Excitation Patterns Research Articles

A common framework for single-molecule localization using sequential structured illumination

Localization of single fluorescent molecules is key for physicochemical and biophysical measurements, such as single-molecule tracking and super-resolution imaging by single-molecule localization microscopy. Over the last two decades, several methods have been developed in which the position of a single emitter is interrogated with a sequence of spatially modulated patterns of light. Among them, the recent MINFLUX technique outstands for achieving a ∼10-fold improvement compared with wide-field camera-based single-molecule localization, reaching ∼1–2 nm localization precision at moderate photon counts. Here, we present a common framework for this type of measurement. Using the Cramér-Rao bound as a limit for the achievable localization precision, we benchmark reported methods, including recent developments, such as MINFLUX and MINSTED, and long-established methods, such as orbital tracking. In addition, we characterize two new proposed schemes, orbital tracking and raster scanning, with a minimum of intensity. Overall, we found that approaches using an intensity minimum have a similar performance in the central region of the excitation pattern, independent of the geometry of the excitation pattern, and that they outperform methods featuring an intensity maximum.

Revealing the Three-Dimensional Orientation and Interplay between Plasmons and Interband Transitions for Single Gold Bipyramids by Photoluminescence Excitation Pattern Imaging

Gold bipyramids (AuBPs) attract significant attention due to the large enhancement of the electric field around their sharp tips and well-defined tunability of their plasmon resonances. Excitation ...

Image reconstruction approach for a high space-bandwidth product structured illumination microscopy system

Conventional structured illumination microscopy (SIM) utilizes a sinusoidal excitation pattern of frequency within the detection passband and provides a maximum of twofold resolution enhancement over the diffraction limit. A transmission approach proposed in an earlier publication [J. Phys. D 53, 044006 (2019)JPAPBE0022-372710.1088/1361-6463/ab4e68] to further improve the lateral resolution requires sequential higher frequency illumination patterns. However, the existing reconstruction algorithms fail to deliver appropriate reconstruction when the excitation frequency lies far from the passband boundary. Here, we present a correlation-based SIM reconstruction approach for sequential high-frequency illumination patterns even if the pattern frequency lies far from the passband limit. The scheme can be suitably implemented in a variety of custom-built systems where illumination frequency lies beyond the passband support (e.g., non-linear SIM and plasmonic SIM).

Bumps, chimera states, and Turing patterns in systems of coupled active rotators

Self-organized coherence-incoherence patterns, called chimera states, have first been reported in systems of Kuramoto oscillators. For coupled excitable units, similar patterns where coherent units are at rest are called bump states. Here, we study bumps in an array of active rotators coupled by nonlocal attraction and global repulsion. We demonstrate how they can emerge in a supercritical scenario from completely coherent Turing patterns: a single incoherent unit appears in a homoclinic bifurcation, undergoing subsequent transitions to quasiperiodic and chaotic behavior, which eventually transforms into extensive chaos with many incoherent units. We present different types of transitions and explain the formation of coherence-incoherence patterns according to the classical paradigm of short-range activation and long-range inhibition.

Recognition of stimulus received by recurrent neural network

The study is concerned with the comparison of two methods for identification of stimulus received by artificial neural network using neural activity pattern that corresponds to the period of storing information about this stimulus in the working memory. We used simple recurrent neural networks learned to pass the delayed matching-to-sample test. Neural activity was detected at the period of pause between receiving stimuli. The analysis of neural excitation patterns showed that neural networks encoded variables that were relevant for the task during the delayed matching-to-sample test, and their activity patterns were dynamic. The method of centroids allowed identifying the type of the received stimuli with efficiency up to 75% while the method of neural network-based decoder showed 100% efficiency. In addition, this method was applied to determine the minimal set of neurons whose activity was the most significant for stimulus recognition.

