Central Spike Research Articles

Clinical Significance of Incidental Rolandic Spikes in Children With Absence Epilepsy.

Absence epilepsy and benign epilepsy of childhood with central temporal spikes are common childhood epilepsy syndromes. Although 3-Hz generalized spike-wave discharges are almost always associated with absence seizures, rolandic spikes can be present in individuals without rolandic seizures. The co-occurrence of 3-Hz generalized spike-wave and rolandic spikes is very rare. Our objective was to compare clinical features of patients with absence epilepsy with and without rolandic spikes, to determine if the additional feature of rolandic spikes has any clinical significance. Clinical information of 17 children with absence epilepsy and rolandic spikes was compared to an age-matched control group of 90 children with absence epilepsy. Although most patients had excellent seizure control at follow-up, epilepsy comorbidities (cognitive and emotional problems) were observed. Comparing study vs control groups, there was no difference with anxiety (2 [11.8%] vs 8 [9%]), behavioral issues (4 [23.5%] vs 10 [11%]), mood disorders (0 vs 2 [2%]), and attention-deficit hyperactivity disorder (4 [24%] vs 10 [11%]). Significant differences were also observed: more global-developmental (5 [29%] vs 5 [6%], P < .009) and expressive-language (4 [24%] vs 5 [6%], P < .034) delay and more difficulties with school performance (11 [65%] vs 32 [36%], P < .025), especially with language-related tasks (6 [35%] vs 5 [6%], P < .001). Our results confirm the presence of additional epilepsy comorbidities in patients with absence epilepsy when rolandic spikes are present. Rolandic spikes in patients with absence epilepsy may be a marker of additional cognitive challenges that physicians should be aware of.

High-power supercontinuum generation by noise-like pulse amplification in Yb-doped fiber amplifier operating in a nonlinear regime.

In this paper, we report on a supercontinuum generation by amplifying noise-like pulses (NLPs) in a nonlinear Yb-doped fiber amplifier. The NLP source is a homemade Yb-doped all-fiber ring oscillator based on nonlinear polarization rotation mode-locking method. NLPs possess a repetition rate of 11.57MHz, energy of 16.5nJ, and 3dB spectral bandwidth of 42nm. The intensity autocorrelation function of NLPs has a broad pedestal and a narrow central spike. The pedestal and the spike have temporal widths of 63ps and 92fs, respectively. The NLPs are amplified by a Yb-doped fiber nonlinear power amplifier to achieve output power of 7.5W. Nonlinear effects in the amplifier drastically broaden the spectrum of NLPs and generate high-power supercontinuum light with 10dB spectral bandwidth of 1130nm (from 1037 to 2167nm). The presented supercontinuum generation system is an all-fiber compact structure and has the advantage of not requiring long single-mode, nonlinear, or photonic crystal fibers.

A SNP-Based High-Density Genetic Map Reveals Reproducible QTLs for Tassel-Related Traits in Maize (Zea mays L.)

The tassel architecture of maize (Zea mays L.), which plays an important role in F1 hybrid seed production and yield performance, is genetically controlled by quantitative trait loci (QTLs). Here, we constructed a high-density SNP-based genetic map using an F2 population containing 148 individuals. This genetic map included 7613 SNPs whose average genetic distance was 0.19 cM. On account of the F2 population, we detected 14 QTLs responsible for tassel branch number (TBN), tassel weight (TW), central spike length (CSL), and meristem length (ML); eight of these QTLs demonstrated a relatively high level of phenotypic variation explanation (PVE) (PVE ≥ 10%), at a high level of significance. qTW-2 was a major QTL (LOD = 10.11 and PVE = 28.82%), and this QTL and qTBN-2 shared the same region, indicating a possible pleiotropic effect. An F2:3 population was developed to further verify QTLs in the F2 population. Finally, qTBN-5, qTW-2 and qCSL_N-10 were detected reproducibly. To help screen potential candidate genes, we chose 12 genes within the regions of qTBN-5, qML-6, qCSL_N-7 and qTW-2 and that were possibly involved in tassel morphogenesis according to Gene Ontology (GO) annotation analysis and performed quantitative real-time polymerase chain reaction (qRT-PCR). The expression of eight of the 12 genes was significantly (P < 0.05) or extremely significantly different (P < 0.01) between parents of the F2 population during the young tassel development stage, suggesting that those eight were possible candidate genes. These results provide insights into the genetic mechanisms controlling tassel architecture and will benefit both tassel-related QTL fine mapping and causal gene cloning in maize.

