Ki-Young Jung

Classification of selective attention to auditory stimuli: Toward vision-free brain-computer interfacing

Brain-computer interface (BCI) is a developing, novel mode of communication for individuals with severe motor impairments or those who have no other options for communication aside from their brain signals. However, the majority of current BCI systems are based on visual stimuli or visual feedback, which may not be applicable for severe locked-in patients that have lost their eyesight or the ability to control their eye movements. In the present study, we investigated the feasibility of using auditory steady-state responses (ASSRs), elicited by selective attention to a specific sound source, as an electroencephalography (EEG)-based BCI paradigm. In our experiment, two pure tone burst trains with different beat frequencies (37 and 43 Hz) were generated simultaneously from two speakers located at different positions (left and right). Six participants were instructed to close their eyes and concentrate their attention on either auditory stimulus according to the instructions provided randomly through the speakers during the inter-stimulus interval. EEG signals were recorded at multiple electrodes mounted over the temporal, occipital, and parietal cortices. We then extracted feature vectors by combining spectral power densities evaluated at the two beat frequencies. Our experimental results showed high classification accuracies (64.67%, 30 commands/min, information transfer rate (ITR) = 1.89 bits/min; 74.00%, 12 commands/min, ITR = 2.08 bits/min; 82.00%, 6 commands/min, ITR = 1.92 bits/min; 84.33%, 3 commands/min, ITR = 1.12 bits/min; without any artifact rejection, inter-trial interval = 6s), enough to be used for a binary decision. Based on the suggested paradigm, we implemented a first online ASSR-based BCI system that demonstrated the possibility of materializing a totally vision-free BCI system.

Determination of optimal electrode positions for transcranial direct current stimulation (tDCS)

The present study introduces a new approach to determining optimal electrode positions in transcranial direct current stimulation (tDCS). Electric field and 3D conduction current density were analyzed using 3D finite element method (FEM) formulated for a dc conduction problem. The electrode positions for minimal current injection were optimized by changing the Cartesian coordinate system into the spherical coordinate system and applying the (2+6) evolution strategy (ES) algorithm. Preliminary simulation studies applied to a standard three-layer head model demonstrated that the proposed approach is promising in enhancing the performance of tDCS.

Influence of task difficulty on the features of event-related potential during visual oddball task.

We present a comprehensive analysis of the change in event-related potential (ERP) due to task difficulty during a visual oddball task. Specifically, we investigated the inter-subject difference in difficulty-related change of ERP patterns using single-trial ERP analysis focusing on P300 and P2 components. ERPs were recorded and analyzed from 14 subjects while performing a visual oddball task with two difficulty levels. After extracting independent components (ICs) from single-trial ERPs, the averaged ERPs were used to identify which ICs originated from major ERP components. The ERP components were estimated from single-trial waveforms by back-projecting relevant ICs onto scalp electrodes after removing all other ICs; thus, the comparison of ERP components could be performed for each subject. The averaged P300 amplitude was smaller and latency was larger for the more difficult task, and this tendency was also observed for single-trial ERP analysis within each subject. P2 amplitude increased for the hard task for both group and individual analyses, suggesting that the P2 may be interpreted as a manifestation of task relevance evaluation or response generation. The P2 amplitude and latency were more notably correlated with response time for the more difficult task.

Cerebral blood flow changes in man by wake‐promoting drug, modafinil: a randomized double blind study

To investigate the effects of a wake‐promoting drug, modafinil on regional cerebral blood flow (rCBF) in healthy volunteers, we performed 99mTc‐ethylcysteinate dimer single photon emission computed tomography (SPECT) before and after modafinil or placebo administration. Twenty‐one healthy subjects received single doses of 400 mg modafinil or placebo in a double blind randomized crossover study design. Administrations of modafinil or placebo in a subject were separated by a 2‐week washout. Brain SPECT was performed twice before and 3 h after modafinil or placebo administration. For statistical parametric mapping analysis, all SPECT images were spatially normalized to the standard SPECT template and then smoothed using a 12‐mm full width at half‐maximum Gaussian kernel. The paired t‐test was used to compare pre‐ versus post‐modafinil and pre‐ versus post‐placebo SPECT images. Differences in rCBF between post‐modafinil and post‐placebo conditions were also tested. Modafinil decreased Epworth and Stanford sleepiness scales whereas placebo did not. The post‐modafinil condition was associated with increased rCBF in bilateral thalami and dorsal pons, whereas the post‐placebo condition showed increased rCBF in a smaller area of the dorsal pons when compared with the drug naïve baseline condition. Compared with the post‐placebo condition, the post‐modafinil condition showed higher rCBF in bilateral frontopolar, orbitofrontal, superior frontal, middle frontal gyri, short insular gyri, left cingulate gyrus, left middle/inferior temporal gyri, left parahippocampal gyrus, and left pons. In healthy volunteers, modafinil increased wakefulness and rCBF in the arousal‐related systems and in brain areas related to emotion and executive function.

