Publications (53)131.1 Total impact
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Article: Pre-attentive, context-specific representation of fear memory in the auditory cortex of rat.
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ABSTRACT: Neural representation in the auditory cortex is rapidly modulated by both top-down attention and bottom-up stimulus properties, in order to improve perception in a given context. Learning-induced, pre-attentive, map plasticity has been also studied in the anesthetized cortex; however, little attention has been paid to rapid, context-dependent modulation. We hypothesize that context-specific learning leads to pre-attentively modulated, multiplex representation in the auditory cortex. Here, we investigate map plasticity in the auditory cortices of anesthetized rats conditioned in a context-dependent manner, such that a conditioned stimulus (CS) of a 20-kHz tone and an unconditioned stimulus (US) of a mild electrical shock were associated only under a noisy auditory context, but not in silence. After the conditioning, although no distinct plasticity was found in the tonotopic map, tone-evoked responses were more noise-resistive than pre-conditioning. Yet, the conditioned group showed a reduced spread of activation to each tone with noise, but not with silence, associated with a sharpening of frequency tuning. The encoding accuracy index of neurons showed that conditioning deteriorated the accuracy of tone-frequency representations in noisy condition at off-CS regions, but not at CS regions, suggesting that arbitrary tones around the frequency of the CS were more likely perceived as the CS in a specific context, where CS was associated with US. These results together demonstrate that learning-induced plasticity in the auditory cortex occurs in a context-dependent manner.PLoS ONE 01/2013; 8(5):e63655. · 4.09 Impact Factor -
Article: Whole-cell recording from Kenyon cells in silkmoths.
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ABSTRACT: Kenyon cells (KCs), which are present in the mushroom bodies (MBs) of the insect brain, play an important role in olfactory information processing and associative learning. However, the intrinsic electrophysiological properties of KCs in silkmoth (Bombyx mori) MBs remain unknown. Here, we use whole-cell patch-clamp recordings to elucidate the functional parameters of membrane voltage and voltage-activated ionic currents of KCs in silkmoth MBs. KCs generated action potentials in response to stepping pulses of depolarizing current, and application of GABA-receptor blocker abolished inhibitory synaptic inputs and depolarized resting membrane potential. Pharmacological isolation of KC voltage-gated ionic currents revealed that KCs express a range of voltage-activated channels, including transient and non-inactivating potassium, sodium, and calcium channels. Our results provide the first electrophysiological characterization of KCs in silkmoth MBs and represent an important step toward understanding neuronal computation that underlies olfactory information processing in silkmoths.Neuroscience Letters 09/2012; 528(1):61-6. · 2.11 Impact Factor -
Article: Concentric zones for pheromone components in the mushroom body calyx of the moth brain.
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ABSTRACT: The spatial distribution of input and output neurons in the mushroom body (MB) calyx was investigated in the silkmoth Bombyx mori. In Lepidoptera, the brain has a specialized system for processing sex pheromones. How individual pheromone components are represented in the MB has not yet been elucidated. To this end, we first compared the distribution of the presynaptic boutons of antennal lobe projection neurons (PNs), which transfer odor information from the antennal lobe to the MB calyx. The axons of PNs that innervate pheromonal glomeruli were confined to a relatively small area within the calyx. In contrast, the axons of PNs that innervate non-pheromonal glomeruli were more widely distributed. PN axons for the minor pheromone component covered a larger area than those for the major pheromone component and partially overlapped with those innervating non-pheromonal glomeruli, suggesting the integration of the minor pheromone component with plant odors. Overall, we found that PN axons innervating pheromonal and non-pheromonal glomeruli were organized into concentric zones. We then analyzed the dendritic fields of Kenyon cells (KCs), which receive inputs from PNs. Despite the strong regional localization of axons of different PN classes, the dendrites of KCs were less classified. Finally, we estimated the connectivity between PNs and KCs and suggested that the dendritic field may be organized to receive different amounts of pheromonal and non-pheromonal inputs. PNs for multiple pheromone components and plant odors enter the calyx in a concentric fashion and they are read-out by the elaborate dendritic field of KCs. J. Comp. Neurol., 2012. © 2012 Wiley Periodicals, Inc.The Journal of Comparative Neurology 08/2012; · 3.81 Impact Factor -
Article: The brain organization of the lichen moth Eilema japonica, which secretes an alkenyl sex pheromone.
