Prepulse Intensity Research Articles

Double-pulse laser peening as a surface enhancement technology

In this paper, we discuss double-pulse laser peening (DPLP) as surface enhancement technology. Although single-pulse laser peening (SPLP) has yielded excellent results across various applications, its processing performance and efficiency are limited. The DPLP technique involves two laser pulses with a controlled irradiation interval and intensity, enhancing laser absorption through the plasma plume and generating high-amplitude laser-induced shock waves. This study involved conducting DPLP experiments on stainless steel, comparing the outcomes with those of conventional SPLP to assess DPLP’s functionality. After the initial prepulse irradiation, the subsequent main pulse was timed and irradiated onto the stainless steel. We evaluated the surface hardness to ascertain the impact of laser peening. The findings indicated that the surface hardness achieved with DPLP was up to 64% greater than that with SPLP. Additionally, the surface hardness achieved through DPLP depended on the delay time between the pulses and the intensity of the initial prepulse. These findings suggest that DPLP can significantly enhance surface hardness, providing a potential pathway for improving material performance in various industrial applications. Furthermore, simulation experiments of DPLP were performed using a one-dimensional simulation code that calculates the laser-matter interaction during the peening process. The pressure profiles generated by the simulation closely matched the experimentally derived hardness profiles, confirming the simulation’s ability to predict the mechanical effects induced by DPLP on the target sample and assist in further optimization of the DPLP process.

Not a Deficit, Just Different: Prepulse Inhibition Disruptions in Autism Depend on Startle Stimulus Intensities.

Sensory processing disruptions are a core symptom of autism spectrum disorder (ASD) and other neurological disorders. The acoustic startle response and prepulse inhibition (PPI) are common metrics used to assess disruptions in sensory processing and sensorimotor gating in clinical studies and animal models. However, often there are inconsistent findings on ASD-related PPI deficits across different studies. Here, we used a novel method for assessing changes in startle and PPI in rodents, using the Cntnap2 knock-out (KO) rat model for neurodevelopmental disorder/ASD that has consistently shown PPI disruptions in past studies. We discovered that not only sex and prepulse intensity but also the intensity of the startle stimulus profoundly impacts whether PPI deficits are evident in the Cntnap2 KO rat or not. We show that rats do not universally exhibit a PPI deficit; instead, impaired PPI is contingent on specific testing conditions. Notably, at lower startle stimulus intensities, Cntnap2 KO rats not only demonstrated intact PPI but also exhibited evidence of enhanced PPI compared with their wild-type counterparts. This finding emphasizes the importance of considering specific testing conditions when evaluating startle and PPI in the context of ASD and other neuropsychiatric conditions and might explain some of the inconsistencies between different studies.

Acute nicotine vapor normalizes sensorimotor gating and reduces locomotor activity deficits in HIV-1 transgenic rats.

Despite improved life expectancy of people with HIV (PWH), HIV-associated neurocognitive impairment (NCI) persists, alongside deficits in sensorimotor gating and neuroinflammation. PWH exhibit high smoking rates, possibly due to neuroprotective, anti-inflammatory, and cognitive-enhancing effects of nicotine, suggesting potential self-medication. Here, we tested the effects of acute nicotine vapor exposure on translatable measures of sensorimotor gating and exploratory behavior in the HIV-1 transgenic (HIV-1Tg) rat model of HIV. Male and female HIV-1Tg and F344 control rats (n=57) were exposed to acute nicotine or vehicle vapor. Sensorimotor gating was assessed using prepulse inhibition (PPI) of the acoustic startle response, and exploratory behavior was evaluated using the behavioral pattern monitor (BPM). Vehicle-treated HIV-1Tg rats exhibited PPI deficits at low prepulse intensities compared to F344 controls, as seen previously. No PPI deficits were observed in nicotine-treated HIV1-Tg rats, however. HIV-1Tg rats were hypoactive in the BPM relative to controls, whilst nicotine vapor increased activity and exploratory behavior across genotypes. Cotinine analyses confirmed comparable levels of the primary metabolite of nicotine across genotypes. Previous findings of PPI deficits in HIV-1Tg rats were replicated and, importantly, attenuated by acute nicotine vapor. Evidence for similar cotinine levels suggest a nicotine-specific effect in HIV-1Tg rats. HIV-1Tg rats had reduced exploratory behavior compared to controls, attenuated by acute nicotine vapor. Therefore, acute nicotine may be beneficial for remediating sensorimotor and locomotor activity deficits in PWH. Future studies should determine the long-term effects of nicotine vapor on similar HIV/NCI-relevant behaviors.

