Distinct Negative Peak Research Articles

Detection and classification of long-latency own-name auditory evoked potential from electroencephalogram

Auditory Evoked Potential (AEP) is an electrophysiological signal elicited from the brain while an auditory stimulus is presented in a time-locked manner. Previous studies reported the occurrence of AEPs in response to different audio stimuli during the time interval up to 600 ms from the onset of the stimulus. In this paper, we report the occurrence and detection of long-latency AEPs, around 1.5 s after the onset of the stimulus, from the Electroencephalogram (EEG) acquired when the participants listen to voice clips of their own-name. The trial averaged AEPs of 24 participants who listened to audio stimuli of their own-name and familiar-names clearly showed the occurrence of a distinct negative peak around 1.5 s after the onset of the own-name stimulus in Fp1 and F7 EEG electrodes. No such long-latency AEPs were observed when the participants listened to familiar-name stimulus. We classified the own-name and familiar-name averaged AEP responses using a quadratic kernel support vector machine (SVM) classifier. The leave-one-participant-out cross-validation was performed, and the classification accuracy achieved is 80.56 % (corresponding to averaging of 8AEP responses) with a sensitivity of 68.52 % and a specificity of 92.59 %. Our study reveals the occurrence of a distinct long-latency AEP around 1.5 s for own-name stimulus and a higher discrimination ability of participants in discarding non-self-referential stimuli (familiar-name) compared to self-referential stimuli (own-name). The method can be applied for the off-line analysis of own-name AEPs to diagnose mild cognitive impairments and also developmental disorders like autism.

Effects of acoustic stimulus duration on cervical vestibular evoked myogenic potentials: A neurophysiological and modeling study.

To analyze and model the effects of acoustic stimulus duration on cervical vestibular evoked myogenic potentials (cVEMPs). Subjects with normal hearing and no vestibular or cervical disorders were tested using 1 kHz tone bursts (TBs) of different durations to evoke cVEMPs from the ipsilateral sternocleidomastoid muscle. VEMP modeling was performed in Labview. The increase in TB duration initially resulted in a non-linear increase in cVEMP amplitude, followed by more complex cVEMP modifications that were mainly related to the appearance of a new wave (nX) that interfered with n23. With long TBs there were two distinct negative peaks with an identical threshold, suggesting a common vestibular nature. A two-level inhibition model qualitatively accounted for the two distinct negative peaks. However, good fitting of the cVEMP waveform required a multi-level model that included an excitatory phase after the inhibitory period. The two negative components (n23 and nX) observed in cVEMPs elicited by long TBs may result from the involvement of two different pathways with different dynamics or a single pathway with quick adaptation in the activity along the vestibulo-collic arc. Excitatory activity following the period of inhibition may represent rebound activity at the motor unit level.

X-ray Absorption Spectroscopy in the Heavy Fermion Compound α-YbAlB4 at High Magnetic Fields

α-YbAlB4 shows strong valence fluctuation as well as heavy fermion behavior at low temperatures. It has been theoretically suggested that the quantum criticality owing to the valence fluctuation found in Yb ions plays an important role in the peculiar properties of this material. In this work, we measured the X-ray absorption spectra (XAS) and X-ray magnetic circular dichroism (XMCD) at the L3 edge of Yb ions in high magnetic fields of up to 40 T. It is found that the XAS are almost independent of the magnetic field at 2 K, which proves that there is no significant valence change in this field range. The XMCD spectrum exhibits a distinct negative peak at the low-energy side of the L3 edge as well as the main positive peak near the white line. The negative XMCD peak is attributed to the quadrupole transition between the 2p and 4f states, and gives us microscopic information on the 4f state. This finding supports the recent theoretical proposal that \(|J_{z} = \pm 5/2\rangle \) is the ground state of the lo...

Event-related potentials to intact and disrupted actions in children and adults

The current research used event-related potentials (ERPs) to investigate neurophysiological responses to intact and disrupted actions embedded within an event in children and adults. Responses were recorded as children (24-month-olds) and adults observed a relatively novel event composed of three actions. In one condition pauses were inserted at intact boundaries (i.e., at the endpoint of each action), whereas in the other condition they were inserted at breakpoints that disrupted the action (i.e., in the middle of each action). Evoked responses revealed differences across conditions in both groups; disrupted actions elicited a prolonged negative slow wave from 100 to 700ms in children, whereas adults demonstrated two distinct negative peaks between 50–150 and 250–350ms. These findings contribute the first electrophysiological evidence that children readily detect disruptions to ongoing events by the end of the second year, even with limited exposure to the event itself. Furthermore, they suggest that adults rely on two distinct mechanisms when processing novel events. Results are discussed in relation to the role of perceptual and conceptual levels of analysis in the development of action processing.