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ABSTRACT: The neuroanatomy of the brain is important for the functional analysis of sex pheromone recognition in moths. Most moths use either of two types of compounds, aliphatic or alkenyl compounds, as sex pheromones. As previous studies on the neuroanatomy of moths have mostly been carried out using moths that use aliphatic compounds, information on the brain of moths that use alkenyl compounds is scarce. Here, we describe the brain anatomy of the male lichen-feeding moth Eilema japonica (Lepidoptera: Arctiidae), which uses a mixture of alkenyl compounds as a sex pheromone. We reconstructed the major neuropils in the midbrain of E. japonica and compared them with those of the silkmoth, which uses an aliphatic derivative as a sex pheromone. The brain organization of the two species was basically similar, except for the size of the macroglomerular complex, where pheromone information is processed. The macroglomerular complex in E. japonica consisted of four large glomeruli, which were positioned along dorsoventral and anterior-posterior axes. The glomerulus at the site of entry of the antennal nerve was shown to have the largest volume. The number of glomeruli was equal to the number of pheromone components that are crucial for orientation behavior in E. japonica.Neuroreport 08/2012; 23(14):857-61. · 1.66 Impact Factor -
Article: Tonotopic-column-dependent variability of neural encoding in the auditory cortex of rats.
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ABSTRACT: Neural computation could benefit from the heterogeneity of neurons to achieve energy efficiency. Beyond a single neuron level, adaptation to biologically important signals should also make functional columns heterogeneous. In the present study, we test a hypothesis that variability of neural response depends on tonotopic columns in the primary auditory cortex (A1) of rats. Mutual information (MI) was estimated from multi-unit responses in A1 of anesthetized rats, to quantify how spike count (SC) and the first spike latency (FSL) carried information about frequency and intensity of test tones. Consequently, for both SC and FSL, we found best frequency (BF)-dependent MI distributions with wide variances in high BF regions. These MI distributions were caused by BF-dependence of the amount of information that neurons conveyed, i.e., total entropy, rather than the transmission efficiency. In addition, the relationship between the transmission efficiency and the total entropy differentiated SC encoding and FSL encoding, suggesting that SC encoding and FSL encoding are not redundant but each plays a different role in intensity encoding. These results provide compelling evidence that BF columns are heterogeneous. Such heterogeneity of columns may make the global computation in A1 more efficient. Thus, the efficient coding in the neural system could be achieved by multiple-scale heterogeneity.Neuroscience 07/2012; 223:377-87. · 3.38 Impact Factor -
Article: Dissociated neuronal culture expressing ionotropic odorant receptors as a hybrid odorant biosensor--proof-of-concept study.
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ABSTRACT: Artificial odorant sensors generally perform poorer than olfactory systems in living organisms. The excellent performances of living odorant systems are achieved by the molecular recognition abilities of odorant receptors and the neuronal information processing that follows. To take advantages of this, here we propose a novel hybrid odorant biosensor by means of expressing ionotropic odorant receptors of insects into dissociated neuronal cultures of rodents. This combination of materials brings significant advantages such as easy functional expression, prolonged lifetime, and an ability to amplify the weak ionic currents of odorant receptors. In the present work, pheromone receptors and co-receptors of silkmoth, i.e., BmOR1 and BmorOrco, were expressed in neuronal cultures via liposome transfection. Consequently, BmOR1 and BmorOrco were co-expressed in 8% of neuronal cells, and both receptors were co-localized on a cell membrane. In Ca++ imaging experiments, synchronous increase of calcium signals at the presentation of BOL was found in both transfected cells and non-transfected cells in a dose-dependent manner. These results provide the proof-of-concept of the proposed hybrid odorant biosensor.The Analyst 06/2012; 137(15):3452-8. · 4.23 Impact Factor -
Article: Functional subnetwork structure in auditory cortex for stream segregation.
