Kiyohisa Natsume

θ-activity-dependent and -independent muscarinic facilitation of long-term potentiation in guinea pig hippocampal slices.

Cholinergic input to the hippocampus originates in the septum and diagonal band. Guinea pig hippocampal slices in a bath of carbachol, a cholinergic agonist, displayed different patterns of rhythmical activities depending on the carbachol concentration. Exposure to 50 or 100 microM led to intermittent induction of theta-like activities (TLAs). Long-term potentiation (LTP), induced by tetanus. was facilitated at concentrations within the optimum range for generating TLAs. This facilitation was blocked by the muscarinic receptor antagonist atropine. Augmentation of LTP during TLAs was greater than that during the rest period of TLAs which, in turn, was greater than that induced without activation of the muscarinic receptors. These results suggest that there are two muscarinic facilitation processes of LTP, one dependent on and the other independent of TLAs, with the former being more easily facilitated than the latter.

The properties of carbachol-induced beta oscillation in rat hippocampal slices

The rhythmical and pharmacological properties of carbachol-induced beta oscillation were studied using rat hippocampal slices. With the application of 30 microM carbachol, beta-range oscillations with frequencies of 13-20 Hz were recorded from the CA3 region. An AMPA receptor antagonist, CNQX, diminished the oscillations. An NMDA receptor antagonist, APV, significantly suppressed the pre-established beta oscillations. The pre-application of APV blocked the start of the carbachol-induced beta oscillations. When bicuculline (BIC), a GABAA receptor antagonist, was applied to the pre-established beta oscillations, the frequency decreased to the theta-range. When 5 microM BIC was applied with 30 microM carbachol, the beta oscillations did not start; instead, theta-like activities were induced. It has been reported that carbachol in hippocampal slices can induce theta-like activities, which are not modulated by BIC, while BICs facilitating the start of the activities. The results of the present study suggest that the GABAA receptor-mediated inhibitory transmission modulates the beta oscillation and that the transmission is needed for the start process of the oscillations. Therefore, the start and generation mechanisms of carbachol-induced beta oscillation will be different from those of carbachol-induced theta-like activities.

Desynchronization of carbachol-induced theta-like activities by α-adrenergic agents in guinea pig hippocampal slices

The effect of alpha-adrenergic agents on theta-like activity (TLA) in guinea-pig hippocampal slices was studied. TLA was induced by a cholinergic agent, carbachol. TLA had a frequency of 4.66+/-0.08 Hz (mean+/-S.E.M.) and an amplitude of 96.3+/-8.3 microV in the dentate gyrus (DG). The alpha-adrenergic agents epinephrine and clonidine increased the frequency and decreased the amplitude of TLA in a concentration-dependent manner. The agents also increased antidromic and orthodromic population spike (PS) amplitudes of the granule cells, but did not have any effect on population EPSP. Another alpha-adrenergic agent, guanabentz, had the same effect as clonidine. The adenylate cyclase inhibitor SQ22536 suppressed the increase in PS amplitude by clonidine. The results suggest that these alpha2-adrenergic agents facilitate the activity of granule cells through the activation of the alpha2-adrenoreceptor and cAMP pathway, and the facilitation causes the desynchronization of TLA.

Circadian rhythm modulates long-term potentiation induced at CA1 in rat hippocampal slices.

Circadian rhythm affects neuronal plasticity. Consistent with this, some forms of synaptic long-term potentiation (LTP) are modulated by the light/dark cycle (LD cycle). For example, this type of modulation is observed in hippocampal slices. In rodents, which are nocturnal, LTP is usually facilitated in the dark phase, but the rat hippocampal CA1 is an exception. The reason why LTP in the dark phase is suppressed in CA1 remains unknown. Previously, LTP was induced with high-frequency stimulation. In this study, we found that in the dark phase, theta-burst stimulation-induced LTP is indeed facilitated in CA1, similar to other regions in the rodent brain. Population excitatory postsynaptic potentials (pEPSP)-LTP and population spikes (PS)-LTP were recorded at CA1. The magnitude of PS-LTP in dark-phase slices was significantly larger than in light-phase slices, while that of pEPSP-LTP was unchanged. Using antidromic-orthodromic stimulation, we found that recurrent inhibition is suppressed in the dark phase. Local gabazine-application to stratum pyramidale in light-phase slices mimicked this disinhibition and facilitated LTP in dark-phase slices. These results suggest that the disinhibition of a GABAA recurrent inhibitory network can be induced in the dark phase, thereby facilitating LTP.