Improved Content Based Image Retrieval Process Based on Deep Convolutional Neural Network and Salp Swarm Algorithm

Digital image and medical image retrieval from several repositories are improving gradually, so the capacity of repositories increases rapidly. The semantic space is the main issue on content-based image retrieval (CBIR), which exists among the semantic level as well as increases the data recognized through human and low level visible data obtained through the image. The CBIR system utilizes the deep convolutional neural network (DCNN), which is trained to medical image characterization and the digital image by salp swarm optimization algorithm (SSA). The average classification accuracy for medical image is 86.805%, a mean average precision is 79%, Average Recall Rate (ARR) is 91.7% and [Formula: see text]-measure is 84.9%, are achieved during retrieval task. For image retrieval, the Average Precision Rate (APR) improved from 39%, 40%, 36% and 42.5% to 86.8% and the ARR enhanced from 39.5%, 40.5%, 35.5% and 42.5% to 86.8%. The [Formula: see text]-measure is improved from 39.5%, 40.5%, 35.5% and 42.5% to 86.8% as different with Local tetra patterns (LTrP), LOOP, local derivative pattern (LDP) and local mean differential excitation pattern (LMDeP) separately on Corel-1K dataset. The presented method is most suitable for multimodal digital images and medical image retrieval for various parts of the body.

Nonlinear dynamics of new magneto-mechanical oscillator

This study presents modelling and analysis of a new magneto-mechanical (MM) oscillator (Wiercigroch et al., 2020), which pays a special attention to mechanical and magnetic nonlinearities for large amplitude responses. The oscillator is comprised of a box structure made of two parallel leaf springs with one end fixed and the other clamped with a proof mass, and an electromagnetic actuator. A solenoid and a permanent magnet are the main parts of the actuator, which acts directly on the proof mass providing an accurate and versatile excitation by varying intensity and frequency of the input current. The new model for a beam of large deflection is based up the constitutive relation of nonlinear beam theory. A new design of the electromagnetic actuator with a pair of identical solenoids and a new concept of quasi-constant force (QCF) are proposed, which aims to generate a nearly constant amplitude force for a constant input current. The mathematical model of the MM oscillator is systematically developed and discussed for different types of excitations depending on designs and parameters of the electromagnetic actuator. The undertaken nonlinear dynamics analysis demonstrates versatility of the electromagnetic actuator to generate a wide spectrum of excitations. The prediction from the modelling were validated by the previous work (Costa et al., 2020). The study exemplify that the electromagnetic actuator provides a wide range of excitation patterns and can be used to study experimentally subtle nonlinear phenomena.

How Does Our Brain Generate Sexual Pleasure?

We present herein an exploratory essay on sexual pleasure, in support of the objective of developing an evidence base of knowledge for the WAS Declaration of Sexual Rights. We have attempted to account for the feeling of erotic sexual pleasure, in terms of what is known about neuronal function. The brain regions that are activated during women’s orgasm, and their perceptual and physiological roles, are compared with brain regions related to chemically induced euphoria and craving. The brain regions that are activated at orgasm match those that are activated by both euphoria and craving. Based on these findings, we propose that erotic, sensual feeling is a simultaneous activation of euphoria plus craving. The importance of sensory stimulation, proprioception, sensations, and feelings is emphasized by evidence that their disruption leads to pathologies. The process of buildup of excitation to a peak and then resolution is proposed as a basic “orgasmic” property of the nervous system shared by multiple systems, as in a sneeze, which we consider to be a non-genital orgasm. We postulate a process by which an excitation pattern feels pleasurable and – at higher intensity – euphoric, if it is congruent with an unconscious dynamic “template,” but aversive and at higher intensity painful, to the extent that it is incongruent with the template. Under this formulation, peak neuronal excitation that is congruent with the unconscious, simultaneously “getting what is craved,” generates orgasmic, erotic, sexual pleasure.