Nonlinear analysis of magnetic liquid free surface deformation in a 3D space

Abstract The nonlinear analysis of magnetic liquid free surface deformation under the influence of a static vertically oriented magnetic field produced by a pair of Helmholtz coils in a 3D space is presented in the article. The hexagonal pattern of peaks resulting from the Rosensweig or normal instability, occurs when the magnetization of the magnetic liquid exceeds the critical value. To predict the amplitudes and distance between peaks in the pattern, nonlinear analysis should be performed with employed higher order terms in the mean curvature expression of the free surface. The computational strategy presented in the article is divided into two stages. At the first stage, the magnetic field in the 3D space is calculated by the FEM based software Opera Field, while the second stage is devoted to determining the surface profile by minimizing the energy functional using a Differential Evolution algorithm in Matlab. The amplitudes of the central spike and wave number have been computed for the various values of the excitation magnetic field.

Phase-resolved spectroscopy of Gaia14aae: line emission from near the white dwarf surface

AM CVn binaries are a class of ultracompact, hydrogen-deficient binaries, each consisting of a white dwarf accreting helium-dominated material from a degenerate or semi-degenerate donor star. Of the 56 known systems, only Gaia14aae undergoes complete eclipses of its central white dwarf, allowing the parameters of its stellar components to be tightly constrained. Here, we present phase-resolved optical spectroscopy of Gaia14aae. We use the spectra to test the assumption that the narrow emission feature known as the `central spike' traces the motion of the central white dwarf. We measure a central spike velocity amplitude of $13.8 \pm 3.2$ km/s, which agrees at the 1 $\sigma$ level with the predicted value of $17.6 \pm 1.0$ km/s based on eclipse-derived system parameters. The orbital phase offset of the central spike from its expected position is $4 \pm 15$ $^\circ$, consistent with 0 $^\circ$. Doppler maps of the He I lines in Gaia14aae show two accretion disc bright spots, as seen in many AM CVn systems. The formation mechanism for the second spot remains unclear. We detect no hydrogen in the system, but we estimate a 3 $\sigma$ limit on H$\alpha$ emission with an equivalent width of -1.14 \AA. Our detection of nitrogen and oxygen with no corresponding detection of carbon, in conjunction with evidence from recent studies, mildly favours a formation channel in which Gaia14aae is descended from a cataclysmic variable with a significantly evolved donor.

Co-existence of Rolandic and 3 Hz Spike-Wave Discharges on EEG in Children with Epilepsy.

Benign epilepsy of childhood with central temporal spikes (BECTS) and absence epilepsy are common epilepsy syndromes in children with similar age of onset and favorable prognosis. However, the co-existence of the electrocardiogram (EEG) findings of rolandic spike and 3 Hz generalized spike-wave (GSW) discharges is extremely rare, with few cases reported in the literature. Our objective was to characterize the EEG findings of these syndromes in children in our center and review the electro-clinical features. All EEGs at BC Children's Hospital are entered in a database, which include EEG findings and clinical data. Patients with both centro-temporal spikes and 3 Hz GSW discharges were identified from the database and clinical data were reviewed. Among the 43,061 patients in the database from 1992 to 2017, 1426 with isolated rolandic discharges and 528 patients with isolated 3 Hz GSW discharges were identified, and 20 (0.05%) patients had both findings: 3/20 had BECTS, and subsequently developed childhood absence epilepsy and 17/20 had no seizures characteristic for BECTS. At follow-up, 17 (85%) were seizure-free, 1 (5%) had rare, and 2 (10%) had frequent seizures. This is the largest reported group of patients to our knowledge with the co-existence of rolandic and 3 Hz GSW discharges on EEGs in one institution, not drug-induced. As the presence of both findings is extremely rare, distinct pathophysiological mechanisms are likely. The majority had excellent seizure control at follow-up, similar to what would be expected for each type of epilepsy alone.

