In situ biochemical characterization of Venus cloud particles using a life-signature detection microscope.

Much of the information about the size and shape of aerosols forming haze and the cloud layer of Venus is obtained from indirect inferences from nephelometers on probes and from the analysis of the variation of polarization with the phase angle and the glory feature from images of Venus. The microscopic imaging of Venus' aerosols has recently been advocated. Direct measurements from a fluorescence microscope can provide information on the morphology, density, and biochemical characteristics of the particles; thus, fluorescence microscopy is attractive for in situ particle characterization of the Venus cloud layer. Fluorescence imaging of Venus cloud particles presents several challenges owing to the sulfuric acid composition and corrosive effects. In this article, we identify the challenges and describe our approach to overcoming them for a fluorescence microscope based on an in situ biochemical and physical characterization instrument for use in the clouds of Venus from a suitable aerial platform. We report that pH adjustment using alkali was effective for obtaining fluorescence images and that fluorescence attenuation was observed after the adjustment, even when the acidophile suspension in concentrated sulfuric acid was used as a sample.

A case of ovarian serous cystadenofibroma with scattered lesions in pelvic cavity, like malignant disseminations.

Ovarian serous cystadenofibroma is a relatively rare subtype of serous cystadenoma classified as ovarian benign epithelial tumor. We report a rare case of ovarian serous cystadenofibroma with scattered lesions in pelvic cavity, like malignant disseminations. The patient was 22 years old, gravida 0, para 0. In the laparoscopic surgery, numerous hard yellowish-white solid masses of various sizes were present in the bilateral ovaries. Grossly similar masses were scattered in the fimbria of the fallopian tubes, peritoneum, and great omentum. Because the intraoperative rapid histological diagnosis was benign tumor, surgery was completed for only tumor excision. Postoperative histopathological diagnosis is serous cystadenofibroma. Similar pathological findings were noted in the scattered lesions in the peritoneum and great omentum. No malignant or borderline malignant finding was observed. Because of a benign disease, careful treatment taking fertility preservation into consideration is necessary, especially for young patients.

A Neural Mechanism of Cue-Outcome Expectancy Generated by the Interaction Between Orbitofrontal Cortex and Amygdala.

Taste perception is important for animals to take adequate nutrients and avoid toxins for their survival. Appetitive and aversive behaviors are produced by value evaluation of taste and taste expectation caused by other sensations. The value evaluation, coupled with a cue presentation, produces outcome expectation and guides flexible behaviors when the environment is changed. Experimental studies demonstrated distinct functional roles of basolateral amygdala (ABL) and orbitofrontal cortex (OFC) in value evaluation and adaptive behavior. ABL is involved in generating a cue-outcome association, whereas OFC makes a contribution of generating a cue-triggered expectation to guide adaptive behavior. However, it remains unclear how ABL and OFC form their functional roles, with the learning of adaptive behavior. To address this issue, we focus on an odor discrimination task of rats and develop a computational model that consists of OFC and ABL, interacting with reward and decision systems. We present the neural mechanisms underlying the rapid formation of cue-outcome association in ABL and late behavioral adaptation mediated by OFC. Moreover, we offer 2 functions of cue-selective neurons in OFC: one is that the activation of cue-selective neurons transmits value information to decision area to guide behavior and another is that persistent activity of cue-selective neurons evokes a weak activity of taste-sensitive OFC neurons, leading to cue-outcome expectation. Our model further accounts for ABL and OFC responses caused by lesions of these areas. The results provide a computational framework of how ABL and OFC are functionally linked through their interactions with the reward and decision systems.

Representation of object's shape by multiple electric images in electrolocation.

Weakly electric fish generate an electric field by discharging an electric organ located on the tail region. An object near the fish modulates the self-generated electric field. The modulated field enables the fish to perceive objects even in complete darkness. The ability to perceive objects is provided by the electrosensory system of the fish. Electroreceptors distributed on the fish's skin surface can sense the modulated field, on the basis of transdermal voltage across the skin surface, called electric images. The fish can extract object's features such as lateral distance, size, shape, and electric property from an electric image. Although previous studies have demonstrated the relationship between electric-image features and object's distance and size, it remains unclear what features of an electric image represent the object's shape. We make here a hypothesis that shape information is not represented by a single image but by multiple images caused by the object's rotation or fish movement around the object. To test the hypothesis, we develop a computational model that can predict electric images produced by the rotation of differently shaped objects. We used five different shapes of resistive objects: a circle, a square, an equilateral triangle, a rectangle, and an ellipsoid. We show that differently shaped objects of a fixed arrangement generate similar Gaussian electric images, irrespective of their shapes. We also show that the features of an electric image such as the peak amplitude, half-maximum width, and peak position exhibit the angle-dependent variations characteristic to object rotation, depending on object shapes and lateral distances. Furthermore, we demonstrate that an integration effect of the peak amplitude and half-maximum width could be an invariant measure of object shape. These results suggest that the fish could perceive an object shape by combining those image features produced during exploratory behaviors around the object.

