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The spike-timing-dependent plasticity function based on a brain sequential learning system using a recurrent neuronal network

100%

Ogata G. , Natsume K. , Ishizuka S. , Hayashi H.

2010

tom Vol. 4, No. 2

25-30

This paper examines the spike-timing-dependent plasticity (STDP) at the synapses of the medial entorhinal cortex (EC) and the dentate gyrus (DG) in the hippocampus. The medial and lateral ECs respectively convey spatial and non-spatial information to the hippocampus, and the DG of the hippocampus integrates or binds them. There is a recurrent neuronal network between the EC and the hippocampus called the EC-hippocampus loop. A computational study has shown that using this loop and STDP phenomena at the recurrent EC synapse, sequential learning can be accomplished. But the STDP functions at the synapses of the EC and DG have not yet been studied by neurophysiological experiments. Experiments on STDP phenomena were performed in rats. The STDP function was asymmetrical in the EC synapse and symmetrical in the DG. The medial EC mainly processes the time-series signals for spatial information about visual landmarks when a rat is running in an environment, the lateral EC processes their features, and the DG binds or integrates the information on the positions and features of the landmarks. Thus, the EC-hippocampus loop processes sequential learning of spatial and non-spatial information in parallel, and the DG binds or integrates the two kinds of signals. A system based on this biological phenomenon could have similar characteristics of parallel processing of object features and positions, and their binding.

Irreversible blocking of polar excitations on frog sciatic nerve using semiconductor pulse laser irradiation

100%

Hirayama Y. , Ishizuka S. , Yamakawa T.

tom Vol. 3, No. 4

210-212

The final purpose of our research is to cripple the epileptogenic focus by laser irradiation. However, the effect of laser irradiation on brain nerves is not well known. In this paper, we observed laser irradiation to the transmission of action potential of a bullfrog sciatic nerve in the experiment. In addition the marginal amplitude of laser energy is obtained. The bullfrog nerve preparations were stimulated supramaximal intensity pulse. The pulse width and the pulse interval are 1 msec and 1 sec, respectively. A semiconductor pulse laser irradiation (the wavelength, the pulse width and the frequency are 808 nm, 990 µsec and 50 Hz, respectively) was employed until when the amplitude of the action potential decreases to 10 %. The laser light was irradiated to the portion between two electrode pairs for recording. The energy of the laser is variable between 13.9- 202.5 mJ/cm2. The laser irradiator is connected to an optical fiber whose diameter is 1 mm. The action potential of the sciatic nerve is observed at 1 day after in order to confirm irreversibility. The experiment was delivered by the laser pulse, the energy of which over 32.9 mJ/cm2. The peak of action potential was decreased gradually by laser irradiation with depending on the time of irradiation. The time to blocking is reciprocally proportional to laser energy. At a day after the experiment, the action potential was not recovered. This result shows the laser irradiation give irreversible blocking to polar excitations. We observed the frog sciatic nerve is damaged by laser irradiation. The results show a possibility that the epileptogenic focus can be crippled by laser irradiation. We are going to have more experiments and obtain important laser parameters. In the future, the experiment and the result are expanded using rat brain and applied human surgery.

Epileptic burst measurement using microelectrodes equipped on a cryogenic microprobe for minimally invasive brain surgery of intractable epilepsy treatment

75%

Yamakawa T. , Yamakawa T. , Ishizuka S. , Grigorievich Z. L. , Suzuki M. , Fujii M.

tom Vol. 3, No. 4

76-79

A microprobing system, which has the functions of measuring the intracranial EEG(IC-EEG) and freezing brain tissue, is proposed for the minimally invasive brain cryogenic surgery of intractable epilepsy treatment. Two fi76 µm platinum electrodes were equipped on a fi0.8 mm cryogenic probe. Epileptic burst, which was evoked on a brain sample of a rat, was measured by the electrodes. The freezing function was confirmed with the experiments with sliced hippocampus samples of a rat.