Application of high-dose Diazepam in epileptic children with electrical status epilepticus during sleep

Objective To explore the therapeutic effects and adverse reaction of high-dose Diazepam (DZP) in patients with electrical status epilepticus during sleep (ESES). Methods Nine patients in the Outpatient of the Department of Pediatrics, Peking University First Hospital from October 2016 to May 2017 with ESES were treated with high-dose DZP.Oral DZP was administered in a dose of 0.75-1.00 mg/kg(maximum: 40 mg) during the first night followed by 0.5 mg/(kg·d) (maximum: 20 mg) from the second night for 1-3 months and tapered over next 1-3 months.The seizures, electroencephalogram (EEG) changes and adverse reactions were observed before and after DZP treatment. Results Six of 9 patients were male and 3 were female.The age of onset was ranged from 1 year and 6 months to 10 years.Benign childhood epilepsy with central temporal spike was diagnosed in 5 cases, epileptic encephalopathy with continuous spike-and-wave during sleep in 1 case, and ESES related epilepsy in 3 cases.Age of onset DZP treatment ranged from 4 years and 4 months to 12 years, and the duration of DZP treatment was ranged from 1 to 5 months (1 case only for the first night). The follow-up interval was 6-12 months.The efficiency of DZP on seizures: intent effective in 5 patients, effective in 2 patients and ineffective in 2 patients, and the effective rate was 78% (7/9 cases). The efficiency of DZP on EEG (1 month after DZP treatment): intent effective in 2 patients (EEG norma-lized), effect in 3 patients and no effect in 2 patients, and the effective rate was 71% (5/7 cases), while 2 patients did not receive EEG examination.Four of 7 patients (57%) with intent effect and effective of DZP on seizures had seizures relapse during drug reduction and after drug withdrawal, and the EEG deteriorated simultaneously.Adverse reactions of DZP included 3 patients (33%) with adverse reactions, bed-wetting in 2 patients and snoring on the first night in 1 patient who withdrew DZP later. Conclusions The high-dose of DZP has a certain effect on seizures control and ESES suppression in patients with ESES, but also has a certain recurrence rate.The adverse reactions are mild and self-limiting.High-dose DZP treatment could be a choice for refractory patients with ESES to alleviate disease. Key words: Electrical status epilepticus during sleep; Diazepam; Epilepsy

Targeting mechanisms of tailed bacteriophages.

Phages differ substantially in the bacterial hosts that they infect. Their host range is determined by the specific structures that they use to target bacterial cells. Tailed phages use a broad range of receptor-binding proteins, such as tail fibres, tail spikes and the central tail spike, to target their cognate bacterial cell surface receptors. Recent technical advances and new structure-function insights have begun to unravel the molecular mechanisms and temporal dynamics that govern these interactions. Here, we review the current understanding of the targeting machinery and mechanisms of tailed phages. These new insights and approaches pave the way for the application of phages in medicine and biotechnology and enable deeper understanding of their ecology and evolution.

Star clusters, self-interacting dark matter halos, and black hole cusps: The fluid conduction model and its extension to general relativity.

We adopt the fluid conduction approximation to study the evolution of spherical star clusters and self-interacting dark matter (SIDM) halos. We also explore the formation and dynamical impact of density cusps that arise in both systems due to the presence of a massive, central black hole. The large N-body, self-gravitating systems we treat are "weakly collisional": the mean free time between star or SIDM particle collisions is much longer than their characteristic crossing (dynamical) time scale, but shorter than the system lifetime. The fluid conduction model reliably tracks the "gravothermal catastrophe" in star clusters and SIDM halos without black holes. For a star cluster with a massive, central black hole, this approximation reproduces the familiar Bahcall-Wolf quasistatic density cusp for the stars bound to the black hole and shows how the cusp halts the "gravothermal catastrophe" and causes the cluster to re-expand. An SIDM halo with an initial black hole central density spike that matches onto to an exterior NFW profile relaxes to a core-halo structure with a central density cusp determined by the velocity dependence of the SIDM interaction cross section. The success and relative simplicity of the fluid conduction approach in evolving such "weakly collisional," quasiequilibrium Newtonian systems motivates its extension to relativistic systems. We present a general relativistic extension here.

