Cortical Activity Measured with EEG during Stepping on a Recumbent Stepper

OBJECTIVE: Recent neuroimaging studies have shown a strong involvement of the cortex as well as brainstem locomotor center in locomotion. In the present study, cortical activity during constant stepping was investigated using electroencephalography (EEG). METHOD: Five healthy volunteers participated in this study. Sixty-four channel EEG was measured for 10 min while the participants performed constant stepping on a cadence of 100 rpm (50 cycles per 1 min) using a recumbent stepper. Surface electromyography (EMG) was also measured at the bilateral vastus medialis muscles. Each stepping cycle was epoched from the onset of EMG signal of the right vastus medialis muscle. Averaged event-related potentials (ERP) and event-related spectral perturbations (ERSP) of all subjects were calculated at all EEG channels. RESULTS: Periodic change of ERP was centered on the CZ and FPZ electrodes. While ERP at the CZ started to increase at 200 and 800 ms, ERP at the FPZ started to increase at -50 and 600 ms. ERSP was remarkable at the CZ during stepping cycles. According to the stepping cycle, power increases were pronounced at low-gamma frequency band and also observed at beta band. CONCLUSION: This study showed cortical activity during constant stepping using EEG in healthy participants. Periodic cortical activities were remarkable at the sensorimotor cortex area, and precedent activities were observed at the prefrontal area. EEG measurement during stepping on a recumbent stepper may be a valuable tool in investigating cortical activates related to walking in patients with gait disorders.

Preoperative Weakness and Demyelination of the Corticospinal Tract in Meningioma Patients : Changes in Diffusion Parameters Using Diffusion Tensor Imaging

OBJECTIVE: Differentiation of demyelination in white matter from axonal damage can be determined using diffusion tensor imaging (DTI). In this study using meningioma patients an attempt was made to evaluate the relationship between preoperative weakness and the changes of diffusion parameters in the corticospinal tract (CST) using DTI. METHODS: Twenty-six patients with meningioma were enrolled in this study. Eleven of them suffered from objective motor weakness and were classified as Group 1. The remaining 15 patients did not present motor weakness and were classified as Group 2. Fiber tractography and CST diffusion parameters were obtained using DTIStudio. The ratios (lesion side mean value/contralateral side mean value) of CST diffusion parameters were compared with 1.0 as a test value using a one-sample t-test. RESULTS: In Group 1, fractional anisotropy (FA), tensor trace (TT), and radial diffusivity (RD, lambda2 and lambda3) of the CST were significantly different between two hemispheres, but axial diffusivity (AD, lambda1) of the CST was not significantly different between two hemispheres. In Group 2, FA and lambda3 of CST did not differ significantly between the hemispheres. In Group 2, TT, lambda1, and lambda2 of CST in the ipsilateral hemisphere were significantly higher than those of the unaffected hemisphere. However, the differences were small. CONCLUSION: Motor weakness was related to a low FA and high TT resulting from increased RD of the CST fibers. CST diffusion changes in patients with weakness are similar to those for demyelination.

Localization Value of Magnetoencephalography Interictal Spikes in Adult Nonlesional Neocortical Epilepsy

Few studies have included magnetoencephalography (MEG) when assessing the diagnostic value of presurgical modalities in a nonlesional epilepsy population. Here, we compare single photon emission computed tomography (SPECT), positron emission tomography (PET), video-EEG (VEEG), and MEG, with intracranial EEG (iEEG) to determine the value of individual modalities to surgical decisions. We analyzed 23 adult epilepsy patients with no abnormal MRI findings who had undergone surgical resection. Localization of individual presurgical tests was determined for hemispheric and lobar locations based on visual analysis. Each localization result was compared with the ictal onset zone (IOZ) defined by using iEEG. The highest to the lowest hemispheric concordance rates were MEG (83%) > ictal VEEG (78%) > PET (70%) > ictal SPECT (57%). The highest to lowest lobar concordance rates were ictal VEEG = MEG (65%) > PET (57%) > ictal SPECT (52%). Statistical analysis showed MEG to have a higher hemispheric concordance than that of ictal SPECT (P = 0.031). We analyzed the effects of MEG clustered-area resection on surgical outcome. Patients who had resection of MEG clusters showed a better surgical outcome than those without such resection (P = 0.038). It is suggested that MEG-based localization had the highest concordance with the iEEG-defined IOZ. Furthermore, MEG cluster resection has prognostic significance in predicting surgical outcome.

Localization Value of Magnetoencephalography Interictal Spikes in Adult Nonlesional Neocortical Epilepsy

Few studies have included magnetoencephalography (MEG) when assessing the diagnostic value of presurgical modalities in a nonlesional epilepsy population. Here, we compare single photon emission computed tomography (SPECT), positron emission tomography (PET), video-EEG (VEEG), and MEG, with intracranial EEG (iEEG) to determine the value of individual modalities to surgical decisions. We analyzed 23 adult epilepsy patients with no abnormal MRI findings who had undergone surgical resection. Localization of individual presurgical tests was determined for hemispheric and lobar locations based on visual analysis. Each localization result was compared with the ictal onset zone (IOZ) defined by using iEEG. The highest to the lowest hemispheric concordance rates were MEG (83%) > ictal VEEG (78%) > PET (70%) > ictal SPECT (57%). The highest to lowest lobar concordance rates were ictal VEEG = MEG (65%) > PET (57%) > ictal SPECT (52%). Statistical analysis showed MEG to have a higher hemispheric concordance than that of ictal SPECT (P = 0.031). We analyzed the effects of MEG clustered-area resection on surgical outcome. Patients who had resection of MEG clusters showed a better surgical outcome than those without such resection (P = 0.038). It is suggested that MEG-based localization had the highest concordance with the iEEG-defined IOZ. Furthermore, MEG cluster resection has prognostic significance in predicting surgical outcome.

