Multi-scale model of neural entrainment by transcranial alternating current stimulation in realistic cortical anatomy.

In this paper, numerical simulations using the finite element method (FEM), were performed to study the electric field (E-field) distributions along ice-covered 220 kV composite insulator with different sizes of grading rings at the high voltage (HV) end. Combining with energized ice accretion tests in artificial climate chamber, the influence of size parameters of grading ring on icing characteristics of composite insulator was analyzed. The results show that the ice accretion of composite insulator with grading ring was more uniform than that without grading ring. With the increase of diameter of grading ring, the E-field distribution along the arcing distance becomes more uniform. The change of pipe diameter has no obvious effect on the E-field distribution at the HV end. The increase of height of grading ring could accordingly lift the main position of E-field distortion and thus enhance the E-field intensity along the string. The ice accretion uniformity, situation of shed space bridged by icicle and the variation of ice weight of composite insulator obtain by icing tests were well accordant with the E-field calculation results.

SiC-based converters can achieve much higher voltage rating and power density than Si- based ones. Therefore, electric field (E-field) intensity inside SiC-based converters can become significantly high and initial partial discharges, especially along the exposed metal or insulator to air interfaces. To achieve discharge free by design, E-field intensity and insulation space in air need be carefully analyzed and well managed. Due to the complicated structure of power converters, sharp edges and corners cannot be fully avoided. Thus, E-field management should be considered for such critical regions, in order to make the E-field distribution more uniform and shrink the insulation size. In this article, by using the self-made medium-voltage power electronics building block (PEBB) as an example, critical regions for insulation design are identified. Then focusing on the region between the cooling system and the heatsink, the influence on E-field distribution with different guard rings' shape, size, and location, is demonstrated. Following the simulation analysis and design comparison, six guard rings are fabricated and experimentally verified. Therefore, a methodology about E-field management for power converters is provided in this article, including critical region analysis, design comparison, guard ring fabrication, and experimental verification.

In order to study the E-field distribution and design a practical shielding device for the ±1100 kV post insulator, follow computer simulation was made. First, the whole indoor DC yard model was established and the E-field intensity of post insulator under different shielding fittings was obtained through FEM and sub-model technique. The maximum E-field strength of the flat-bottom fitting was lowest, only 584V/mm, 15.0% lower than spherical type, 22.6% lower than mushroom-head type and 32.1% lower than double-ring type. Next, the concave-bottom device was proposed to further reduce E-field intensity and satisfy practical installation. The E-field distribution of both the flat-bottom fitting and the concave-bottom fitting were calculated under 2600kV impulse voltage, different chamfer radius and different opening diameter. When the concave-bottom device opening diameter was 360mm and chamfer radius was 100mm, the maximum E-field intensity was 952V/mm on opening chamfer, 1095V/mm on insulator sheath surface and 1988V/mm on shield surface. Compare to the flat-bottom fitting, the concave-bottom device could significantly reduce the maximum E-field intensity on the opening hole and insulator sheath surface, though the maximum E-field intensity on the shield surface was little higher. Furthermore, the change trend of geometric parameters on the E-field distribution was summarized. For the flat-bottom fitting, the maximum E-field intensity increased with the opening diameter increasing. However, for the concave-bottom fitting, there was inverse proportional relationship between the maximum E-field intensity and the opening diameter. Based on the results, the concave-bottom fitting was firstly recommended for the installation of ±1100 kV DC post insulator. It could provide reference for the ±1100 kV UHVDC construction.

Frequency-Band Coupling in Surface EEG Reflects Spiking Activity in Monkey Visual Cortex

BackgroundTranscranial direct current stimulation (tDCS) is a non-invasive brain stimulation modality that can alter cortical excitability. However, it remains unclear how the subcellular elements of different neuron types are polarized by specific electric field (E-field) distributions. ObjectiveTo quantify neuronal polarization generated by tDCS in a multi-scale computational model. MethodsWe embedded layer-specific, morphologically-realistic cortical neuron models in a finite element model of the E-field in a human head and simulated steady-state polarization generated by conventional primary-motor-cortex–supraorbital (M1–SO) and 4 × 1 high-definition (HD) tDCS. We quantified somatic, axonal, and dendritic polarization of excitatory pyramidal cells in layers 2/3, 5, and 6, as well as inhibitory interneurons in layers 1 and 4 of the hand knob. ResultsAxonal and dendritic terminals were polarized more than the soma in all neurons, with peak axonal and dendritic polarization of 0.92 mV and 0.21 mV, respectively, compared to peak somatic polarization of 0.07 mV for 1.8 mA M1–SO stimulation. Both montages generated regions of depolarization and hyperpolarization beneath the M1 anode; M1–SO produced slightly stronger, more diffuse polarization peaking in the central sulcus, while 4 × 1 HD produced higher peak polarization in the gyral crown. The E-field component normal to the cortical surface correlated strongly with pyramidal neuron somatic polarization (R2>0.9), but exhibited weaker correlations with peak pyramidal axonal and dendritic polarization (R2:0.5–0.9) and peak polarization in all subcellular regions of interneurons (R2:0.3–0.6). Simulating polarization by uniform local E-field extracted at the soma approximated the spatial distribution of tDCS polarization but produced large errors in some regions (median absolute percent error: 7.9 %). ConclusionsPolarization of pre- and postsynaptic compartments of excitatory and inhibitory cortical neurons may play a significant role in tDCS neuromodulation. These effects cannot be predicted from the E-field distribution alone but rather require calculation of the neuronal response.

