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Cortical Orchestra Conducted by Purpose and Function
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ν©ν λμ§λλ€λ‘λΆν° 체μ±κ°κ° κ΄λ ¨ λ μμμ 곡κ°μ λΆν¬κ° 체μ±κ°κ° κΈ°λ₯μ λ°λΌ μλ‘ λ¬λκ³ , κ·Έμ ν΄λΉνλ κ° μμλ€μ μλ‘ λλ ·νκ² λ€λ₯Έ μκ°μ λ€μ΄λλ―Ήμ€λ₯Ό κ°μ§κ³ μμ°¨μ μΌλ‘ νμ±νλμλ€. μ΄λ¬ν κ²°κ³Όλ€μ 체μ±κ°κ°μ λν κ±°μμ μ κ²½κ³ νλ‘μΈμ€κ° κ·Έ μ§κ°μ κΈ°λ₯μ λ°λΌ λλ ·μ΄ λ€λ₯Έ κ³μΈ΅μ λ€νΈμν¬λ₯Ό κ°μ§λ€λ μ μ μμ¬νλ€. λ λμκ°, λ³Έ μ°κ΅¬μμμ κ²°κ³Όλ€μ 체μ±κ°κ° μμ€ν
μ μ§κ°-νλ κ΄λ ¨ μ κ²½νλ νλ¦μ κ΄ν μ΄λ‘ μ μΈ κ°μ€μ λνμ¬ μ€λλ ₯ μλ μ¦κ±°λ₯Ό μ μνκ³ μλ€.Tactile and proprioceptive perceptions are crucial for our daily life as well as survival. At the peripheral level, the transduction mechanisms and characteristics of mechanoreceptive afferents containing information required for these functions, have been well identified. However, our knowledge about the cortical processing mechanism for them in human is limited. The present series of studies addressed the macroscopic neural mechanism for perceptual processing of tactile and proprioceptive perception in human cortex.
In the first study, I investigated the macroscopic neural characteristics for various vibrotactile and texture stimuli including artificial and naturalistic ones in human primary and secondary somatosensory cortices (S1 and S2, respectively) using electrocorticography (ECoG). I found robust tactile frequency-specific high-gamma (HG, 50β140 Hz) activities in both S1 and S2 with different temporal dynamics depending on the stimulus frequency. Furthermore, similar HG patterns of S1 and S2 were found in naturalistic stimulus conditions such as coarse/fine textures. These results suggest that human vibrotactile sensation involves macroscopic multi-regional hierarchical processing in the somatosensory system, even during the simplified stimulation.
In the second study, I tested whether the movement-related HG activities in parietal region mainly represent somatosensory feedback such as proprioception from periphery or primarily indicate cortico-cortical neural processing for movement preparation and control. I found that sensorimotor HG activities are more dominant in S1 than in M1 during voluntary movement. Furthermore, the results showed that movement-related HG activities in S1 mainly represent proprioceptive and tactile feedback from periphery.
Given the results of previous two studies, the final study aimed to identify the large-scale cortical networks for perceptual processing in human. To do this, I combined direct cortical stimulation (DCS) data for eliciting somatosensation and ECoG HG band (50 to 150 Hz) mapping data during tactile stimulation and movement tasks, from 51 (for DCS mapping) and 46 patients (for HG mapping) with intractable epilepsy. The results showed that somatosensory perceptual processing involves neural activation of widespread somatosensory-related network in the cortex. In addition, the spatial distributions of DCS and HG functional maps showed considerable similarity in spatial distribution between high-gamma and DCS functional maps. Interestingly, the DCS-HG combined maps showed distinct spatial distributions depending on the somatosensory functions, and each area was sequentially activated with distinct temporal dynamics. These results suggest that macroscopic neural processing for somatosensation has distinct hierarchical networks depending on the perceptual functions. In addition, the results of the present study provide evidence for the perception and action related neural streams of somatosensory system.