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ABSTRACT: Perceptual integration and segregation of alternating tone sequence differing in frequency (ABA-ABA-...) depend on the frequency differences (Delta-Fs) between A and B tones and the inter-tone intervals (ITIs) between successive tones. In the auditory cortex, tonotopic separation, forward suppression and multisecond habituation have been considered as possible neural correlates of this perceptual phenomenon. This model, however, cannot completely account for the van Noorden's perceptual boundary and the temporally continuous perception of auditory streaming. Here we examined the temporal changes of the functional network properties in auditory cortex to tone sequences with different Delta-Fs and ITIs. Specifically, we recorded local field potentials using microelectrode arrays from anesthetized and awake rats and constructed the functional network based on phase synchrony in gamma-band oscillation. As the results, the networks consisted of sub-networks highly correlated with tonotopy, and the sub-network selective to B tones lasted for a prolonged period at large Delta-F. Such characteristic substructures of functional network are a possible candidate of neural mechanisms of auditory stream segregation.The Journal of the Acoustical Society of America 04/2012; 131(4):3514. · 1.55 Impact Factor -
Article: Uncertainty in action-value estimation affects both action choice and learning rate of the choice behaviors of rats.
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ABSTRACT: The estimation of reward outcomes for action candidates is essential for decision making. In this study, we examined whether and how the uncertainty in reward outcome estimation affects the action choice and learning rate. We designed a choice task in which rats selected either the left-poking or right-poking hole and received a reward of a food pellet stochastically. The reward probabilities of the left and right holes were chosen from six settings (high, 100% vs. 66%; mid, 66% vs. 33%; low, 33% vs. 0% for the left vs. right holes, and the opposites) in every 20-549 trials. We used Bayesian Q-learning models to estimate the time course of the probability distribution of action values and tested if they better explain the behaviors of rats than standard Q-learning models that estimate only the mean of action values. Model comparison by cross-validation revealed that a Bayesian Q-learning model with an asymmetric update for reward and non-reward outcomes fit the choice time course of the rats best. In the action-choice equation of the Bayesian Q-learning model, the estimated coefficient for the variance of action value was positive, meaning that rats were uncertainty seeking. Further analysis of the Bayesian Q-learning model suggested that the uncertainty facilitated the effective learning rate. These results suggest that the rats consider uncertainty in action-value estimation and that they have an uncertainty-seeking action policy and uncertainty-dependent modulation of the effective learning rate.European Journal of Neuroscience 04/2012; 35(7):1180-9. · 3.63 Impact Factor -
Article: Light-addressed single-neuron stimulation in dissociated neuronal cultures with sparse expression of ChR2.
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ABSTRACT: Individual neurons are heterogeneous and have profound impact on population activity in a complex cortical network. Precise experimental control of the firing of multiple neurons would be therefore beneficial to advance our understanding of cell-network interactions. Except for direct intracellular stimulation, however, it is difficult to gain precise control of targeted neurons without inducing antidromic activation of untargeted neurons. To overcome this problem, we attempt to create a sparse group of photosensitized neurons via transfection of Channelrhodopsin-2 (ChR2) in primary dissociated cultures and then deliver light-addressed stimulation exclusively to these target neurons. We first show that liposome transfection was able to express ChR2 in 0.3-1.9% of cells plated depending on cell density. This spatially sparse but robust expression in our neuronal cultures offered the capability of single cell activation by illuminating a spot of light. We then demonstrated that delivering a pulsed train to photo-activate a single neuron had a substantial effect on the activity level of an entire neuronal culture. Furthermore, the activity level was controllable by altering the frequency of light illumination when 4 neurons were recruited as stimulation targets. These results suggest that organized activation of a very small population of neurons can provide better control over global activity of neuronal circuits than can single-neuron activities by themselves.Bio Systems 02/2012; 107(2):106-12. · 1.27 Impact Factor -
Article: State-dependent precursors of seizures in correlation-based functional networks of electrocorticograms of patients with temporal lobe epilepsy.