Study on gene mutation in benign familial neonatal epilepsy

Objective To investigate the gene mutations in benign familial neonatal epilepsy(BFNE) in China. Methods Data of all BFNE probands and their family members were collected from Peking University First Hospital from January 2012 to December 2013.Clinical phenotypes of affected members were analyzed.Genomic DNA was extracted from peripheral blood samples with standard protocol.Mutations in candidate genes mutations were further screened by next-generation sequencing. Results A total of 4 families were collected, from which there were 10 affected members, 6 males and 4 females.The age of epilepsy onset was from 1 day to 4 days after birth.The age of last seizure was from 3 days to 3 years and 10 months old.The age of last follow-up was from 4 years and 3 months old to 37 years old.All affected members had normal development.Genetic testing identified KCNQ2 mutations in 3 families (75%, 3/4 cases). Two families had missense KCNQ2 mutations (c.1048A>C/p.N350H and c. 242T>C/p.L81P). One family had nonsense KCNQ2 mutation(c.2506G>T/p.E836X). The other 3 KCNQ2 mutations were novel.The remaining BFNE family was not detected with any pathogenic mutation.The age of inital seizure onset of the proband was 1 day after birth.The seizures got controlled at 3 months old.However, this proband had another 2 afebrile seizures during sleep at 3 years and 10 months old.Electroenlephalography monitoring showed focal central temporal spikes.It is speculated that the seizures had evolved into benign epilepsy of childhood with central temporal spikes. Conclusions Mutations in KCNQ2 are major genetic causes in Chinese families with BFNE.KCNQ2 mutation c. 1048A>C/p.N350H, c.242T>C/p.L81P, and c. 2506G>T/p.E836X are novel mutations.Identification of underlying gene mutation can be helpful for clinical diagnosis and judgment of the prognosis. Key words: Benign familial neonatal epilepsy; KCNQ2 gene; Gene mutation

Quantum square-well with logarithmic central spike

Singular repulsive barrier [Formula: see text] inside a square-well is interpreted and studied as a linear analog of the state-dependent interaction [Formula: see text] in nonlinear Schrödinger equation. In the linearized case, Rayleigh–Schrödinger perturbation theory is shown to provide a closed-form spectrum at sufficiently small [Formula: see text] or after an amendment of the unperturbed Hamiltonian. At any spike strength [Formula: see text], the model remains solvable numerically, by the matching of wave functions. Analytically, the singularity is shown regularized via the change of variables [Formula: see text] which interchanges the roles of the asymptotic and central boundary conditions.

The double helium-white dwarf channel for the formation of AM CVn binaries

Most close double helium white dwarfs will merge within a Hubble time due to orbital decay by gravitational wave radiation. However, a significant fraction with low mass ratios will survive for a long time as a consequence of stable mass transfer. Such stable mass transfer between two helium white dwarfs (HeWDs) provides one channel for the production of AM CVn binary stars. In previous calculations of double HeWD progenitors, the accreting HeWD was treated as a point mass. We have computed the evolution of 16 double HeWD models in order to investigate the consequences of treating the evolution of both components in detail. We find that the boundary between binaries having stable and unstable mass transfer is slightly modified by this approach. By comparing with observed periods and mass ratios, we redetermine masses of eight known AM CVn stars by our double HeWDs channel, i.e. HM Cnc, AM CVn, V406 Hya, J0926, J1240, GP Com, Gaia14aae and V396 Hya.We propose that central spikes in the triple-peaked emission spectra of J1240, GP Com and V396 Hya and the surface abundance ratios of N/C/O in GP Com can be explained by the stable double HeWD channel. The mass estimates derived from our calculations are used to discuss the predicted gravitational wave signal in the context of the Laser Interferometer Space Antenna (LISA) project.

AGO18b negatively regulates determinacy of spikelet meristems on the tassel central spike in maize.

The maize tassel represents an indeterminate male inflorescence. The number of primordia that a given inflorescence meristem produces is related to its determinacy, i.e., capacity for continued meristem activity. Transcription factors (TFs) controlling determinacy in tassel axillary meristems are well studied in maize, and small RNAs are known to influence tassel development by repressing targets, including tassel-related TFs. As core components of the RNA-inducible silence complex (RISC), Argonaute (AGO) proteins are required for small RNA-mediated repression. Here, we characterized the biological function of AGO18b, a tassel-enriched AGO. The abundance of AGO18b transcripts gradually increased during tassel development from inception to gametogenesis and were enriched in the inflorescence meristem and axillary meristems of the tassel. Repressing AGO18b expression resulted in more spikelets, which contributed to a longer central spike of the tassel. Additionally, the transcripts of several HD-ZIP III TFs that were canonical targets of microRNA166 (miR166) accumulated in the AGO18b-repressed lines. We propose that AGO18b is a negative regulator of the determinacy of inflorescence and axillary meristems, and that it acts by interacting with the miR166-HD-ZIP III TF regulatory pathway.

