P1 Peak Research Articles

Evoked Compound Action Potentials Reveal Spinal Cord Dorsal Column Neuroanatomy

The electrically evoked compound action potential (ECAP) is a measure of the response from a population of fibers to an electrical stimulus. ECAPs can be assessed during spinal cord stimulation (SCS) to elucidate the relationship between stimulation, electrophysiological response, and neuromodulation. This has consequences for the design and programming of SCS devices. Sheep were implanted with linear epidural SCS leads. After a stimulating pulse, electrodes recorded ECAPs sequentially as they propagated orthodromically or antidromically. After filtering, amplification, and signal processing, ECAP amplitude and dispersion (width) was measured, and conduction velocity was calculated. Similar clinical data was also collected. A single-neuron computer model that simulated large-diameter sensory axons was used to explore and explain the observations. ECAPs, both animal and human, have a triphasic structure, with P1, N1, and P2 peaks. Conduction velocity in sheep was 109 ms-1 , which indicates that the underlying neural population includes fibers of up to 20 μm in diameter. For travel in both directions, propagation distance was associated with decrease in amplitude and increase in dispersion. Importantly, characteristics of these changes shifted abruptly at various positions along the cord. ECAP dispersion increases with propagation distance due to the contribution of slow-conducting small-diameter fibers as the signal propagates away from the source. An analysis of the discontinuities in ECAP dispersion changes with propagation revealed that these are due to the termination of smaller-diameter, slower-conducting fibers at corresponding segmental levels. The implications regarding SCS lead placement, toward the goal of maximizing clinical benefit while minimizing side-effects, are discussed. John Parker is the founder and CEO of Saluda Medical and holds stock options. Milan Obradovic, Nastaran Hesam Shariati, Dean M. Karantonis, Peter Single, James Laird-Wah, Robert Gorman and Mark Bickerstaff are employees of Saluda Medical with stock options. At the time the data was collected for the study, Prof. Cousins was a paid consultant for Saluda Medical. John Parker, Milan Obradovic, Dean Karantonis, James Laird-Wah, Robert Gorman and Peter Single are co-inventors in one or more patents related to the topics discussed in this work.

Влияние малых доз гамма-излучения на оптические свойства наноструктурированного кремния, полученного методом металл-стимулированного химического травления in situ

Влияние малых доз гамма-излучения на оптические свойства наноструктурированного кремния, полученного методом металл-стимулированного химического травления in situ

Evaluation of the Function of Ganglion Cells in Myopic Patients Using Pattern Electroretinogram (PERG)

<i>Objective</i>: Assessment of the macular ganglion cells function in myopic subjects using pattern electroretinogram (PERG) in comparison with healthy controls to help in diagnosing of retinal diseases, and studying the relationship of the changes seen in PERG with the axial length (AL) of the eye. <i>Methods</i>: The study was cross sectional, included 62 subjects (121 eyes). Three groups were examined: group 1: controls or emmetropics; group 2: mild myopics; group 3: moderate myopics. For all participants, a detailed pathological story was taken, a comprehensive eye examination was performed, AL was measured, and PERG was recorded, then the variables of the recorded waves (peak time and amplitude) were analyzed. <i>Results</i>: A statistically significant decrease in mean amplitudes of (P50, N95) waves was observed in group 2 (36 eyes) and 3 (25 eyes) compared to group 1 (60 eyes) (P-value <0.01), and a statistically significant elongation of mean N95 peak time was observed in (group 2 and 3) compared to group 1 (P-value <0.01) without being associated with elongation of mean P50 peak time. By studying the relationship between AL and each of peak time and amplitude of (P50, N95) waves, we have found that when AL increased, amplitudes decreased and peak times prolonged in a statistically significant way (P-value <0.01). <i>Conclusion</i>: The decreased amplitude of P50 wave may indicate a functional impairment of the macula in myopic subjects, and the decreased amplitude of N95 wave may be due to a functional impairment of their ganglion cells. The elongation of P50 peak time with increasing of AL may be due to a delay of the synaptic transmission between photoreceptors, bipolar cells, and ganglion cells.