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ABSTRACT: Accurate prediction of epileptic seizures will open novel therapeutic possibilities for patients with intractable epilepsy. We attempted to identify precursors of seizures in the functional networks of electrocorticograms by applying graph theory. Long-term electrocorticograms for periods of 39-76 h from three patients with temporal lobe epilepsy were investigated using pair-wise cross-correlations. Time-varying network properties suggested that there were several distinct brain states. Although functional networks during seizures could be characterized as having a regular topography, no consistent characteristics of functional networks were found immediately prior to seizure onsets. However, it was found that seizures under an identical state were followed by similar transients of the network properties. These results suggest that network properties themselves could not serve as reliable predictors of seizure onset. Yet, some significant pre-seizure changes in the parameters tested appear likely to depend on the brain state. To predict seizures, it may be necessary to take into consideration the states of the brain. In addition to stationary network properties we characterized in the present study, dynamic interactions of epileptic activities with the network might be taken into account to predict the spread of a seizure.Neurological Sciences 01/2012; · 1.32 Impact Factor -
Article: Use of bilateral information to determine the walking direction during orientation to a pheromone source in the silkmoth Bombyx mori.
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ABSTRACT: Odor source localization is an important animal behavior. Male moths locate mates by tracking sex pheromone emitted by conspecific females. During this type of behavior, males exhibit a combination of upwind surge and zigzagging flight. Similarly, the male walking moth Bombyx mori responds to transient pheromone exposure with a surge in movement, followed by sustained zigzagging walking. The initial surge direction is known to be influenced by the pheromone input pattern. Here, we identified the sensory input patterns that determine the initial walking direction of males. We first quantified the stimulus by measuring electroantennogram values, which were used as a reference for subsequent tests. We used a brief stimulus pulse to examine the relationship between sensory stimulus patterns and the turning direction of initial surge. We found that the difference in input timing and intensity between left and right antennae affected the walking direction, indicating that B. mori integrate bilateral pheromone information during orientation behavior. When we tested pheromone stimulation for longer periods, turning behavior was suppressed, which was induced by stimulus cessation. This study contributes toward understanding efficient strategies for odor-source localization that is utilized by walking insects.Journal of Comparative Physiology 01/2012; 198(4):295-307. · 2.01 Impact Factor -
Article: Development of a scheme and tools to construct a standard moth brain for neural network simulations.
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ABSTRACT: Understanding the neural mechanisms for sensing environmental information and controlling behavior in natural environments is a principal aim in neuroscience. One approach towards this goal is rebuilding neural systems by simulation. Despite their relatively simple brains compared with those of mammals, insects are capable of processing various sensory signals and generating adaptive behavior. Nevertheless, our global understanding at network system level is limited by experimental constraints. Simulations are very effective for investigating neural mechanisms when integrating both experimental data and hypotheses. However, it is still very difficult to construct a computational model at the whole brain level owing to the enormous number and complexity of the neurons. We focus on a unique behavior of the silkmoth to investigate neural mechanisms of sensory processing and behavioral control. Standard brains are used to consolidate experimental results and generate new insights through integration. In this study, we constructed a silkmoth standard brain and brain image, in which we registered segmented neuropil regions and neurons. Our original software tools for segmentation of neurons from confocal images, KNEWRiTE, and the registration module for segmented data, NeuroRegister, are shown to be very effective in neuronal registration for computational neuroscience studies.Computational Intelligence and Neuroscience 01/2012; 2012:795291. -
Article: Heterogeneity in dendritic morphology of moth antennal lobe projection neurons.
