Dynamic organization of cerebellar climbing fiber response and synchrony in multiple functional components reduces dimensions for reinforcement learning.

Cerebellar climbing fibers convey diverse signals, but how they are organized in the compartmental structure of the cerebellar cortex during learning remains largely unclear. We analyzed a large amount of coordinate-localized two-photon imaging data from cerebellar Crus II in mice undergoing 'Go/No-go' reinforcement learning. Tensor component analysis revealed that a majority of climbing fiber inputs to Purkinje cells were reduced to only four functional components, corresponding to accurate timing control of motor initiation related to a Go cue, cognitive error-based learning, reward processing, and inhibition of erroneous behaviors after a No-go cue. Changes in neural activities during learning of the first two components were correlated with corresponding changes in timing control and error learning across animals, indirectly suggesting causal relationships. Spatial distribution of these components coincided well with boundaries of Aldolase-C/zebrin II expression in Purkinje cells, whereas several components are mixed in single neurons. Synchronization within individual components was bidirectionally regulated according to specific task contexts and learning stages. These findings suggest that, in close collaborations with other brain regions including the inferior olive nucleus, the cerebellum, based on anatomical compartments, reduces dimensions of the learning space by dynamically organizing multiple functional components, a feature that may inspire new-generation AI designs.

Improved hyperacuity estimation of spike timing from calcium imaging.

Two-photon imaging is a major recording technique used in neuroscience. However, it suffers from several limitations, including a low sampling rate, the nonlinearity of calcium responses, the slow dynamics of calcium dyes and a low SNR, all of which severely limit the potential of two-photon imaging to elucidate neuronal dynamics with high temporal resolution. We developed a hyperacuity algorithm (HA_time) based on an approach that combines a generative model and machine learning to improve spike detection and the precision of spike time inference. Bayesian inference was performed to estimate the calcium spike model, assuming constant spike shape and size. A support vector machine using this information and a jittering method maximizing the likelihood of estimated spike times enhanced spike time estimation precision approximately fourfold (range, 2-7; mean, 3.5-4.0; 2SEM, 0.1-0.25) compared to the sampling interval. Benchmark scores of HA_time for biological data from three different brain regions were among the best of the benchmark algorithms. Simulation of broader data conditions indicated that our algorithm performed better than others with high firing rate conditions. Furthermore, HA_time exhibited comparable performance for conditions with and without ground truths. Thus HA_time is a useful tool for spike reconstruction from two-photon imaging.

Electrical coupling controls dimensionality and chaotic firing of inferior olive neurons.

We previously proposed, on theoretical grounds, that the cerebellum must regulate the dimensionality of its neuronal activity during motor learning and control to cope with the low firing frequency of inferior olive neurons, which form one of two major inputs to the cerebellar cortex. Such dimensionality regulation is possible via modulation of electrical coupling through the gap junctions between inferior olive neurons by inhibitory GABAergic synapses. In addition, we previously showed in simulations that intermediate coupling strengths induce chaotic firing of inferior olive neurons and increase their information carrying capacity. However, there is no in vivo experimental data supporting these two theoretical predictions. Here, we computed the levels of synchrony, dimensionality, and chaos of the inferior olive code by analyzing in vivo recordings of Purkinje cell complex spike activity in three different coupling conditions: carbenoxolone (gap junctions blocker), control, and picrotoxin (GABA-A receptor antagonist). To examine the effect of electrical coupling on dimensionality and chaotic dynamics, we first determined the physiological range of effective coupling strengths between inferior olive neurons in the three conditions using a combination of a biophysical network model of the inferior olive and a novel Bayesian model averaging approach. We found that effective coupling co-varied with synchrony and was inversely related to the dimensionality of inferior olive firing dynamics, as measured via a principal component analysis of the spike trains in each condition. Furthermore, for both the model and the data, we found an inverted U-shaped relationship between coupling strengths and complexity entropy, a measure of chaos for spiking neural data. These results are consistent with our hypothesis according to which electrical coupling regulates the dimensionality and the complexity in the inferior olive neurons in order to optimize both motor learning and control of high dimensional motor systems by the cerebellum.

[From Cerebellum to Cerebrum].

My study has been a chain of successes and failures, including those of cerebellar efferent system and laminar dependency of visual cortical circuitry and plasticity. It could have never been in existence but for Professor Masao Ito.

