Relaxing-Precessional Magnetization Switching

A new way of magnetization switching employing both the spin-transfer torque and the torque by a magnetic field is proposed. The solution of the Landau-Lifshitz-Gilbert equation shows that the dynamics of the magnetization in the initial stage of the switching is similar to that in the precessional switching, while that in the final stage is rather similar to the relaxing switching. We call the present method the relaxing-precessional switching. It offers a faster and lower-power-consuming way of switching than the relaxing switching and a more controllable way than the precessional switching

Stability of Bose-Einstein Condensates Confined in Traps

Bose-Einstein condensation has been realized in dilute atomic vapors. This achievement has generated immerse interest in this field. Presented is a review of recent theoretical research into the properties of trapped dilute-gas Bose-Einstein condensates. Among them, stability of Bose-Einstein condensates confined in traps is mainly discussed. Static properties of the ground state are investigated by use of the variational method. The anlysis is extended to the stability of two-component condensates. Time-development of the condensate is well-described by the Gross-Pitaevskii equation which is known in nonlinear physics as the nonlinear Schr\"odinger equation. For the case that the inter-atomic potential is effectively attractive, a singularity of the solution emerges in a finite time. This phenomenon which we call collapse explains the upper bound for the number of atoms in such condensates under traps.Comment: 74 pages with 12 figures, submitted to the review section of International Journal of Modern Physics

Gamma-band auditory steady-state response after frontal tDCS: A double-blind, randomized, crossover study

<div><p>The effects of transcranial direct current stimulation (tDCS) likely depend on cortical N-methyl-D-aspartic acid (NMDA) neurotransmission; however, no previous studies have reported tDCS-mediated modulation of cortical NMDA neurotransmission in humans. The gamma-band auditory steady-state response (ASSR) to a 40 Hz stimulation likely reflects the integrity of cortical NMDA neurotransmission. The present study tested whether the effect of tDCS is reflected in gamma-band ASSRs during a 40 Hz stimulation. Using a double-blind, randomized, crossover study, we performed magnetoencephalography (MEG) and measured the ASSR in 24 healthy participants during 40 Hz of auditory stimulation after prefrontal tDCS (2 mA) or sham (i.e., placebo) treatment. Our results failed to reveal significant differences in any brain between the two conditions after the application of a frequency of approximately 40 Hz. Based on these results, the ASSR is an insufficient method to detect the effect of tDCS on cortical NMDA neurotransmission. Unexpectedly, the results revealed an enhanced beta-band event-related spectral perturbation (ERSP) in the left motor cortex after tDCS compared with that observed after the sham stimuli. Given that beta-band oscillations reflect many functions in motor cortices, the tDCS for the frontal areas had some effect on the left motor cortex while the participants were focusing on not pressing the button with their right index finger. An additional study with an adequate psychological task is necessary to draw a conclusion regarding this unexpected result.</p></div

Magnetoencephalography Imaging Reveals Abnormal Information Flow in Temporal Lobe Epilepsy.

Background/Introduction: Widespread network disruption has been hypothesized to be an important predictor of outcomes in patients with refractory temporal lobe epilepsy (TLE). Most studies examining functional network disruption in epilepsy have largely focused on the symmetric bidirectional metrics of the strength of network connections. However, a more complete description of network dysfunction impacts in epilepsy requires an investigation of the potentially more sensitive directional metrics of information flow. Methods: This study describes a whole-brain magnetoencephalography-imaging approach to examine resting-state directional information flow networks, quantified by phase-transfer entropy (PTE), in patients with TLE compared with healthy controls (HCs). Associations between PTE and clinical characteristics of epilepsy syndrome are also investigated. Results: Deficits of information flow were specific to alpha-band frequencies. In alpha band, while HCs exhibit a clear posterior-to-anterior directionality of information flow, in patients with TLE, this pattern of regional information outflow and inflow was significantly altered in the frontal and occipital regions. The changes in information flow within the alpha band in selected brain regions were correlated with interictal spike frequency and duration of epilepsy. Conclusions: Impaired information flow is an important dimension of network dysfunction associated with the pathophysiological mechanisms of TLE

<i>T</i>-maps of the differences in ERSPs (upper row) and ITPCs (lower row) in the transverse temporal gyrus between the tDCS and sham conditions.