Effects of modulator shape at thresholds and supra-thresholds spectral modulation perception

Spectral modulation detection is common method to assess spectral envelope perception in research and clinical settings. Prior investigations into spectral modulation (SM) detection have used two different modulator shapes: a sinusoidal envelope on a logarithmic amplitude scale or a sinusoidal envelope on a linear amplitude scale. The former creates a sinusoidally shaped excitation pattern, while the latter creates an excitation pattern with broad peaks and sharp valleys. What impact, if any, modulator shape has on SM perception at detection threshold or at supra-threshold levels is unknown. To investigate potential perceptual differences between waveform shapes: (1) SM detection was measured for modulation frequencies ranging from 0.5 to 8.0 cycles/octave; (2) Spectral modulation masking was measured for SM frequencies of 0.5 and 2.0 cycles/octave. The SM phase of the masker was manipulated (0, 90, or 180 degrees) so that maskers had a peak, a midpoint, or a valley at 1147 Hz. Tone detection (1147 Hz) was measured for the logarithmic and linear sinusoidal SM envelope shapes for each of the three phases. Results revealed significant differences between the two spectral envelope shapes for both spectral modulation detection and for spectral modulation masking. [Work supported by NIH R01DC015051].

Reflection-mode acousto-optic imaging using plane wave ultrasound pulses.

.Significance: Performance of an acousto-optic imaging system is limited by light fluence rate and acoustic pressure field distributions characteristics. In optically scattering media, the former determines the achievable contrast, whereas the latter the imaging resolution. The system parameters can be shaped by changing relative positions of ultrasound (US) transducer array and optodes. However, in the case of many potential clinical applications, optimization possibilities in this regard are limited, as a sample is accessible from one side only and using a water tank for coupling is not feasible.Aim: We investigate the possibilities of improving performance of an acousto-optic imaging system operating in reflection mode geometry with linear US array in direct contact with a sample using plane wave instead of focused US pulses.Approach: Differences in acoustic pressure field distributions for various transducer excitation patterns were determined numerically and experimentally. Acousto-optic images of phantoms with and without optically absorbing inclusions were acquired by measuring laser speckle contrast decrease due to the light modulation by plane wave and focused US pulses with different apodization patterns.Results: The residual acoustic pressure field components occupy relatively large volume and contribute to light modulation. Using nonsteered plane wave US pulses instead of focused ones allows one to mitigate their influence. It also allows one to obtain clear two-dimensional reconstructions of light fluence rate maps by shifting transducer apodization along the lateral direction.Conclusions: Using nonsteered plane wave US pulses allows one to achieve better imaging performance than with focused pulses in the assumed system geometry.

Motor excitability in bilateral moyamoya vasculopathy and the impact of revascularization.

Motor cortical dysfunction has been shown to be reversible in patients with unilateral atherosclerotic disease after cerebral revascularization. Moyamoya vasculopathy (MMV) is a rare bilateral stenoocclusive cerebrovascular disease. The aim of this study was to analyze the corticospinal excitability and the role of bypass surgery in restoring cortical motor function in patients by using navigated transcranial magnetic stimulation (nTMS). Patients with bilateral MMV who met the criteria for cerebral revascularization were prospectively included. Corticospinal excitability, cortical representation area, and intracortical inhibition and facilitation were assessed by nTMS for a small hand muscle (first dorsal interosseous) before and after revascularization. The clinically and/or hemodynamically more severely affected hemisphere was operated first as the leading hemisphere. Intra- and interhemispheric differences were analyzed before and after direct or combined revascularization. A total of 30 patients with bilateral MMV were examined by nTMS prior to and after revascularization surgery. The corticospinal excitability was higher in the leading hemisphere compared with the non-leading hemisphere prior to revascularization. This hyperexcitability was normalized after revascularization as demonstrated in the resting motor threshold ratio of the hemispheres (preoperative median 0.97 [IQR 0.89-1.08], postoperative median 1.02 [IQR 0.94-1.22]; relative effect = 0.61, p = 0.03). In paired-pulse paradigms, a tendency for a weaker inhibition of the leading hemisphere was observed compared with the non-leading hemisphere. Importantly, the paired paradigm also demonstrated approximation of excitability patterns between the two hemispheres after surgery. The study results suggested that, in the case of a bilateral chronic ischemia, a compensation mechanism between both hemispheres seemed to exist that normalized after revascularization surgery. A potential role of nTMS in predicting the efficacy of revascularization must be further assessed.