Shared neural mechanisms for processing emotions in music and vocalizations.

The neural mechanisms involved in the processing of vocalizations and music were compared, in order to observe possible similarities in the encoding of their emotional content. Positive and negative emotional vocalizations (e.g. laughing, crying) and violin musical stimuli digitally extracted from them were used as stimuli. They shared the melodic profile and main pitch/frequency characteristics. Participants listened to vocalizations or music while detecting rare auditory targets (bird tweeting, or piano's arpeggios). EEG was recorded from 128 sites. P2, N400 and Late positivity responses of ERPs were analysed. P2 peak was earlier in response to vocalizations, while P2 amplitude was larger to positive than negative stimuli. N400 was greater to negative than positive stimuli. LP was greater to vocalizations than music and to positive than negative stimuli. Source modelling using swLORETA suggested that, among N400 generators, the left middle temporal gyrus and the right uncus responded to both music and vocalizations, and more to negative than positive stimuli. The right parahippocampal region of the limbic lobe and the right cingulate cortex were active during music listening, while the left superior temporal cortex only responded to human vocalizations. Negative stimuli always activated the right middle temporal gyrus, whereas positively valenced stimuli always activated the inferior frontal cortex. The processing of emotional vocalizations and music seemed to involve common neural mechanisms. Notation obtained from acoustic signals showed how emotionally negative stimuli tended to be in Minor key, and positive stimuli in Major key, thus shedding some lights on the brain ability to understand music.

A new electrophysiological non-invasive method to assess retinocortical conduction time in the Dark Agouti rat through the simultaneous recording of electroretinogram and visual evoked potential.

To develop a non-invasive method exploiting simultaneous recording of epidermal visual evoked potential (VEP) and epicorneal electroretinogram (ERG) to study retinocortical function and to evaluate its reliability and repeatability over time. Female wild-type DA rats were anesthetized with ketamine/xylazine (40/5mg/kg). Epidermal VEP (Ag/AgCl cup electrode on scalp) and epicorneal ERG (gold ring electrode on eye surface) were recorded simultaneously in response to flash stimulation. ANOVA for repeated measures showed that peak times of ERG b-wave and of VEP N1 and P2 were stable across 6weekly time-points, as well as the corresponding amplitudes. Mean retinocortical time from b-wave to N1 (RCT1) was 7.6ms and remained comparable across the 6 time-points. Mean retinocortical time from b-wave to P2 (RCT2) was 28.7ms and did not show significant variations over time. Coefficient of variation (CoV%) and CoV% adjusted for sample size, namely relative standard error (RSE%), were calculated as indexes of repeatability. Good RSE% over time was obtained (< 5% for b-wave, N1 and P2 peak times; < 20% and < 7% for RCT1 and RCT2, respectively). Simultaneous recording of ERG and VEP has been previously achieved through invasive methods requiring surgery. Here, we present a new non-invasive method, which allowed to obtain peak and retinocortical times that were constant across a long period and had a good repeatability over time. This method will ensure not only a gain in animal welfare, but will also avoid stress and eye or brain lesions which can interfere with experimental variables.

Spectral Change of E− Band Emission in a GaAs:N δ-Doped Superlattice Due to Below-Gap Excitation and Its Discrimination from Thermal Activation

In this study, we examined the E− band luminescence of a GaAs:N δ-doped superlattice (SL) grown by metal organic vapor phase epitaxy with 0.15% nitrogen (N) using two-wavelength excited photoluminescence. It was observed that the photoluminescence (PL) intensity of the low-energy peak (P2) at 1.38 eV of the E− band was quenched larger compared to the high-energy peak (P1) at 1.41 eV. This was due to the superposition of below-gap excitation (BGE) light of energy 0.95 eV over the above-gap excitation light of energy 1.45 eV on the SL structure at a fixed temperature of 12 K. On the other hand, at higher temperatures, the PL intensity of the high-energy peak P1 was quenched higher compared to the low-energy peak P2 without any addition of the BGE light. We interpreted the experimental results by considering the carrier recombination (CR) model and concluded that the observed PL spectral and intensity change of the E− band emission due to BGE does not result from the thermal activation, but from the optical excitation among the E− band, conduction band, and CR levels in GaAs:N δ-doped structure. We concluded that to achieve high-efficiency intermediate band-type solar cells, it is essential to understand the CR mechanism through CR levels by determining their origin and eliminating them from the material.