Chronic tubal pregnancy manifesting as a heterogeneous adnexal mass with prominent neovascularization in a woman with a negative serum ß-human chorionic gonadotropin level.

A 41-year-old woman (gravida 2, para 1) underwent elective termination of pregnancy at approximately 7 weeks of gestation. At 1 month after the elective abortion, she was referred due to abnormal results in a cervical cytological examination. Transvaginal ultrasonography showed a heterogeneous mass of 16 mm in diameter in the left adnexal region. At 3 months after her referral, the asymptomatic left adnexal mass had increased to 55 mm in diameter. Prominent vascular flow was detected in the solid portion by color Doppler ultrasonography. Magnetic resonance imaging showed suspected hemorrhage in the left adnexal cystic mass. Three-dimensional computerized tomographic angiography showed the prominent development of tortuous blood vessels in the left adnexal region, which originated from the left ovarian artery. The patient had a negative ß-human chorionic gonadotropin (hCG) level. Left salpingectomy was performed by a single-port laparoscopic approach. A pathological examination revealed degenerated villous tissue with ß-hCG-positive syncytiotrophoblasts.

A Neural Mechanism of Taste Perception Modulated by Odor Information.

Taste perception is significantly affected by other sensory modalities such as vision, smell, and somatosensation. Such taste sensation elicited by integrating gustatory and other sensory information is referred to as flavor. Although experimental studies have demonstrated the characteristics of flavor perception influenced by other sensory modalities and the involved brain areas, it remains unknown how flavor emerges from the brain circuits. Of the involved brain areas, orbitofrontal cortex (OFC), as well as gustatory cortex (GC), plays a dominant role in flavor perception. We develop here a neural model of gustatory system which consists of GC and OFC networks and examine the neural mechanism of odor-induced taste perception. Using the model, we show that flavor perception is shaped by experience-dependent learning of foods with congruent taste-odor pairs, providing a unique representation of flavor through the interaction between OFC and GC neurons. Our model also shows that feedback signals from OFC to GC modulate the dynamic stability of taste attractors in GC, leading to the enhancement or suppression of taste responses by smells. Furthermore, modeling shows that spatial variability in GC activity evoked by tastants determines to what extent odor enhances congruent taste responses. The results suggest that flavor perception is deeply associated with dynamic stability of GC attractors through the interaction between GC and OFC.

An efficient and straightforward online vector quantization method for a data stream through remove-birth updating.

The growth of network-connected devices has led to an exponential increase in data generation, creating significant challenges for efficient data analysis. This data is generated continuously, creating a dynamic flow known as a data stream. The characteristics of a data stream may change dynamically, and this change is known as concept drift. Consequently, a method for handling data streams must efficiently reduce their volume while dynamically adapting to these changing characteristics. This article proposes a simple online vector quantization method for concept drift. The proposed method identifies and replaces units with low win probability through remove-birth updating, thus achieving a rapid adaptation to concept drift. Furthermore, the results of this study show that the proposed method can generate minimal dead units even in the presence of concept drift. This study also suggests that some metrics calculated from the proposed method will be helpful for drift detection.

Bacterial and fungal bioburden reduction on material surfaces using various sterilization techniques suitable for spacecraft decontamination.

