Kyoobin Lee

Integration of a Rehabilitation Robotic System (KARES II) with Human-Friendly Man-Machine Interaction Units

In this paper, we report some important results of design and evaluation of a wheelchair-based robotic arm system, named as KARES II (KAIST Rehabilitation Engineering Service System II), which is newly developed for the disabled. KARES II is designed in consideration of surveyed necessary tasks for the target users (that is, people with spinal cord injury). At first, we predefined twelve important tasks according to extensive interviews and questionnaires. Next, based on these tasks, all subsystems are designed, simulated and developed. A robotic arm with active compliance and intelligent visual servoing capability is developed by using cable-driven mechanism. Various kinds of human-robot interfaces are developed to provide broad range of services according to the levels of disability. Eye-mouse, shoulder/head interface, EMG signal-based control subsystems are used for this purpose. Besides, we describe the process of integration of our rehabilitation robotic system KARES II, and discuss about user trials. A mobile platform and a wheelchair platform are two main platforms in which various subsystems are installed. For a real-world application of KARES II system, we have performed user trials with six selected potential end-users (with spinal cord injury).

CaV2.3 Channels Are Critical for Oscillatory Burst Discharges in the Reticular Thalamus and Absence Epilepsy

Neurons of the reticular thalamus (RT) display oscillatory burst discharges that are believed to be critical for thalamocortical network oscillations related to absence epilepsy. Ca²+-dependent mechanisms underlie such oscillatory discharges. However, involvement of high-voltage activated (HVA) Ca²+ channels in this process has been discounted. We examined this issue closely using mice deficient for the HVA Ca(v)2.3 channels. In brain slices of Ca(v)2.3⁻/⁻, a hyperpolarizing current injection initiated a low-threshold burst of spikes in RT neurons; however, subsequent oscillatory burst discharges were severely suppressed, with a significantly reduced slow afterhyperpolarization (AHP). Consequently, the lack of Ca(v)2.3 resulted in a marked decrease in the sensitivity of the animal to γ-butyrolactone-induced absence epilepsy. Local blockade of Ca(v)2.3 channels in the RT mimicked the results of Ca(v)2.3⁻/⁻ mice. These results provide strong evidence that Ca(v)2.3 channels are critical for oscillatory burst discharges in RT neurons and for the expression of absence epilepsy.

Human-friendly interfaces of wheelchair robotic system for handicapped persons

With an increase in the number of handicapped persons, there is a growing demand for human friendly interface as mobility aids. To meet this need, we have developed two interfaces with using shoulder and head motion for powered wheelchair control. To acquire proper wheelchair control instruction signal, workspaces of shoulder and head are analyzed by magnetic position sensor. Two interfaces are developed to meet four guidelines :human friendly design, easiness of wearability, intuitive drive function, and low cost. FSR (force sensing resistor) is used to measure changes in the shoulder and head motion. Interfaces usefulness is verified by clinical experiment with six subjects who are spinal cord injured with C4 or C5.

Deletion of phospholipase C β4 in thalamocortical relay nucleus leads to absence seizures

Absence seizures are characterized by cortical spike-wave discharges (SWDs) on electroencephalography, often accompanied by a shift in the firing pattern of thalamocortical (TC) neurons from tonic to burst firing driven by T-type Ca2+ currents. We recently demonstrated that the phospholipase C β4 (PLCβ4) pathway tunes the firing mode of TC neurons via the simultaneous regulation of T- and L-type Ca2+ currents, which prompted us to investigate the contribution of TC firing modes to absence seizures. PLCβ4-deficient TC neurons were readily shifted to the oscillatory burst firing mode after a slight hyperpolarization of membrane potential. TC-limited knockdown as well as whole-animal knockout of PLCβ4 induced spontaneous SWDs with simultaneous behavioral arrests and increased the susceptibility to drug-induced SWDs, indicating that the deletion of thalamic PLCβ4 leads to the genesis of absence seizures. The SWDs were effectively suppressed by thalamic infusion of a T-type, but not an L-type, Ca2+ channel blocker. These results reveal a primary role of TC neurons in the genesis of absence seizures and provide strong evidence that an alteration of the firing property of TC neurons is sufficient to generate absence seizures. Our study presents PLCβ4-deficient mice as a potential animal model for absence seizures.