Segmental Bayesian estimation of gap-junctional and inhibitory conductance of inferior olive neurons from spike trains with complicated dynamics.

The inverse problem for estimating model parameters from brain spike data is an ill-posed problem because of a huge mismatch in the system complexity between the model and the brain as well as its non-stationary dynamics, and needs a stochastic approach that finds the most likely solution among many possible solutions. In the present study, we developed a segmental Bayesian method to estimate the two parameters of interest, the gap-junctional (gc ) and inhibitory conductance (gi ) from inferior olive spike data. Feature vectors were estimated for the spike data in a segment-wise fashion to compensate for the non-stationary firing dynamics. Hierarchical Bayesian estimation was conducted to estimate the gc and gi for every spike segment using a forward model constructed in the principal component analysis (PCA) space of the feature vectors, and to merge the segmental estimates into single estimates for every neuron. The segmental Bayesian estimation gave smaller fitting errors than the conventional Bayesian inference, which finds the estimates once across the entire spike data, or the minimum error method, which directly finds the closest match in the PCA space. The segmental Bayesian inference has the potential to overcome the problem of non-stationary dynamics and resolve the ill-posedness of the inverse problem because of the mismatch between the model and the brain under the constraints based, and it is a useful tool to evaluate parameters of interest for neuroscience from experimental spike train data.

Four-component assembly in the crystalline state driven by amidinium-carboxylate salt bridge formation from an aqueous solution.

A series of diamidine dihydrochlorides was prepared utilizing a spacer unit to control the distance between the two amidinium groups. The introduction of two amidinium groups to the 1,8-position of each spacer unit (i.e., 9,10-dihydroanthracene, anthracene, biphenylene) can control the direction of formation of a self-assembled structure. The fine-tuning of the distances between the two amidinium groups in the spacer units can help control the stabilizing interactions of two carboxylic acid units (intermolecular attraction) after the four-component assembly (see ). Based on this concept, we succeeded in the formation of a four-component box-like assembled structure using amidinium-carboxylate salt bridge formation in the crystalline state from aqueous solutions.

Solution to the inverse problem of estimating gap-junctional and inhibitory conductance in inferior olive neurons from spike trains by network model simulation.

The inferior olive (IO) possesses synaptic glomeruli, which contain dendritic spines from neighboring neurons and presynaptic terminals, many of which are inhibitory and GABAergic. Gap junctions between the spines electrically couple neighboring neurons whereas the GABAergic synaptic terminals are thought to act to decrease the effectiveness of this coupling. Thus, the glomeruli are thought to be important for determining the oscillatory and synchronized activity displayed by IO neurons. Indeed, the tendency to display such activity patterns is enhanced or reduced by the local administration of the GABA-A receptor blocker picrotoxin (PIX) or the gap junction blocker carbenoxolone (CBX), respectively. We studied the functional roles of the glomeruli by solving the inverse problem of estimating the inhibitory (gi) and gap-junctional conductance (gc) using an IO network model. This model was built upon a prior IO network model, in which the individual neurons consisted of soma and dendritic compartments, by adding a glomerular compartment comprising electrically coupled spines that received inhibitory synapses. The model was used in the forward mode to simulate spike data under PIX and CBX conditions for comparison with experimental data consisting of multi-electrode recordings of complex spikes from arrays of Purkinje cells (complex spikes are generated in a one-to-one manner by IO spikes and thus can substitute for directly measuring IO spike activity). The spatiotemporal firing dynamics of the experimental and simulation spike data were evaluated as feature vectors, including firing rates, local variation, auto-correlogram, cross-correlogram, and minimal distance, and were contracted onto two-dimensional principal component analysis (PCA) space. gc and gi were determined as the solution to the inverse problem such that the simulation and experimental spike data were closely matched in the PCA space. The goodness of the match was confirmed by an analysis of variance (ANOVA) of the PCA scores between the experimental and simulation spike data. In the PIX condition, gi was found to decrease to approximately half its control value. CBX caused an approximately 30% decrease in gc from control levels. These results support the hypothesis that the glomeruli are control points for determining the spatiotemporal characteristics of olivocerebellar activity and thus may shape its ability to convey signals to the cerebellum that may be used for motor learning or motor control purposes.

