Auditory Cortical Temporal Processing and Hemispheric Asymmetry Revealed by N1 Dipole Source Activity in Adult Cochlear Implant Users / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Cochlear implant (CI) changes the way that sound inputs are processed in the brain, possibly causing brain reorganization. Given that the pattern and degree of reorganization are known to be related to speech perception skill, information regarding hemispheric asymmetry can be used to predict behavioral performances in CI users. The current study investigated the hemispheric asymmetry of N1 dipole cortical activity in response to the temporally varied speech sounds and its relationship to speech perception abilities in adult CI users. SUBJECTS AND METHOD: The cortical activity was recorded from 64 scalp electrodes in 10 CI users and 11 normal-hearing controls. Speech stimuli were synthesized consonant-vowels, the /ba/-/pa/ continuum that ranged from 0 to 50 ms with a 6-step voice onset time (VOT). N1 dipole amplitudes, latencies, and locations were analyzed as a function of VOT and the direction of implantation. Also investigated was the relationship between N1 dipole lateralization and speech perception. RESULTS: For the N1 dipole location, significant location differences between CI and normal hearing groups were seen at 40 ms VOT in the anterior-posterior direction. For hemispheric asymmetry, the N1 dipole activity in good CI performers was higher in the auditory cortex contralateral to the stimulated ear, while poor CI performers showed greater ipsilateral activity. In addition, a lateralization index at 20 ms VOT showed significant correlation with the /ba/-/pa/ consonant perception scores in noise. CONCLUSION: The results suggest that the hemispheric asymmetry of N1 dipole activity in response to stimuli of temporally varied speech has a substantial clinical value, and that this can be used to estimate CI speech perception.

Time-varying source analysis of auditory-visual stimuli evoked event-related potentials / 国际生物医学工程杂志

Objective Dipole source analysis was employed to investigate the transient changes in brain mechanisms at earlier latencies.Methods Fourteen healthy volunteers were recruited in this research and evoked event-related potentials (ERPs) of unimodal and bimodal visual auditory stimuli were recorded by 64-electrodes electroencephalograph (EEG) recording system.All these earlier phases of the stimuli were divided into several subphases by specific time window for source analysis.Results The results showed that ERPs sources were mainly generated from visual and audio cortex,and there were changes in the location and strength of the dipole sources in each sub-phase.Conclusions The result of this study implies a serial processing of sensory information in human cortices in early phase of visual and auditory stimuli.

Current-Source Dipole of Anterior Temporal Spikes: Clinical Significance of Orientation

BACKGROUND: The voltage topography of temporal spikes has two distinct patterns, designated type I and type II; the orientation of the current-dipole source (O-CDS) of type I spikes tends to be oblique, while that of type II spikes tends to be horizontal. The purpose of this study was to identify the effects of the O-CDS of anterior temporal spikes on clinical factors including onset age, seizure frequency, secondary generalization, disease duration, intractability, polytherapy, febrile seizure, hippocampal sclerosis, and neocortical-temporal aura. METHODS: We examined the scalp electroencephalograms of 24 patients with temporal lobe epilepsy (TLE) and anterior temporal spikes. A spatiotemporal dipole model was applied to determine the O-CDS of the averaged spikes in each patient. We performed current-source analysis of multiple spatiotemporal dipole models using Brain Electrical Source Analysis software. The patients were divided into two subgroups according to their O-CDS pattern: oblique and horizontal. Clinical factors were compared between the two groups. RESULTS: Sixteen patients were classified into the oblique group, and 8 patients into the horizontal group. A neocortical-temporal aura was more commonly observed in the horizontal group (p<0.05), while drug-resistance tendencies were more commonly observed in the oblique group (p<0.1). CONCLUSIONS: The horizontal O-CDS of anterior temporal spikes may be more frequently associated with a neocortical-temporal aura than the oblique O-CDS in TLE. In addition, the oblique O-CDS pattern suggests a tendency toward drug resistance. The findings of this study imply that the oblique O-CDS pattern of anterior temporal spikes may provide additional electrophysiologic information regarding drug-resistant mesial TLE.