Evoked Frontal and Parietal Field Potential Signatures of Target Detection and Response Inhibition in Rats Performing an Equiprobable Auditory Go/No-Go Task.

To characterize the rat as a potential model of frontal-parietal auditory processing during sustained attention, target detection, and response inhibition, we recorded field potentials (FPs) at multiple sites in medial-dorsal frontal and posterior parietal cortex simultaneously while rats performed an equiprobable auditory go/no-go discrimination task. Event-related potentials (ERPs) were calculated by averaging tone-triggered FPs across hit, miss, false alarm (FA), and correct rejection (CR) trials separately for each recording session, and five peak amplitudes (termed N1, P2, N2, P3E, and P3L) were extracted from the individual-session ERPs. Comparing peak amplitudes across different trials types indicated a statistically significant amplification of the P2 peak on hit trials that accompanies detection of the target tone prior to the behavioral go response. This result appears analogous to human ERP phenomena during auditory target discrimination. Conversely, the rat P3 responses were not associated with target detection as in the human ERP literature. Likewise, we did not observe the "no-go N2" or "no-go P3" responses reported in the human literature in association with response inhibition, which might reflect differences in task context or a difference in auditory processing between rats and humans. We also present analyses of stimulus-induced spectral power and interarea coherence to characterize oscillatory synchronization which may contribute to ERPs, and discuss possible error-related processing at the N2, P3E, and P3L peaks.

From finger friction to brain activation: Tactile perception of the roughness of gratings

The formation of tactile perception is related to skin receptors and the cerebral cortex. In order to systematically study the tactile perception from finger friction to the brain response, a 32-channel Brain Products system and two tri-axial force sensors were used to obtain electroencephalograph (EEG) and friction signals during fingers exploring grating surfaces. A finite element finger model was established to analyze the stress changes of the skin receptors during tactile perception. Samples with different grating widths and spaces were chosen. The results indicated that different gratings induced different stress concentrations within skin that stimulated Meissner and Merkel receptors. Skin friction was affected by gratings during the tactile perception. It was also found that P300 evoked by gratings was related with the skin deformation, contact area, friction force, and stress around cutaneous mechanoreceptors. The wider grating width generated larger skin deformation, friction force, and stress, which induced stronger tactile stimulation. The smaller grating spacing generated higher vibration frequency, inducing stronger tactile stimulation. The latency of the P300 peak was related to the difference between the textured target stimulus and the smooth non-target stimulus. This study proofed that there was a relationship between the activation in brain regions, surface friction, and contact conditions of skin during the tactile perception. It contributes to understanding the formation process and cognitive mechanism of tactile perception of different surface textures.

Differential diagnostic method of initial implications and degree I of the chronic mercury intoxication

Currently available methods for diagnosis of chronic mercury intoxication (CMI) are applied at the any stage of the disease. Changes in these indices sometimes have no the specificity for any CMI stage, and a conclusion on them has the descriptive character. In addition, the above mentioned methods possess not sufficiently high accuracy in the diagnosis of intoxication at early stages of the development of the disease. The purpose of the research is the development of the method permitting to make the differential diagnosis between the initial symptoms of mercury poisoning and its first degree. 118 men who work/worked in the contact with mercury vapor were examined. There were evaluated electroencephalogram, long-latency auditory and cognitive evoked potentials, cerebral hemodynamics, noradrenaline (NA)content in the blood plasma. Statistical processing was performed with the use of «Statistica 6.0» software. The levels of NA in the development of CMI were shown to increase, by the time of the shaping of this disease the noted change was decompensated in the nature. The study of reactivity of cerebral vessels revealed the presence of abnormal responses during hypercapnic load in 14 - 24% of examined cases. In the analysis of auditory evoked potentials there was established the change in indices of latency and amplitude of the V- wave, which pronounced in the prolong response time, significant elongation in the P1 peak latency and the gain in the latency of N1 peak. There was established the presence of the wave-like change in the index of the latency of P300. In workers without an occupational disease, there was noted the marked elongation of the latent period of cognitive potential, while in patients with the newly made diagnosis the latency of P300 corresponded to standard values, and in the long term there was observed a sharp deterioration in this index. With the aid of the discriminant analysis with the calculation of canonical value there were revealed the most informative neurobiochemical indices, reoencephalogric ones and evoked potentials. The developed method of diagnosis allows to distinguish between the initial symptoms of mercury intoxication and the first stage of the disease.