Planetary protection is a guiding principle aiming to prevent microbial contamination of the solar system by spacecraft (forward contamination) and extraterrestrial contamination of the Earth (backward contamination). Bioburden reduction on spacecraft, including cruise and landing systems, is required to prevent microbial contamination from Earth during space exploration missions. Several sterilization methods are available; however, selecting appropriate methods is essential to eliminate a broad spectrum of microorganisms without damaging spacecraft components during manufacturing and assembly. Here, we compared the effects of different bioburden reduction techniques, including dry heat, UV light, isopropyl alcohol (IPA), hydrogen peroxide (H2O2), vaporized hydrogen peroxide (VHP), and oxygen and argon plasma on microorganisms with different resistance capacities. These microorganisms included Bacillus atrophaeus spores and Aspergillus niger spores, Deinococcus radiodurans, and Brevundimonas diminuta, all important microorganisms for considering planetary protection. Bacillus atrophaeus spores showed the highest resistance to dry heat but could be reliably sterilized (i.e., under detection limit) through extended time or increased temperature. Aspergillus niger spores and D. radiodurans were highly resistant to UV light. Seventy percent of IPA and 7.5% of H2O2 treatments effectively sterilized D. radiodurans and B. diminuta but showed no immediate bactericidal effect against B. atrophaeus spores. IPA immediately sterilized A. niger spores, but H2O2 did not. During VHP treatment under reduced pressure, viable B. atrophaeus spores and A. niger spores were quickly reduced by approximately two log orders. Oxygen plasma sterilized D. radiodurans but did not eliminate B. atrophaeus spores. In contrast, argon plasma sterilized B. atrophaeus but not D. radiodurans. Therefore, dry heat could be used for heat-resistant component bioburden reduction, and VHP or plasma for non-heat-resistant components in bulk bioburden reduction. Furthermore, IPA, H2O2, or UV could be used for additional surface bioburden reduction during assembly and testing. The systemic comparison of sterilization efficiencies under identical experimental conditions in this study provides basic criteria for determining which sterilization techniques should be selected during bioburden reduction for forward planetary protection.

AlphaDDA: strategies for adjusting the playing strength of a fully trained AlphaZero system to a suitable human training partner.

Artificial intelligence (AI) has achieved superhuman performance in board games such as Go, chess, and Othello (Reversi). In other words, the AI system surpasses the level of a strong human expert player in such games. In this context, it is difficult for a human player to enjoy playing the games with the AI. To keep human players entertained and immersed in a game, the AI is required to dynamically balance its skill with that of the human player. To address this issue, we propose AlphaDDA, an AlphaZero-based AI with dynamic difficulty adjustment (DDA). AlphaDDA consists of a deep neural network (DNN) and a Monte Carlo tree search, as in AlphaZero. AlphaDDA learns and plays a game the same way as AlphaZero, but can change its skills. AlphaDDA estimates the value of the game state from only the board state using the DNN. AlphaDDA changes a parameter dominantly controlling its skills according to the estimated value. Consequently, AlphaDDA adjusts its skills according to a game state. AlphaDDA can adjust its skill using only the state of a game without any prior knowledge regarding an opponent. In this study, AlphaDDA plays Connect4, Othello, and 6x6 Othello with other AI agents. Other AI agents are AlphaZero, Monte Carlo tree search, the minimax algorithm, and a random player. This study shows that AlphaDDA can balance its skill with that of the other AI agents, except for a random player. AlphaDDA can weaken itself according to the estimated value. However, AlphaDDA beats the random player because AlphaDDA is stronger than a random player even if AlphaDDA weakens itself to the limit. The DDA ability of AlphaDDA is based on an accurate estimation of the value from the state of a game. We believe that the AlphaDDA approach for DDA can be used for any game AI system if the DNN can accurately estimate the value of the game state and we know a parameter controlling the skills of the AI system.

Approximate spectral clustering using both reference vectors and topology of the network generated by growing neural gas.

Spectral clustering (SC) is one of the most popular clustering methods and often outperforms traditional clustering methods. SC uses the eigenvectors of a Laplacian matrix calculated from a similarity matrix of a dataset. SC has serious drawbacks: the significant increases in the time complexity derived from the computation of eigenvectors and the memory space complexity to store the similarity matrix. To address the issues, I develop a new approximate spectral clustering using the network generated by growing neural gas (GNG), called ASC with GNG in this study. ASC with GNG uses not only reference vectors for vector quantization but also the topology of the network for extraction of the topological relationship between data points in a dataset. ASC with GNG calculates the similarity matrix from both the reference vectors and the topology of the network generated by GNG. Using the network generated from a dataset by GNG, ASC with GNG achieves to reduce the computational and space complexities and improve clustering quality. In this study, I demonstrate that ASC with GNG effectively reduces the computational time. Moreover, this study shows that ASC with GNG provides equal to or better clustering performance than SC.

Modeling the electric image produced by objects with complex impedance in weakly electric fish.

