The present thesis explains the development of an integral system solution for the required motor and sensor function restoration to support people with disabilities in activities of daily living. Humans complete tasks in daily activities in which they are unconscious of the bodily control processes as they interact with the environment. The interaction between the sensor and motor modalities in the human body forms a sensory-motor coupling that allows us to adapt to the world around us. However, this sensory-motor coupling can be disrupted by illness, such as stroke, neural damage, paraplegia, or hemiplegia, and by accidents, including those that result in amputations. When the communication between motor and sensor modalities is broken, what once was done effortlessly requires the application of continuous conscious effort or cannot be done at all. In other words, the brain loses the ability to control and adapt to changes in the environment.

In this respect, rehabilitation engineering has focused on the recovery of lost function after illness or accident. In general, the efforts made to support the daily activities were focused on the transmission of sensorial information or the support of movement. These two areas of study have been developed separately. However, most tasks in daily activities require both sensor and motor capacity. Therefore, this dissertation proposes an integral solution to provide both sensorial information and motor function support using electrical stimulation. In order to fulfill the different requirements for sensory and motor functions a functional electrical stimulation device is proposed. Electrical stimulation of the nerves and the muscle fibers presents 3 challenges: 1) low muscle selectivity due to the use of high voltages; 2) habituation to the electrical stimulus; 3) Difficulty in predicting the reaction of the human body to the electrical stimulation due to the nonlinear nature of the skin impedance. To deal with the 3 challenges described before, a multichannel functional electrical stimulation system is proposed. With the interaction of the different communication channels, we propose the use of an integral system to increase the efficiency in the restoration of lost function considering both sensory and motor function.

From previous studies involving walking assistance and sensory feedback systems, we identified three channels for bodily interaction: sensory, motor and reflexive. The sensory channel relates to the afferent nerve system for communication with the central nervous system (CNS). The motor channel can be actuated using the body's efferent channel. The reflexive system allows the generation of movement by stimulating afferent nerves. The electrical stimulation of the nerves can be used to interact with the three different channels.

Recently, several researchers have addressed the need for an integral system for function restoration. Most neuroprostheses are currently open-loop systems, where the lack of sensory information produces user fatigue. The introduction of closed-loop systems allows the nervous system to adapt to different situations, something that open-loop systems do not provide. In previous studies, electrical stimulation has been used to provide the required sensory feedback in neuroprostheses. Ambulation systems benefited from the insertion of sensory feedback by promoting body awareness in the paraplegic patients.

To increase the effectiveness of the sensor and motor function recovery, the brain needs to take an active role in the motor function control and the sensory feedback process. Even though current rehabilitation systems, mostly neuroprosthetic systems, make use of prediction methods to automate the control of the electrical stimulation, the patient does not have control of the pre-programmed stimulation patterns, which limits the efficiency of the system. Recently, the importance of the volitional involvement of the patient for the rehabilitation process has been addressed. The introduction of a control strategy called "patient-driven motion reinforcement" (PDMR), address the problem of lack of involvement of a patient in the rehabilitation process. The "patient-driven motion reinforcement" use an inverse dynamic model to predict the electrical stimulation pattern required to continue the volitional movement started by the patient in an FES-supported standing-up and sitting-down application for paraplegic patients. The involvement of the patient in the control system allowed the optimization in the insertion timing of the stimulation patterns. However, the calculations of the inverse dynamic model for each patient require cumbersome and time-consuming parameters adjustment which limits its functionality.

Since the nervous system requires the interaction of the motor and sensor modalities to form a closed-loop control system, we think that in order to increase the remaining function in the body for sensory and motor function restoration we need to treat both modalities together. For an individual to recover the ability to perform ADL, the system needs to be portable and safe, have low power consumption, and be capable of providing the appropriate stimulation configurations for each function modality.

In this dissertation we propose the use of surface electrical stimulation or transcutaneous electrical stimulation to avoid trauma to the body caused by the surgery required for electrode placement. Surface electrical stimulation has several advantages over implanted electrodes; for example, it does not require a surgical procedure for placement, there is no bodily rejection, and the electrodes are easily replaced when necessary. Caution is necessary when using small electrodes because of the high voltages required for eliciting the current level for the generation of nerve action potentials.

