Donghyeon Kim

A Rat Model of Photothrombotic Capsular Infarct with a Marked Motor Deficit: A Behavioral, Histologic, and microPET Study

We present a new method for inducing a circumscribed subcortical capsular infarct (SCI), which imposes a persistent motor impairment in rats. Photothrombotic destruction of the internal capsule (IC) was conducted in Sprague Dawley rats (male; n=38). The motor performance of all animals was assessed using forelimb placing, forelimb use asymmetry, and the single pellet reaching test. On the basis of the degree of motor recovery, rats were subdivided into either the poor recovery group (PRG) or the moderate recovery group (MRG). Imaging assessment of the impact of SCI on brain metabolism was performed using 2-deoxy-2-[18F]-fluoro-D-glucose ([18F]-FDG) microPET (positron emission tomography). Photothrombotic lesioning using low light energy selectively disrupted circumscribed capsular fibers. The MRG showed recovery of motor performance after 1 week, but the PRG showed a persistent motor impairment for >3 weeks. Damage to the posterior limb of the IC (PLIC) is more effective for producing a severe motor deficit. Analysis of PET data revealed decreased regional glucose metabolism in the ipsilesional motor and bilateral sensory cortex and increased metabolism in the contralesional motor cortex and bilateral hippocampus during the early recovery period after SCI. Behavioral, histologic, and functional imaging findings support the usefulness of this novel SCI rat model for investigating motor recovery.

Computational Study on Subdural Cortical Stimulation - The Influence of the Head Geometry, Anisotropic Conductivity, and Electrode Configuration

Subdural cortical stimulation (SuCS) is a method used to inject electrical current through electrodes beneath the dura mater, and is known to be useful in treating brain disorders. However, precisely how SuCS must be applied to yield the most effective results has rarely been investigated. For this purpose, we developed a three-dimensional computational model that represents an anatomically realistic brain model including an upper chest. With this computational model, we investigated the influence of stimulation amplitudes, electrode configurations (single or paddle-array), and white matter conductivities (isotropy or anisotropy). Further, the effects of stimulation were compared with two other computational models, including an anatomically realistic brain-only model and the simplified extruded slab model representing the precentral gyrus area. The results of voltage stimulation suggested that there was a synergistic effect with the paddle-array due to the use of multiple electrodes; however, a single electrode was more efficient with current stimulation. The conventional model (simplified extruded slab) far overestimated the effects of stimulation with both voltage and current by comparison to our proposed realistic upper body model. However, the realistic upper body and full brain-only models demonstrated similar stimulation effects. In our investigation of the influence of anisotropic conductivity, model with a fixed ratio (1∶10) anisotropic conductivity yielded deeper penetration depths and larger extents of stimulation than others. However, isotropic and anisotropic models with fixed ratios (1∶2, 1∶5) yielded similar stimulation effects. Lastly, whether the reference electrode was located on the right or left chest had no substantial effects on stimulation.

Computational study of subdural and epidural cortical stimulation of the motor cortex

Cortical stimulation (CS) has gained wide attention for its use in augmenting neurological recovery in various conditions. Noninvasive cortical stimulations using transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) are less invasive when delivering the electrical current to the patients brain, but have several limitations. Direct cortical stimulation (DCS) using an implantable stimulation system consisting of epidurally or subdurally placed electrodes and pulse generators, provides cortical stimulation and concurrent rehabilitative training in a stable fashion without limiting a patients activities. The effectiveness of these two types of DCS — epidural cortical stimulation (ECS) and subdural cortical stimulation (SCS) — has not been compared. In this work, a computer simulation study was conducted to predict the current density distributions (CDD) through cortical stimulations using subdurally or epidurally placed electrodes. The simulation study is based on the human motor cortex model with a three-dimensional finite element model (FEM). The change in CDD depending on the shape of the electrode (disc or ring) is discussed. The output current induced by SCS was about four times larger than that of ECS when voltage stimulations with the same magnitude were regulated. Thus, SCS showed substantially better penetration of the current into gray or white matter. Further, the ring electrode performed comparably or slightly inferior to the disc electrode in both cortical stimulations.

