131 research outputs found

    EEG-fMRI in epilepsy and sleep

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    This thesis used simultaneous electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) to investigate both epilepsy and sleep. Initially, EEG-fMRI was used in a cohort of patients with complex epilepsy referred from a tertiary epilepsy clinic for both pre-surgical evaluation and diagnostic reasons. The results suggest a limited utility of EEG-fMRI in the epilepsy clinic with a very complex patient group. Following on, investigation of early blood oxygen level dependent (BOLD) signal changes in a group of patients with focal epilepsy demonstrated potentially meaningful BOLD changes occurring six seconds prior to interictal epileptiform discharges, and modelling less than this six seconds can result in overlap of the haemodynamic response function used to model BOLD changes. The same analysis was used to model endogenously occurring sleep paroxysms; K-complexes (KCs), vertex sharp waves (VSWs) and sleep spindles (SSs), finding early BOLD signal changes with SSs in group data. Finally, KCs and VSWs were investigated in more detail in a group of participants under both sleep deprived and non-deprived conditions, demonstrating an increase in overall activation for both KCs and VSWs following sleep deprivation. Overall, we find early BOLD changes are not restricted to pathological events and sleep deprivation can enhance BOLD responses

    Early haemodynamic changes observed in patients with epilepsy, in a visual experiment and in simulations

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    Objective: The objective of this study was to investigate whether previously reported early blood oxygen level dependent (BOLD) changes in epilepsy could occur as a result of the modelling techniques rather than physiological changes. Methods: EEG-fMRI data were analysed from seven patients with focal epilepsy, six control subjects undergoing a visual experiment, in addition to simulations. In six separate analyses the event timing was shifted by either -9,-6,-3,+3,+6 or +9 s relative to the onset of the interictal epileptiform discharge (IED) or stimulus. Results: The visual dataset and simulations demonstrated an overlap between modelled haemodynamic response function (HRF) at event onset and at \ub13 s relative to onset, which diminished at \ub16 s. Pre-spike analysis at -6 s improved concordance with the assumed IED generating lobe relative to the standard HRF in 43% of patients. Conclusion: The visual and simulated dataset findings indicate a form of "temporal bleeding", an overlap between the modelled HRF at time 0 and at \ub13 s which attenuated at \ub16 s. Pre-spike analysis at -6 s may improve concordance. Significance: This form of analysis should be performed at 6 s prior to onset of IED to minimise temporal bleeding effect. The results support the presence of relevant BOLD responses occurring prior to IEDs

    The hippocampus as the switchboard between perception and memory.

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    Adaptive memory recall requires a rapid and flexible switch from external perceptual reminders to internal mnemonic representations. However, owing to the limited temporal or spatial resolution of brain imaging modalities used in isolation, the hippocampal–cortical dynamics supporting this process remain unknown. We thus employed an object-scene cued recall paradigm across two studies, including intracranial electroencephalography (iEEG) and high-density scalp EEG. First, a sustained increase in hippocampal high gamma power (55 to 110 Hz) emerged 500 ms after cue onset and distinguished successful vs. unsuccessful recall. This increase in gamma power for successful recall was followed by a decrease in hippocampal alpha power (8 to 12 Hz). Intriguingly, the hippocampal gamma power increase marked the moment at which extrahippocampal activation patterns shifted from perceptual cue toward mnemonic target representations. In parallel, source-localized EEG alpha power revealed that the recall signal progresses from hippocampus to posterior parietal cortex and then to medial prefrontal cortex. Together, these results identify the hippocampus as the switchboard between perception and memory and elucidate the ensuing hippocampal–cortical dynamics supporting the recall process.post-print1844 K

    Study of J /ψ production in Jets

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    The production of J/ψ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the J/ψ meson, z(J/ψ)≡pT(J/ψ)/pT(jet), is measured using jets with pT(jet)>20 GeV in the pseudorapidity range 2.5<η(jet)<4.0. The observed z(J/ψ)distribution for J/ψ mesons produced in b-hadron decays is consistent with expectations. However, the results for prompt J/ψ production do not agree with predictions based on fixed-order nonrelativistic QCD. This is the first measurement of the pT fraction carried by prompt J/ψ mesons in jets at any experiment

    Hippocampal neurons code individual episodic memories in humans

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    The hippocampus is an essential hub for episodic memory processing. However, how human hippocampal single neurons code multi-element associations remains unknown. In particular, it is debated whether each hippocampal neuron represents an invariant element within an episode or whether single neurons bind together all the elements of a discrete episodic memory. Here we provide evidence for the latter hypothesis. Using single-neuron recordings from a total of 30 participants, we show that individual neurons, which we term episode-specific neurons, code discrete episodic memories using either a rate code or a temporal firing code. These neurons were observed exclusively in the hippocampus. Importantly, these episode-specific neurons do not reflect the coding of a particular element in the episode (that is, concept or time). Instead, they code for the conjunction of the different elements that make up the episode

    Study of J=ψ Production in Jets

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    The production of J/ψ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the J/ψ meson, z(J/ψ)≡p[subscript T](J/ψ)/p[subscript T](jet), is measured using jets with p[subscript T](jet) > 20  GeV in the pseudorapidity range 2.5<η(jet)<4.0. The observed z(J/ψ) distribution for J/ψ mesons produced in b-hadron decays is consistent with expectations. However, the results for prompt J/ψ production do not agree with predictions based on fixed-order nonrelativistic QCD. This is the first measurement of the p[subscript T] fraction carried by prompt J/ψ mesons in jets at any experiment.National Science Foundation (U.S.