Relating neuronal firing patterns to functional differentiation of cerebral cortex.

It has been empirically established that the cerebral cortical areas defined by Brodmann one hundred years ago solely on the basis of cellular organization are closely correlated to their function, such as sensation, association, and motion. Cytoarchitectonically distinct cortical areas have different densities and types of neurons. Thus, signaling patterns may also vary among cytoarchitectonically unique cortical areas. To examine how neuronal signaling patterns are related to innate cortical functions, we detected intrinsic features of cortical firing by devising a metric that efficiently isolates non-Poisson irregular characteristics, independent of spike rate fluctuations that are caused extrinsically by ever-changing behavioral conditions. Using the new metric, we analyzed spike trains from over 1,000 neurons in 15 cortical areas sampled by eight independent neurophysiological laboratories. Analysis of firing-pattern dissimilarities across cortical areas revealed a gradient of firing regularity that corresponded closely to the functional category of the cortical area; neuronal spiking patterns are regular in motor areas, random in the visual areas, and bursty in the prefrontal area. Thus, signaling patterns may play an important role in function-specific cerebral cortical computation.

Different pedunculopontine tegmental neurons signal predicted and actual task rewards.

The dopamine system has been implicated in guiding behavior based on rewards. The pedunculopontine tegmental nucleus (PPTN) of the brainstem receives afferent inputs from reward-related structures, including the cerebral cortices and the basal ganglia, and in turn provides strong excitatory projections to dopamine neurons. This anatomical evidence predicts that PPTN neurons may carry reward information. To elucidate the functional role of the PPTN in reward-seeking behavior, we recorded single PPTN neurons while monkeys performed a visually guided saccade task in which the predicted reward value was informed by the shape of the fixation target. Two distinct groups of neurons, fixation target (FT) and reward delivery (RD) neurons, carried reward information. The activity of FT neurons persisted between FT onset and reward delivery, with the level of activity associated with the magnitude of the expected reward. RD neurons discharged phasically after reward delivery, with the levels of activity associated with the actual reward. These results suggest that separate populations of PPTN neurons signal predicted and actual reward values, both of which are necessary for the computation of reward prediction error as represented by dopamine neurons.

A hierarchical Bayesian method to resolve an inverse problem of MEG contaminated with eye movement artifacts.

The magnetic fields generated by eye movements are major artifacts in MEG measurements. We propose a hybrid hierarchical variational Bayesian method to remove eye movement artifacts from MEG data. Our method is an extension of the hierarchical variational Bayesian method for MEG source localization proposed by Sato et al. [Sato, M., Yoshioka, T., Kajihara, S., Toyama, K., Goda, N., Doya, K., and Kawato, M., (2004). Hierarchical Bayesian estimation for MEG inverse problem. NeuroImage 23(3), 806-826]. First, we assumed a single dipole at each left and right eyeball as a source of eye artifacts. Second, we constructed an EOG forward model describing the relationship between eye dipoles and electric potentials, i.e., EOG. Based on the Bayesian framework, the proposed method concurrently estimates eye and brain current sources from both MEG and EOG data. Thereby the brain current sources can be isolated from eye artifacts. The new method was tested in two ways. In the simulation experiments, the performance of eye artifact removal was evaluated from various aspects; locations of brain current sources, temporal correlation between eye and brain current sources, the level of MEG observation noise and so on. In real MEG experiments, we measured MEG and EOG data during smooth pursuit eye movements for a horizontally or circularly moving target. Our method successfully removed eye artifacts from the simulated and real MEG data with the estimation of brain current sources that were located in eye movement related areas. Our method should be widely applicable to MEG data obtained in tasks with non-negligible eye movements.

Evaluation of hierarchical Bayesian method through retinotopic brain activities reconstruction from fMRI and MEG signals.

