議論

本研究では、刺激の特徴によりシナプス可塑性の時空間的特性をうまく使い分 けることで、刺激から情報を分離抽出することが可能であることを示した。本研 究の成果は、感覚情報処理における神経ネットワークレベルでのシナプス可塑性 の役割を解明する上で、重要な知見を与えるものと考えられる。

さらに今後次のようなことをさらに研究していく。第6章で用いたコミュニケー ション刺激によるビートは25Hzである。このコミュニケーションによるビート は実際の環境では20 から80Hzである。Fortuneはこの周波数領域に注目してい

る [19]。この周波数領域は丁度ガンマ周波数帯であり、第6章で取り扱ったよう

な問題は脳情報処理におけるガンマ周波数発火の機能的役割の理解に貢献すると

Fortuneは考えている。自然の環境では弱電器魚は一匹が隔離されているようなも

のではなく、他の魚の影響を受けている場合が多いと考えられる。つまり、多く の場合ビート信号を伴って物体情報を取り扱うのである。そのような状況が多い ならば、ガンマ周波数帯のビートを情報処理において有効活用していても不思議 ではない。さらに他の魚のEODにより生じたビートを伴った電気刺激による物体 認識の研究を進めることで、ガンマ周波数の発火の機能的役割の理解に貢献でき る可能性がある。

また、シナプス可塑性についてはスパイクタイミング依存シナプス可塑性とい うものが存在する。弱電器魚においてもELLフィードバック経路にシナプス可塑 性が確認されている。ELLの錐体細胞のバースト発火のようなスパイクの特異な 時間的特性の変化とスパイクタイミング依存シナプス可塑性の相互作用が感覚情 報処理になにか機能的役割を果たしているのではないかと考えられる。今後スパ イクタイミング依存シナプス可塑性についても研究を進めていきたい。

本研究を進めるにあたり、多くの方々に指導、助言、協力をしていただき感謝 します。神原武志先生、樫森与志喜助先生には、研究の指導はもとより、研究成果 の国際会議や学術雑誌などでの発表という貴重な経験をさせていただき、とても うれしく思います。また、本研究は数多くのフリーソフトにより支えられており ます。それら素晴らしいフリーソフトの開発に携わった方々に感謝いたします。

一般用語の省略形

ISI inter spike interval インタースパイクインターバル

PSP post synaptic potential シナプス後電位 PSTH peri stimulus time histgram PSTヒストグラム

メンフクロウの用語の省略形

IC inferior colliculus 下丘

ICc central nucleus of inferior colliculus 下丘中心核 ICcls lateral shell of central nucleus of inferior colliculus 側面下丘中心核 ICx external nucleus of inferior colliculus 下丘外側核

ILD interaural lebel difference 両耳音圧差

IPD interaural phase difference 両耳位相時間差

ITD interaural time difference 両耳到着時間差

NA nucleus anguralis 角状核

NL nucleus laminaris 層状核

NM nucleus magnocellularis 大細胞核

OT optic tectum 視蓋

VLVp nucleus ventralis lemnisci lateralis pars posterior 後外側毛帯核

bp cell basilar pyramidal cell 錐体細胞 EGP eminentialis granularis posterior 顆粒隆起後部 ELL electrosensory lateral line lobe 電気感覚側線葉

EOD electric organ discharge 発電器官の発電

EOD AM EOD amplitude modulation EODの振幅変調 JAR jamming avoidance response 混信回避応答

NP nucleus praeeminetialis 隆起前域核

OT optic tectum 視蓋

TS torus semicircuralis 半円隆起

[1] L. F. Abbott, and G. Regehr, Synaptic Computation, Nature, 431, pp 796-803 (2004) [2] R. Adolphs, Bilateral inhibition generates neuronal responses tuned to interaural level differences in the auditory brainstem of the barn owl, J.Neurosci, 13, 3647-4668 (1993)

[3] J. Bastian, Electloreception, behavior, anatomy, and physiology, in: T. H. Bullock, W. Heiligenberg, eds, Electroreception(Wiely, N.Y, 1986) 577-612.