A Computational Model for the Simulation of Prepulse Inhibition and Its Modulation by Cortical and Subcortical Units.

The sensorimotor gating is a nervous system function that modulates the acoustic startle response (ASR). Prepulse inhibition (PPI) phenomenon is an operational measure of sensorimotor gating, defined as the reduction of ASR when a high intensity sound (pulse) is preceded in milliseconds by a weaker stimulus (prepulse). Brainstem nuclei are associated with the mediation of ASR and PPI, whereas cortical and subcortical regions are associated with their modulation. However, it is still unclear how the modulatory units can influence PPI. In the present work, we developed a computational model of a neural circuit involved in the mediation (brainstem units) and modulation (cortical and subcortical units) of ASR and PPI. The activities of all units were modeled by the leaky-integrator formalism for neural population. The model reproduces basic features of PPI observed in experiments, such as the effects of changes in interstimulus interval, prepulse intensity, and habituation of ASR. The simulation of GABAergic and dopaminergic drugs impaired PPI by their effects over subcortical units activity. The results show that subcortical units constitute a central hub for PPI modulation. The presented computational model offers a valuable tool to investigate the neurobiology associated with disorder-related impairments in PPI.

Optically tunable proton acceleration with a controlled prepulse in ultrashort intense laser double-foil target interaction

Competition and transition of the dominated mechanisms for proton acceleration were investigated in experiments by optically tuning the preplasma density profile using an additional femtosecond pre-ablation laser beam. Two groups of proton beams with angular separation were measured along the laser propagation axis and target normal direction from a vacuum-gapped double-foil target. A transition of proton acceleration from a target normal sheath acceleration regime to relativistically induced transparency (RIT) domination was observed when increasing the prepulse intensity. Two-dimensional particle-in-cell simulations qualitatively verify the experimental observations that a proton component along the laser axis is mainly generated by the RIT induced breakout afterburner from the tailored pre-expanded ultrathin front-layer foil with spatial-intensity distribution improvement by the second-layer foil. Our method can be popularized in manipulating the laser-driven proton acceleration and beam spatial quality for wide applications.

Optimization of proton beam quality by obliquely incident laser pre-pulse

An investigation has been made to enhance the proton acceleration through the use of an additional obliquely incident lower intense pre-pulse. We observed by means of two-dimensional particle-in-cell simulation that the surface plasma waves can be generated on a flat target using a low-intensity pre-pulse, which is beneficial for enhancing the laser self-focusing and consequently boosting the proton acceleration. We noticed that the proton acceleration is driven by a hybrid acceleration process. The obtained proton beam peak energy and the maximum energy are found to increase by about 205% and 68%, respectively, for the case with pre-pulse in comparison to the cases where the pre-pulse is absent. Moreover, significant degradation of the proton beam energy spread and angular divergence are also seen.

Propagation of intense laser pulses in plasma with a prepared phase-space distribution

Optimizing the laser wakefield accelerator (LWFA) requires control of the intense driving laser pulse and its stable propagation. This is usually challenging because of mode mismatching arising from relativistic self-focusing, which invariably alters the velocity and shape of the laser pulse. Here we show how an intense pre-pulse can prepare the momentum/density phase-space distribution of plasma electrons encountered by a trailing laser pulse to control its propagation. This can also be used to minimize the evolution of the wakefield thus enhancing the stability of the LWFA, which is important for applications.