Validation of Computational Studies for Electrical Brain Stimulation With Phantom Head Experiments

BACKGROUND Although computational studies of electrical brain stimulation (EBS) have received attention as a cost-effective tool, few studies have validated the technique, particularly in invasive cortical stimulation. OBJECTIVE In order to validate such studies, we used EBS to compare electric potential distributions generated by both numerical simulations and empirical measurements in three phantom head models (one-/three-layered spherical heads and MRI-based head). METHODS We constructed spherical phantom heads that consisted of one or three layers, and an anatomical, MRI-based phantom that consisted of three layers and represented the brain or brain/skull/scalp in order to perform both numerical simulations using the finite element method (FEM) and experimental measurements. Two stimulation electrodes (cathode and anode) were implanted in the phantoms to inject regulated input voltage, and the electric potential distributions induced were measured at various points located either on the surface or deep within the phantoms. RESULTS We observed that both the electric potential distributions from the numerical simulations and experiments behaved similarly and resulted in average relative differences of 5.4% (spherical phantom) and 10.3% (MRI-based phantom). CONCLUSIONS This study demonstrated that numerical simulation is reasonably consistent with actual experimental measurements; thus, because of its cost-effectiveness, EBS computational studies may be an attractive approach for necessary intensive/extensive studies.

The computational study of subdural cortical stimulation: A quantitative analysis of voltage and current stimulation

We investigated the effect of electrode type and stimulation condition (voltage stimulation and current stimulation) in bi-polar subdural cortical stimulation (SCS). For this study, we developed a 3D realistic head model using MRI data with 1 mm3 spatial resolution and simulated the model using the finite element method (FEM). For each study, we used three types of electrodes - disc, ring, and covered-disc - and three efficiency measures - effective depth of penetration, effective volume, and amount of CSF leakage current - to compare the effectiveness of the stimulation between two stimulation conditions. With voltage stimulation, there was no difference in effectiveness between the disc and ring electrodes. However, the amount of CSF leakage current for the covered-disc type was lower than that for the others. The effective depth of penetration and volume for the ring and disc type electrodes were higher than those for the covered-disc type. The current stimulation using the covered-disc electrode penetrated deeper than the other types of electrodes, and the CSF leakage current was still low. The result for voltage and current stimulation was quite different, as the substrate design manipulated the impedance and output current. In the current simulation, if the electrode was covered with the substrate, more current flowed to the cortex. On the other hand, with voltage stimulation, this substrate design makes the impedance between electrodes high, and the total current is reduced.

Classification of K-Pop Dance Movements Based on Skeleton Information Obtained by a Kinect Sensor

This paper suggests a method of classifying Korean pop (K-pop) dances based on human skeletal motion data obtained from a Kinect sensor in a motion-capture studio environment. In order to accomplish this, we construct a K-pop dance database with a total of 800 dance-movement data points including 200 dance types produced by four professional dancers, from skeletal joint data obtained by a Kinect sensor. Our classification of movements consists of three main steps. First, we obtain six core angles representing important motion features from 25 markers in each frame. These angles are concatenated with feature vectors for all of the frames of each point dance. Then, a dimensionality reduction is performed with a combination of principal component analysis and Fisher’s linear discriminant analysis, which is called fisherdance. Finally, we design an efficient Rectified Linear Unit (ReLU)-based Extreme Learning Machine Classifier (ELMC) with an input layer composed of these feature vectors transformed by fisherdance. In contrast to conventional neural networks, the presented classifier achieves a rapid processing time without implementing weight learning. The results of experiments conducted on the constructed K-pop dance database reveal that the proposed method demonstrates a better classification performance than those of conventional methods such as KNN (K-Nearest Neighbor), SVM (Support Vector Machine), and ELM alone.