To interact with the different channels in the human body, we propose the use of a high-frequency squared waveform as carrier signal for a burst-controlled electrical stimulation method for recovery of motor and sensory functions.

The present dissertation consists of a total of 6 sections: Introduction, Conclusions, and 4 chapters. The contents of each section are described below.

The Introduction describes the need for an integral solution for recovery of sensory and motor modalities in prosthetic applications for activities of daily living using transcutaneous electrical stimulation.

Chapter 2 explains of the basics of transcutaneous electrical stimulation for nerve & muscle stimulation. Electrical stimulation is preferred over other interaction means due to its capacity to interact with the afferent and efferent neural paths. Transcutaneous electrical stimulation reduces the trauma received by the human body since it does not require the insertion into the body to produce nerve's action potentials. In addition, it presents the efforts done up to now in order to transmit information into the human body using electrical stimulation of the mechanoreceptors in the skin for sensory feedback.

Chapter 3 describes the development of a low voltage multichannel electric stimulation system for prosthetic applications. We proposed a high-frequency squared carrier signal to reduce the voltage requirements for transcutaneous electrical stimulation to restore motor control and sensory feedback. The insertion of a carrier signal permit reduction of adaptation to electrical stimulation, and integral muscle contractions. We confirmed its functionality for muscle contraction using low voltage with a lower limb paralyzed patient. For sensory feedback, different stimulation patterns were tested to increase the amount of information transmitted from the artificial sensory system to the user of either a prosthetic device or a neuroprosthesis.

Chapter 4 presents the evaluation of motor function recovery in prosthetic applications with a hemiplegic walking support system case study. In order to develop an integral system it shall cover the needs of muscle contraction in the different body parts as well as to administer sensory feedback. The system is evaluated in a lower limb hemiplegic patient. The patient presents higher neural damage on the left leg than the right leg. People with spinal cord damage present some neural reorganization which affects the way their body reacts to the electrical stimulation compared with healthy persons. We tested the multi-channel functional electric stimulation system motor function recovery capabilities with a lower limb semi-paralyzed patient. To increase the patient involvement in the rehabilitation process, we applied the minimum required stimulation parameters to elicit the withdrawal reflex in the paralyzed leg. We tested the volitional control of the paralyzed leg with stairs climbing and changes in the walking speed over a flat surface.

Chapter 5 presents the evaluation of the integration of motor and sensory function using a functional magnetic resonance imaging (fMRI) study. Although there are several studies on the brain activation resulting from manipulating an EMG-controlled prosthetic hand, there are no studies on the activation in the brain when the manipulation of the EMG-controlled prosthetic devices includes sensory feedback. The inclusion of sensory feedback opens new areas of understanding in the interaction of the brain with the environment. To test the correlative behavior of the brain we used an fMRI device to measure the changes in hemoglobin consumption in the brain. The changes in hemoglobin in the brain show the areas in the brain with higher activity. By detecting these changes, we can know approximately where the activation of the brain neurons for a given task. We used statistical parametric mapping (spm) tools version 2000(spm2) to analyze the data acquired from the fMRI scanning. We used an EMG-controlled robot hand for the motor function recovery. The use of the EMG signals permits the acquisition of the user's intention. Pressure sensors were placed on the robot hand to detect the interaction with surrounding objects. The signal from the sensors was translated into electrical stimulation of the skin to transmit the tactile information. Our results show that the inclusion of sensory feedback, even a simple on-off signal, allow the adaptation of the brain to the prosthetic system, developing a tactile illusion, that is, the person using the system is convinced that is touching the objects with the robot system. Since the lack of sensory feedback increase fatigue in the control of our body, this system can be applied to both prosthetic and neuroprosthetic systems. This helps us solve the "disembodiment" problem that many spinal cord injured people and amputees experiment. Since upper limbs sensory requirements are higher than lower limb functions, we decided to test the electric stimulation on upper limbs prosthetic applications. We pursued further understanding of the relation between motor and sensor modalities by stimulating in different body areas, subtracting sensor modalities (visual feedback) and inserting a time delay between the activation of the pressure sensors and the application of electrical stimulation on the skin.