High-contrast sub-Doppler absorption spikes in a hot atomic vapor cell exposed to a dual-frequency laser field

The saturated absorption technique is an elegant method widely used in atomic and molecular physics for high-resolution spectroscopy, laser frequency standards and metrology purposes. We have recently discovered that a saturated absorption scheme with a dual-frequency laser can lead to a significant sign reversal of the usual Doppler-free dip, yielding a deep enhanced-absorption spike. In this paper, we report detailed experimental investigations of this phenomenon, together with a full in-depth theoretical description. It is shown that several physical effects can support or oppose the formation of the high-contrast central spike in the absorption profile. The physical conditions for which all these effects act constructively and result in very bright Doppler-free resonances are revealed. Apart from their theoretical interest, results obtained in this manuscript are of great interest for laser spectroscopy and laser frequency stabilization purposes, with applications in laser cooling, matter-wave sensors, atomic clocks or quantum optics.

Pluto occultation on 2015 June 29 UTC with central flash and atmospheric spikes just before the New Horizons flyby

We observed the occultation by Pluto of a 12th magnitude star, one of the two brightest occultation stars ever in our dozen years of continual monitoring of Pluto's atmosphere through such studies, on 2015 June 29 UTC.At the Univ. of Canterbury Mt. John Observatory (New Zealand), under clear skies throughout, we used a POETS frame-transfer CCD at 10Hz with GPS timing on the 1-m McLellan telescope as well as an infrared camera on an 0.6-m telescope and three-color photometry at a slower cadence on a second 0.6-m telescope. At the Auckland Observatory, we used a POETS and a PICO on 0.5-m and 0.4-m telescopes, with 0.4s and 2s cadences, respectively, obtaining ingress observations before clouds moved in. The Mt. John light curves show a central flash, indicating that we were close to the center of the occultation path. Analysis of our light curves show that Pluto's atmosphere remains robust.The presence of spikes at both sites in the egress and ingress shows atmospheric layering. We coordinated our observations with aircraft observations (Bosh et al., 2017) with the Stratospheric Observatory for Infrared Astronomy (SOFIA). Our chords helped constrain the path across Pluto that SOFIA saw. Our ground-based and airborne stellar-occultation effort came only just over two weeks of Earth days and two Pluto days before the flyby of NASA's New Horizons spacecraft.

Central MONDian spike in spherically symmetric systems

Under a MONDian view, astrophysical systems are expected to follow Newtonian dynamics whenever the local acceleration is above the critical $a_{0}=1.2 \times 10^{-10} m s^{-2}$, and enter a modified regime for accelerations below this critical value. Indeed, the dark matter phenomenology on galactic and subgalactic scales appears always, and only, at low accelerations. It is standard to find the $a<a_{0}$ regime towards the low density outskirts of astronomical systems, where under a Newtonian interpretation, dark matter becomes conspicuous. Thus, it is standard to find, and to think, of the dense central regions of observed systems as purely Newtonian. However, under spherical symmetry in the MONDian as in the Newtonian case, the local acceleration will tend to zero as one approaches the very centre of a mass distribution. It is clear that for spherically symmetric systems, an inner $a<a_{0}$ region will necessarily appear interior to a critical radius which will depend on the details of the density profile in question. Here we calculate analytically such a critical radius for a constant density core, and numerically for a cored isothermal profile. Under a Newtonian interpretation, such a central MONDian region will be interpreted as extra mass, analogous to the controversial black holes sometimes inferred to lie at the centres of globular clusters, despite an absence of nuclear activity detected to date. We calculate this effect and give predictions for the "central black hole" mass to be expected under Newtonian interpretations of low density Galactic globular clusters.

Clinical characteristics and treatment strategies of the variants of benign childhood epilepsy with central temporal spikes

目的 探讨儿童良性癫痫伴中央颞区棘波(BECT)变异型的临床特点及治疗策略。 方法 回顾分析2010年1月至2015年1月就诊于本院的15例BECT变异型患儿的临床资料。 结果 15例BECT变异型患儿的起病年龄中位数为5岁7个月(1岁1个月～10岁)；病程9个月～7年。87.0%(13/15例)患儿符合BECT变异型Ⅰ型的临床表现。88.0%(10/12例)随访儿童存在一定程度的学习障碍，所有患儿脑电图均显示一侧或双侧中央、顶区和(或)中、后颞区(Rolandic区)散在的棘慢波或棘波发放，睡眠后明显增多。33%(5/15例)患儿合并不典型失神，47%(7/15例)患儿清醒期可监测到负性肌阵挛的发作，同期可明确发现相应的脑电图改变。丙戊酸钠加用左乙拉西坦、丙戊酸钠加用氯硝西泮和丙戊酸钠加用左乙拉西坦及氯硝西泮为较为常用的抗癫痫药物组合。对于口服抗癫痫药物无效的患儿可予甲泼尼龙冲击治疗。 结论 BECT变异型均伴有明显的脑电图恶化，认识其临床和脑电图变化的特点及规律，可提高对BECT变异型的诊断。抗癫痫药物目的不仅是控制临床发作，更重要的是减少脑电图的异常放电。