Plasmonically enhanced Faraday effect in metal and ferrite nanoparticles composite precipitated inside glass

Using femtosecond laser irradiation and subsequent annealing, nanocomposite structures composed of spinel-type ferrimagnetic nanoparticles (NPs) and plasmonic metallic NPs have been formed space-selectively within glass doped with both α-Fe(2)O(3) and Al. The Faraday rotation spectra exhibit a distinct negative peak at around 400 nm, suggesting that the ferrimagnetic Faraday response is enhanced by the localized surface plasmon resonance (LSPR) due to metallic Al NPs. At the interfaces in the nanocomposites, the ferrimagnetism of magnetite NPs is directly coupled with the plasmon in the Al NPs. The control of the resonance wavelength of the magneto-optical peaks, namely, the size of plasmonic NPs has been demonstrated by changing the irradiation or annealing conditions.

Characterization of buried inundated peat on seismic (Chirp) data, inferred from core information

AbstractPeat horizons provide a wide range of critical environmental and direct archaeological information for both archaeologists and Quaternary geologists. At present, such data are typically obtained from terrestrial exposures or cores, and occasional offshore cores. These data can provide invaluable and detailed site‐specific environmental information but require a relatively high spatial sampling strategy to provide more regional‐scale information. Through a comparison of laboratory, in situ acoustic and sedimentary analyses, this paper presents evidence to suggest that peat buried in fine to medium grained, marine, siliciclastic sediments has an easily identifiable acoustic signature. The very low densities recorded by buried peats result in a distinct negative peak in the reflectivity series. Comparison of synthetic seismograms with in situ seismic data confirms that this negative peak can be easily identified from seismic profiles. Reanalysis of a decade of Chirp (sub‐bottom) data, acquired from the Solent Estuary, indicates that possible extensive peat deposits, dating from the Late‐glacial to early Holocene, can be traced at depth in this estuary using geophysical methods. The results of this study could be significant for future research into submerged landscape reconstructions. Copyright © 2007 John Wiley & Sons, Ltd.

Vacuum-ultraviolet circular dichroism study of saccharides by synchrotron radiation spectrophotometry

Vacuum-ultraviolet circular dichroism (VUVCD) spectra of five monosaccharides ( d-glucose, d-mannose, d-galactose, d-xylose, and d-lyxose) and five disaccharides (maltose, isomaltose, cellobiose, gentiobiose, and lactose) were measured to 160 nm using a synchrotron-radiation VUVCD spectrophotometer in aqueous solution under high vacuum at 25 °C. Most of the saccharides show a positive peak with some shoulders at around 170 nm, except for d-galactose and lactose, which show two distinct negative peaks at around 165 and 177 nm. These spectra are influenced by such structural factors as α and β anomers at C-1, axial and equatorial hydroxyl groups at C-2 and C-4, trans (T) and gauche (G) conformations of the hydroxymethyl group at C-5, and the type of glycosidic linkage. Deconvolution of the VUVCD spectra of d-glucose, d-mannose, and d-galactose into six independent Gaussian components for α-GG, α-GT, α-TG, β-GG, β-GT, and β-TG conformations suggests that the α anomer has red-shifted spectra relative to the β anomer, and that GG and GT conformations have positive and negative circular dichroism signs, respectively, while the sign for TG conformation is anomer dependent. These speculations from the deconvolution analyses are also supported by the VUVCD spectra of disaccharides. These results give new insight into the equilibrium conformations of saccharides, demonstrating the usefulness of synchrotron-radiation VUVCD spectroscopy.

Comparison of touch- and laser heat-evoked cortical field potentials in conscious rats

Field potentials and multiunit activities from chronically implanted cortical electrodes were used to study tactile and nociceptive information processing from the tail of the rat. Fourteen stainless steel screws implanted in the skull were used as electrodes to record field potentials in different cortical areas. Electrical, mechanical, and laser pulses were applied to the tail to induce evoked cortical field potentials. Evoked responses were compared before and after sodium pentobarbital anesthesia (50 mg/kg, i.p.). In both electrical- and mechanical-evoked potential (EEP and MEP) studies, two major peaks were found in the conscious animal. The polarity of the late component was modified after pentobarbital anesthesia. In the laser-evoked potential (LEP) study, two distinct negative peaks were found. Both peaks were very sensitive to anesthesia. Following quantitative analysis, our data suggest that the first positive peak of EEP and MEP corresponded to the activation of the Aβ fiber, the second negative peak of MEP and the first peak of LEP corresponded to Aδ fiber activation, while the second peak of LEP corresponded to C fiber activation. The absolute magnitudes of all cortical components were positively related to the intensity of the stimulation. From spatial mapping analysis, a localized concentric source of field potential was observed in the primary somatosensory cortex (SI) only after activation of the Aβ fiber. Larger responsive cortical areas were found in response to Aδ and C fiber activation. In an intracortical recording experiment, both tactile and nociceptive stimulation evoked heightened unit activity changes at latencies corresponding to respective field potentials. We conclude that different cortical areas are involved in the processing of A and C fiber afferent inputs, and barbiturate anesthesia modifies their processing.