The conclusions contain the summary of the contributions made by this study. We introduced the need for an integral system for motor and sensory function recovery to increase the rehabilitation process. We proposed a high-frequency squared carrier signal for a burst-controlled transcutaneous electrical stimulator to comply with the motor and sensory function stimulation requirements. We presented the contributions made by the developed system by reducing the peak voltage to elicit the electrical stimulation of the nerves and the use of functional electrical stimulation to transmit tactile information through the skin. The proposed system presented a reduction on the habituation to the electrical stimulation problem, with an average discrimination rate of 90%.

Following, we presented the evaluation of the integral method in two instances: Walking assistance system and a FMRI study of an upper limb EMG controlled prosthetic system with feedback. First we evaluated the proposed system in walking assistance system for lower-limb semi-paralyzed patients. We presented the improvement in volitional control from using the proposed system with minimum stimulation requirement, and introduce the use of multi-scale information transference to measure the balance in the walking gait.

In order to measure directly the effects of the integral system, we presented an fMRI study of an upper limb EMG-controlled prosthetic system. This study opened new insights on how the brain process simultaneous events. We discuss the apparition of a tactile illusion when the persons while using the EMG-controlled prosthetic system, received sensory feedback in the form of electrical stimulation. We presented the increase in brain activation when actively using both sensory and motor system. Although this study has limited test subjects, the results points the importance of active involvement in an integral system for rehabilitation.

Hernandez Arieta, Alejandro(ヘルナンデス・アリエタ・アレハンドロ) 提出の本論文はDevelopment of a multi-channel functional electrical stimulation system for prosthetic applications of limbs(四肢の運動機能補助のための多チャンネル機能的電気刺激システムの開発)」と題し,全6章よりなり,神経及び四肢の障害者の日常生活支援に必要な感覚や運動機能を回復するための統合システムの開発目的として執筆した論文である.

一般に障害者に対して,これまで行われてきた日常生活支援機器の開発は,感覚情報提示に主眼を置いたものか,それとも,運動機能補助を行うものなどの二種類に大きく分類され,これらの研究が独自に進められてきた.しかしながら,人の感覚と運動の機能は,多くの場合,協調して仕事を行うように作られているため,能動的な運動意図に適合する感覚情報が随意に取得できる必要がある.そこで,この論文では,感覚情報提示と運動機能補助の両方が同時に提供できるような電気刺激法と装置を提案し,随意の運動意図を反映した感覚フィードバック付の目的行動の遂行を補助するシステムの開発を試みている.また,電気刺激法による感覚情報提示と運動機能補助に特有の課題は次の3項目に整理される.1)高電圧な電気刺激を用いると,筋肉を特定して刺激を行うことが困難となること.2)一定の電気刺激に対して個人差や刺激への慣れを起こすこと.3)刺激に対する挙動が非線形であるため,身体の応答が予測困難となることなどが挙げられる.これら3項目の課題に対応するために,多チャンネル機能的電気刺激システムが提案されている.本論文は,序論と結論の他,4つの章により構成されており,以下に各章における要約を記述する.

序論では,日常生活の環境下において必要となる運動と感覚の機能について概観し,経皮的電気刺激を使用することで運動と感覚の機能を代替する基本的な考え方と,その必要性、および適用範囲について述べている.

第二章は,経皮的電気刺激の神経および筋に対する影響に関する研究背景について述べられている.経皮的電気刺激が求心性と遠心性の両方の神経経路に作用し,感覚系と運動系に対する刺激が,反射やそれに伴う筋紡錘の収縮現象を発生する原理について示されている.また,他の機械的刺激法や侵襲型の刺激法に対する優位性についての論拠が示されており,経皮的電気刺激法を用いて,筋紡錘へ刺激を行う研究や,上皮受容器に対して電気的に知覚フィードバックを提示する研究についての詳しい動向についても示されている.

