中川 誠司

Several studies have reported that high-frequency sounds of more than 20,000 Hz can be perceived by the profoundly sensorineural deaf subjects, as well as normal-hearing, through bone conduction. Although the mechanisms of how bone-conducted ultrasound (BCU) is perceived remain unclear, several characteristics that differ from air-conducted audible sounds are reported; for example, the pitch of BCU is independent of the frequency. In this study, the effects of BCU frequency on the activities of auditory cortex were investigated by magnetoencephalography (MEG). Auditory-evoked magnetic fields evoked by four kinds of BCU stimuli, 22,000, 27,000, 32,000, and 37,000 Hz tone bursts, were measured, and equivalent current dipoles (ECDs) of N1m were estimated. No significant differences were observed among the four kinds of BC-U stimuli, not only in pitch, but also in N1m latency, ECD moment, and ECD location; whereas obvious differences were observed between the air-conducted sounds and BCUs. These results suggest that the mechanisms for BCU perception are different from those for air-conducted audible sounds. (c) 2004 Elsevier B.V. All rights reserved.

The cortical areas involved in processing of emotional prosody (EP), such as joy or sadness, have been reported to be localized in the right basal ganglia, frontal lobes or bilateral temporal lobes in recent fMRI studies. Moreover, event-related brain potentials have not been shown to have ERP components with latencies associated with EP recognition, namely N1, P2 and P3. So, we investigated a processing of EP using magnetoencephalograpby (MEG), which has a high time and space resolution. In the test session, an emotional voice (expressing joy, sadness or normal mood, and calling a name consisting of 5 moras) was presented, followed by a 900 ins interstimulus interval and then an emotional face (the same emotion as the voice) was displayed for 1000 ms. The subjects were requested to judge whether or not the emotional features of the voice and face were identical. In the control session, the emotional voices were presented while the subjects carried out visual working memory (n-back) tasks between two sessions, and significant differences in the cortical activities associated with processing of EP were observed during the latencies in different periods after the onset of stimuli in both hemispheres. (c) 2004 Elsevier B.V. All rights reserved.

We previously investigated the effect of movement-associated intention on nervous activities using neurophysiologic indexes in order to estimate how movement is generated under expected or unexpected conditions. In this study, we measured magnetoencephalographic (MEG) signals during passive finger movement, and evaluated the effect of the existence of anticipation on cortical activities. The subjects were 10 right-handed healthy volunteers. The subjects anticipated the passive movement by receiving warning signals before the movement, and the passive movement was generated as the result of the subjects' anticipation. In the first experiment (Experiment I), a series of warning signals was presented to indicate the onset of passive movement. In the second experiment (Experiment II), a warning signal was given to indicate the direction of passive movement. The passive movement was lifting or lowering the right middle finger (only lifting was applied in Experiment I). Consequently, in Experiment I, for passive movement with a warning signal, MEG deflection before the movement and shortening of the peak latency with a reduction in the amplitude of somatosensory evoked field (SEF) components were observed, compared to values under the condition of no warning signal. However, in Experiment II, there was no change in peak latency, but reduction in the SEF amplitude under the conditions of a warning signal being given. The present results indicate a possibility that anticipation prior to the predictable passive movement modulated the cortical activities in physiological condition.

これまでの骨導超音波知覚に関する研究成果を利用して,重度難聴者を対象とした携帯型骨導超音波補聴器を開発し,その有用性を検証するため,試作した補聴器を用いて難聴者および聴覚健常者に対して聴取実験を行った.聴覚健常者では全員,中等度難聴者では9割以上が何らかの音声を聴取できた.重度難聴者に関しては,その割合は4割程度にとどまったが,その中には完全難聴者や人工内耳装用者も含まれていた.聴覚健常者では8割以上が周波数の高低を判断できたが,中等度難聴者では6割,重度難聴者では5割と,聴力の低下に伴って正答率が低下した.語音の明瞭度に関しても,同様に聴力の低下に伴って低くなる傾向を確認した