Weakly electric fish generate an electric field around their body by electric organ discharge (EOD). By measuring the modulation of the electric field produced by an object in the field these fish are able to accurately locate an object. Theoretical and experimental studies have focused on the amplitude modulations of EODs produced by resistive objects. However, little is known about the phase modulations produced by objects with complex impedance. The fish must be able to detect changes in object impedance to discriminate between food and nonfood objects. To investigate the features of electric images produced by objects with complex impedance, we developed a model that can be used to map the electric field around the fish body. The present model allows us to calculate the spatial distribution of the amplitude and phase shift in an electric image. This is the first study to investigate the changes in amplitude and phase shift of electric images induced by objects with complex impedance in wave-type fish. Using the model, we show that the amplitude of the electric image exhibits a sigmoidal change as the capacitance and resistance of an object are increased. Similarly, the phase shift exhibits a significant change within the object capacitance range of 0.1-100 nF. We also show that the spatial distribution of the amplitude and phase shifts of the electric image resembles a "Mexican hat" in shape for varying object distances and sizes. The spatial distribution of the phase shift and the amplitude was dependent on the object distance and size. Changes in the skin capacitance were associated with a tradeoff relationship between the magnitude of the amplitude and phase shift of the electric image. The specific range of skin capacitance (1-100 nF) allows the receptor afferents to extract object features that are relevant to electrolocation. These results provide a useful basis for the study of the neural mechanisms by which weakly electric fish recognize object features such as distance, size, and impedance.

Tadalafil, a long-acting inhibitor of PDE5, improves pulmonary hemodynamics and survival rate of monocrotaline-induced pulmonary artery hypertension in rats.

The aim of this study was to assess the effect of tadalafil (0.5, 2.5, and 10 mg/kg per day) on the progression of pulmonary arterial hypertension (PAH) in early treatment and on the survival rate in late treatment on the monocrotaline (MCT)-induced PAH rat model. Tadalafil was administered once daily to rats for 3 weeks from the day of MCT-injection or 21 days after the injection. With early treatment, tadalafil at 10 mg/kg per day prevented the development of PAH by maintaining mean pulmonary artery pressure within the normal range and attenuated right ventricular hypertrophy. With late treatment, tadalafil tended to increase the partial pressure of oxygen in arterial blood and dose-dependently improved the survival rate by 55%, 60%, and 70% at 0.5, 2.5, and 10 mg/kg per day, respectively, versus 40% in the MCT-control group. Both early and late treatments with tadalafil were associated with elevated lung cyclic guanosine monophosphate (cGMP). These results suggest that tadalafil relaxes pulmonary arteries by elevating cGMP in lungs and extend survival time by improving pulmonary hemodynamics even when treatment occurs in the late phase of PAH. Thus, it is expected that tadalafil may be an effective, once-daily treatment option in humans with PAH.

Transport of impact ejecta from Mars to its moons as a means to reveal Martian history.

Throughout the history of the solar system, Mars has experienced continuous asteroidal impacts. These impacts have produced impact-generated Mars ejecta, and a fraction of this debris is delivered to Earth as Martian meteorites. Another fraction of the ejecta is delivered to the moons of Mars, Phobos and Deimos. Here, we studied the amount and condition of recent delivery of impact ejecta from Mars to its moons. Using state-of-the-art numerical approaches, we report, for the first time, that materials delivered from Mars to its moons are physically and chemically different from the Martian meteorites, which are all igneous rocks with a limited range of ages. We show that Mars ejecta mixed in the regolith of its moons potentially covers all its geological eras and consists of all types of rocks, from sedimentary to igneous. A Martian moons sample-return mission will bring such materials back to Earth, and the samples will provide a wealth of "time-resolved" geochemical information about the evolution of Martian surface environments.

Enhanced Antibacterial Property of Facet-Engineered TiO2 Nanosheet in Presence and Absence of Ultraviolet Irradiation.

Titania (TiO2) has attracted much attention recently for reducing bacterial diseases by the generation of reactive oxygen species (ROS) under UV irradiation. However, demand for higher photocatalytic activity due to higher recombination of electron and hole remains. The aims of this study were to make titania with higher antibacterial property and show the mechanisms of the bactericidal effect. In this study, we hydrothermally synthesized TiO2 nanosheets (NS) with highly-oriented structures. Samples were divided into five groups, depending on the fluorine/titanium ratio in the raw material, namely NS1.0, NS1.2, NS1.5, NS1.8, and NS2.0. Facet ratio and nanosheet size increased with an increase of fluorine/titanium ratio. The photocatalytic activity of TiO2 nanosheet was assessed by the generation of ROS. Hydroxyl radicals and superoxides were generated efficiently by ultraviolet light irradiation on NS1.5 and NS1.0, respectively. Antibacterial activity against Streptococcus mutans was assessed in the presence and absence of UV irradiation; NS1.0 showed superior antibacterial properties compared to commercially available TiO2 nanoparticles, under both conditions, due to the oxidation of intracellular components and cell membrane. These results together suggested TiO2 nanosheet induced bacterial cell death by oxidation, and TiO2 facet engineering resulted in enhancement of both photocatalytic and antibacterial activities of TiO2.