Sleep spindles are generated in the absence of T-type calcium channel-mediated low-threshold burst firing of thalamocortical neurons

Significance This study addresses one of the most fundamental issues in sleep rhythm generation. The theory that low-threshold burst firing mediated by T-type calcium channels in thalamocortical neurons is the key component for sleep spindles, has been accepted as dogma and appears throughout the literature. In this study, however, in vivo and in vitro evidence shows that sleep spindles are generated normally in the absence of T-type channels and burst firing in thalamocortical neurons. Furthermore, our data indicate a potentially important role of tonic firing in this rhythm generation. This study advances the knowledge of sleep and vigilance control to another level of understanding. T-type Ca2+ channels in thalamocortical (TC) neurons have long been considered to play a critical role in the genesis of sleep spindles, one of several TC oscillations. A classical model for TC oscillations states that reciprocal interaction between synaptically connected GABAergic thalamic reticular nucleus (TRN) neurons and glutamatergic TC neurons generates oscillations through T-type channel-mediated low-threshold burst firings of neurons in the two nuclei. These oscillations are then transmitted from TC neurons to cortical neurons, contributing to the network of TC oscillations. Unexpectedly, however, we found that both WT and KO mice for CaV3.1, the gene for T-type Ca2+ channels in TC neurons, exhibit typical waxing-and-waning sleep spindle waves at a similar occurrence and with similar amplitudes and episode durations during non-rapid eye movement sleep. Single-unit recording in parallel with electroencephalography in vivo confirmed a complete lack of burst firing in the mutant TC neurons. Of particular interest, the tonic spike frequency in TC neurons was significantly increased during spindle periods compared with nonspindle periods in both genotypes. In contrast, no significant change in burst firing frequency between spindle and nonspindle periods was noted in the WT mice. Furthermore, spindle-like oscillations were readily generated within intrathalamic circuits composed solely of TRN and TC neurons in vitro in both the KO mutant and WT mice. Our findings call into question the essential role of low-threshold burst firings in TC neurons and suggest that tonic firing is important for the generation and propagation of spindle oscillations in the TC circuit.

Wearable master device using optical fiber curvature sensors for the disabled

This paper addresses a wearable master device for physically handicapped persons whose arms are disabled. Optical fiber curvature sensors are used to measure the human body motion. For the developed wearable master device, a calibration and mapping method of the sensors is proposed to extract 2-DOF human shoulder motions. An experiment shows that the wearable master device can be used for a 2-DOF input device effectively for handicapped persons. It has also shown that a subject can control a mobile robot with the wearable master device.

Letters: Synaptic plasticity model of a spiking neural network for reinforcement learning

This paper presents a reward-related synaptic modification method of a spiking neuron model. The proposed algorithm determines which synapse is eligible for reinforcement by a reward signal. According to the proposed algorithm, a synapse is determined to be eligible when a presynaptic spike occurs shortly before a postsynaptic spike. A pre- and postsynaptic spike correlator (PPSC) is defined and used to determine synaptic eligibility, and to modify synaptic efficacy in cooperation with a reward signal. A simulation is conducted to demonstrate how the interaction between the PPSC and the reward signal influences synaptic plasticity.

Sensors and actuators of wearable haptic master device for the disabled

This paper addresses sensors and actuators for a wearable haptic master device for physically handicapped persons whose arms are disabled. In the first part of this paper, optical fiber curvature sensors are used to measure the human body motion. An efficient calibration and interpolation method of the sensors is then proposed to extract 2-DOF human shoulder motions. In the second part of this paper, solenoid vibrotactile actuators are used to feed back the contact force. Experimental results show that tactile-force substitution is helpful for force regulating tasks and that the frequency and magnitude of vibrotactile stimulus should be increased exponentially to achieve the linearly increased force sensing.

Four DoF gesture recognition with an event-based image sensor

An algorithm to recognize four degrees of freedom gesture by using event-based image sensor is developed. The gesture motion includes three translations and one rotation. Each pixel of the event-based image sensor produces an event when temporal intensity change is larger than a pre-defined value. From the time-stamps of the events, a map of pseudo optical flow is calculated. The proposed algorithm achieves the gesture recognition based on this optical flow. It provides not only directions but also magnitudes of velocity. The proposed algorithm is memory-wise and computationally efficient because it uses only a current time-stamp map and local computation. This advantage will facilitate applications for mobile devices or on-chip development.

Wearable master device for spinal injured persons as a control device for motorized wheelchairs

This paper describes a wearable, master device for people with a spinal injury who can move their neck and shoulders but cannot move their legs and arms. A device that measures the movements of their neck or shoulder can help them to drive a wheelchair. The sensors of such a wearable master device must be lightweight, small, and easily attached to cloth. Therefore, optical fiber curvature sensors are used to measure the human body motion. For a previously developed wearable master device, two calibration and mapping methods with, the sensors are proposed to extract 2-DOF human shoulder motions. One is constructed with simple geometric equations. The other is constructed with a multilayered artificial neural network. The two methods are compared. Experimental results show that the wearable master device can be used effectively for a 2-DOF input device for handicapped persons. It was also shown that a subject can control a mobile robot with the wearable master device.