Throughout this series of studies, I suggest that macroscopic somatosensory network and structures of our brain are intrinsically organized by perceptual function and its purpose, not by somatosensory modality or submodality itself. Just as there is a purpose for human behavior, so is our brain.PART I. INTRODUCTION 1
CHAPTER 1: Somatosensory System 1
1.1. Mechanoreceptors in the Periphery 2
1.2. Somatosensory Afferent Pathways 4
1.3. Cortico-cortical Connections among Somatosensory-related Areas 7
1.4. Somatosensory-related Cortical Regions 8
CHAPTER 2: Electrocorticography 14
2.1. Intracranial Electroencephalography 14
2.2. High-Gamma Band Activity 18
CHAPTER 3: Purpose of This Study 24
PART II. EXPERIMENTAL STUDY 26
CHAPTER 4: Apparatus Design 26
4.1. Piezoelectric Vibrotactile Stimulator 26
4.2. Magnetic Vibrotactile Stimulator 29
4.3. Disc-type Texture Stimulator 33
4.4. Drum-type Texture Stimulator 36
CHAPTER 5: Vibrotactile and Texture Study 41
5.1. Introduction 42
5.2. Materials and Methods 46
5.2.1. Patients 46
5.2.2. Apparatus 47
5.2.3. Experimental Design 49
5.2.4. Data Acquisition and Preprocessing 50
5.2.5. Analysis 51
5.3. Results 54
5.3.1. Frequency-specific S1/S2 HG Activities 54
5.3.2. S1 HG Attenuation during Flutter and Vibration 62
5.3.3. Single-trial Vibration Frequency Classification 64
5.3.4. S1/S2 HG Activities during Texture Stimuli 65
5.4. Discussion 69
5.4.1. Comparison with Previous Findings 69
5.4.2. Tactile Frequency-dependent Neural Adaptation 70
5.4.3. Serial vs. Parallel Processing between S1 and S2 72
5.4.4. Conclusion of Chapter 5 73
CHAPTER 6: Somatosensory Feedback during Movement 74
6.1. Introduction 75
6.2. Materials and Methods 79
6.2.1. Subjects 79
6.2.2. Tasks 80
6.2.3. Data Acquisition and Preprocessing 82
6.2.4. S1-M1 HG Power Difference 85
6.2.5. Classification 86
6.2.6. Timing of S1 HG Activity 86
6.2.7. Correlation between HG and EMG signals 87
6.3. Results 89
6.3.1. HG Activities Are More Dominant in S1 than in M1 89
6.3.2. HG Activities in S1 Mainly Represent Somatosensory Feedback 94
6.4. Discussion 100
6.4.1. S1 HG Activity Mainly Represents Somatosensory Feedback 100
6.4.2. Further Discussion and Future Direction in BMI 102
6.4.3. Conclusion of Chapter 6 103
CHAPTER 7: Cortical Maps of Somatosensory Function 104
7.1. Introduction 106
7.2. Materials and Methods 110
7.2.1. Participants 110
7.2.2. Direct Cortical Stimulation 114
7.2.3. Classification of Verbal Feedbacks 115
7.2.4. Localization of Electrodes 115
7.2.5. Apparatus 116
7.2.6. Tasks 117
7.2.7. Data Recording and Processing 119
7.2.8. Mapping on the Brain 120
7.2.9. ROI-based Analysis 122
7.3. Results 123
7.3.1. DCS Mapping 123
7.3.2. Three and Four-dimensional HG Mapping 131
7.3.3. Neural Characteristics among Somatosensory-related Areas 144
7.4. Discussion 146
7.4.1. DCS on the Non-Primary Areas 146
7.4.2. Two Streams of Somatosensory System 148
7.4.3. Functional Role of ventral PM 151
7.4.4. Limitation and Perspective 152
7.4.5. Conclusion of Chapter 7 155
PART III. CONCLUSION 156
CHAPTER 8: Conclusion and Perspective 156
8.1. Perspective and Future Work 157
References 160
Abstract in Korean 173Docto