Assessment of the probability of microbial contamination for sample return from Martian moons I: Departure of microbes from Martian surface.

Potential microbial contamination of Martian moons, Phobos and Deimos, which can be brought about by transportation of Mars ejecta produced by meteoroid impacts on the Martian surface, has been comprehensively assessed in a statistical approach, based on the most probable history of recent major gigantic meteoroid collisions on the Martian surface. This article is the first part of our study to assess potential microbial density in Mars ejecta departing from the Martian atmosphere, as a source of the second part (Kurosawa et al., 2019) where statistical analysis of microbial contamination probability is conducted. Potential microbial density on the Martian surface as the source of microorganisms was estimated by analogy to the terrestrial areas having the similar arid and cold environments, from which a probabilistic function was deduced as the asymptotic limit. Microbial survival rate during hypervelocity meteoroid collisions was estimated by numerical analysis of impact phenomena with and without taking internal friction and plastic deformation of the colliding meteoroid and the target ground into consideration. Trajectory calculations of departing ejecta through the Martian atmosphere were conducted with taking account of aerodynamic deceleration and heating by the aid of computational fluid dynamic analysis. It is found that Mars ejecta smaller than 0.03 m in diameter hardly reach the Phobos orbit due to aerodynamic deceleration, or mostly sterilized due to significant aerodynamic heating even though they can reach the Phobos orbit and beyond. Finally, the baseline dataset of microbial density in Mars ejecta departing for Martian moons has been presented for the second part of our study.

Assessment of the probability of microbial contamination for sample return from Martian moons II: The fate of microbes on Martian moons.

This paper presents a case study of microbe transportation in the Mars-satellites system. We examined the spatial distribution of potential impact-transported microbes on the Martian moons using impact physics by following a companion study (Fujita et al., in this issue). We used sterilization data from the precede studies (Patel et al., 2018; Summers, 2017). We considered that the microbes came mainly from the Zunil crater on Mars, which was formed during 1.0-0.1 Ma. We found that 70-80% of the microbes are likely to be dispersed all over the moon surface and are rapidly sterilized due to solar and galactic cosmic radiation except for those microbes within a thick ejecta deposit produced by natural meteoroids. The other 20-30% might be shielded from radiation by thick regolith layers that formed at collapsed layers in craters produced by Mars rock impacts. The total number of potentially surviving microbes at the thick ejecta deposits is estimated to be 3-4 orders of magnitude lower than at the Mars rock craters. The microbe concentration is irregular in the horizontal direction due to Mars rock bombardment and is largely depth-dependent due to the radiation sterilization. The surviving fraction of transported microbes would be only ∼1 ppm on Phobos and ∼100 ppm on Deimos, suggesting that the transport processes and radiation severely affect microbe survival. The microbe sampling probability from the Martian moons was also investigatesd. We suggest that sample return missions from the Martian moons are classified into Unrestricted Earth-Return missions for 30 g samples and 10 cm depth sampling, even in our conservative scenario. We also conducted a full statistical analysis pertaining to sampling the regolith of Phobos to include the effects of uncertainties in input parameters on the sampling probability. The most likely probability of microbial contamination for return samples is estimated to be two orders of magnitude lower than the 10-6 criterion defined by the planetary protection policy of the Committee on Space Research (COSPAR).

Regulation of periodontal ligament-derived cells by type III collagen-coated hydroxyapatite.