High-frequency component in flash visual evoked potentials in type 3 Gaucher disease

ObjectiveTo characterize the visual evoked potentials (VEP) in patients with type 3 Gaucher disease (GD) with or without progressive myoclonus epilepsy. MethodsThree young adults with progressive myoclonus epilepsy (type 3a GD) and two children without progressive myoclonus epilepsy (type 3b GD) were enrolled. Flash visual and somatosensory evoked potentials (F-VEP and SEP, respectively) were retrospectively reviewed in all patients under enzyme replacement therapy. Pattern reversal visual evoked potentials (PR-VEP) were recorded in the type 3a group. ResultHigh-frequency components were provoked at early latencies on averaged F-VEP in all patients with type 3a and one patient with type 3b GD. Conversely, no activities were recorded in PR-VEP. The onset latency of the components began at 15.3–19.8 ms after flash stimulation. Four-five of the F-VEP examination the activities’ duration overrode the N75 waveforms and were prolonged toward the P100 peak latency. The F-VEP amplitude did not differ between the type 3a and type 3b groups, while the SEP amplitude was higher in the type 3a than in the type 3b group. SignificanceHigh-frequency components on F-VEP using bandpass filter at 10–200 Hz may help assess augmented excitability in the visual cortex of type 3 GD patients.

Revisiting mental rotation with stereoscopic disparity: A new spin for a classic paradigm

To understand how the presence of stereoscopic disparity influences cognitive and neural processing, we recorded participants’ behavior and scalp electrical activity while they performed a mental rotation task. Participants wore active shutter 3D goggles, allowing us to present stimuli with or without stereoscopic disparity on a trial-by-trial basis. Participants were more accurate and faster when stimuli were presented with stereoscopic disparity. This improvement in performance was accompanied by changes in neural activity recorded from scalp electrodes at parietal and occipital regions; stereoscopic disparity produced earlier P2 peaks, larger N2 amplitudes, and earlier, smaller P300 peak amplitudes. The presence of stereoscopic disparity also produced greater neural entropy at occipital electrode sites, and lower entropy at frontal sites. These findings suggest that the nature of the benefit afforded by stereoscopic disparity occurs at both low-level perceptual processing and higher-level cognitive processing, and results in more accurate and rapid performance.