Organic Hyperbolic Material Assisted Illumination Nanoscopy.

Resolution capability of the linear structured illumination microscopy (SIM) plays a key role in its applications in physics, medicine, biology, and life science. Many advanced methodologies have been developed to extend the resolution of structured illumination by using subdiffraction‐limited optical excitation patterns. However, obtaining SIM images with a resolution beyond 40 nm at visible frequency remains as an insurmountable obstacle due to the intrinsic limitation of spatial frequency bandwidth of the involved materials and the complexity of the illumination system. Here, a low‐loss natural organic hyperbolic material (OHM) that can support record high spatial‐frequency modes beyond 50k 0, i.e., effective refractive index larger than 50, at visible frequencies is reported. OHM‐based speckle structured illumination microscopy demonstrates imaging resolution at 30 nm scales with enhanced fluorophore photostability, biocompatibility, easy to use and low cost. This study will open up a new route in super‐resolution microscopy by utilizing OHM films for various applications including bioimaging and sensing.

JNK activation in TA and EDL muscle is load-dependent in rats receiving identical excitation patterns

As the excitation–contraction coupling is inseparable during voluntary exercise, the relative contribution of the mechanical and neural input on hypertrophy-related molecular signalling is still poorly understood. Herein, we use a rat in-vivo strength exercise model with an electrically-induced standardized excitation pattern, previously shown to induce a load-dependent increase in myonuclear number and hypertrophy, to study acute effects of load on molecular signalling. We assessed protein abundance and specific phosphorylation of the four protein kinases FAK, mTOR, p70S6K and JNK after 2, 10 and 28 min of a low- or high-load contraction, in order to assess the effects of load, exercise duration and muscle-type on their response to exercise. Specific phosphorylation of mTOR, p70S6K and JNK was increased after 28 min of exercise under the low- and high-load protocol. Elevated phosphorylation of mTOR and JNK was detectable already after 2 and 10 min of exercise, respectively, but greatest after 28 min of exercise, and JNK phosphorylation was highly load-dependent. The abundance of all four kinases was higher in TA compared to EDL muscle, p70S6K abundance was increased after exercise in a load-independent manner, and FAK and JNK abundance was reduced after 28 min of exercise in both the exercised and control muscles. In conclusion, the current study shows that JNK activation after a single resistance exercise is load-specific, resembling the previously reported degree of myonuclear accrual and muscle hypertrophy with repetition of the exercise stimulus.

PL2. Noninvasive brain stimulation – The past, the present and the future

Non-invasive brain stimulation started in the antiquity by treating headache with electric fishes (∼ 1 A, ∼ 700 V). Transcranial direct current stimulation dominated research in the 19 th century after the invention of the voltaic pile (∼ 1 mA, ∼10 V). At present the main applications involve either weak electric stimulation of many different types (transcranial direct, alternating, random noise or combinations) of currents or high energy pulsed stimulations (∼8 kA, ∼ 10 µs) mediated by transcranial magnetic energy transfer (transcranial magnetic stimulation: TMS). Inhibitory or excitatory after-effects are guided by stimulus intensity, duration and intervals (cf. theta burst, quadripulse and others). In general, lower intensities lead to inhibition and higher intensities to excitation. There is no linear correlation between the duration of stimulation and the size of the after-effects, prolongation of stimulus duration may lead to an oscillating pattern of inhibition or excitation. Missing the right windows in time or in amplitude may lead to no or opposite results explaining the variability and conflicting data in the field. Intracellular calcium increase may be a key leader for deciding between LTD- or LTP-like after-effects. Uncontrolled consumption of nicotine and caffeine increase variability further. Co-application of drugs may guide after-effects in terms of selectivity and duration of after-effects. Current developments encompass new physical techniques such as varying TMS pulse widths, multi-electrode stimulation, interference fields, ultrasound or near infrared stimulation, hypothesis driven protocols based on neurophysiological features of cortical neurons, optimized techniques on realistic individual head models for targeting current flow to predefined areas and others. Clinical applications targeting cortical excitability increases (e.g. depression, pain) or decreases (e.g. epilepsy, migraine) seem to be more rewarding than those requiring structural repair (e.g. stroke).