The effect of prepulse amplitude and timing on the perception of an electrotactile pulse

The perceived intensity of an intense stimulus as well as the startle reflex it elicits can both be reduced when preceded by a weak stimulus (prepulse). Both phenomena are used to characterise the processes of sensory gating in clinical and non-clinical populations. The latter phenomenon, startle prepulse inhibition (PPI), is conceptualised as a measure of pre-attentive sensorimotor gating due to its observation at short latencies. In contrast, the former, prepulse inhibition of perceived stimulus intensity (PPIPSI), is believed to involve higher-order cognitive processes (e.g., attention), which require longer latencies. Although conceptually distinct, PPIPSI is often studied using parameters that elicit maximal PPI, likely limiting what we can learn about sensory gating’s influence on conscious perception. Here, we tested an array of stimulus onset asynchronies (SOAs; 0–602 ms) and prepulse intensities (0–3× perceptual threshold) to determine the time course and sensitivity to the intensity of electrotactile PPIPSI. Participants were required to compare an ‘unpleasant but not painful’ electric pulse to their left wrist that was presented alone with the same stimulus preceded by an electric prepulse, and report which pulse stimulus felt more intense. Using a 2× perceptual threshold prepulse, PPIPSI emerged as significant at SOAs from 162 to 602 ms. We conclude that evidence of electrotactile PPIPSI at SOAs of 162 ms or longer is consistent with gating of perception requiring higher-level processes, not measured by startle PPI. The possible role of attentional processes, stimuli intensity, modality-specific differences, and methods of investigating PPIPSI further are discussed.

Threshold target thickness in high-contrast laser-driven ion acceleration

The experiments have revealed a “threshold” target thickness for proton acceleration by a femtosecond petawatt class laser above which the forward accelerated proton energy weakly depends on the target thickness, while for thinner targets, it gradually decreases. For targets thicker than the threshold, the pre-pulse-induced preplasma at the target front can boost ion acceleration by increasing laser absorption, while this is ineffective for thinner targets due to prepulse-induced plasma formation at the target rear. This dual nature of the preplasma is described analytically, and particle-in-cell simulations confirm this concept. A linear dependence of threshold target thickness on the prepulse intensity is predicted.

Test-retest reliability of prepulse inhibition (PPI) and PPI correlation with working memory.

Sensorimotor gating is experimentally operationalized by the prepulse inhibition (PPI) of the startle response (SR). Previous studies suggest high test-retest reliability of PPI and potential correlation with working memory (WM). Here, we aimed to validate and extend the test-retest reliability of PPI in healthy humans and its correlation with WM performance. We applied an acoustic startle PPI paradigm with four different prepulse intensities (64, 68, 72 and 76 dB) and two different WM tasks [n-back, change detection task (CDT)] in a group of 26 healthy adults (final sample size n = 23). To assess test-retest reliability, we performed all tests on two separate days ~27 days (range: 21-32 days) apart. We were able to confirm high test-retest reliability of the PPI with a mean intraclass correlation (ICC) of > 0.80 and significant positive correlation of PPI with n-back but not with CDT performance. Detailed analysis showed that PPI across all prepulse intensities significantly correlated with both the 2-back and 0-back conditions, suggesting regulation by cross-conditional processes (e.g. attention). However, when removing the 0-back component from the 2-back data, we found a specific and significant correlation with WM for the 76-dB PPI condition. With the present study, we were able to confirm the high test-retest reliability of the PPI in humans and could validate and expand on its correlation with WM performance.

Within-subjects vs between-subjects co-variation of prepulse-elicited reaction and the diminution of startle to the succeeding pulse stimulus in the prepulse inhibition paradigm

Prepulse inhibition (PPI) refers to the diminution of the startle reflex to a sudden and intense acoustic stimulus (pulse) when this startle-eliciting pulse is preceded shortly by a weaker prepulse stimulus. PPI is widely used in evaluating the effects of psychomimetic and antipsychotic drugs on sensorimotor gating, but individual differences in PPI expression have received scant attention. We have previously shown that mice and rats exhibiting stronger motor response to the prepulse also exhibit more PPI. It remains unexplored, however, if this between-subjects correlation may be similarly observed across trials from a within-subjects perspective. Here, we mapped the prepulse-elicited response to the diminution of the startle response to the succeeding pulse stimulus, trial-by-trial, across nine prepulse-pulse definitions with varying prepulse and pulse intensities. The resulting within-subjects correlation independently obtained in 113 adult C57BL6 mice revealed that trials registering a stronger prepulse reaction also recorded a larger startle response to the pulse stimulus, indicative of weaker PPI, especially when higher-intensity prepulses were paired with low-intensity pulses. The within- and between-subjects analyses have apparently yielded two contrasting relationships between the direct motor response to the prepulse and the inhibition of subsequent startle reaction induced by the same prepulse. One interpretation is that the within-subjects correlation reflects state-dependent variation, whereas the between-subjects correlation stems from trait-dependent individual variation. Finally, whether our present findings may depend on the nature of the prepulse reaction is further discussed.