Central Part of the Auditory Analyser in Children with Type 1 Diabetes

Aim. The present article assesses the state of the central part of the auditory analyser in children with type 1 diabetes.Materials and methods. The study included 71 children with type 1 diabetes mellitus who were treated at the Endocrinology Department of the Children’s Territorial Clinical Hospital from September 2017 to February 2018. The children’s age ranged from 7 to 15 years (8±2.6). Group A comprised 34 children who were fi rst diagnosed with type 1 diabetes, with the duration of clinical manifestations not exceeding 3 months; whereas group B included 37 children who had been suffering from type 1 diabetes for 1–5 years. The control group was represented by 30 children of the same age group without a somatic pathology (group K). The functional state of the central part of the auditory analyser was assessed when studying brainstem evoked potentials of short, middle and long latency.Results. In the course of studying short-latency brainstem evoked potentials at a broadband-click stimulus frequency of 10 Hz and an intensity of 70 dB, the latent periods of peaks and peak-topeak intervals were analysed in groups A, B and K. Statistically signifi cant differences were observed for I and V latent periods of peaks, as well as for the I–V inter-peak interval. At a click stimulus intensity of 70 dB, peaks and peak-to-peak intervals of middle-latency brainstem evoked potentials revealed differences in the values of NO, PO, Na, Pa and NO–PO between the groups of patients with type 1 diabetes and the control group. Greater statistical differences, as compared to the control group, were observed in the latent periods of long-latency brainstem evoked potentials for interval P1 in group A and intervals P2 and N2 in group B (unfavourable course) during 100 dB stimulation at a repetition frequency of 1 Hz in a time window of 50 ms. The presence of differences between groups A and B in the parameters of peak P2 (p ≤ 0.07), as well as peak intervals P2–N2, N1–N2, N1–P1, N2–P2 and N1–P2, may indicate signifi cant differences in the centres of the auditory analyser (p ≤ 0.1). At the same time, the maximum activity of the studied parameters was found in the group of patients with newly diagnosed type 1 diabetes.Conclusions. The study of different types of brainstem evoked potentials, characterising the central parts of the auditory analyser, in children with type 1 diabetes allowed the authors to register functional disorders both in the brainstem segment and in the cortical structures. This fact indirectly indicates initial manifestations of diabetic neuropathy in the studied category of patients and can be used in the future for diagnosing CNS disorders.

Moderate Cardiovascular Exercise Speeds Up Neural Markers of Stimulus Evaluation During Attentional Control Processes.

Moderate intensity cardiovascular exercise appears to provide a low-cost “intervention” on neurocognitive processes such as attentional control, yet the effects vary depending, for example, on cognitive task, time of testing, or exercise intensity. However, while a number of studies show that brief bouts of acute exercise can modulate behavioral indices of cognitive control, relatively few studies have attempted to identify the brain activity associated with these changes immediately following exercise. Here, we tested 11 young adults in a crossover design with a Flanker task at rest and immediately (within 2–3 min) following 20 min of acute exercise at 60% of the individual VO2max. In order to prevent delayed exercise effects that might confound or dilute immediate effects, a short version of the Flanker task (8 min) was chosen and an EEG was recorded simultaneously. The N2 and P3 ERP components were analyzed in addition to accuracy and response time. The N2 reflects conflict resolution, and the P3 has been linked to stimulus evaluation processes. No effect of exercise was found for behavioral data but P3 peak latencies were shorter following exercise as compared to rest. The N2 amplitude data suggest that exercise seems to prevent a decline in resources of attentional control over time. These data indicate that acute exercise, at a moderate intensity level, speeds up neural processing of attentional control by modulating stimulus evaluation processes immediately following exercise and that exercise helps maintain a steady level of neurocognitive resources.

Outer Retinal Dysfunction on Multifocal Electroretinography May Help Differentiating Multiple Sclerosis From Neuromyelitis Optica Spectrum Disorder.

Purpose: To evaluate the intermediate and outer retina of patients with multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) using OCT and multifocal electroretinography (mf-ERG).Methods: Patients with MS (n = 30), NMOSD (n = 30), and healthy controls (n = 29) underwent visual field (VF), OCT, and mf-ERG testing. The eyes were distributed into 5 groups: MS with or without history of ON (MS+ON, MS–ON), NMOSD with or without ON (NMOSD+ON, NMOSD–ON), and controls. The thickness of the macular retinal nerve fiber layer (mRNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer, outer plexiform layer, outer nuclear layer, and photoreceptor layer was measured. mf-ERG P1 and N1 responses were registered and grouped in 3 sets of rings. The groups were compared using GEE models, and effect size (ES) calculated.Results: Compared to controls, GCL and IPL thickness was significantly smaller in MS+ON (both p < 0.01), MS–ON (p < 0.01 and p = 0.015, respectively), NMOSD+ON (both p < 0.01) and NMOSD–ON (p = 0.03 and p = 0.018, respectively). ES was >0.80. mRNFL was smaller in three of the above groups (p < 0.01, p < 0.001, and p = 0.028; ES > 0.80) but not in MS–ON eyes (p = 0.18). No significant difference was observed for the remaining layers. Compared to controls, P1 and N1 peak times were shorter in MS (p-values in the range 0.049–0.002, ES < 0.50; and 0.049–0.010; ES < 0.50, respectively) but not in NMOSD. These abnormalities were strongly correlated with intermediate and outer retinal layer thickness.Conclusions: mf-ERG data suggest outer retinal abnormalities in MS, but not in NMOSD. Our results may help understand how the two conditions differ regarding retinal damage.