Auditory stimuli are often rhythmic in nature. Brain activity synchronizes with auditory rhythms via neural entrainment, and entrainment seems to be beneficial for auditory perception. However, it is not clear to what extent neural entrainment in the auditory system is reliable over time, which is a necessary prerequisite for targeted intervention. The current study aimed to establish the reliability of neural entrainment over time and to predict individual differences in auditory perception from associated neural activity. Across two different sessions, human listeners (21 females, 17 males) detected silent gaps presented at different phase locations of a 2 Hz frequency-modulated (FM) noise while EEG activity was recorded. As expected, neural activity was entrained by the 2 Hz FM noise. Moreover, gap detection was sinusoidally modulated by the phase of the 2 Hz FM into which the gap fell. Critically, both the strength of neural entrainment as well as the modulation of performance by the stimulus rhythm were highly reliable over sessions. Moreover, gap detection was predictable from pregap neural 2 Hz phase and alpha amplitude. Our results demonstrate that neural entrainment in the auditory system and the resulting behavioral modulation are reliable over time, and both entrained delta and nonentrained alpha oscillatory activity contribute to near-threshold stimulus perception. The latter suggests that improving auditory perception might require simultaneously targeting entrained brain rhythms as well as the alpha rhythm.SIGNIFICANCE STATEMENT Neural activity synchronizes to the rhythms in sounds via neural entrainment, which seems to be important for successful auditory perception. A natural hypothesis is that improving neural entrainment, for example, via brain stimulation, should benefit perception. However, the extent to which neural entrainment is reliable over time, a necessary prerequisite for targeted intervention, has not been established. Using electroencephalogram recordings, we demonstrate that both neural entrainment to FM sounds and stimulus-induced behavioral modulation are reliable over time. Moreover, moment-by-moment fluctuations in perception are best predicted by entrained delta phase and nonentrained alpha amplitude. This work suggests that improving auditory perception might require simultaneously targeting entrained brain rhythms as well as the alpha rhythm.

[This corrects the article on p. 216 in vol. 3, PMID: 22833726.].

Investigation on picosecond laser-induced damage in HfO2/SiO2 high-reflective coatings

A study of microwave-enhanced catalytic degradation of benzene using Co-Mn metal oxides combined with numerical simulation

Brain stimulation and neural entrainment rely on noninvasive techniques that, applied to sports, might enhance brain activity in healthy athletes to improve their physical performance. In the past, several studies have employed stimulation procedures, either during athletic training or during separate sessions, to enhance physical and mental performance. In this chapter, we review the available physiological and behavioural studies to clarify if and under which conditions brain stimulation and neural entrainment might enhance athletic performance. Even though many studies suffer from small sample size, the outcomes, compared to traditional training procedures, seem to provide notable advantages with regard to motor learning, motion perception, muscular strength or decrements in muscle fatigue. Further, these techniques seem to be useful in fine-tuning crucial aspects of competitive sports such as speeding up the learning rate in specific motor skills and better sleeping quality. Although more research is needed to fully understand the effects brain stimulation and neural entrainment exerted on athletic performance, we conclude that these emerging techniques are a promising and legitimate tool to enhance physical and mental performances in sports.

Reliable quantification of neural entrainment to rhythmic auditory stimulation: simulation and experimental validation

