京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18991号 / 工博第4033号 / 新制||工||1621(附属図書館) / 31942 / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 引原 隆士, 教授 土居 伸二, 教授 小林 哲生 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Real neurons, and their networks, are far too complex to be described exactly by simple deterministic equations. Any description of their dynamics must therefore incorporate noise to some degree. It is my thesis that the nervous system is organized in such a way that its performance is optimal, subject to this constraint. I further contend that neuronal dynamics may even be enhanced by noise, when compared with their deterministic counter-parts. To support my thesis I will present and analyze three case studies. I will show how noise might (i) extend the dynamic range of mammalian cold-receptors and other cells that exhibit a temperature-dependent discharge; (ii) feature in the perception of ambiguous figures such as the Necker cube; (iii) alter the discharge pattern of single cells.

A ressonância estocástica (RE) mostra que certos níveis de ruído ajudam na detecção e transmissão de sinais subliminares. Melhorias no desempenho do sistema somato-sensorial e motor (dentre outros) têm sido obtidos por meio da RE gerada pela utilização de sinais aditivos de intensidade ótima. O sinal aditivo (SA) mais comumente utilizado é o ruído branco gaussiano (RBG). Este estudo teve como objetivo verificar se é possível gerar RE no sistema sensorial tátil usando como SA um sinal senoidal e comparar estes resultados com os obtidos realizando o mesmo experimento com SA de tipo RBG. Os sinais usados no experimento foram definidos como sinal de estímulo (SE) de 3Hz a ser reconhecido com a ajuda dos SA, sinal aditivo senoidal (SAS) de 150Hz e sinal aditivo de ruido branco gaussiano (SARBG) filtrado a 150Hz. Na primeira parte do estudo foi feita uma simulação do modelo de neurônio de Hodgkin e Huxley para verificar se na teoria podia se obter RE para SE e SA senoidais. Foi injetado um sinal senoidal de 3Hz no modelo com uma intensidade para a qual o neurônio não conseguia gerar potencial de ação (PA). Quando a este sinal inicial foi adicionado um sinal senoidal de frequência superior, o neurônio conseguiu responder. A mesma resposta foi obtida quando o SA usado foi RBG, conseguindo mostrar de forma qualitativa a nossa hipótese a partir de um modelo simulado. Posteriormente foi realizado um estudo psicofísico com 20 voluntários (11 homens e 9 mulheres) para verificar o desempenho do SAS e comparar este com o desempenho de SARBG para a detecção sensorial do SE. Primeiro foi achado o limiar de detecção (LD) para cada um dos sinais usados e no experimento este valor foi usado para determinar a intensidade de estímulo. No caso do SE a intensidade foi definida como 80% do LD de cada voluntário. No caso dos SA a intensidade foi variando entre 0% até 80% do LD, com o objetivo de se encontrar a melhor proporção de SA adicionado para detectar o SE. Em 90% dos casos conseguiu-se gerar RE tanto empregando um sinal senoidal de frequência rápida como SA, quanto utilizando-se RBG. Ambos SAs apresentaram uma melhoria estatisticamente significativa na proporção de detecção (PD) do SE. Porém, nenhum dos SA apresentou um melhor desempenho em relação ao outro, de maneira que poderia ser usado tanto um quanto outro tipo de SA para gerar RE no sistema somato-sensorial. Este trabalho é pioneiro em usar uma combinação de senóides para gerar RE e abre as portas à elaboração e desenvolvimento de dispositivos biomédicos que contenham uma parte geradora de RE e consigam melhorar a estabilidade e controle postural em pessoas com deficiência motora ou somato-sensorial. / Stochastic ressonance (SR) shows that certain levels of noise help to detect and transmit subliminal signals. Improvements in the performance of the somatosensory and motor systems (among others) have been obtained through the SR generated using additive signals with optimal intensity. The most commonly used additive signal (AS) is white Gaussian noise (WGN). This study aimed to verify whether it is possible to generate SR in the tactile sensory system using a sinusoidal signal as the AS and, at the same time, compare the results when the AS was WGN. The signals used in the experiments were defined as 3Hz for the stimulus signal (SS), to be recognized with the aid of ASs. These were either a sinuoid of 150Hz additive sinusoidal signal (ASS) or a white Gaussian noise additive signal (WGNAS) filtered at 150Hz. In the first part of the study a simulation of the Hodgkin and Huxley neuron model was made to verify if it could undergo SR for the same types of SS and AS mentioned before. A 3Hz sine signal was injected into the model with an intensity at which the neuron could not generate action potentials. When a higher frequency sine wave was added to this initial signal, the neuron could respond. The same behaviour was obtained when the additive signal used was WGN, giving, hence, a qualitative confirmation of our hypothesis. A psychophysical study was then carried out with 20 volunteers (11 men and 9 women) to verify the performance of the ASS and compare it with the WGNAS for the sensory detection of the sinusoidal SS. Initially, the detection threshold (DT) was found for each of the signals used. During the experiment, this value was used to determine the stimulus intensity. In the case of the SS the intensity was defined as 80 % of the DT of each volunteer. In the case of ASs, the intensity varied from 0% to 80% of the DT, in order to find the best proportion of AS added to detect the SS. In 90% of the cases it was possible to generate SR using either a fast frequency ASS or the WGNAS. Both ASs showed a statistically significant improvement in the detection rate (DR) of the SS. However, none of ASs performed better than the other, so that both types could be used to generate SR in the somatosensory system. This work has pioneered the use of a combination of sinusoids to generate SR and opens the door to the development of biomedical devices that help generate SR to provide stability improvement and better postural control for people with motor or somatosensory impairment.