Effect of atrial artificial electrical stimulation on depolarization and repolarization and hemodynamics of the heart ventricle in rainbow trout Oncorhynchus mykiss.

The spatial-temporal organization of the activation, repolarization and hemodynamics of the heart ventricle in rainbow trout, Oncorhynchus mykiss, adapted to a temperature of 5-7°C, were studied from the normal sinus rhythm (21.6 ± 4.9bpm) to the highest possible heart rhythm (HR) (60bpm), during which deterioration of the contractile activity of the myocardium occurred. Regardless of the HR, the main pattern of excitation of the heart ventricle was the movement of the depolarization wave from the dorsal areas of the base in the base-apical and ventral directions with the capture of the entire thickness of the walls, with a slight difference in the time of activation of the subendocardium compared to the subepicardium. The increase in HR above the sinus rhythm caused significant shortening of local repolarization durations in all areas and layers (endocardial, intramural and subepicardial) of the heart ventricle. Changes in local durations of repolarization led to an increase in the heterogeneity of repolarization of the ventricular myocardium; as a result, a deterioration of its contractility was observed. In relation to the sinus rhythm, the maximal systolic pressure in the heart ventricle decreased, the diastolic and end-diastolic pressure increased, and the maximum rates of pressure rise and fall decreased. In rainbow trout adapted to a temperature of 5-7°C at sinus rhythm, the pumping function of the heart was probably within the upper limit of the physiological norm, and a further increase in the heart rate led to a decline in myocardial contractility.

Comprehensive understanding of the ignition process of a pulsed capacitively coupled radio frequency discharge: the effect of power-off duration

The effect of the pulse-off duration on the time evolution of the plasma and electrical parameters during the ignition phase in a pulsed capacitively coupled radio frequency argon discharge operated at 450 mTorr and 12.5 MHz is investigated synergistically by multifold experimental diagnostics, particle-in-cell/Monte Carlo collision simulations and an analytical model. In the experiment, the electron density is measured time-resolved by a hairpin probe, the spatio-temporal distribution of the electron impact excitation dynamics is studied by phase resolved optical emission spectroscopy, and the amplitudes and the relative phase, φ vi, of the discharge voltage and current are determined based on the waveforms measured by a voltage and a current probe. The experimental results show that the plasma and electrical parameters during the ignition process depend strongly on the duration of the afterglow period, T off, primarily because of the dependence of the remaining charge density on this parameter. Computed values of φ vi show a similar time-dependence compared to the experiment, if the simulations are initialized with specific initial charged particle densities, n ini. This allows us to further understand the time evolution of φ vi for different values of T off based on the simulation results together with an analytical model. In particular, the optical emission intensity is found to change with time in the same fashion as the power deposition into the system at T off ⩾ 100 μs, suggesting that the power is primarily absorbed by the electrons, which dissipate their energy via inelastic collisions. The system goes through different mode transitions of electron power absorption during the ignition phase depending on T off. Specifically, for short T off (high n ini), the α mode dominates during the entire ignition process, as the electric field is largely shielded by the abundant charge located in the interelectrode space. For intermediate values of T off (moderate n ini), another excitation pattern caused by an enhanced drift electric field at the center of the gap is observed, since a large fraction of the externally applied potential can penetrate into the central region in the absence of high charged particle densities. For longer T off (very low n ini), the ignition of the pulsed plasma behaves like a gas breakdown.

A space-fractional bidomain framework for cardiac electrophysiology: 1D alternans dynamics.