Dipole Source Localization of Periodic Sharp Wave Complexes in Creutzfeldt-Jakob Disease

BACKGROUND: Patients with Creutzfeldt-Jakob disease (CJD) show periodic sharp wave complexes (PSWCs) on electroencephalography (EEG) during the course of their illness. However, the source location of PSWCs and the pathophysiological mechanism remains unclear. METHODS: Ten patients with sporadic CJD who showed typical PSWCs on EEG underwent brain magnetic resonance imaging (MRI) and positron emission tomography (PET, n=8) or single-photon emission computed tomography (SPECT, n=2) scans. A 30-second epoch from the EEG was selected for analysis. The recording was separated blindly using independent component analysis. The separate independent components were subjected to dipole source localization using a single dipole model. The source locations were compared with neuroimaging findings in each patient. RESULTS: Two to three independent components responsible for the PSWCs seen in CJD were identified. The EEG recording reconstructed from the selected independent components accounted for about 70% of the variance in the original recording. All but one patient had dipole sources localized in both cortical and subcortical areas. One patient had only subcortical dipole sources in both caudate nuclei. The cortical locations included the cingulate, insula, frontal, temporal, and occipital areas. The subcortical sources were located in the striate, thalamic, and subthalamic nuclei. All the dipole sources were localized within lesions seen as neuroimaging abnormalities. CONCLUSIONS: These results suggest that a subcortical mechanism, in addition to cortical structures, is involved in producing the generalized periodic discharges in CJD.

Dipole Source Localization and Low Resolution Electromagnetic Tomography(LORETA) of Interictal Spikes in Mesial and Lateral Temporal Lobe Epilepsy / 대한간질학회지

PURPOSE: To investigate the usefulness of dipole source localization (DSL) and low resolution electromagnetic tomography (LORETA) in localizing epileptic focus, we performed DSL and LORETA of interictal spikes in patients with mesial and lateral temporal lobe epilepsy (TLE). METHOD: We analyzed representative interictal spikes in 17 patients with TLE (9:mesial TLE; 8:lateral TLE). We used ASA3 (Advanced Neuro Technology, Netherlands) for DSL, voltage topography (VT) and LORETA of interictal spikes. RESULT: Most interictal spikes for analysis have their maximum amplitudes at electrode F7, 8 or T7, 8 except one patient with lateral TLE (P7). In mesial TLE, VT showed a maximum negative electrical field in ipsilateral fronto-temporal region. DSL showed dipole sources in ipsilateral anterior mesial temporal lobe (33.3%, 3/9), temporal pole (44.5%, 4/9), orbitofrontal (11.1%, 1/9) and anterior inferior frontal (11.1%, 1/9) regions. LORETA showed maximum current density in ipsilateral fronto-temporal or anterior-mid temporal areas with lateral temporal maximum. In lateral TLE, dipole sources were in ipsilateral temporal pole (62.5%, 5/8), thalamus (12.5%, 1/8) and in posterosuperior temporal area (2/8, 25%). VT of spikes at F7 or F8 showed similar results as those of mesial TLE while that of spikes at T7, T8 and P7 had a tendency of electrical fields more extending to the mid- and posterior temporal regions. LORETA showed more diffuse current distribution in whole temporal lobe (anterior to posterior) with lateral temporal maximum. CONCLUSION: The patterns of DSL and LORETA were somewhat helpful to differentiate mesial from lateral TLE. LORETA usually showed more diffuse activity beyond the epileptic focus.

Comparison of Source Characteristics between Typical and Atypical Rolandic Epilepsy in Childhood / 대한간질학회지

PURPOSE: has been reported that benign rolandic epilepsy of childhood (BRE) does not always show benign nature in a clinical course. We hypothesized that children with atypical feature showed different characteristics of dipole sources of rolandic spikes. METHODS: Twenty-nine children with BRE were enrolled. Twenty patients showed typical features of BRE (typical BRE group). Nine patients were classified as atypical BRE, because each met one or more of the following criteria:(i) neurodevelopmental abnormalities such as mental retardation or delayed development;(ii) abnormal neuroimaging findings; and (iii) poor seizure control. Routine waking and sleep EEG recordings were obtained for at least 30 min from each patients, using a 32-channel digital EEG machine. Centrotemporal spikes were averaged which was used to do dipole source localization. The source location was estimated within a four-shell ellipsoidal model of the head. Voltage topography, orientation and propagation pattern of dipole source, as well as clinical characteristics were compared between two groups. RESULTS: The clinical characteristics such as age, sex, seizure onset age, and seizure outcome were same in both groups. The negative maximum of spikes was mainly on the central and temporal electrodes in both groups. Two thirds of patients in each group demonstrated dipole sources with tangential orientation. 40% of the typical BRE revealed two sources indicating propagation of spikes around rolandic areas, which was not observed in atypical group. The pattern of propagation was mostly from tangential to radial in anterior direction. CONCLUSIONS: These results suggest that the pathophysiological mechanism generating centrotemporal spikes of atypical BRE is different from that of typical ones.