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ABSTRACT: A population of projection neurons (PNs) in the antennal lobe (AL) integrates sensory information from the antenna and is essential for processing odor information in the insect brain. We examined the anatomy of this neuronal population in the brain of the silkmoth Bombyx mori. Using intracellular dye injection, we labeled a total of 246 PNs and systematically analyzed their morphological features, including the soma position, antennocerebral tract, and number of innervating glomeruli. For example, we analyzed PNs that had somata in the different cell clusters, innervated overlapping but different groups of glomeruli, and ran through different pathways. We also identified glomeruli innervated by PNs using a previously established procedure that first classifies glomeruli into regional groups and then identifies individual glomeruli. We analyzed uniglomerular PNs (75.6% of the total) and found heterogeneity in the dendritic morphology of the PNs that was dependent on the regions and/or the innervating glomeruli. For example, most PNs innervating the macroglomerular complex did not have extraglomerular processes, whereas most PNs innervating ordinary glomeruli did. Moreover, PNs innervating the toroid glomerulus showed heterogeneity in their dendritic morphology. These PNs had dendritic arborization in different areas within the glomerulus. We found that, in some cases, the innervation pattern of the PN dendrite correlated with individual variation in the glomerular organization. These results indicate that PNs are not homogeneous populations, and in some cases morphological heterogeneity in PNs correlated with change in glomerular organization in the silkmoth AL. J. Comp. Neurol. , 2011. © 2011 Wiley-Liss, Inc.The Journal of Comparative Neurology 12/2011; 519(17):Spc1. · 3.81 Impact Factor -
Article: Sex-linked transcription factor involved in a shift of sex-pheromone preference in the silkmoth Bombyx mori.
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ABSTRACT: In the sex-pheromone communication systems of moths, odorant receptor (Or) specificity as well as higher olfactory information processing in males should be finely tuned to the pheromone of conspecific females. Accordingly, male sex-pheromone preference should have diversified along with the diversification of female sex pheromones; however, the genetic mechanisms that facilitated the diversification of male preference are not well understood. Here, we explored the mechanisms involved in a drastic shift in sex-pheromone preference in the silkmoth Bombyx mori using spli mutants in which the genomic structure of the gene Bmacj6, which encodes a class IV POU domain transcription factor, is disrupted or its expression is repressed. B. mori females secrete an ∼11:1 mixture of bombykol and bombykal. Bombykol alone elicits full male courtship behavior, whereas bombykal alone shows no apparent activity. In the spli mutants, the behavioral responsiveness of males to bombykol was markedly reduced, whereas bombykal alone evoked full courtship behavior. The reduced response of spli males to bombykol was explained by the paucity of bombykol receptors on the male antennae. It was also found that, in the spli males, neurons projecting into the toroid, a compartment in the brain where bombykol receptor neurons normally project, responded strongly to bombykal. The present study highlights a POU domain transcription factor, Bmacj6, which may have caused a shift of sex-pheromone preference in B. mori through Or gene choice and/or axon targeting.Proceedings of the National Academy of Sciences 11/2011; 108(44):18038-43. · 9.68 Impact Factor -
Article: Heterogeneity in dendritic morphology of moth antennal lobe projection neurons.
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ABSTRACT: A population of projection neurons (PNs) in the antennal lobe (AL) integrates sensory information from the antenna and is essential for processing odor information in the insect brain. We examined the anatomy of this neuronal population in the brain of the silkmoth Bombyx mori. Using intracellular dye injection, we labeled a total of 246 PNs and systematically analyzed their morphological features, including the soma position, antennocerebral tract, and number of innervating glomeruli. For example, we analyzed PNs that had somata in the different cell clusters, innervated overlapping but different groups of glomeruli, and ran through different pathways. We also identified glomeruli innervated by PNs using a previously established procedure that first classifies glomeruli into regional groups and then identifies individual glomeruli. We analyzed uniglomerular PNs (75.6% of the total) and found heterogeneity in the dendritic morphology of the PNs that was dependent on the regions and/or the innervating glomeruli. For example, most PNs innervating the macroglomerular complex did not have extraglomerular processes, whereas most PNs innervating ordinary glomeruli did. Moreover, PNs innervating the toroid glomerulus showed heterogeneity in their dendritic morphology. These PNs had dendritic arborization in different areas within the glomerulus. We found that, in some cases, the innervation pattern of the PN dendrite correlated with individual variation in the glomerular organization. These results indicate that PNs are not homogeneous populations, and in some cases morphological heterogeneity in PNs correlated with change in glomerular organization in the silkmoth AL.The Journal of Comparative Neurology 08/2011; 519(17):3367-86. · 3.81 Impact Factor -
Article: Central projections of the wing afferents in the hawkmoth, Agrius convolvuli.