[4] J. Bastian, m. J. Chacron, and L. Maler, Receptive field organization determines pyramidal cell stimulus-encoding capability and spatial stimulus selectivity, j. Neu-rosci., 22, 4577-4590 (2002)

[5] CC. Bell, Y. Han, Y. Sugawara, and K. Grant, Synaptic plasticity in a cerebellum-like structure depends on temporal order, nature, 387, 278-281 (1997)

[6] M. S. Brainard, E. I. Knudsen, and S. D. Esterly, Neural derivation of sound source location: Resolution of spatial ambiguities in binaural cues, J. Acoust. Soc. Am., 91, 1015-1027 (1992)

[7] N. J. Berman, and L. Maler Neural architecture of the electorsensory lateral line lobe: adaptations for coincidence detection, a sensory searchlight and frequency-dependent adaptive filtering, J. Exp. Biol., 202, 1243-1253 (1999)

[8] R. Brandman, and M. E. Nelson, A simple model of long-term spuke train regular-ization, Neural Comp, 14, 1575-1597 (2002)

[10] M. J. Chacron, A. Longtin, and L. Maler, Negative interspike interval correlation increase the neuronal capacity for encoding time-dependent stimuli, J. Neurosci., 5328-5343 (2001)

[11] M. J. Chacron , B. Doiron, L. Maler, A. Longtin, and J. Bastian, Non-classical receptive field mediates switch in a sensory neuron’s frequeny tuning, Nature, 423, 77-81 (2003)

[12] M. J. Chacron, A. Longtin, and L. Maler, To burst or not to burst?, J. Comp.

Neurosci., 127-136 (2004)

[13] B. Doiron, A. Longtin, N. Berman, and L. Maler, Subtractive and divisive inhibi-tion: effect of voltage-dependent inhibition conductances and noise, Neural Comp., 13, 227-248 (2000)

[14] B. Doiron, A. Longtin, R. W. Turner, and L. Maler, Model of gamma frequeny burst discharge generated by conditional backpropagation, J. Neurophysiol., 86, 1523-1545 (2001)

[15] B. Doiron, C Laing, A. Longtin, Ghostbursting: A novel neuronal burst mecha-nism, J. Comp. Neurosci., 12, 5-25 (2002)

[16] B. Doiron, M. J. Chacron, L. Maler, A. Longtin, and J. Bastian, Inhibitory feed-back required for network oscillatory responses to communication but not prey stim-uli, Nature, 421, 539-543 (2003)

[17] E. S. Fortune, and G. J. Rose, Short-term synaptic plasticity as a temporal filter, TINS, 24, 381-385 (2001)

[18] E. S. Fortune, and G. J. Rose, Roles of short-term synaptic plasticity in behavior, J. Physiol., 96, 539-545 (2002)

[19] E. S. Fortune, The decoding of electrosensory systems, Current Opinion in Neu-robiol., 16, 1-7, (2006)

[20] I. Fujita and M. Konishi, The Role of GABAergic Inhibition in Processing of Inter-aural Time Difference in the Owl Auditory System, J Neurosci., 11, 722-739 (1991)

[21] K. Fujita, Y. Kashimori, M H. Zheng, and T. Kambara, A role of burst firings in encoding of spatiotemporally-varying stimulus, Biosystems, Volume 76, 21-31 (2004)

[22] K. Fujita, S Q. Huang, Y. Kashimori, and T. Kambara, Neural Mechanism of Bind-ing ITD Information with IID One for GeneratBind-ing Brain Map of Sound Localization Lecture Notes in Computer Science, Volume 3316, 44-49 (2004)

[23] K. Fujita, Y. Kashimori, and T. Kambara, Dynamic population coding for detecting the distance and size of an object in electrolocation, Neurocomputing, Volumes 65-66, 243-251 (2005)