A ressonância estocástica (RE) mostra que certos níveis de ruído ajudam na detecção e transmissão de sinais subliminares. Melhorias no desempenho do sistema somato-sensorial e motor (dentre outros) têm sido obtidos por meio da RE gerada pela utilização de sinais aditivos de intensidade ótima. O sinal aditivo (SA) mais comumente utilizado é o ruído branco gaussiano (RBG). Este estudo teve como objetivo verificar se é possível gerar RE no sistema sensorial tátil usando como SA um sinal senoidal e comparar estes resultados com os obtidos realizando o mesmo experimento com SA de tipo RBG. Os sinais usados no experimento foram definidos como sinal de estímulo (SE) de 3Hz a ser reconhecido com a ajuda dos SA, sinal aditivo senoidal (SAS) de 150Hz e sinal aditivo de ruido branco gaussiano (SARBG) filtrado a 150Hz. Na primeira parte do estudo foi feita uma simulação do modelo de neurônio de Hodgkin e Huxley para verificar se na teoria podia se obter RE para SE e SA senoidais. Foi injetado um sinal senoidal de 3Hz no modelo com uma intensidade para a qual o neurônio não conseguia gerar potencial de ação (PA). Quando a este sinal inicial foi adicionado um sinal senoidal de frequência superior, o neurônio conseguiu responder. A mesma resposta foi obtida quando o SA usado foi RBG, conseguindo mostrar de forma qualitativa a nossa hipótese a partir de um modelo simulado. Posteriormente foi realizado um estudo psicofísico com 20 voluntários (11 homens e 9 mulheres) para verificar o desempenho do SAS e comparar este com o desempenho de SARBG para a detecção sensorial do SE. Primeiro foi achado o limiar de detecção (LD) para cada um dos sinais usados e no experimento este valor foi usado para determinar a intensidade de estímulo. No caso do SE a intensidade foi definida como 80% do LD de cada voluntário. No caso dos SA a intensidade foi variando entre 0% até 80% do LD, com o objetivo de se encontrar a melhor proporção de SA adicionado para detectar o SE. Em 90% dos casos conseguiu-se gerar RE tanto empregando um sinal senoidal de frequência rápida como SA, quanto utilizando-se RBG. Ambos SAs apresentaram uma melhoria estatisticamente significativa na proporção de detecção (PD) do SE. Porém, nenhum dos SA apresentou um melhor desempenho em relação ao outro, de maneira que poderia ser usado tanto um quanto outro tipo de SA para gerar RE no sistema somato-sensorial. Este trabalho é pioneiro em usar uma combinação de senóides para gerar RE e abre as portas à elaboração e desenvolvimento de dispositivos biomédicos que contenham uma parte geradora de RE e consigam melhorar a estabilidade e controle postural em pessoas com deficiência motora ou somato-sensorial. / Stochastic ressonance (SR) shows that certain levels of noise help to detect and transmit subliminal signals. Improvements in the performance of the somatosensory and motor systems (among others) have been obtained through the SR generated using additive signals with optimal intensity. The most commonly used additive signal (AS) is white Gaussian noise (WGN). This study aimed to verify whether it is possible to generate SR in the tactile sensory system using a sinusoidal signal as the AS and, at the same time, compare the results when the AS was WGN. The signals used in the experiments were defined as 3Hz for the stimulus signal (SS), to be recognized with the aid of ASs. These were either a sinuoid of 150Hz additive sinusoidal signal (ASS) or a white Gaussian noise additive signal (WGNAS) filtered at 150Hz. In the first part of the study a simulation of the Hodgkin and Huxley neuron model was made to verify if it could undergo SR for the same types of SS and AS mentioned before. A 3Hz sine signal was injected into the model with an intensity at which the neuron could not generate action potentials. When a higher frequency sine wave was added to this initial signal, the neuron could respond. The same behaviour was obtained when the additive signal used was WGN, giving, hence, a qualitative confirmation of our hypothesis. A psychophysical study was then carried out with 20 volunteers (11 men and 9 women) to verify the performance of the ASS and compare it with the WGNAS for the sensory detection of the sinusoidal SS. Initially, the detection threshold (DT) was found for each of the signals used. During the experiment, this value was used to determine the stimulus intensity. In the case of the SS the intensity was defined as 80 % of the DT of each volunteer. In the case of ASs, the intensity varied from 0% to 80% of the DT, in order to find the best proportion of AS added to detect the SS. In 90% of the cases it was possible to generate SR using either a fast frequency ASS or the WGNAS. Both ASs showed a statistically significant improvement in the detection rate (DR) of the SS. However, none of ASs performed better than the other, so that both types could be used to generate SR in the somatosensory system. This work has pioneered the use of a combination of sinusoids to generate SR and opens the door to the development of biomedical devices that help generate SR to provide stability improvement and better postural control for people with motor or somatosensory impairment.