第三章では,本論文で提案する四肢の運動機能補助のための多チャンネル機能的電気刺激システムについて述べられている.刺激関数は,リハビリテーションやスポーツ医学で一般的に用いられているロシア式矩形波型電気刺激を基礎として用い,これを拡張することにより経皮電気的刺激を発生させる方法を採用している.拡張方法は,ロシア式矩形波に対して,高調波の搬送波信号を重畳し,さらに間欠区間を導入することにより,刺激侵入深度の調整と電気エネルギー強度の調整を可能としている.提案システムの基本機能の評価結果として,電気刺激への慣れが減少すると,低電圧でも総体的な筋収縮を発生させられることが確認されており,筋収縮を随意的に制御できる最適な刺激パターンを発見している.さらに、触覚情報の感覚フィードバックにおいても筋収縮を阻害せず,同時に最も高い識別率を達成する刺激パターンを発見している.

第四章では,下肢に麻痺を有する者の運動補助の課題に対して応用が試みられており,歩行と階段昇降の機能の補助に関して述べられている.下肢の筋収縮は筋繊維への電気刺激でも起こすことは可能であるが,神経支配とは無関係な運動となるため,本論文では対象外とされ,反射経路への電気刺激に限定して行うことにより,随意的な運動を誘発することに成功している.被験者は,腰椎L4L5S1の疾患により,大腿直筋,腓腹筋を除くほとんどの筋への神経支配を損傷しており,立上がり動作のみが可能であり,脚の振り出し・振り戻し動作は左右ともに不可能な状態である.本論文では,この被験者に対して,提案システムを適用することにより,随意に脚の振り出し・振り戻しを可能とし,歩行の前進後退と階段の昇降を実現している.

第五章では,触覚情報の感覚フィードバックのアプリケーションのひとつとして,筋電義手の触覚センサーとして提案法を利用した場合の効果について述べている.効果を確かめるために,筋電義手を用いたときの全脳の賦活パターンをfMRIとSPMを用いて解析しており,種々の条件での触覚フィードバックに対する応答を定量化している.特筆すべき成果は,筋電義手に精密な触覚フィードバックを入れることにより,世界に先駆けて錯覚などの特異な脳活動が大脳一次運動感覚野および頭頂連合野,帯状回,運動前野で発生する効果が得られており,その結果として,人の能動触覚の機能が復活することが確かめられている. 被験者は,右手根関節離断の前腕切断者1人と健常者2名に対して,10パターンの制御自由度を有する5指筋電義手を用いて,球握りと鉛筆握りの識別実験を行っている.実験条件は,触覚フィードバックの有無,触覚フィードバックに応答遅れを入れた場合,視覚フィードバックの有無である.実験結果は,触覚フィードバックを入れずに筋電義手を作動させた場合においては,頭頂連合野の賦活が顕著であり,視覚に頼った運動制御が行われていることと,運動野の賦活強度が,実験回数に比例して強くなっていくこと,感覚野に賦活は見られないことが示されている.一方,触覚フィードバックを入れた場合には,その応答遅れが0.5sまでは,頭頂連合野の賦活が消えてゆくこと.また,触覚フィードバックを入れる場所に因らず,常に,右手感覚野に強い賦活が観察され,錯覚現象が現れること.さらに,運動野のみならず,前頭前野を除くほとんどの部位で,実験回数に反比例して賦活強度が減少することが確認されている.

結論では,本研究の成果ついてまとめられている.

・日常生活における人の感覚と運動の機能再建を図ることを目的として,多チャンネル機能的電気刺激システムを提案することにより,感覚情報提示と運動機能補助の両方が同時に提供できる機能が実現されていること.

・提案システムを下肢に麻痺を有する者の運動補助の課題に対して応用した結果,反射経路への電気刺激に限定して行うことにより,随意に脚の振り出し・振り戻しを可能とし,歩行の前進後退と階段の昇降を実現していること.

・筋電義手の触覚センサーとして提案法を応用した結果,錯覚などの特異な脳活動が大脳一次運動感覚野および頭頂連合野,帯状回,運動前野で発生する効果が得られており,その結果として,人の能動触覚の機能が復活することを確かめたこと.

これらの成果は,感覚と運動の機能を再建するための方法論の新規性と有効性を示していると考えられる.これはロボット工学において,また福祉工学の研究において価値ある成果を得たと評価でき,工学全般の発展に寄与するところが大である.

よって本論文は博士(工学)学位請求論文として合格と認められる.