A hierarchical Bayesian method estimated current sources from MEG data, incorporating an fMRI constraint as a hierarchical prior whose strength is controlled by hyperparameters. A previous study [Sato, M., Yoshioka, T., Kajihara, S., Toyama, K., Goda, N., Doya, K., Kawato, M., 2004. Hierarchical Bayesian estimation for MEG inverse problem. Neuroimage 23, 806-826] demonstrated that fMRI information improves the localization accuracy for simulated data. The goal of the present study is to confirm the usefulness of the hierarchical Bayesian method by the real MEG and fMRI experiments using visual stimuli with a fan-shaped checkerboard pattern presented in four visual quadrants. The proper range of hyperparameters was systematically analyzed using goodness of estimate measures for the estimated currents. The robustness with respect to false-positive activities in the fMRI information was also evaluated by using noisy priors constructed by adding artificial noises to real fMRI signals. It was shown that with appropriate hyperparameter values, the retinotopic organization and temporal dynamics in the early visual area were reconstructed, which were in a close correspondence with the known brain imaging and electrophysiology of the humans and monkeys. The false-positive effects of the noisy priors were suppressed by using appropriate hyperparameter values. The hierarchical Bayesian method also was capable of reconstructing retinotopic sequential activation in V1 with fine spatiotemporal resolution, from MEG data elicited by sequential stimulation of the four visual quadrants with the fan-shaped checker board pattern at much shorter intervals (150 and 400 ms) than the temporal resolution of fMRI. These results indicate the potential capability for the hierarchical Bayesian method combining MEG with fMRI to improve the spatiotemporal resolution of noninvasive brain activity measurement.

Bone morphogenetic protein-7 and interferon-alpha synergistically suppress hepatitis C virus replicon.

Various cytokines contribute to control hepatitis C virus (HCV) viral replication. HCV subgenomic replicon systems have been developed, and cell-cycle-dependent replication has been reported. But the molecules involved in this processes is not totally elucidated. The aim of this study is to investigate the involvement of the bone morphogenetic protein (BMP)-7, a member of TGF-beta superfamily, to the in vitro HCV replication. BMP-7 dose-dependently suppressed the replication and protein expression from the HCV replicon in Huh7/Rep-Feo cells and was associated with cell-cycle arrest at the G1 phase. These results were consistent with the effect of TGF-beta in a previous study. Combination of BMP-7 and interferon-alpha showed a synergic decrease of HCV replication, and was more effective compared to the treatment with interferon-alpha alone. This synergistic effect was also present in HCV-JFH1 virus cell culture. While BMP-7 alone did not stimulate expression of the interferon-stimulated genes (ISGs), it augmented interferon-induced expression of the ISGs independently of the interferon-induced Jak/STAT pathway. Taken together, BMP-7 may constitute a novel molecule to suppress HCV replication.

Hierarchical Bayesian estimation for MEG inverse problem.

Source current estimation from MEG measurement is an ill-posed problem that requires prior assumptions about brain activity and an efficient estimation algorithm. In this article, we propose a new hierarchical Bayesian method introducing a hierarchical prior that can effectively incorporate both structural and functional MRI data. In our method, the variance of the source current at each source location is considered an unknown parameter and estimated from the observed MEG data and prior information by using the Variational Bayesian method. The fMRI information can be imposed as prior information on the variance distribution rather than the variance itself so that it gives a soft constraint on the variance. A spatial smoothness constraint, that the neural activity within a few millimeter radius tends to be similar due to the neural connections, can also be implemented as a hierarchical prior. The proposed method provides a unified theory to deal with the following three situations: (1) MEG with no other data, (2) MEG with structural MRI data on cortical surfaces, and (3) MEG with both structural MRI and fMRI data. We investigated the performance of our method and conventional linear inverse methods under these three conditions. Simulation results indicate that our method has better accuracy and spatial resolution than the conventional linear inverse methods under all three conditions. It is also shown that accuracy of our method improves as MRI and fMRI information becomes available. Simulation results demonstrate that our method appropriately resolves the inverse problem even if fMRI data convey inaccurate information, while the Wiener filter method is seriously deteriorated by inaccurate fMRI information.

A neural correlate of reward-based behavioral learning in caudate nucleus: a functional magnetic resonance imaging study of a stochastic decision task.

Humans can acquire appropriate behaviors that maximize rewards on a trial-and-error basis. Recent electrophysiological and imaging studies have demonstrated that neural activity in the midbrain and ventral striatum encodes the error of reward prediction. However, it is yet to be examined whether the striatum is the main locus of reward-based behavioral learning. To address this, we conducted functional magnetic resonance imaging (fMRI) of a stochastic decision task involving monetary rewards, in which subjects had to learn behaviors involving different task difficulties that were controlled by probability. We performed a correlation analysis of fMRI data by using the explanatory variables derived from subject behaviors. We found that activity in the caudate nucleus was correlated with short-term reward and, furthermore, paralleled the magnitude of a subject's behavioral change during learning. In addition, we confirmed that this parallelism between learning and activity in the caudate nucleus is robustly maintained even when we vary task difficulty by controlling the probability. These findings suggest that the caudate nucleus is one of the main loci for reward-based behavioral learning.