The Effect of Glutathione Deficit During Early Postnatal Brain Development on the Prepulse Inhibition and Monoamine Levels in Brain Structures of Adult Sprague-Dawley Rats.

Recent studies suggest that impaired glutathione synthesis and distorted dopaminergic transmission are important factors in the pathophysiology of schizophrenia. In the present study, on the postnatal days p5-p16, male pups were treated with the inhibitor of glutathione synthesis, L-buthionine-(S,R)- sulfoximine (BSO, 3.8 or 7.6mmol/kg), and the dopamine uptake inhibitor, GBR 12,909 (5mg/kg) alone or in combination, and prepulse inhibition of the acoustic startle response (PPI) was evaluated in adult 90-day-old rats. Moreover, the monoamine levels in the cortex and hippocampus of 16-day-old rats or 91-day-old rats were measured. The present results showed that administration of BSO at 3.8mmol/kg led to a decreasing tendency in PPI for all tested prepulse intensities. In contrast, a combined treatment with BSO in both studied doses and GBR 12,909 did not induce significant deficits in PPI. Moreover, the results of biochemical studies indicated that treatment with BSO or GBR 12,909 alone induced a weak increase in the activity of dopaminergic, serotonergic, and noradrenergic systems in the frontal cortex and hippocampus of 16-day-old rats and 91-day-old rats. However, the combined administration of both substances allowed for maintaining the normal activity of monoaminergic systems in the rat brain. The most significant changes in the functioning of monoaminergic systems were observed in the frontal cortex of 16-day-old rats. Therefore, it seems that the frontal cortex of rat puppies is most sensitive to glutathione deficiencies resulting in increased oxidative stress in neurons. As a result, it can lead to cognitive and memory impairment.

Neuroplastin expression is essential for hearing and hair cell PMCA expression

Hearing deficits impact on the communication with the external world and severely compromise perception of the surrounding. Deafness can be caused by particular mutations in the neuroplastin (Nptn) gene, which encodes a transmembrane recognition molecule of the immunoglobulin (Ig) superfamily and plasma membrane Calcium ATPase (PMCA) accessory subunit. This study investigates whether the complete absence of neuroplastin or the loss of neuroplastin in the adult after normal development lead to hearing impairment in mice analyzed by behavioral, electrophysiological, and in vivo imaging measurements. Auditory brainstem recordings from adult neuroplastin-deficient mice (Nptn−/−) show that these mice are deaf. With age, hair cells and spiral ganglion cells degenerate in Nptn−/− mice. Adult Nptn−/− mice fail to behaviorally respond to white noise and show reduced baseline blood flow in the auditory cortex (AC) as revealed by single-photon emission computed tomography (SPECT). In adult Nptn−/− mice, tone-evoked cortical activity was not detectable within the primary auditory field (A1) of the AC, although we observed non-persistent tone-like evoked activities in electrophysiological recordings of some young Nptn−/− mice. Conditional ablation of neuroplastin in Nptnlox/loxEmx1Cre mice reveals that behavioral responses to simple tones or white noise do not require neuroplastin expression by central glutamatergic neurons. Loss of neuroplastin from hair cells in adult NptnΔlox/loxPrCreERT mice after normal development is correlated with increased hearing thresholds and only high prepulse intensities result in effective prepulse inhibition (PPI) of the startle response. Furthermore, we show that neuroplastin is required for the expression of PMCA 2 in outer hair cells. This suggests that altered Ca2+ homeostasis underlies the observed hearing impairments and leads to hair cell degeneration. Our results underline the importance of neuroplastin for the development and the maintenance of the auditory system.