Independent component analysis of generalized spike-and-wave discharges: primary versus secondary bilateral synchrony

OBJECTIVE To differentiate between primary and secondary bilateral synchrony (PBS and SBS, respectively) in generalized spike-and-wave discharges (GSWD), we applied independent component analysis (ICA) to GSWD, and analyzed the characteristic patterns of independent components. METHODS EEGs from 19 patients with GSWD (9 PBS patients, 10 SBS patients) were studied. Thirty GSWD epochs were selected and concatenated to construct an EEG data matrix that was subjected to ICA. Selected independent components were localized by mapping them on a spherical model of the head by means of brain electrical source analysis (BESA) to define dipole sources. RESULTS Epileptic components of GSWD were clearly separated by the ICA algorithm in all patients. Between one and three components per patient were responsible for GSWD. In PBS patients, 70.6% of the independent components had dipole sources within the dorsolateral frontal region, and 56.5% of the independent components in SBS patients were within the medial frontal region (P=0.012). The orientation of all of the independent components in PBS patients was radial, whereas 47.8% of the independent components in SBS patients were tangential; this difference was statistically significant (P=0.001). CONCLUSIONS Spatiotemporal decomposition of GSWD by using ICA might be helpful for differentiating SBS from PBS. SIGNIFICANCE The localization of the dipole sources of the independent components may provide insight into the pathophysiological origins of GSWD.

Anti‐LGI1 Encephalitis is Associated with Unique HLA Subtypes

Autoimmune encephalitis (AE), represented by anti–leucine‐rich glioma‐inactivated 1 (anti‐LGI1) and anti–N‐methyl‐D‐aspartate receptor (anti‐NMDAR) encephalitis, has increasing clinical significance based on recent discoveries of neuronal autoantibodies. However, its immunopathogenesis is not fully understood. Here, we investigated whether AE is associated with the human leukocyte antigen (HLA) subtypes.

Clinical manifestations of patients with CASPR2 antibodies.

Contactin-associated protein-like 2 (CASPR2) is one of the target antigens of voltage-gated potassium channels (VGKC) complex antibodies. There has been relatively little information in the literature regarding CASPR2 autoimmunity, especially in Asian population. We investigated the presence of CASPR2 antibodies in patients with presumed autoimmune neurological disorders and described the clinical features, laboratory findings, and responses to immunotherapy. Five patients were identified to be positive for CASPR2 antibodies. The results obtained here suggested that CASPR2 antibodies might be the possible cause of epilepsy even in the absence of typical features of limbic encephalitis and that immunotherapy could provide a favorable outcome.

Source Localization of Triphasic Waves: Implications for the Pathophysiological Mechanism

To investigate the current source location from the electroencephalograms (EEGs) of 12 patients who showed typical triphasic waves attributable to various causes, using the combination of a dipole source model and a distributed source model. The triphasic waves were explained by a single main dipole in 10 of the 12 patients, and 2 patients had two dipoles responsible for the triphasic waves. All the main dipoles had a radial orientation with respect to the frontal pole. The current density of the triphasic waves was distributed mainly in the bilateral medial frontal regions along the cingulate cortices. These findings suggest that current sources located in the medial frontal area are crucial for generating triphasic waves. The source localization may be useful for elucidating the pathophysiologic mechanism of generalized non-epileptic EEG activities, such as triphasic waves.

Nonlinear dynamic characteristics of electroencephalography in a high-dose pilocarpine-induced status epilepticus model

We applied nonlinear analysis to the results of electroencephalography (EEG) in a pilocarpine-induced status epilepticus (SE) model to characterize nonlinear dynamics according to SE phase. Nine male Sprague-Dawley rats weighing 150-250 g were used. EEG was classified into four phases in addition to baseline EEG (phase 0) as follows: phase 1, discrete seizures; phase 2, continuous ictal discharges; phase 3, early periodic epileptiform discharges (PEDs); and phase 4, late PEDs. High-dose diazepam was administered at phase 4 to terminate SE. Diazepam controlled SE in five rats (group 1), while it failed to stop SE in the rest (group 2). The presence of nonlinearity was determined by time reversal asymmetry statistics using a surrogate data set. The correlation dimension (D(2)) was calculated to characterize the dimensional complexity of each phase of SE. EEG of later phases of SE showed strong nonlinearity, whereas no or only weak nonlinearity was noted at phases 0 and 1. D(2) showed the highest value at phase 0 and decreased progressively. Considering therapeutic responsiveness, D(2) showed significant differences between the two groups at phases 2 and 4. These results suggest that nonlinear dynamic changes in the later SE phases reflect underlying pathophysiological changes that contribute to determining therapeutic responsiveness in the pilocarpine-induced SE model.

Marital status of people with epilepsy in Korea

A multicentre face-to-face interview was conducted to identify factors contributing to the marital status of people with epilepsy (PWE) in Korea. The marriage rate of PWEs was only 80% and the divorce rate was more than double that in the general population. Among the single subjects, 34% replied that they were unmarried because of epilepsy, and 76% of divorced PWEs replied that epilepsy was the cause of the divorce. The factors affecting the single and divorced status in PWEs included gender, an earlier onset of seizure and seizure onset before marriage. Not informing the spouse of the disease before marriage for fear of discrimination was not related to disadvantage in marriage negotiation or to divorce. Social stigmatization of epilepsy continues and impacts on the marital status of PWEs in Korea. However, there is no correlation between the perceived and the enacted stigmas of epilepsy.