Regulation of drug transporters by the farnesoid X receptor in mice.

The farnesoid X receptor (FXR, NR1H4) regulates bile acid and lipid homeostasis by acting as an intracellular bile acid-sensing transcription factor, resulting in altered expression of enzymes and transporters involved in bile acid synthesis and transport. Here, we quantitatively analyzed the alterations in expression levels of drug transporters, mainly organic anion-transporting polypeptides (oatp), in wild-type and FXR-null mice to evaluate the role of FXR in their expression and regulation by cholic acid. Changes in the mRNA amounts in liver, kidney, small intestine, and testis in FXR-null mice fed with or without a supplement of 0.5% cholic acid in the diet were analyzed by semiquantitative RT-PCR. In FXR-null mice, the mRNA levels of oatp1, oatp2, oatp3, and octn1 were lower than those of wild-type mice in kidney and testis, while there was no difference in liver or small intestine. Cholic acid feeding led to significantly decreased levels of expression of oatp1 and oct1 and an increased level of expression of oatp2 in wild-type mouse liver. In FXR-null mice, oatp1 and other transporters were downregulated in liver, kidney, and testis, whereas small intestine ASBT, octn2, and pept1 were upregulated. Our results suggested that FXR is involved in the transcriptional regulation of oatp and other transporters in a tissue-specific manner. Furthermore, the effect of cholic acid treatment indicates the involvement of regulatory mechanism(s) other than FXR.

Effects of TNFalpha on the growth and sensitivity to cytosine arabinoside of blast progenitors in acute myelogenous leukemia with special reference to the role of NF-kappaB.

Leukemic blasts in acute myelogenous leukemia (AML) are derived from a minor population of cells called blast progenitors. Hematopoietic growth factors (HGFs) stimulate their growth and simultaneously sensitize them to cytosine arabinoside (Ara-C), a cell-cycle-specific cytotoxic drug. Since tumor necrosis factor alpha (TNFalpha) modifies HGF activities, we examined the effects of TNFalpha in combination with HGFs on in vitro growth and Ara-C sensitivity of AML blast progenitors in patient samples. TNFalpha variably affected HGF-supported colony formation and the self-renewal of blast progenitors. However, the combination of TNFalpha with IL-3 uniformly rendered blast progenitors more resistant to Ara-C irrespective of whether TNFalpha suppressed or augmented IL-3-supported growth, indicating that TNFalpha regulates the Ara-C sensitivity of leukemic progenitors independently of their cell cycle status. Since nuclear factor-kappaB (NF-kappaB) is activated by TNFalpha and induces expression of prosurvival genes, effects of the antisense oligodeoxynucleotides to NF-kappaB subunits, p65 and p50, were examined. Antisense oligodeoxynucleotides sensitized HL60 cells to Ara-C but rendered leukemic progenitors in patient samples even more resistant to Ara-C in the presence of TNFalpha and IL-3 in combination, indicating that NF-kappaB is involved in the Ara-C sensitivity of leukemic blast progenitors but may exert opposite dual functions, namely protection from and induction of apoptosis, under different conditions.

Development of functional thalamocortical synapses studied with current source-density analysis in whole forebrain slices in the rat.

We analysed the laminar distribution of transmembrane currents from embryonic (E) day 17 until adulthood after selective thalamic stimulation in slices of rat forebrain to study the development of functional thalamocortical and cortico-cortical connections. At E18 to birth a short-latency current sink was observed in the subplate and layer 6, which was decreased, but not fully abolished in a cobalt containing solution or after the application of glutamate receptor blockers (APV and DNQX). This indicated that embryonic thalamic axons were capable of conducting action potentials to the cortex and some of them had already formed functional synapses there. Between birth and P3, when thalamic axons were completing their upward growth, a sink gradually appeared more superficially in the dense cortical plate and synchronously, a current source aroused in layer 5. Both sinks and sources completely disappeared after blocking synaptic transmission. The adult-like distribution of CSDs became apparent after P7. The component in layer 6 cannot be blocked completely after this age suggesting antidromic activation. This study demonstrated that cells of the lowest layers of the cortex received functional thalamic input before birth and that thalamocortical axons formed synapses with more superficial cells as they grew into the cortical plate.