The effects of ASE contrast and beams mutual alignment on the γ-ray yield in laser-plasma interactions with artificial prepulse

We present experimental study of the bremsstrahlung γ-rays generation in a plasma interacting with 50 fs laser pulse in slightly relativistic regime (intensity ∼2-1018 W/cm2). A pre-plasma layer on the surface of the molybdenum target is formed by an additional laser pulse with a duration of 8 ns and an intensity of ∼2-1012 W/cm2. The energy and intensity of the artificial pre-pulse exceed those of the amplified spontaneous emission (ASE) pedestal of the main pulse by ∼103 and 10 times (for contrast 10−7), respectively. It was shown that the low ASE contrast (>10−7) is the crucial condition for increasing (in comparison to the case without artificial pre-pulse) of the integral γ-rays yield when the nanosecond pulse is ahead of the femtosecond one by >20 ns. Interferometry data show that the reason of the γ-rays yield increasing is a pre-plasma layer initially produced by artificial pre-pulse and re-created by the ASE. The optimum conditions for γ-rays yield achieved if (i) the pre-pulse comes ∼25 ns in advance, (ii) ASE contrast is 10−7 and lower and (iii) the femtosecond focal point is shifted by ∼100 μm from the center of the nanosecond pre-pulse focal spot and by ∼100 μm above the target surface.

Numerical Study of the Effect of Pre-Pulse on THz Generation by Two-Color Laser-Induced Microplasma

In this article, a photocurrent model is used to investigate terahertz (THz) generation in two-color laser-induced preformed air microplasma. Comprehensive 2-D numerical particle-in-cell (PIC) simulations are done to understand the most important mechanism of THz generation in laser-induced microplasma. The model used in this simulation involves both ionization current (transverse current) and ponderomotive forces (longitudinal current). The laser pulse is divided into two types, a pre-pulse and a delayed main pulse, which propagate in a parallel direction (i.e., collinear configuration). Our simulation shows that the THz amplitude significantly reduces in the presence of a pre-pulse compared to the case with no pre-pulse. Also, in the study of how a time delay between the pre-pulse and the main pulse affects THz radiation, it has been demonstrated that THz radiation decreases as the time delay increases. Finally, through the investigation of the main pulse and pre-pulse intensity ratio, it emerged that the THz amplitude decreased with an increase in that ratio. The results point to the major role of tunneling ionization in THz generation via laser-induced microplasma.

Effect of mild and chronic neonatal hypothyroidism on sensory information processing in a rodent model: A behavioral and electrophysiological study

Thyroid hormones are essential for neonatal brain development. It is well established that absence of thyroid hormones during critical periods of development can alter sensory functions such as visual and auditory processing, but there are few studies on rat somatosensory system development at mild, long-term, and irreversible neonatal hypothyroidism. Thus, the current study was conducted to investigate whether chronic thyroid hormone insufficiency would alter different cognitive aspects of tactile information processing and sensory motor filtering at behavioral or neuronal levels. Neonatal Wistar male rats were exposed to 0 and 6 ppm of propylthiouracil for 150 days. Behavioral tests including tactile discrimination tests and acoustic startle reflex test were performed. Using extracellular single unit recording technique, barrel cortex neurons’ excitatory and inhibitory responses to controlled displacement of whiskers were evaluated. Results indicated that percentage of correct choice in tactile learning and discrimination of a new texture decreased in hypothyroid group compared to the control group (P < 0.05). In addition, acoustic startle reflex of hypothyroid group significantly decreased compared to the control rats when the prepulse intensity was 71 dB (P < 0.05). Data obtained from electrophysiological tests showed that spontaneous activity and response magnitude of barrel cortex neurons decreased in hypothyroid group compared to the control group (P < 0.05). It is concluded that, thyroid hormones can regulate tactile and auditory sensory processing in male rats, and mild and long-term absence of these hormones can result in deficiency in natural functions of these sensory systems.

A simple way to introduce an adjustable femtosecond pre-pulse to enhance laser-driven proton acceleration

We demonstrate a simple way to introduce a femtosecond pre-pulse with adjustable intensity and delay without using an additional compressor to enhance laser-driven proton acceleration. Targets with different thicknesses were shoot at normal incidence by varying the pre-pulses. Experimental results show that significant enhancement of the proton energy can be achieved when the intensity of pre-pulse is optimized. Density profile of preplasma was obtained by hydrodynamic simulations. PIC simulations reveal that the preplasma generated by a femtosecond pre-pulse can increase the intensity of main pulse.