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ABSTRACT: Flight behaviors in various insect species are closely correlated with their mechanical and neuronal properties. Compared to locusts and flies which have been intensively studied, moths have "intermediate" properties in terms of the neurogenic muscle activations, power generation by indirect muscles, and two-winged-insect-like flapping behavior. Despite these unique characteristics, little is known about the neuronal mechanisms of flight control in moths. We investigated projections of the wing mechanosensory afferents in the central nervous system (CNS) of the hawkmoth, Agrius convolvuli, because the mechanosensory proprioceptive feedback has an essential role for flight control and would be presumably optimized for insect species. We conducted anterograde staining of nine afferent nerves from the fore- and hindwings. All of these afferents projected into the prothoracic, mesothoracic and metathoracic ganglia (TG1, 2 and 3) and had ascending fibers to the head ganglia. Prominent projection areas in the TG1-3 and suboesophageal ganglion (SOG) were common between the forewing, hindwing and contralateral forewing afferents, suggesting that information from different wings are converged at multiple levels presumably for coordinating wing flapping. On the other hand, differences of projections between the fore- and hindwing afferents were observed especially in projection areas of the tegulae in the TG1 and contralateral projections of the anterior forewing nerve in the TGs and SOG, which would reflect functional differences between corresponding mechanoreceptors on each wing. Afferents comprising groups of the campaniform sensilla at the wing bases had prominent ascending pathways to the SOG, resembling the head-neck motor system for gaze control in flies. Double staining of the wing afferents and flight or neck motoneurons also indicated potential connectivity between them. Our results suggest multiple roles of the wing proprioceptive feedback for flight and provide the anatomical basis for further understanding of neuronal mechanisms of the flight system in moths.Journal of insect physiology 08/2011; 57(11):1518-36. · 2.24 Impact Factor -
Article: A single sex pheromone receptor determines chemical response specificity of sexual behavior in the silkmoth Bombyx mori.
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ABSTRACT: In insects and other animals, intraspecific communication between individuals of the opposite sex is mediated in part by chemical signals called sex pheromones. In most moth species, male moths rely heavily on species-specific sex pheromones emitted by female moths to identify and orient towards an appropriate mating partner among a large number of sympatric insect species. The silkmoth, Bombyx mori, utilizes the simplest possible pheromone system, in which a single pheromone component, (E, Z)-10,12-hexadecadienol (bombykol), is sufficient to elicit full sexual behavior. We have previously shown that the sex pheromone receptor BmOR1 mediates specific detection of bombykol in the antennae of male silkmoths. However, it is unclear whether the sex pheromone receptor is the minimally sufficient determination factor that triggers initiation of orientation behavior towards a potential mate. Using transgenic silkmoths expressing the sex pheromone receptor PxOR1 of the diamondback moth Plutella xylostella in BmOR1-expressing neurons, we show that the selectivity of the sex pheromone receptor determines the chemical response specificity of sexual behavior in the silkmoth. Bombykol receptor neurons expressing PxOR1 responded to its specific ligand, (Z)-11-hexadecenal (Z11-16:Ald), in a dose-dependent manner. Male moths expressing PxOR1 exhibited typical pheromone orientation behavior and copulation attempts in response to Z11-16:Ald and to females of P. xylostella. Transformation of the bombykol receptor neurons had no effect on their projections in the antennal lobe. These results indicate that activation of bombykol receptor neurons alone is sufficient to trigger full sexual behavior. Thus, a single gene defines behavioral selectivity in sex pheromone communication in the silkmoth. Our findings show that a single molecular determinant can not only function as a modulator of behavior but also as an all-or-nothing initiator of a complex species-specific behavioral sequence.PLoS Genetics 06/2011; 7(6):e1002115. · 8.69 Impact Factor -
Article: Distributed representation of tone frequency in highly decodable spatio-temporal activity in the auditory cortex.