骨導振動子による呈示では,気導音では可聴帯域外となる20kHz以上の高周波であっても知覚可能であることが知られている.また,高度感音性難聴者においても,骨導可聴音提示では知覚できないが,骨導超音波であれば知覚可能であることが報告されている.我々は重度難聴者のための骨導超音波補聴器の実用化を目指している.実用化を目指すうえで音声の明瞭性が重要となる.これを解決するためには骨導超音波知覚のメカニズムを明らかにしなければならない.知覚メカニズムには幾つかの仮説が存在するが,我々は蝸牛関与説を重視している.知覚メカニズムの解明に向けた第一段階として,本報告では振動子から蝸牛へ至る波動伝搬を数値的に解析し,その特性を観察することとした.

骨導振動子による呈示では,気導音では可聴帯域外となる20kHz以上の高周波であっても知覚可能であることが知られている.また,高度感音性難聴者においても,骨導可聴音提示では知覚できないが,骨導超音波であれば知覚可能であることが報告されている.我々は重度難聴者のための骨導超音波補聴器の実用化を目指している.実用化を目指すうえで音声の明瞭性が重要となる.これを解決するためには骨導超音波知覚のメカニズムを明らかにしなければならない.知覚メカニズムには幾つかの仮説が存在するが,我々は蝸牛関与説を重視している.知覚メカニズムの解明に向けた第一段階として,本報告では振動子から蝸牛へ至る波動伝搬を数値的に解析し,その特性を観察することとした.

Magnetoencephalography (MEG) is widely used for studying brain functions, but clinical applications of MEG have been less prevalent. One reason is that only clinicians who have highly specialized knowledge can use MEG diagnostically, and such clinicians are found at only a few major hospitals. Another reason is that MEG data analysis is getting more and more complicated, and deals with a large amount of data, and thus requires high-performance computing. These problems can be solved by the collaboration of human and computing resources distributed in multiple facilities. A new computing infrastructure for brain scientists and clinicians in distant locations was therefore developed by the Grid technology, which provides virtual computing environments composed of geographically distributed computers and experimental devices. A prototype system connecting an MEG system at the AIST in Japan, a Grid environment composed of PC clusters at Osaka University in Japan and Nanyang Technological University in Singapore, and user terminals in Baltimore was developed. MEG data measured at the AIST were transferred in real-time through a 1-GB/s network to the PC clusters for processing by a wavelet cross-correlation method, and then monitored in Balimore. The current system is the basic model for remote-access to MEG equipment and high-speed processing of MEG data.

This study investigated the effect of word familiarity of visual stimuli on the word recognizing function of the human brain. Word familiarity is an index of the relative ease of word perception, and is characterized by facilitation and accuracy on word recognition. We studied the effect of word familiarity, using "Hiragana" (phonetic characters in Japanese orthography) characters as visual stimuli, on the elicitation of visually evoked magnetic fields with a word-naming task. The words were selected from a database of lexical properties of Japanese. The four "Hiragana" characters used were grouped and presented in 4 classes of degree of familiarity. The three components were observed in averaged waveforms of the root mean square (RMS) value on latencies at about 100ms, 150ms and 220ms. The RMS value of the 220ms component showed a significant positive correlation (F=(3/36) 5.501 p=0.035) with the value of familiarity. ECDs of the 220ms component were observed in the intraparietal sulcus (IPS). Increments in the RMS value of the 220ms component, which might reflect ideographical word recognition, retrieving "as a whole" were enhanced with increments of the value of familiarity. The interaction of characters, which increased with the value of familiarity, might function "as a large symbol" and enhance a "pop-out" function with an escaping character inhibiting other characters and enhancing the segmentation of the character (as a figure) from the ground.