A link between durability of WC-Co coated cutting tools and mechanical damping spectra

• WC-Co exhibits three IF peaks. Peaks P1 and P2 are related to the cobalt phase and P3 to the WC-WC grain boundaries. • IF peaks P1 and P2 coexist over several annealing processes. • The coating induces a temperature variation of the Peak P1, showing an effect of the coating on the cobalt bulk material. • Clear correlation between peak P1 temperature-shift and tool-life. • The damping process related to the Peak P1 may be related to a strain-glass transition occurring in the cobalt phase.

Encoding Pleasant and Unpleasant Expression of the Architectural Window Shapes: An ERP Study.

The evaluation of building facades is one of the most important elements in built environments for helping architects and professionals to develop future designs. The form or shape of windows in building facades has direct impacts on perceivers’ affective state and emotions. To understand the impacts of geometric windows on the subject’s feedback and cortical activity, psychophysics experiments and electroencephalogram (EEG) recordings were measured from the participants. Our behavioral results show a distinguished categorization of the window shapes as pleasant and unpleasant stimuli. The rectangular, square, circular and semi-circular arch were determined as the pleasant window shapes, while the triangular and triangular arch window shapes were distinguished as unpleasant. Furthermore, event-related potential (ERP) components (N1, P2 and P3) were investigated to determine the influence of window shapes on the local brain activity. To measure reliable cortical responses, a Butterworth notch filter (50 Hz), band pass filter (0.1–60 Hz) and ADJUST filter were employed to remove the artifacts. The electrophysiological results show increased activity for the unpleasant in comparison to the pleasant windows (p < 0.05, Rank-Sum test) in both frontal (for P2 component) and posterio-occipital (ERP amplitudes; the N1 through to the P3 peak) channels. The ERP amplitudes of the right hemisphere were significantly larger than in the left hemisphere, not only in response to the unpleasant (p < 0.001) but also to the pleasant window stimuli (p < 0.001, Signed-Rank test). However, the unpleasant stimuli evoked significantly larger ERP amplitude than the pleasant stimuli. Moreover, the significant ERPP2 amplitude was more distinguished for unpleasant (p = 0.01, Signed-Rank test) than pleasant windows (p = 0.01, Rank-Sum test) between frontal and central cortical lobes. Overall, our behavioral and electrophysiological studies demonstrate a distinguished categorization of pleasant and unpleasant window shapes and more significant ERP modulations in the right than left hemisphere for unpleasant windows compared to pleasant ones.

Comparison between a Passive and Active response task and their effect on the Amplitude and Latency of the P300 component for Visual Stimuli while using Low Fidelity Equipment.

In this paper, we investigate the effect, in terms of amplitude and latency, of the P300 component in a separate active and passive task response condition. This work is based on the P300 speller BCI (oddball) paradigm and the xDAWN algorithm, with five healthy subjects; while using a noninvasive Brain-Computer Interface (BCI) based on low fidelity electroencephalographic (EEG) equipment. Our results suggest that an active task yielded a larger P300 peak amplitude while there was no discriminable difference in the peak latency. The signal was also morphological consistent in both scenarios, even though they did not yield identical P300 components. This groundwork yields imperative data for future work where we plan to introduce several distractions, including communication with the user while performing the P300 speller paradigm.

Markers of Novelty Processing in Older Adults Are Stable and Reliable.