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ABSTRACT: Although the place code of tone frequency, or tonotopic map, has been widely accepted in the auditory cortex, tone-evoked activation becomes less frequency-specific at moderate or high sound pressure levels. This implies that sound frequency is not represented by a simple place code but that the information is distributed spatio-temporally irrespective of the focal activation. In this study, using a decoding-based analysis, we investigated multi-unit activities in the auditory cortices of anesthetized rats to elucidate how a tone frequency is represented in the spatio-temporal neural pattern. We attempted sequential dimensionality reduction (SDR), a specific implementation of recursive feature elimination (RFE) with support vector machine (SVM), to identify the optimal spatio-temporal window patterns for decoding test frequency. SDR selected approximately a quarter of the windows, and SDR-identified window patterns led to significantly better decoding than spatial patterns, in which temporal structures were eliminated, or high-spike-rate patterns, in which windows with high spike rates were selectively extracted. Thus, the test frequency is also encoded in temporal as well as spatial structures of neural activities and low-spike-rate windows. Yet, SDR recruited more high-spike-rate windows than low-spike-rate windows, resulting in a highly dispersive pattern that probably offers an advantage of discrimination ability. Further investigation of SVM weights suggested that low-spike-rate windows play significant roles in fine frequency differentiation. These findings support the hypothesis that the auditory cortex adopts a distributed code in tone frequency representation, in which high- and low-spike-rate activities play mutually complementary roles.Neural networks: the official journal of the International Neural Network Society 01/2011; 24(4):321-32. · 1.88 Impact Factor -
Article: Optimization of thin‐film configuration for light‐addressable stimulation electrode
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ABSTRACT: Light addressing is an emerging technique to optically address a virtual electrode on a photoconductive substrate. A thinner photoconductive layer of a light-addressable planar electrode can improve the spatial resolution of the light-addressed electrode. Voltage application to the electrode, however, causes a strong electric field across the thin photoconductive layer with a significant avalanche effect, which induces an undesired increase of dark current. In order to overcome this problem, we investigated how photoconductive-layer thickness and passivation-layer conductivity affect voltage-application-induced bright and dark charge densities. Suppression of the dark charge density with a thick photoconductive layer and a low-conductive passivation layer is found to be a key factor for optimization of the light-addressable electrode. With this design strategy, we developed a novel light-addressable electrode using titanium dioxide as a photoconductor. To suppress the avalanche effect, the thickness of the titanium-dioxide layer was designed to be 1.5 μm. The fabricated electrode turned out to have sufficient photoelectric properties: the bright charge density reached 70 μC/cm2 and the bright-to-dark charge density ratio was greater than 10, which allows stimulation to cultured dissociated neurons. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 94(1): 61–68, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10241Electronics and Communications in Japan 12/2010; 94(1):61 - 68. · 0.08 Impact Factor -
Article: Direction control of information transfer between neuronal populations with asymmetric three‐dimensional microstructure
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ABSTRACT: Information transfer among neuronal populations has a directional bias. Some past studies demonstrated that microstructure could bias the direction of information transfer at a cellular level. However, the transfer at a population level has hardly been controlled to date. In order to control the information transfer, we attempt to bias the direction of neurite outgrowth of cultured neurons using a three-dimensional asymmetric microstructure. The proposed microstructure is an embossed barrier with a right-triangle cross section, namely, an ascending slope and vertical wall. Because of the asymmetricity, the neurite growth rate from the wall-side to the slope-side is expected to be lower than that of the slope-to-wall. We fabricated the microstructure on a polystyrene substrate by hot pressing, simultaneously embedding line electrodes for probing stimulation. To confirm the impact of the microstructure on neurite outgrowth, and thus the signal transfer direction between neuronal populations separated by the structure, we stimulated cultured neurons on both sides of the structure. There was a difference in neuronal responses to wall-side stimulation and slope-side stimulation, demonstrating the directional characteristic of information transfer. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(12): 17–25, 2010; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10240Electronics and Communications in Japan 11/2010; 93(12):17 - 25. · 0.08 Impact Factor
Top co-authors
Top Journals
Institutions
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2012
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Hyogo University
- School of Human Science and Environment
Akō, Hyogo-ken, Japan -
Okinawa Institute of Science and Technology
Okinawa, Okinawa-ken, Japan
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2005–2012
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The University of Tokyo
- • Research Center for Advanced Science and Technology
- • Graduate School of Information Science and Technology
- • Department of Mechano-Informatics
Tokyo, Tokyo-to, Japan
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2002–2012
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University of Tsukuba
- Institute of Biological Sciences
Tsukuba, Ibaraki-ken, Japan
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