Effect of Anatomically Realistic Full-Head Model on Activation of Cortical Neurons in Subdural Cortical Stimulation—A Computational Study

Electrical brain stimulation (EBS) is an emerging therapy for the treatment of neurological disorders, and computational modeling studies of EBS have been used to determine the optimal parameters for highly cost-effective electrotherapy. Recent notable growth in computing capability has enabled researchers to consider an anatomically realistic head model that represents the full head and complex geometry of the brain rather than the previous simplified partial head model (extruded slab) that represents only the precentral gyrus. In this work, subdural cortical stimulation (SuCS) was found to offer a better understanding of the differential activation of cortical neurons in the anatomically realistic full-head model than in the simplified partial-head models. We observed that layer 3 pyramidal neurons had comparable stimulation thresholds in both head models, while layer 5 pyramidal neurons showed a notable discrepancy between the models; in particular, layer 5 pyramidal neurons demonstrated asymmetry in the thresholds and action potential initiation sites in the anatomically realistic full-head model. Overall, the anatomically realistic full-head model may offer a better understanding of layer 5 pyramidal neuronal responses. Accordingly, the effects of using the realistic full-head model in SuCS are compelling in computational modeling studies, even though this modeling requires substantially more effort.

Computational Study of Subdural Cortical Stimulation: Effects of Simulating Anisotropic Conductivity on Activation of Cortical Neurons

Subdural cortical stimulation (SuCS) is an appealing method in the treatment of neurological disorders, and computational modeling studies of SuCS have been applied to determine the optimal design for electrotherapy. To achieve a better understanding of computational modeling on the stimulation effects of SuCS, the influence of anisotropic white matter conductivity on the activation of cortical neurons was investigated in a realistic head model. In this paper, we constructed pyramidal neuronal models (layers 3 and 5) that showed primary excitation of the corticospinal tract, and an anatomically realistic head model reflecting complex brain geometry. The anisotropic information was acquired from diffusion tensor magnetic resonance imaging (DT-MRI) and then applied to the white matter at various ratios of anisotropic conductivity. First, we compared the isotropic and anisotropic models; compared to the isotropic model, the anisotropic model showed that neurons were activated in the deeper bank during cathodal stimulation and in the wider crown during anodal stimulation. Second, several popular anisotropic principles were adapted to investigate the effects of variations in anisotropic information. We observed that excitation thresholds varied with anisotropic principles, especially with anodal stimulation. Overall, incorporating anisotropic conductivity into the anatomically realistic head model is critical for accurate estimation of neuronal responses; however, caution should be used in the selection of anisotropic information.

Comparison of neuronal excitation between extruded slab partial head model and full head model in subdural cortical stimulation

Cortical stimulation (CS) is an appealing and emerging treatment for neurological disorders. CS is known to promote functional recovery effectively; however, its underlying mechanism and the optimal parameters for the effective treatment are not clearly understood. In this work, we developed a realistic three-dimensional full head and chest model for subdural CS. Our proposed model was compared at the neuron level with an existing simplified extruded slab partial head model depicting around precentral gyral cortex only. Each model was coupled with the pyramidal neuronal model in order to investigate an extent of neuronal excitation. We found that the crown of the cortex was the most excitable area in the unipolar stimulation, while in the bipolar stimulation, the lip and bank were excited more easily than other areas. Finally, it was evident that our proposed model was substantially different in excitation threshold from the existing simplified model, which is compelling to do computational CS study on more realistic head models.

A comparative study of the 3D precentral gyrus model for unipolar and bipolar current stimulations

Cortical stimulation (CS) is an appealing method for treating stroke and other disorders by promoting functional recovery. It is necessary to study the effect of different cortical stimulation types through numerical simulations in order to understand the underlying mechanism. In this paper, we simulated four types of invasive CS - unipolar ECS (epidural CS), bipolar ECS, unipolar SCS (subdural CS), and bipolar SCS - to investigate and compare the effects of stimulation types. Current stimulation was considered to increase the observability of the comparison between ECS and SCS. The simulation results obtained from the 3D precentral gyrus model showed ECS and SCS had similar current density distributions with higher stimulated current. However, the differences between bipolar and unipolar stimulation are significant with higher stimulated current. As stimulated current increased, unipolar CS penetrated deeper and wider regions than bipolar CS, so it can be more effective for functional recovery.