[24] K. Fujita, and Y. Kashimori, Population coding of electrosensory stimulus in re-ceptor network, Neurocomputing 69: 1206-1210 (2006)

[25] K. Fujita, Yoshiki Kashimori, M H. Zheng and T. Kambara, A role of synchronic-ity of neural activsynchronic-ity based on dynamic plasticsynchronic-ity of synapses in encoding spatiotem-poral features of electrosensory stimuli, Mathematical Biosciences, 201, 113-124 (2006)

[26] F. Gabbiani, W. Metzner, and C. Koch, From stimulus encoding to feature extrac-tion in weakly electric fish, Nature, 384, 564-567 (1996)

[27] D.O. Hebb, The Organization of Behavior Wiley, N.Y. (1949)

[28] W. Heiligenberg, Theoretical and experimental approaches to spatila aspects of electrolocation, J.Comp.Physiol. 103, 247-272, (1975)

[29] W. Heiligenberg, Neural nets in electric fish, MIT press, Cambridge (1991) [30] D. Hirayama, K. Fujita, S. Inoue, Y. Kashimori, and T. Kambara, Functional role

of bilateral mutual inhibitory interaction in encoding interaural intensity difference for sound localization Proc. of 12th International Conference on Neural Information processing/APNN 2005/11, pp 307-311 (2005)

[32] E. M. Izhikevich, N. S. Desai, E. C. Walcot, and F. C. Hoppensteadt, Bursts as a unit of neural information: selective communication via resonance, Trends in Neu-rosci, 26, 161-167 (2003)

[33] Kepecs A, Wang X-J, Lisman J, Bursting neurons signal input slope. J Neurosci 22:9053-9062 (2002)

[34] M. Konishi, Listening with two ears, Scientific American, 268, pp 66-73 (1993) [35] R. Krahe, G. Kreiman, F. Gabbiani, C. Koch, and W. Metzner, Stimulus encoding

and feature extraction by multiple sensory neurons, J. Neurosci. 22 (2002) 2374-2382.

[36] R. Krahe and F. Gabbiani, Burst firing in sensory system, Nature Review neuro-science, 5, 13-24 (2004)

[37] E. I. Kunudsen, E. Zheng, and W. M. DeBello, Traces of learning in the auditory localization pathway Proc. Natl. Acad. Sci. USA , 97, 11815-11820 (2000)

[38] J. E. Lewis and L. Maler, Neuronal Population Codes and the Perception of Object Distance in Weakly Electric Fish, J. Neurosci. 21 2842-2850 (2001)

[39] J. E. Lewis, and L. Maler, Synaptic dynamics on different time scales in a parallel fiber feedback pathway of the weakly electric fish, J. Neurophysiol. 91:1064-1070 (2004)

[40] H. Markram, Y. Wang, and M. Tsodyks, Differential signaling via the same axon of neocortical pyramidal neurons, Proc. Natl. Acad. Sci. USA, 95, 5323-5328 (1998) [41] H. Morisawa, D. Hirayama, K. Fujita, and Y. Kashimori and Takeshi Kambara, Binding Mechanism of Frequency-Specific ITD and IID Information in Sound Lo-calization of Barn Owl, Lecture Notes in Computer Science, 4232, 255-262 (2006) [42] A-M. M. Oswald, M. J. Chacron, B. Doiron, J. Bastian, and L. Maler Parallel

Processing of Sensory Input by Bursts and Isolated Spikes, J. Neurosci, 24(18), 4351-4362 (2004)

[43] J. L. Pena, and M. Konishi, Auditory spatial receptive field created by multiplica-tion, Science, 292, 249-252 (2001)

[44] R. Ratnam and M.E. Nelson, Nonrenewal statics of electrosensory afferent spike trains: Implications for the detection of weakly sensory signals, J. Neurosci., 20, 6672-6683 (2000)