Overlapped Partitioning for Ensemble Classifiers of P300-Based Brain-Computer Interfaces

A P300-based brain-computer interface (BCI) enables a wide range of people to control devices that improve their quality of life. Ensemble classifiers with naive partitioning were recently applied to the P300-based BCI and these classification performances were assessed. However, they were usually trained on a large amount of training data (e.g., 15300). In this study, we evaluated ensemble linear discriminant analysis (LDA) classifiers with a newly proposed overlapped partitioning method using 900 training data. In addition, the classification performances of the ensemble classifier with naive partitioning and a single LDA classifier were compared. One of three conditions for dimension reduction was applied: the stepwise method, principal component analysis (PCA), or none. The results show that an ensemble stepwise LDA (SWLDA) classifier with overlapped partitioning achieved a better performance than the commonly used single SWLDA classifier and an ensemble SWLDA classifier with naive partitioning. This result implies that the performance of the SWLDA is improved by overlapped partitioning and the ensemble classifier with overlapped partitioning requires less training data than that with naive partitioning. This study contributes towards reducing the required amount of training data and achieving better classification performance.

The model of glutamate-induced intracellular Ca2+ oscillation and intercellular Ca2+ wave in brain astrocytes

Abstract Astrocyte have glutamate (Glu) receptors as well as neurons do and they have been suggested to participate in the information processing of brain with neurons. The cultured hippocampal astrocytes have spontaneous oscillation of intracellular Ca2+ concentration ([Ca2+]i). The application of Glu induces not only [Ca2+]i oscillation but also Ca2+ wave which is propagating among the astrocytes. In the present study, we proposed the PLCδ model which could induce some types of glutamate-induced [Ca2+]i responses and the intercellular Ca2+ wave observed in the experiment. Our simulation results suggested that PLCδ is a key molecule for [Ca2+]i oscillation and wave.

Suppression of pair-pulse depression of the population spike in the dentate gyrus during carbachol-induced theta-like activity in guinea pig hippocampal slices

In pair-pulse stimulation experiments, pair-pulse depression (PPD) of the population spike (PS) occurred at intervals shorter than 20 ms in the dentate gyrus in guinea pig hippocampal slices. Application of 50 microM carbachol resulted in an increase in the test PS amplitude and caused suppression of PPD. This suppression was antagonized by atropine sulfate, a muscarinic receptor antagonist. Carbachol at 50 microM induced intermittent bursts of theta-like activity (TLA). We compared the pair-pulse index (PPI) during TLA with that in a rest period between bursts of TLA. The PPI was defined as the ratio of the amplitude of the test PS to that of the conditioning PS. The PPI during TLA were significantly larger than that during the rest period, although there were no significant differences in the conditioning PS amplitude and the test pEPSP slope. When TLA was induced, the PPI during the rest period was increased by bicuculline. The PPI during TLA did not change significantly with the drug. The increase by bicuculline in the PPI during the rest period was caused by increase in the test PS amplitude. PPD can occur due to inhibition of granule cell activity by inhibitory neurons. Our findings suggest that the action of inhibitory neurons on granule cell activity is suppressed by activation of muscarinic receptors, with stronger suppression during TLA than during the rest period between bursts of TLA.

A new online event related potential based brain-computer interfaces using an ensemble classifier

The brain computer interface (BCI) records brain signals, then translates them into commands for control devices for a better quality of life. The event related potential (ERP) has been used to drive the BCIs, but they still have room for improving its performance toward a practical use. In this study we evaluated an online ERP-based BCI system that had an ensemble classifier with overlapped partitioning and a stimulator which provided image intensifications. We also employed and compared four types of visual stimuli: a neutral, a positive, a negative and a traditional gray/white letter stimulus. As a result, ERP-based BCI system with the neutral, the positive and the negative image achieved significantly higher information transfer rate (41.0 ± 2.2 bits per minute at best) than that with the conventional gray/white letter stimulus.

Research on multi-system learning theory: A case study of Brain-Inspired System research

This paper explains how multi-system learning theory has been established, as an example of Brain-IS research. Here the term ‘Brain-IS’ means ‘Brain-Inspired Systems’, which are expected to be developed as a result of inspiration from the brain science field. To establish Brain-IS as a new research field, we need not only the concept and philosophy of Brain-IS but also a methodology to accomplish the aim. The work on multi-system learning presented here provides an example of the methodology for Brain-IS research.

The bereitschaftspotential for rise of stand-up towards robot-assist device preparation

Recently, many researchers have been exploiting brain computer interface systems that provide a path to assist neurocognitive disorder and motor-disabled persons. In this study, the electroencephalography and electromyography were recorded in the complex, dynamic and voluntary behavior, the rise of stand-up. The negative-going potential, Bereitschaftspotential (BP), was induced before the onset of the rise. Before the onset of the movement BP had the negative peak. After the peak, the motor- and post motor-related potential were evoked. BP negative peak values significantly correlated with the latency from the start-cue to the onset of the movement. BP could be used for the support devices for the rise of stand-up. This is the first step toward developing the robot-assisted device for the motor-disabled persons to stand up.