<p>Research on children with Attention Deficit Hyperactivity Disorder (ADHD) has shown that they are extremely sensitive to distraction from external stimuli that lead to poor cognitive performance. This thesis shows that cognitive performance can be improved if this external stimulus is smooth and continuous (e.g. auditory white noise). Control children attenuate their performance under such conditions. The first Study proposes the moderate brain arousal model (MBA). This neurocomputational model predicts selective improvement from noise in ADHD children. Noise through a phenomenon called stochastic resonance (SR), can be beneficial in dopamine deprived neural systems. The statistical phenomenon of SR explains how the signal-to-noise ratio can be improved by noise in neural systems where the passing a threshold is required. The second Study provides experimental support for the MBA-model by showing that ADHD children improve performance in a free recall task while exposed to auditive noise. Control children declines in the same condition. The third Study generalizes this finding among low achieving children, which it is argued have low dopamine levels. Noise exposure improves performance in low achievers, but inhibits performance in high achievers. The conclusion is that external auditory noise can restore low dopamine levels and thus improve cognitive performance. It is also proposed that dopamine levels modulate the SR effect; this means that low dopamine persons require more noise to obtain an SR effect. Both excessive and insufficient dopamine is detrimental for cognitive performance. The MBA model can be used to explain several shortcomings where changes in the dopamine system have been identified. The MBA model can also help create appropriate and adaptive environments, especially in schools, for persons with a deficient dopamine function, such as ADHD children.</p>

<p>Previous findings have suggested that auditive white noise benefits cognitive performance under certain circumstances. The primary purpose of the present pilot study was to explore the effects of visual white noise on verbal episodic memory performance in a normal participant population. Performance was assessed by an immediate free recall test. A secondary purpose was to explore whether participants` eye blink rates and/or temporal processing alters in different noise conditions. The findings of the present study suggest that visual white noise does not affect recall performance among normal participants. However, partially different memory systems and/or memorizing techniques might be used in different noise conditions. Furthermore, noise was not found to affect participants` blink rates or temporal processing.</p>

In the case of wideband (aperiodic) signals, the classical signal and noise measures used to characterize stochastic resonance do not work because their way of distinguishing signal from noise fails. In a study published earlier (L. B. Kish, 1996), a new way of measuring and identifying noise and aperiodic (wideband) signals during strongly nonlinear transfer was introduced. The method was based on using cross-spectra between the input and the output. According to the study, in the case of linear transfer and sinusoidal signals, the method gives the same results as the classical method and in the case of aperiodic signals it gives a sensible measure. In this paper we refine the theory and present detailed simulations which validate and refine the conclusions reached in that study. As neural and ion channel signal transfer are nonlinear and aperiodic, the new method has direct applicability in membrane biology and neural science (S.M. Bezrukov and I. Vodyanoy, 1997).