The ability to discover regularities in the environment, such as syllable patterns in speech, is known as statistical learning. Previous studies have shown that statistical learning is accompanied by neural entrainment, in which neural activity temporally aligns with repeating patterns over time. However, it is unclear whether these rhythmic neural dynamics play a functional role in statistical learning or whether they largely reflect the downstream consequences of learning, such as the enhanced perception of learned words in speech. To better understand this issue, we manipulated participants' neural entrainment during statistical learning using continuous rhythmic visual stimulation. Participants were exposed to a speech stream of repeating nonsense words while viewing either (1) a visual stimulus with a "congruent" rhythm that aligned with the word structure, (2) a visual stimulus with an incongruent rhythm, or (3) a static visual stimulus. Statistical learning was subsequently measured using both an explicit and implicit test. Participants in the congruent condition showed a significant increase in neural entrainment over auditory regions at the relevant word frequency, over and above effects of passive volume conduction, indicating that visual stimulation successfully altered neural entrainment within relevant neural substrates. Critically, during the subsequent implicit test, participants in the congruent condition showed an enhanced ability to predict upcoming syllables and stronger neural phase synchronization to component words, suggesting that they had gained greater sensitivity to the statistical structure of the speech stream relative to the incongruent and static groups. This learning benefit could not be attributed to strategic processes, as participants were largely unaware of the contingencies between the visual stimulation and embedded words. These results indicate that manipulating neural entrainment during exposure to regularities influences statistical learning outcomes, suggesting that neural entrainment may functionally contribute to statistical learning. Our findings encourage future studies using non-invasive brain stimulation methods to further understand the role of entrainment in statistical learning.

A comprehensive understanding of the neural mechanisms of cognitive function requires an understanding of how neural representations are transformed across different scales of neural organization: from within local microcircuits to across different brain areas. However, the neural transformations within the local microcircuits are poorly understood. Particularly, the role that two main cell classes of neurons in cortical microcircuits (i.e. pyramidal neurons and interneurons) have in auditory behaviour and cognition remains unknown. In this study, we tested the hypothesis that pyramidal cells and interneurons in the auditory cortex play a differential role in auditory categorization. To test this hypothesis, we recorded single-unit activity from the auditory cortex of rhesus monkeys while they categorized speech sounds. Based on the spike-waveform shape, a neuron was classified as either a narrow-spiking putative interneuron or a broad-spiking putative pyramidal neuron. We found that putative interneurons and pyramidal neurons in the auditory cortex differentially coded category information: interneurons were more selective for auditory categories than pyramidal neurons. These differences between cell classes may be an essential property of the neural computations underlying auditory categorization within the microcircuitry of the auditory cortex.

Neural entrainment is the phase synchronization of a population of neurons to an external rhythmic stimulus such as applied in the context of transcranial alternating current stimulation (tACS). tACS can cause profound effects on human behavior. However, there remain a significant number of studies that find no behavioral effect when tACS is applied to human subjects. To investigate this discrepancy, we applied time sensitive phase lock value (PLV) based analysis to single unit data from the rat motor cortex. The analysis revealed that detection of neural entrainment depends critically on the epoch length within which spiking information is accumulated. Increasing the epoch length allowed for detection of progressively weaker levels of neural entrainment. Based on this single unit analysis, we hypothesized that tACS effects on human behavior would be more easily detected in a behavior paradigm which utilizes longer epoch lengths. We tested this by using tACS to entrain tremor in patients and healthy volunteers. When the behavioral data were analyzed using short duration epochs tremor entrainment effects were not detectable. However, as the epoch length was progressively increased, weak tremor entrainment became detectable. These results suggest that tACS behavioral paradigms that rely on the accumulation of information over long epoch lengths will tend to be successful at detecting behavior effects. However, tACS paradigms that rely on short epoch lengths are less likely to detect effects.

According to the sensory-neural Temporal Sampling theory of developmental dyslexia, neural sampling of auditory information at slow rates (<10 Hz, related to speech rhythm) is atypical in dyslexic individuals, particularly in the delta band (0.5–4 Hz). Here we examine the underlying neural mechanisms related to atypical sampling using a simple repetitive speech paradigm. Fifty-one children (21 control children [15M, 6F] and 30 children with dyslexia [16M, 14F]) aged 9 years with or without developmental dyslexia watched and listened as a ‘talking head’ repeated the syllable “ba” every 500 ms, while EEG was recorded. Occasionally a syllable was “out of time”, with a temporal delay calibrated individually and adaptively for each child so that it was detected around 79.4% of the time by a button press. Phase consistency in the delta (rate of stimulus delivery), theta (speech-related) and alpha (control) bands was evaluated for each child and each group. Significant phase consistency was found for both groups in the delta and theta bands, demonstrating neural entrainment, but not the alpha band. However, the children with dyslexia showed a different preferred phase and significantly reduced phase consistency compared to control children, in the delta band only. Analysis of pre- and post-stimulus angular velocity of group preferred phases revealed that the children in the dyslexic group showed an atypical response in the delta band only. The delta-band pre-stimulus angular velocity (−130 ms to 0 ms) for the dyslexic group appeared to be significantly faster compared to the control group. It is concluded that neural responding to simple beat-based stimuli may provide a unique neural marker of developmental dyslexia. The automatic nature of this neural response may enable new tools for diagnosis, as well as opening new avenues for remediation.