Exploratory behavior and responsiveness to novelty play an important role in maintaining cognitive function in older adults. Inferences about age- or disease-related differences in neural and behavioral responses to novelty are most often based on results from single experimental testing sessions. There has been very limited research on whether such findings represent stable characteristics of populations studied, which is essential if investigators are to determine the result of interventions aimed at promoting exploratory behaviors or draw appropriate conclusions about differences in the processing of novelty across diverse clinical groups. The goal of the current study was to investigate the short-term test-retest reliability of event-related potential (ERP) and behavioral responses to novel stimuli in cognitively normal older adults. ERPs and viewing durations were recorded in 70 healthy older adults participating in a subject-controlled visual novelty oddball task during two sessions occurring 7 weeks apart. Mean midline P3 amplitude and latency, mean midline amplitude during successive 50 ms intervals, temporospatial factors derived from principal component analysis (PCA), and viewing duration in response to novel stimuli were measured during each session. Analysis of variance (ANOVA) revealed no reliable differences in the value of any measurements between Time 1 and 2. Intraclass correlation coefficients (ICCs) between Time 1 and 2 were excellent for mean P3 amplitude (ICC = 0.86), the two temporospatial factors consistent with the P3 components (ICC of 0.88 and 0.76) and viewing duration of novel stimuli (ICC = 0.81). Reliability was only fair for P3 peak latency (ICC = 0.56). Successive 50 ms mean amplitude measures from 100 to 1,000 ms yielded fair to excellent reliabilities, and all but one of the 12 temporospatial factors identified demonstrated ICCs in the good to excellent range. We conclude that older adults demonstrate substantial stability in ERP and behavioral responses to novel visual stimuli over a 7-week period. These results suggest that older adults may have a characteristic way of processing novelty that appears resistant to transient changes in their environment or internal states, which can be indexed during a single testing session. The establishment of reliable measures of novelty processing will allow investigators to determine whether proposed interventions have an impact on this important aspect of behavior.

Rotationally driven VHE emission from the Vela pulsar

Context. The recent detection of pulsedγ-ray emission from the Vela pulsar in the ∼10 to 100 GeV range by H.E.S.S. promises important potential to probe into the very high energy (VHE) radiation mechanisms of pulsars.Aims. A combined analysis of H.E.S.S. andFermi-LAT data suggests that the leading wing of the P2 peak shows a new, hard gamma-ray component (with photon index as hard as Γ ∼ 3.5), setting in above 50 GeV and extending beyond 100 GeV. We study these findings in the context of rotationally driven (centrifugal) particle acceleration.Methods. We analyze achievable particle energies in the magnetosphere of the Vela pulsar and calculate the resultant emission properties.Results. Inverse Compton up-scattering of thermal photons from the surface of the star is shown to lead a pulsed VHE contribution reaching into the TeV regime with spectral characteristics compatible with current findings. If confirmed by further observations this could be the second case where rotationally driven processes turn out to be important to understand the VHE emission in young pulsars.

Tracking the implicit acquisition of nonadjacent transitional probabilities by ERPs

The implicit acquisition of complex probabilistic regularities has been found to be crucial in numerous automatized cognitive abilities, including language processing and associative learning. However, it has not been completely elucidated how the implicit extraction of second-order nonadjacent transitional probabilities is reflected by neurophysiological processes. Therefore, this study investigated the sensitivity of event-related brain potentials (ERPs) to these probabilistic regularities embedded in a sequence of visual stimuli without providing explicit information on the structure of the stimulus stream. Healthy young adults (N = 32) performed a four-choice RT task that included a sequential regularity between nonadjacent trials yielding a complex transitional probability structure. ERPs were measured relative to both stimulus and response onset. RTs indicated the rapid acquisition of the sequential regularity and the transitional probabilities. The acquisition process was also tracked by the stimulus-locked and response-locked P3 component: The P3 peak was larger for the sequence than for the random stimuli, while the late P3 was larger for less probable than for more probable short-range relations among the random stimuli. According to the RT and P3 effects, sensitivity to the sequential regularity is assumed to be supported by the initial sensitivity to the transitional probabilities. These results suggest that stimulus–response contingencies on the probabilistic regularities of the ongoing stimulus context are implicitly mapped and constantly revised. Overall, this study (1) highlights the role of predictive processes during implicit memory formation, and (2) delineates a potential to gain further insight into the dynamics of implicit acquisition processes.