Cardiac electrophysiology modeling deals with a complex network of excitable cells forming an intricate syncytium: the heart. The electrical activity of the heart shows recurrent spatial patterns of activation, known as cardiac alternans, featuring multiscale emerging behavior. On these grounds, we propose a novel mathematical formulation for cardiac electrophysiology modeling and simulation incorporating spatially non-local couplings within a physiological reaction-diffusion scenario. In particular, we formulate, a space-fractional electrophysiological framework, extending and generalizing similar works conducted for the monodomain model. We characterize one-dimensional excitation patterns by performing an extended numerical analysis encompassing a broad spectrum of space-fractional derivative powers and various intra- and extracellular conductivity combinations. Our numerical study demonstrates that (i) symmetric properties occur in the conductivity parameters' space following the proposed theoretical framework, (ii) the degree of non-local coupling affects the onset and evolution of discordant alternans dynamics, and (iii) the theoretical framework fully recovers classical formulations and is amenable for parametric tuning relying on experimental conduction velocity and action potential morphology.

HCN1 channels: A versatile tool for signal processing by primary sensory neurons

Most primary sensory neurons (PSNs) generate a slowly-activating inward current in response to membrane hyperpolarization (Ih) and express HCN1 along with additional isoforms coding for hyperpolarization-activated channels (HCN). Changes in HCN expression may affect the excitability and firing patterns of PSNs, but retinal and inner ear PSNs do not fire action potentials, suggesting HCN channel roles may extend beyond excitability and cell firing control. In patients taking Ih blockers, photopsia triggered in response to abrupt changes in luminance correlates with impaired visual signal processing via parallel rod and cone pathways. Furthermore, in a mouse model of inherited retinal degeneration, HCN blockers or Hcn1 genetic ablation may worsen photoreceptors' demise. PSN's use of HCN channels to adjust either their firing rate or process signals generated by sensory transduction in non-spiking PSNs indicates HCN1 channels as a versatile tool with a novel role in sensory processing beyond firing control.

Local excitation universal parallel transmit pulses at 9.4T.

To demonstrate that the concept of "universal pTx pulses" is applicable to local excitation applications. A database of B0 / maps from eight different subjects was acquired at 9.4T. Based on these maps, universal pulses that aim at local excitation of the visual cortex area in the human brain (with a flip angle of 90° or 7°) were calculated. The remaining brain regions should not experience any excitation. The pulses were designed with an extension of the "spatial domain method." A 2D and a 3D target excitation pattern were tested, respectively. The pulse performance was examined on non-database subjects by Bloch simulations and in vivo at 9.4T using a GRE anatomical MRI and a presaturated TurboFLASH mapping sequence. The calculated universal pulses show excellent performance in simulations and in vivo on subjects that were not contained in the design database. The visual cortex region is excited, while the desired non-excitation areas produce the only minimal signal. In simulations, the pulses with 3D target pattern show a lack of excitation uniformity in the visual cortex region; however, in vivo, this inhomogeneity can be deemed acceptable. A reduced field of view application of the universal pulse design concept was performed successfully. The proposed design approach creates universal local excitation pulses for a flip angle of 7° and 90°, respectively. Providing universal pTx pulses for local excitation applications prospectively abandons the need for time-consuming subject-specific B0 / mapping and pTx-pulse calculation during the scan session.

Reconfigurable electronic circuits for magnetic fields controlled by structured light

Dynamic control over the conduction band electrons of a semiconductor is a central technological pursuit. Beyond electronic circuitry, flexible control over the spatial and temporal character of semiconductor currents enables precise spatiotemporal structuring of magnetic fields. Despite their importance in science and technology, the control of magnetic fields at the micrometre spatial scale and femtosecond temporal scale using conventional electromagnets remains challenging. Here, we apply structured light beams to interfering photoexcitation pathways in gallium arsenide to sculpt the spatial and momentum configuration of its conduction band population. Programmable control over several hundred micrometre-scale current elements is achieved by manipulating the wavefronts of an optical beam using a spatial light modulator, enabling vast flexibility in the excited current patterns. Using this platform, we demonstrate dynamic optoelectronic interconnects, circuits for spatially tailored magnetic fields and magnetic field lattices. Structured beams of light are used to engineer conduction band populations and pattern currents. Using the approach, dynamic optoelectronic interconnects and other applications are demonstrated.