Intergrain Ordering of a Superconductive Ceramic of YBa2Cu4O8at Zero External Magnetic Field Studied by Linear and Nonlinear Transport Coefficients

The intergrain ordering in a superconductive ceramic of YBa 2 Cu 4 O 8 at zero external magnetic field is investigated by AC resistivity measurements. The third harmonic in-phase voltage component V ' 3ω to a weak AC current shows a distinct negative peak across the intergrain transition temperature T C2 , but not across the intragrain one T C1 ( T C2 < T C1 ). A divergence of the nonlinear resistivity ρ 2 is concluded at T C2 in the limit of vanishing AC current, while the linear resistivity ρ 0 remains finite even at and below T C2 . Such characteristic critical behaviors of the intergrain ordering of the present superconductive ceramic strongly suggest a chiral glass ordering recently predicted to occur in high- T C superconductive ceramics.

Structural changes associated with the spontaneous inactivation of the serine proteinase human tryptase.

Human skin tryptase, a serine proteinase stored within mast cell secretory granules, rapidly loses enzymatic activity in solutions of physiological salt concentration, pH, and temperature. The inactivation of tryptase can be slowed and even reversed by addition of heparin, a highly sulfated glycosaminoglycan also found in the secretory granules. These properties may be relevant to tryptase regulation after secretion from mast cells. To further characterize the molecular changes underlying the functional instability of tryptase, circular dichroism (CD) and analytical ultracentrifugation were used to investigate structural changes during spontaneous inactivation. The CD spectra of active and spontaneously inactivated tryptase are different, particularly in the region around 230 nm where active tryptase displays a distinct negative peak. This peak is also observed in the CD spectrum of bovine chymotrypsin but not in trypsin, elastase, or chymotrypsinogen. Loss of activity resulting from spontaneous inactivation was accompanied by a diminution of the 230-nm signal. The kinetics for the signal loss appeared to be first-order and closely paralleled the rate of enzymatic activity loss. Dextran sulfate, a highly sulfated polysaccharide, was capable of reactivating tryptase and restoring the CD signal. After 2 h of decay (> 90% loss of activity), addition of dextran sulfate resulted in an almost immediate return of the CD signal to that of active tryptase. The return of the CD signal appeared to be more rapid than the return of enzymatic activity, thereby suggesting the presence of an unidentified step which is rate-limiting for activity return (and loss) and subsequent (prior) to the CD change accompanying activity loss. Ultracentrifugation analysis of tryptase showed a marked change in its association state upon inactivation. Sedimentation equilibrium under stabilizing conditions demonstrated the presence of a single species with the molecular weight of a tetramer. After spontaneous inactivation, a mixture of species was evident, which was characterized as monomers and tetramers in equilibrium. These results demonstrate that spontaneous inactivation of tryptase is associated with reversible conformational changes and that a consequence of inactivation is the formation of a destabilized tetrameric form. Although the molecular mechanism initiating these changes remains unclear, possible insights into the process are discussed on the basis of the similarity between the CD spectra of tryptase and chymotrypsin.

Click-evoked responses from the cochlear nucleus: a study in human

Recordings from the vicinity of the cochlear nucleus in 9 patients undergoing microvascular decompression operations to relieve hemifacial spasm, trigeminal neuralgia, tinnitus, and disabling positional vertigo were conducted by placing a monopolar electrode in the lateral recess of the fourth ventricle (through the foramen of Luschka), the floor of which is the dorsolateral surface of the dorsal cochlear nucleus. The click-evoked potentials recorded by such an electrode display a slow negative wave with a peak latency of about 6–7 msec on which several sharp peaks are superimposed. None of the peaks in the recordings from the vicinity of the cochlear nucleus coincided with any vertex-positive peaks of the brain-stem auditory evoked potentials. In recordings from the lateral aspect of the floor of the fourth ventricle near the cochlear nucleus 1 patient showed 2 positive peaks, the earliest of which had a latency close to that of peak II and the second of which had a latency close to the negative peak between peaks III and IV of the brain-stem auditory evoked potentials. There is a distinct negative peak in the responses recorded from the midline of the floor of the fourth ventricle, the latency of which is only slightly shorter than that of peak V of the brain-stem auditory evoked potentials, supporting earlier findings that the sharp tip of peak V of the brain-stem auditory evoked potentials is generated by the termination of the lateral lemniscus in the inferior colliculus.