<p>Color indicates <i>t</i>-values at each time-frequency point. No significant differences were found in either ERSPs or ITPCs when the statistical threshold was set to <i>p</i> < 0.05 with an FDR correction.</p

ERSPs in the left precentral gyrus.

<p>(A) <i>T</i>-maps of the differences in the ERSPs between the tDCS and sham conditions. The threshold of <i>p</i> < 0.05 (FDR corrected) is highlighted with a red rectangle. The color indicates the <i>t</i>-values at each time-frequency point. Significantly higher ERSPs were observed in the beta-band (20 Hz; a red rectangle) after tDCS than after the sham condition. (B) The grand average of the time-frequency maps of ERSPs in the left precentral gyrus under both tDCS (upper row) and sham (lower row) conditions. In each map, the x-axis indicates time (ms), and the y-axis indicates frequency (Hz). The color indicates ERSPs at each time-frequency point (reflected as the percentage change from baseline).</p

The grand average of the time-frequency maps for the ITPC in the transverse temporal gyrus under both tDCS and sham conditions.

<p>In each map, the x-axis indicates time (ms), and the y-axis indicates frequency (Hz). The color indicates the ITPCs at each time-frequency point. The ITPC peak in the gamma-band (40 Hz) was clearly observed during the 40 Hz auditory stimulation.</p

Study design: A double-blind, randomized, crossover study.

<p>Twenty-four participants were recruited and randomly assigned to receive either tDCS or sham stimulation during the first trial. After an interval of at least four weeks, the second trial was conducted. The order of the two stimulation conditions (i.e., tDCS or sham) was counterbalanced across participants. After delivering one of the two stimulus conditions, ASSRs were recorded using MEG. We excluded two participants from the statistical analysis because they met the exclusion criteria. ASSR, auditory steady-state response.</p

Electrode placement.

<p>(A) Anodal (F3) and cathodal (F4) electrodes marked on the scalp surface. (B) The computational simulation of brain current flow during the delivery of the tDCS. Major changes in the brain current flow were observed in the dorsal-frontal areas during stimulation [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193422#pone.0193422.ref037" target="_blank">37</a>].</p

Cortical Synchrony and Information Flow during Transition from Wakefulness to Light Non-Rapid Eye Movement Sleep.

Sleep is a highly stereotyped phenomenon, requiring robust spatiotemporal coordination of neural activity. Understanding how the brain coordinates neural activity with sleep onset can provide insights into the physiological functions subserved by sleep and the pathologic phenomena associated with sleep onset. We quantified whole-brain network changes in synchrony and information flow during the transition from wakefulness to light non-rapid eye movement (NREM) sleep, using MEG imaging in a convenient sample of 14 healthy human participants (11 female; mean 63.4 years [SD 11.8 years]). We furthermore performed computational modeling to infer excitatory and inhibitory properties of local neural activity. The transition from wakefulness to light NREM was identified to be encoded in spatially and temporally specific patterns of long-range synchrony. Within the delta band, there was a global increase in connectivity from wakefulness to light NREM, which was highest in frontoparietal regions. Within the theta band, there was an increase in connectivity in fronto-parieto-occipital regions and a decrease in temporal regions from wakefulness to Stage 1 sleep. Patterns of information flow revealed that mesial frontal regions receive hierarchically organized inputs from broad cortical regions upon sleep onset, including direct inflow from occipital regions and indirect inflow via parieto-temporal regions within the delta frequency band. Finally, biophysical neural mass modeling demonstrated changes in the anterior-to-posterior distribution of cortical excitation-to-inhibition with increased excitation-to-inhibition model parameters in anterior regions in light NREM compared with wakefulness. Together, these findings uncover whole-brain corticocortical structure and the orchestration of local and long-range, frequency-specific cortical interactions in the sleep-wake transition.SIGNIFICANCE STATEMENT Our work uncovers spatiotemporal cortical structure of neural synchrony and information flow upon the transition from wakefulness to light non-rapid eye movement sleep. Mesial frontal regions were identified to receive hierarchically organized inputs from broad cortical regions, including both direct inputs from occipital regions and indirect inputs via the parieto-temporal regions within the delta frequency range. Biophysical neural mass modeling revealed a spatially heterogeneous, anterior-posterior distribution of cortical excitation-to-inhibition. Our findings shed light on the orchestration of local and long-range cortical neural structure that is fundamental to sleep onset, and support an emerging view of cortically driven regulation of sleep homeostasis