Numerical modeling of a glow discharge through a supersonic bow shock in air

The interaction between a glow discharge and the bow shock of a Mach 3 air flow around a truncated conical model with a central spike is modeled, and comparison is made with prior experimental results. The KRONOS workflow for plasma modeling in flow fields, which has recently been developed at ONERA, was used for the modeling. Based on the quasi-neutral approximation, it couples hypersonic and reactive flow fields with electron chemistry, including the effect of non-Maxwellian electron energy distribution function. The model used for the discharge involves 12 species and 82 reactions, including ionization, electronic and vibrational excitation, and attachment. The simulations reproduce the main features of the discharge observed experimentally well, in particular, the very recognizable topology of the discharge. It was found from the simulations that behind the bow shock, in the afterglow, the negative ion flow ensures the electrical conduction and the establishment of the glow discharge. The influence of kinetic rates on the voltage-current characteristics is discussed.

Partial deletion of DEPDC5 in a child with focal epilepsy.

SummaryWe report on a child, aged 47/12 years, with borderline intelligence quotient, normal brain magnetic resonance imaging, and focal epilepsy. The polysomnographic electroencephalogram recording revealed asynchronous central spikes at both brain hemispheres resembling the features observed in focal idiopathic epileptic syndromes. Array comparative genomic hybridization analysis revealed a 32‐kb partial deletion of the DEP domain‐containing protein 5 (DEPDC5) gene, involved in a wide spectrum of inherited focal epileptic syndromes. The parental origin of the deletion could not be fully ascertained because the pregnancy had been achieved through anonymous egg donation and insemination by intracytoplasmic sperm injection. However, we demonstrate that the deletion, shared by all alternatively spliced isoforms of DEPDC5, produces a transcript presumably generating a DEPDC5 protein missing the entire DEP domain. Our findings suggest that partial deletion of DEPDC5 may be sufficient to cause the focal epilepsy in our patient, highlighting the importance of the DEP domain in DEPDC5 function. This study expands the phenotypic spectrum of DEPDC5 to sporadic forms of focal idiopathic epilepsy and underscores the fact that partial deletions, albeit probably very rare, are part of the genetic spectrum of DEPDC5 mutations.

28SiOv= 0J= 1–0 emission from evolved stars

Observations of 28SiO v=0 J=1-0 line emission (7-mm wavelength) from AGB stars show in some cases peculiar profiles, composed of a central intense component plus a wider plateau. Very similar profiles have been observed in CO lines from some AGB stars and most post-AGB nebulae and, in these cases, they are clearly associated with the presence of conspicuous axial symmetry and bipolar dynamics. We present systematic observations of 28SiO v=0 J=1-0 emission in 28 evolved stars, performed with the 40~m radio telescope of the IGN in Yebes, Spain. We find that the composite core plus plateau profiles are almost always present in O-rich Miras, OH/IR stars, and red supergiants. They are also found in one S-type Mira ($\chi$ Cyg), as well as in two semiregular variables (X Her and RS Cnc) that are known to show axial symmetry. In the other objects, the profiles are simpler and similar to those of other molecular lines. The composite structure appears in the objects in which SiO emission is thought to come from the very inner circumstellar layers, prior to dust formation. The central spectral feature is found to be systematically composed of a number of narrow spikes, except for X Her and RS Cnc, in which it shows a smooth shape that is very similar to that observed in CO emission. These spikes show a significant (and mostly chaotic) time variation, while in all cases the smooth components remain constant within the uncertainties. The profile shape could come from the superposition of standard wide profiles and a group of weak maser spikes. Alternatively, we speculate that the very similar profiles detected in objects that are axisymmetric may be indicative of the systematic presence of a significant axial symmetry in the very inner circumstellar shells around AGB stars; the presence of such symmetry would be independent of the probable weak maser effects in the central spikes.