BACKGROUND: The periodontal ligament (PDL), which maintains homeostasis in the periodontium, is a group of specialized connective tissue fibers attached to both the cementum and alveolar bone. Regeneration of periodontium with PDL cells has been investigated, and the chemical and molecular structures of scaffolds control the adhesion and differentiation of cells. Therefore, the development of adequate materials for PDL-derived cells is essential to regenerate the periodontium. OBJECTIVE: We evaluated the suitable passage time for PDL-derived cells and investigated the behaviors of PDL-derived cells grown on hydroxyapatite (HAp) scaffolds coated with type I and type III collagen. METHODS: PDL-derived cells were isolated with enzyme from the upper molars of male Wister rats. After characterization of HAp, type I collagen, and type III collagen, PDL-derived cells at passage 2 were seeded onto collagen-coated HAp. Cell adhesion, proliferative potential, and osteoconductivity were analyzed with immunostaining, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays, Alizarin S staining, and real-time polymerase chain reaction. RESULTS: Type I and III collagens were successfully coated on HAp. Gene expression analysis revealed that passage 2 was suitable for maintaining differentiation potential. Proliferative potential and cell adhesion were significantly higher on type III collagen than on HAp alone or type I collagen. In contrast, the osteoconductivity of type III collagen was significantly lower than those of HAp and type I collagen. CONCLUSION: PDL-derived cells on type I collagen differentiated into osteogenic cells and formed hard tissues. However, type III collagen enhanced the adhesion of PDL-derived cells and inhibited mineralization.

A role of synchronicity of neural activity based on dynamic plasticity of synapses in encoding spatiotemporal features of electrosensory stimuli.

It is quite important for investigation of sensory mechanism to understand how dynamical property of neurons is used for encoding the feature of spatiotemporally varying stimuli. To consider concretely the problem, we focus our study on electrosensory system of a weakly electric fish. Weakly electric fish generate electric field around their body using electric organ discharge (EOD) and accurately detect the location of an object through the modulation of electric field induced by the object. We made a neural network model of electrosensory lateral-line lobe (ELL). Here we show that the features of EOD modulation depending specifically distance and size of an object are encoded into the timing of burst firing of ELL neurons. These features can be represented by the spatial area of synchronous burst firing and the interburst interval in the ELL network. We show that short-term changes of excitatory and inhibitory synapses, induced by efferent signals, regulate the ELL activity so as to effectively encode the features of EOD modulation.

A neural mechanism of dynamic gating of task-relevant information by top-down influence in primary visual cortex.

Visual recognition involves bidirectional information flow, which consists of bottom-up information coding from retina and top-down information coding from higher visual areas. Recent studies have demonstrated the involvement of early visual areas such as primary visual area (V1) in recognition and memory formation. V1 neurons are not passive transformers of sensory inputs but work as adaptive processor, changing their function according to behavioral context. Top-down signals affect tuning property of V1 neurons and contribute to the gating of sensory information relevant to behavior. However, little is known about the neuronal mechanism underlying the gating of task-relevant information in V1. To address this issue, we focus on task-dependent tuning modulations of V1 neurons in two tasks of perceptual learning. We develop a model of the V1, which receives feedforward input from lateral geniculate nucleus and top-down input from a higher visual area. We show here that the change in a balance between excitation and inhibition in V1 connectivity is necessary for gating task-relevant information in V1. The balance change well accounts for the modulations of tuning characteristic and temporal properties of V1 neuronal responses. We also show that the balance change of V1 connectivity is shaped by top-down signals with temporal correlations reflecting the perceptual strategies of the two tasks. We propose a learning mechanism by which synaptic balance is modulated. To conclude, top-down signal changes the synaptic balance between excitation and inhibition in V1 connectivity, enabling early visual area such as V1 to gate context-dependent information under multiple task performances.

Efficacy of levetiracetam in primary hemifacial spasm.

Hemifacial spasm (HFS) is a peripherally-induced movement disorder characterized by the involuntary, unilateral, intermittent, irregular, tonic or clonic contractions of muscles innervated by the ipsilateral facial nerve. Kindling-like hyperactivity of the facial nucleus induced by constant stimulation of compressing artery is considered as the predominant mechanism underlying the pathogenesis of HFS. As a treatment for HFS, microsurgical decompression and botulinum toxin injection have been shown to be highly successful. Anticonvulsant drugs relieve HFS in some patients; however, the use of such drugs is limited owing to their side effects, predominantly in elderly patients. We experienced two elderly HFS patients who exhibited a marked response to levetiracetam (LEV) without side effects. Although the exact underlying pharmacological mechanism remains unknown, we assume anti-kindling effect as one of the important pharmacological mechanism underlying the effect of LEV against HFS. Moreover, LEV is considered to be suitable for use in elderly patients because of its good tolerability. In addition, the lack of hepatic induction or inhibition makes it an easy and safe drug when used in addition to other anticonvulsants. Although the long-term benefit remains unknown, LEV may represent an alternative treatment for elderly HFS patients who are unable to undergo or decline surgical intervention and/or botulinum toxin injections or are intolerant to other anticonvulsants.