    Search for long-lived scalar particles in B + → K + χ ( ÎŒ + ÎŒ − ) decays

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    A search for a long-lived scalar particle χ is performed, looking for the decay B[superscript +]→K[superscript +]χ with χ→Ό[superscript +]ÎŒ[superscript -] in pp collision data corresponding to an integrated luminosity of 3  fb[superscript -1], collected by the LHCb experiment at center-of-mass energies of √s =7 and 8 TeV. This new scalar particle, predicted by hidden sector models, is assumed to have a narrow width. The signal would manifest itself as an excess in the dimuon invariant mass distribution over the Standard Model background. No significant excess is observed in the accessible ranges of mass 250<m(χ)<4700  MeV/c[superscript 2] and lifetime 0.1<τ(χ)<1000  ps. Upper limits on the branching fraction B(B[superscript +]→K[superscript +]χ(ÎŒ[superscript +]ÎŒ[superscript -])) at 95% confidence level are set as a function of m(χ) and τ(χ), varying between 2×10[superscript -10] and 10[superscript -7]. These are the most stringent limits to date. The limits are interpreted in the context of a model with a light inflaton particle.National Science Foundation (U.S.

    Search for the decays Bs0→τ+τ− and B0→τ+τ−

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    A search for the rare decays B0 s → Ï„ĂŸÏ„âˆ’ and B0 → Ï„ĂŸÏ„âˆ’ is performed using proton–proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3 fb−1 collected in 2011 and 2012. The τ leptons are reconstructed through the decay τ− → Ï€âˆ’Ï€ĂŸÏ€âˆ’ÎœÏ„. Assuming no contribution from B0 → Ï„ĂŸÏ„âˆ’ decays, an upper limit is set on the branching fraction BĂ°B0 s → Ï„ĂŸÏ„âˆ’Ăž &lt; 6.8 × 10−3 at the 95% confidence level. If instead no contribution from B0 s → Ï„ĂŸÏ„âˆ’ decays is assumed, the limit is BĂ°B0 → Ï„ĂŸÏ„âˆ’Ăž &lt; 2.1 × 10−3 at the 95% confidence level. These results correspond to the first direct limit on BĂ°B0 s → Ï„ĂŸÏ„âˆ’Ăž and the world’s best limit on BĂ°B0 → Ï„ĂŸÏ„âˆ’Ăž

    Measurements of prompt charm production cross-sections in pp collisions at root s=13 TeV

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    Production cross-sections of prompt charm mesons are measured with the first data from pp collisions at the LHC at a centre-of-mass energy of 13 TeV. The data sample corresponds to an integrated luminosity of 4.98 +/- 0.19 pb(-1) collected by the LHCb experiment. The production cross-sections of D-0, D+, D (s) (+) , and D*+ mesons are measured in bins of charm meson transverse momentum, p(T), and rapidity, y, and cover the range 0 &lt;p(T) &lt;15GeV/c and 2.0 &lt;y &lt;4.5. The inclusive cross-sections for the four mesons, including charge conjugation, within the range of 1 &lt;p(T) &lt;8 GeV/c are found to besigma(pp -&gt; D-0 X) = 2460 +/- 3 +/- 130 mu bsigma(pp -&gt; D+ X) = 1000 +/- 3 +/- 110 mu bsigma(pp -&gt; Ds+X) = 460 +/- 13 +/- 100 mu bsigma(pp -&gt; D*+ X) = 880 +/- 5 +/- 140 mu bwhere the uncertainties are due to statistical and systematic uncertainties, respectively.</p

    Observation of the Decay Ξb−→pK−K−

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    Decays of the Ξ − b and Ω − b baryons to the charmless final states p h − h ' − , where h ( ' ) denotes a kaon or pion, are searched for with the LHCb detector. The analysis is based on a sample of proton-proton collision data collected at center-of-mass energies √ s = 7 and 8 TeV, corresponding to an integrated luminosity of 3     fb − 1 . The decay Ξ − b → p K − K − is observed with a significance of 8.7 standard deviations, and evidence at the level of 3.4 standard deviations is found for the Ξ − b → p K − π − decay. Results are reported, relative to the B − → K + K − K − normalization channel, for the products of branching fractions and b -hadron production fractions. The branching fractions of Ξ − b → p K − π − and Ξ − b → p π − π − relative to Ξ − b → p K − K − decays are also measured
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