Unsere alltägliche Erfahrung ist mit verschiedenen akustischen Einfluessen wie Lärm, aber auch Musik verbunden. Jeder weiss, wie Lärm stören kann und Kommunikation behindert oder gar unterbindet. Ähnliche optische Effekte sind bekannt: starkes Schneetreiben oder Regengüsse verschlechtern die Sicht und lassen uns Umrisse nur noch schemenhaft erkennen. Jedoch koennen ähnliche Stimuli auch sehr positive Auswirkungen haben: Autofahrer fahren bei leiser Musik konzentrierter -- die Behauptung von Schulkindern, nur bei dröhnenden Bässen die Mathehausaufgaben richtig rechnen zu können, ist allerdings nicht wissenschaftlich erwiesen. Außerordentlich interessant aus dieser Sicht sind auch Reizleitungsprozesse: Reize werden nur weitergleitet, wenn die strukturlosen Signale der Neuronen mit ausreichend starker Intensität erfolgen, also ein Schwellwert überschritten ist. <br /> <br /> Der Physiker Dr. Alexei Zaikin von der Universität Potsdam beschäftigt sich mit sogenannten rauschinduzierten Phänomenen aus theorischer Sicht. Sein Forschungsgebiet sind Prozesse, bei denen Rauschen mehrfach das Systemverhalten beeinflusst: ist es ausreichend gross, d.h. größer als ein kritischer Wert, wird eine reguläre Struktur gebildet, die durch das immernoch vorhandene Rauschen mit der Struktur des Nachbarsystems synchronisiert. Um ein solches System mit kritischem Wert zu erhalten, bedarf es einer weiteren Rauschquelle. Herr Zaikin analysierte noch weitere Beispiele solcher doppelt stochastischen Effekte. Die Ausarbeitung derartiger theoretischer Grundlagen ist wichtig, da diese Prozesse in der Neurophysik, in technischen Kommunikationssystemen und in den Lebenswissenschaften eine Rolle spielen. / Our every-day experience is connected with different acoustical noise or music. Usually noise plays the role of nuisance in any communication and destroys any order in a system. Similar optical effects are known: strong snowing or raining decreases quality of a vision. In contrast to these situations noisy stimuli can also play a positive constructive role, e.g. a driver can be more concentrated in a presence of quiet music. Transmission processes in neural systems are of especial interest from this point of view: excitation or information will be transmitted only in the case if a signal overcomes a threshold.<br /> <br /> Dr. Alexei Zaikin from the Potsdam University studies noise-induced phenomena in nonlinear systems from a theoretical point of view. Especially he is interested in the processes, in which noise influences the behaviour of a system twice: if the intensity of noise is over a threshold, it induces some regular structure that will be synchronized with the behaviour of neighbour elements. To obtain such a system with a threshold one needs one more noise source. Dr. Zaikin has analyzed further examples of such doubly stochastic effects and developed a concept of these new phenomena. These theoretical findings are important, because such processes can play a crucial role in neurophysics, technical communication devices and living sciences.

Research on children with Attention Deficit Hyperactivity Disorder (ADHD) has shown that they are extremely sensitive to distraction from external stimuli that lead to poor cognitive performance. This thesis shows that cognitive performance can be improved if this external stimulus is smooth and continuous (e.g. auditory white noise). Control children attenuate their performance under such conditions. The first Study proposes the moderate brain arousal model (MBA). This neurocomputational model predicts selective improvement from noise in ADHD children. Noise through a phenomenon called stochastic resonance (SR), can be beneficial in dopamine deprived neural systems. The statistical phenomenon of SR explains how the signal-to-noise ratio can be improved by noise in neural systems where the passing a threshold is required. The second Study provides experimental support for the MBA-model by showing that ADHD children improve performance in a free recall task while exposed to auditive noise. Control children declines in the same condition. The third Study generalizes this finding among low achieving children, which it is argued have low dopamine levels. Noise exposure improves performance in low achievers, but inhibits performance in high achievers. The conclusion is that external auditory noise can restore low dopamine levels and thus improve cognitive performance. It is also proposed that dopamine levels modulate the SR effect; this means that low dopamine persons require more noise to obtain an SR effect. Both excessive and insufficient dopamine is detrimental for cognitive performance. The MBA model can be used to explain several shortcomings where changes in the dopamine system have been identified. The MBA model can also help create appropriate and adaptive environments, especially in schools, for persons with a deficient dopamine function, such as ADHD children.

Previous findings have suggested that auditive white noise benefits cognitive performance under certain circumstances. The primary purpose of the present pilot study was to explore the effects of visual white noise on verbal episodic memory performance in a normal participant population. Performance was assessed by an immediate free recall test. A secondary purpose was to explore whether participants` eye blink rates and/or temporal processing alters in different noise conditions. The findings of the present study suggest that visual white noise does not affect recall performance among normal participants. However, partially different memory systems and/or memorizing techniques might be used in different noise conditions. Furthermore, noise was not found to affect participants` blink rates or temporal processing.