Psychopathy traits and reinforcement sensitivity theory: Prepulse inhibition and ERP responses

This study examined the associations between Reinforcement Sensitivity Theory (RST-PQ, Corr & Cooper, 2016) and psychopathy traits (LSRPS, Levenson et al., 1995) in university students. The aim was to identify psychopathy and RST traits associated with prepulse inhibition (PPI) of acoustic startle and ERP responses by using two prepulse-stimulus intensities (70 and 85 dB) combined with a 105 dB startle pulse (200 ms prepulse-plus-pulse interval). The higher intensity prepulse produced a larger PPI, although both prepulse stimuli reliably activated the startle system. Higher Primary Psychopathy was associated with a higher Defensive-Fight trait and both measures were associated with larger PPI. A principal components factor analysis disclosed an N1-startle factor that was a significant predictor of both reward reactivity and Goal-Drive Persistence scores. Results appear in line with Newman’s response modulation hypothesis emphasizing the engagement of attention and recognition of stimulus salience, which may be disrupted in psychopathy.

Well collimated MeV electron beam generation in the plasma channel from relativistic laser-solid interaction

Efficient direct electron acceleration in the plasma channel with injection through the breaking of plasma waves generated by parametric instabilities was demonstrated experimentally and reproduced in the 2D3V PIC simulations. The electron bunch was produced using the specific plasma profile containing arbitrary sharp, ∼0.5λ, gradient at the vicinity of 0.1–0.5 critical density and a long tail of a tenuous preplasma. Such a preplasma profile was formed by an additional nanosecond laser pulse with intensity of 5 × 1012 W cm−2. In the case of optimal preplasma parameters femtosecond laser pulse with an intensity of 5 × 1018 W cm−2 and an energy of 50 mJ generates a collimated electron bunch having divergence of 50 mrad, exponential spectrum with the slope of ∼2 MeV and charge of tens of pC. The charge was confirmed measuring neutron yield from Be(g, n) photonuclear reaction with threshold of 1.7 MeV. By the contrast, a ring-like electron beam with divergency of 300 mrad and significantly lower charge is generated if the prepulse intensity drops to 5 × 1011 W cm−2. The 2D PIC simulations confirmed beamed electron’s acceleration in the plasma channel (so-called direct laser acceleration). This channel is formed in a long tail of teneous preplasma by the laser pulse specularly reflected from the arbitrary sharp gradient. The ring-like electron beam was attributed to the longer gradient case enlarging divergence of the reflected laser beam, preventing channel’s formation and electron acceleration by the so-called vacuum laser acceleration, or VLA. We also showed that injected electrons appeared from the wave breaking of plasma waves of hybrid SRS-TPD instability for the both gradients. Electrons received an initial momentum from this breaking to be effectively injected into the plasma channel.

Different pharmaceutical preparations of Δ9 -tetrahydrocannabinol differentially affect its behavioral effects in rats.

Based on the contribution of the endocannabinoid system to the pathophysiology of schizophrenia, the primary pro-psychotic ingredient of Cannabis sativa, Δ-9-tetrahydrocannabinol (Δ-9-THC), is used in preclinical as well as clinical research to mimic schizophrenia-like symptoms. While it is common to administer lipid-based formulations of Δ-9-THC in human studies orally, intraperitoneal injections of water-based solutions are used in animal models. Because of the poor water solubility of Δ-9-THC, solubilizers such as ethanol and/or emulsifiers are needed for these preparations. In order to test whether a lipid-based solvent would be superior over a water-based vehicle in rats, we compared the effects on locomotor activity and prepulse inhibition (PPI) of the acoustic startle reaction, as well as pharmacokinetic data obtained from rats' serum and brain tissue samples. Up to 50mg/kg Δ-9-THC in the lipid-based formulation was not able to induce any behavioral alterations, while already 5mg/kg of the water-based Δ-9-THC preparation significantly reduced locomotor activity. This also induced a small but significant PPI reduction, which was prepulse intensity dependent. Interestingly, the reflexive motor response to the startle stimulus was not affected by the water-based Δ-9-THC solution. Analysis of serum and brain Δ-9-THC levels by high-performance liquid chromatography/mass spectrometry revealed that although the final concentration reached in the brain was comparable for both pharmaceutical preparations, the water-based formulation achieved a faster kinetic. We, therefore, conclude that the slope of the Δ-9-THC concentration-time curve and the resulting cannabinoid receptor type 1 activation per time unit are responsible for the induction of behavioral alterations.