[45] C. A. Shumway, Multiple Electrosensory Maps in the Medulla of Weakly Electric Gymnotiform Fish. I. Physiological Differences, J. Neurosci., 9, 4388-4399, (1989) [46] A. M. Silito and H. E. Jones, Corticothalamic interactions in the transfer of visual

information, Phil. Trans., 357, 1739-1752 (2002)

[47] G. Von der Emde, S. Schwarz, L. Gomez, R. Budelli, and K. Grant, Electric fish measure distance in the dark, Nature, 395, 890-894 (1998)

1. Kazuhisa Fujita and Yoshiki Kashimori,

論文題目「Population coding of electrosensory stimulus in receptor network」

2006年6月Neurocomputing, Volume 69, pp. 1206-1210 (第4章に関連) 2. Kazuhisa Fujita, Yoshiki Kashimori, and Takeshi Kambara,

論文題目「Dynamic population coding for detecting the distance and size of an object in electrolocation」

2005年6月Neurocomputing, Volumes 65-66, pp. 243-251(第5章に関連) 3. Kazuhisa Fujita, ShungQuang Huang, Yoshiki Kashimori, and Takeshi Kambara,

論文題目「Neural Mechanism of Binding ITD Information with IID One for Gen-erating Brain Map of Sound Localization」

2004年11月Lecture Notes in Computer Science, Volume 3316, pp. 44-49 (Pro-ceedings of 11th International Conference on Neural Information Processing) (第 2章に関連)

1. Kazuhisa Fujita, Yoshiki Kashimori, MeiHong Zheng, and Takeshi Kambara, 論文題目「A role of synchronicity of neural activity based on dynamic plasticity of synapses in encoding spatiotemporal features of electrosensory stimuli」

2006年5月Mathematical Biosciences, Volume 201, 113-124

2. Kazuhisa Fujita, Yoshiki Kashimori, MeiHong Zheng, and Takeshi Kambara, 論文題目「A role of burst firings in encoding of spatiotemporally-varying stim-ulus」

2004年8月Biosystems, Volume 76, 21-31

3. Kazuhisa Fujita, Eigo Kamata, Satoru Inoue, Yoshiki Kashimori, and Takeshi Kambara,

論文題目「A functional role of FM sweep rate of biosonar in echolocation of bat」

2004年11月Lecture Notes in Computer Science, Volume 3316, pp 78-83 4. Kazuhisa Fujita and Yoshiki Kashimori,

論文題目「A neural model for encoding information of object distance and size in electrolocation」

2005年11月 Proceedings of 12th International Conference on Neural Informa-tion Processing, pp. 318-321

5. Yoshiki Kashimori, Nobuyuki Suzuki, Kazuhisa Fujita, Meihong Zheng, and Takeshi Kambara,

論文題目「A functional role of multiple spatial resolution maps in form

percep-in Sound Localization of Barn Owl」

2006年10月Lecture Notes in Computer Science, Volume 4232, pp. 255-262 7. Seiichi Hirooka, Kazuhisa Fujita, and Yoshiki Kashimori,

論文題目「Effect of Feedback Signals on Tuning Shifts of Subcortical Neurons in Echolocation of Bat」

2006年10月Lecture Notes in Computer Science, Volume 4232, pp. 255-262 8. Daisuke Hirayama, Kazuhisa Fujita, Satoru Inoue, Yoshiki Kashimori, and Takeshi

Kambara,

論文題目「Functional role of bilateral mutual inhibitory interaction in encoding interaural intensity difference for sound localization」

2005年11月Proceedings of 12th International Conference on Neural Informa-tion processing, pp. 307-311 (2005)

9. Yu Ichinose, Yoshiki Kashimori, Kazuhisa Fujita, and Takeshi Kambara,

論文題目「A Neural Model of Visual System Based on Multiple Resolution Maps for Categorizing Visual Stimuli」

2005年11月Proc. of 12th International Conference on Neural Information Pro-cessing pp. 515-520