Cortical areas involved in processing of emotional prosody (EP) in spoken language, such as joy or sadness, have been found in functional magnetic resonance imaging (fMRI) studies bilaterally or dominantly in the right frontal or temporal lobes. In this study, we investigated spatiotemporal patterns of cortical activity related to EP processing using magnetoencephalography (MEG). In this experiment, a joyful face (JF) or a sad face (SF) was displayed after voices which had emotional features of joy (joy prosody: JP) or sadness (sad prosody: SP) were presented. Subjects were requested to judge whether emotional features of the voice and the face were identical or not. MEG signals evoked by emotional voices were measured and significant differences of cortical activities associated with processing of emotional feature were observed between the right and left hemisphere during the latency of 100-150 ms that includes the N1m component. Our study suggests that MEG is a useful method, in addition to fMRI and event-related scalp potentials (ERP) for studying non-invasively EP processing in the human brain.

This study investigated the effect of word familiarity of visual stimuli on the word recognizing function of the human brain. Word familiarity is an index of the relative ease of word perception, and is characterized by facilitation and accuracy on word recognition. We studied the effect of word familiarity, using "Hiragana" (phonetic characters in Japanese orthography) characters as visual stimuli, on the elicitation of visually evoked magnetic fields with a word-naming task. The words were selected from a database of lexical properties of Japanese. The four "Hiragana" characters used were grouped and presented in 4 classes of degree of familiarity. The three components were observed in averaged waveforms of the root mean square (RMS) value on latencies at about 100ms, 150ms and 220ms. The RMS value of the 220ms component showed a significant positive correlation (F=(3/36) 5.501 p=0.035) with the value of familiarity. ECDs of the 220ms component were observed in the intraparietal sulcus (IPS). Increments in the RMS value of the 220ms component, which might reflect ideographical word recognition, retrieving "as a whole" were enhanced with increments of the value of familiarity. The interaction of characters, which increased with the value of familiarity, might function "as a large symbol" and enhance a "pop-out" function with an escaping character inhibiting other characters and enhancing the segmentation of the character (as a figure) from the ground.

Magnetoencephalography (MEG) is widely used for studying brain functions, but clinical applications of MEG have been less prevalent. One reason is that only clinicians who have highly specialized knowledge can use MEG diagnostically, and such clinicians are found at only a few major hospitals. Another reason is that MEG data analysis is getting more and more complicated, and deals with a large amount of data, and thus requires high-performance computing. These problems can be solved by the collaboration of human and computing resources distributed in multiple facilities. A new computing infrastructure for brain scientists and clinicians in distant locations was therefore developed by the Grid technology, which provides virtual computing environments composed of geographically distributed computers and experimental devices. A prototype system connecting an MEG system at the AIST in Japan, a Grid environment composed of PC clusters at Osaka University in Japan and Nanyang Technological University in Singapore, and user terminals in Baltimore was developed. MEG data measured at the AIST were transferred in real-time through a 1-GB/s network to the PC clusters for processing by a wavelet cross-correlation method, and then monitored in Balimore. The current system is the basic model for remote-access to MEG equipment and high-speed processing of MEG data.

Cortical areas involved in processing of emotional prosody (EP) in spoken language, such as joy or sadness, have been found in functional magnetic resonance imaging (fMRI) studies bilaterally or dominantly in the right frontal or temporal lobes. In this study, we investigated spatiotemporal patterns of cortical activity related to EP processing using magnetoencephalography (MEG). In this experiment, a joyful face (JF) or a sad face (SF) was displayed after voices which had emotional features of joy (joy prosody: JP) or sadness (sad prosody: SP) were presented. Subjects were requested to judge whether emotional features of the voice and the face were identical or not. MEG signals evoked by emotional voices were measured and significant differences of cortical activities associated with processing of emotional feature were observed between the right and left hemisphere during the latency of 100-150 ms that includes the N1m component. Our study suggests that MEG is a useful method, in addition to fMRI and event-related scalp potentials (ERP) for studying non-invasively EP processing in the human brain.