone channels, however, we found significant population‐wide increases in preictal trends relative to interictal periods. Using a data‐driven analysis, we identified a subset of 11 patients in whom either preictal HFO rates or their continuous trends were significantly increased relative to those of interictal baseline and the rest of the population.SignificanceThese results corroborate existing findings that HFO rates within epileptic tissue are higher during interictal periods. We show this finding is also present in preictal, ictal, and postictal data, and identify a novel biomarker of preictal state: an upward trend in HFO rate leading into seizures in some patients. Overall, our findings provide preliminary evidence that HFOs can function as a temporal biomarker of seizure onset.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163961/1/epi16680.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163961/2/epi16680_am.pd

25th annual computational neuroscience meeting: CNS-2016

The same neuron may play different functional roles in the neural circuits to which it belongs. For example, neurons in the Tritonia pedal ganglia may participate in variable phases of the swim motor rhythms [1]. While such neuronal functional variability is likely to play a major role the delivery of the functionality of neural systems, it is difficult to study it in most nervous systems. We work on the pyloric rhythm network of the crustacean stomatogastric ganglion (STG) [2]. Typically network models of the STG treat neurons of the same functional type as a single model neuron (e.g. PD neurons), assuming the same conductance parameters for these neurons and implying their synchronous firing [3, 4]. However, simultaneous recording of PD neurons shows differences between the timings of spikes of these neurons. This may indicate functional variability of these neurons. Here we modelled separately the two PD neurons of the STG in a multi-neuron model of the pyloric network. Our neuron models comply with known correlations between conductance parameters of ionic currents. Our results reproduce the experimental finding of increasing spike time distance between spikes originating from the two model PD neurons during their synchronised burst phase. The PD neuron with the larger calcium conductance generates its spikes before the other PD neuron. Larger potassium conductance values in the follower neuron imply longer delays between spikes, see Fig. 17.Neuromodulators change the conductance parameters of neurons and maintain the ratios of these parameters [5]. Our results show that such changes may shift the individual contribution of two PD neurons to the PD-phase of the pyloric rhythm altering their functionality within this rhythm. Our work paves the way towards an accessible experimental and computational framework for the analysis of the mechanisms and impact of functional variability of neurons within the neural circuits to which they belong

A taxonomy of seizure dynamotypes

複雑なてんかん発作を新規の数学モデルにより分類 --理論と臨床が一致--. 京都大学プレスリリース. 2020-07-28.Seizures are a disruption of normal brain activity present across a vast range of species and conditions. We introduce an organizing principle that leads to the first objective Taxonomy of Seizure Dynamics (TSD) based on bifurcation theory. The ‘dynamotype’ of a seizure is the dynamic composition that defines its observable characteristics, including how it starts, evolves and ends. Analyzing over 2000 focal-onset seizures from multiple centers, we find evidence of all 16 dynamotypes predicted in TSD. We demonstrate that patients’ dynamotypes evolve during their lifetime and display complex but systematic variations including hierarchy (certain types are more common), non-bijectivity (a patient may display multiple types) and pairing preference (multiple types may occur during one seizure). TSD provides a way to stratify patients in complement to present clinical classifications, a language to describe the most critical features of seizure dynamics, and a framework to guide future research focused on dynamical properties