Surround suppression in the human visual cortex: an analysis using magnetoencephalography.

The responses of neurons in the primate and cat primary visual cortices (V1s) to the stimuli within their classical receptive fields (CRFs) are markedly suppressed by the surrounding stimuli outside CRFs. In the present study, we show that a similar suppressive effect occurs for visually evoked magnetic responses in the human visual cortex. The initial peak amplitude of the magnetic response (at a latency of around 90 ms) to a test grating accompanied by high-contrast surround gratings was smaller than that for the test without the surround. Current source localization with a single dipole model indicated that the initial response originated from cortical activity near the occipital pole in the contralateral hemisphere to the visual stimulation. The peak amplitude for the test decreased with increasing surround contrast, and increased with increasing test contrast. The contrast dependence and the early development of the surround suppression were in agreement with the results of the V1 single-cell studies of monkeys and cats. We suggest that the surround suppression of the initial peak amplitude of the magnetic response may be ascribed to the inhibition of the neural activity at the early processing stage(s), presumably at V1, in the human visual cortex.

Magnetic responses of human visual cortex to illusory contours.

To examine the neural mechanism underlying illusory-contour perception, we measured the magnetic responses of the human visual cortex to an abutting-line grating inducing illusory contours (test stimulus) and a non-abutting-line grating (control stimulus) using the technique of magnetoencephalography (MEG). In the initial latency period of 60-80 ms, the MEG response to the test stimulus was nearly identical with that to the control stimulus, but in the subsequent period of 80-150 ms, the former was larger than the latter. The origin of the peak MEG response to the test stimulus was estimated to be in the vicinity of striate cortex/extrastriate visual cortex for two of the four subjects. These results suggest that, in accord with those of the previous electrophysiological and functional magnetic resonance imaging studies, illusory-contour signals are generated in the very early stage(s) of processing in the primate visual cortex.

Megakaryocytic Maturation is Regulated by Maintaining a Balance Against Cytokine Induced-cell Proliferation: Steel Factor Retards Thrombopoietin-induced Megakaryocytic Differentiation While Synergistically Stimulating Mitogenesis; Hematopoiesis.

Using a factor-dependent cell line MO7ER, which contains a stably transduced human erythropoietin (EPO) receptor gene in human megakaryoblastic cell line MO7e and which resulted in concomitant expression of EPO receptor, c-Mpl and c-Kit, we investigated the biological effects of these cytokines in terms of cell growth and differentiation. Thrombopoietin (TPO), EPO and Steel factor (SLF) all stimulated MO7ER cell proliferation in a dose-dependent manner. Combined stimulation of cells with SLF plus either TPO or EPO resulted in striking synergistic enhancement of MO7ER cell growth as compared with each cytokine alone, whereas combination of TPO plus EPO showed only an additive effect on cell proliferation. With regards to cell differentiation, either TPO or EPO treatment induced enhancement of platelet glycoprotein (GP) IIb/IIIa and GPIb expression. SLF induced GPIIb/IIIa and GPIb expression, but the effect was much weaker than that of EPO or TPO. However, addition of SLF to either TPO- or EPO- containing cultures (which induced potent mitogenesis in MO7ER cells) resulted in suppression of these megakaryocyte specific antigens. Addition of low-dose cytosine arabinoside (Ara-C)(1 to 10 ng/ml) enhanced TPO- or EPO- induced megakaryocytic differentiation in MO7ER cells while mildly suppressing cell growth. Treatment the cells with low-dose Ara-C plus TPO plus SLF overrode the proliferative enhancing effects of SLF and induced GPIIb/IIIa and GPIb expression as efficient as TPO alone. Retardation of TPO-induced megakaryocytic maturation was also observed in normal murine bone marrow cells by combined stimulation with TPO and SLF as assessed by the numbers of acetylcholinesterase staining-positive cells and megakaryocyte nuclear polyploidy. These results suggest that megakaryocytic maturation is, at least in part, regulated by countering cytokine-induced cell proliferation.