Magnetoencephalography Interictal Spike Clustering in Relation with Surgical Outcome of Cortical Dysplasia

OBJECTIVE: The aim of this study was to devise an objective clustering method for magnetoencephalography (MEG) interictal spike sources, and to identify the prognostic value of the new clustering method in adult epilepsy patients with cortical dysplasia (CD). METHODS: We retrospectively analyzed 25 adult patients with histologically proven CD, who underwent MEG examination and surgical resection for intractable epilepsy. The mean postoperative follow-up period was 3.1 years. A hierarchical clustering method was adopted for MEG interictal spike source clustering. Clustered sources were then tested for their prognostic value toward surgical outcome. RESULTS: Postoperative seizure outcome was Engel class I in 6 (24%), class II in 3 (12%), class III in 12 (48%), and class IV in 4 (16%) patients. With respect to MEG spike clustering, 12 of 25 (48%) patients showed 1 cluster, 2 (8%) showed 2 or more clusters within the same lobe, 10 (40%) showed 2 or more clusters in a different lobe, and 1 (4%) patient had only scattered spikes with no clustering. Patients who showed focal clustering achieved better surgical outcome than distributed cases (p=0.017). CONCLUSION: This is the first study that introduces an objective method to classify the distribution of MEG interictal spike sources. By using a hierarchical clustering method, we found that the presence of focal clustered spikes predicts a better postoperative outcome in epilepsy patients with CD.

Magnetoencephalography in Pediatric Lesional Epilepsy Surgery

This study was performed to assess the usefulness of magnetoencephalography (MEG) as a presurgical evaluation modality in Korean pediatric patients with lesional localization-related epilepsy. The medical records and MEG findings of 13 pediatric patients (6 boys and 7 girls) with localization-related epilepsy, who underwent epilepsy surgery at Seoul National University Children's Hospital, were retrospectively reviewed. The hemispheric concordance rate was 100% (13/13 patients). The lobar or regional concordance rate was 77% (10/13 patients). In most cases, the MEG spike sources were clustered in the proximity of the lesion, either at one side of the margin (nine patients) or around the lesion (one patient); clustered spike sources were distant from the lesion in one patient. Among the patients with clustered spike sources near the lesion, further extensions (three patients) and distal scatters (three patients) were also observed. MEG spike sources were well lateralized and localized even in two patients without focal epileptiform discharges in the interictal scalp electroencephalography. Ten patients (77%) achieved Engel class I postsurgical seizure outcome. It is suggested that MEG is a safe and useful presurgical evaluation modality in pediatric patients with lesion localization-related epilepsy.

Psychoacoustic Characteristics of Prepulse Gap in Tinnitus Patients: A Preliminary Study to Develop an Objective Test Detecting Tinnitus / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The objective of this study was to observe whether there are differences in detecting ability of pre-pulse gaps between tinnitus patients and normal subjects. SUBJECTS AND METHOD: Ten tinnitus patients and eight normal subjects were recruited. Fifty stimuli composed of a background noise and a pulse noise were presented to the subjects. For certain stimuli, a short gap preceding the pulse noise was inserted but for others, no gaps were inserted. The two groups were subjected to a gap lasting 300 and 200 msec. The subjects were then asked if they detected the gap during the stimulus and the number of correct answers were counted. RESULTS: In the tinnitus patient group, the number of correct answers for gap-stimuli detection was significantly smaller when the gap was shortened to 200 msec. In the control group, however, there was only a slight difference in the score. When the length of the gap was shortened to 200 msec, the score significantly decreased in 50% of the tinnitus patients whereas the score increased in only 12% of the control group. CONCLUSION: The ability to detect pre-pulse gaps is affected by tinnitus in humans just as in the animal models.

Functional Reorganization Associated with Semantic Language Processing in Temporal Lobe Epilepsy Patients after Anterior Temporal Lobectomy : A Longitudinal Functional Magnetic Resonance Image Study

OBJECTIVE: The focus of this study is brain plasticity associated with semantic aspects of language function in patients with medial temporal lobe epilepsy (mTLE). METHODS: Using longitudinal functional magnetic resonance imaging (fMRI), patterns of brain activation were observed in twelve left and seven right unilateral mTLE patients during a word-generation task relative to a pseudo-word reading task before and after anterior temporal section surgery. RESULTS: No differences were observed in precentral activations in patients relative to normal controls (n = 12), and surgery did not alter the phonological-associated activations. The two mTLE patient groups showed left inferior prefrontal activations associated with semantic processing (word-generation > pseudo-word reading), as did control subjects. The amount of semantic-associated activation in the left inferior prefrontal region was negatively correlated with epilepsy duration in both patient groups. Following temporal resection, semantic-specific activations in inferior prefrontal region became more bilateral in left mTLE patients, but more left-lateralized in right mTLE patients. The longer the duration of epilepsy in the patients, the larger the increase in the left inferior prefrontal semantic-associated activation after surgery in both patient groups. Semantic activation of the intact hippocampus, which had been negatively correlated with seizure frequency, normalized after the epileptic side was removed. CONCLUSION: These results indicate alternation of semantic language network related to recruitment of left inferior prefrontal cortex and functional recovery of the hippocampus contralateral to the epileptogenic side, suggesting an intra- and inter-hemispheric reorganization following surgery.

Localization of Broca's Area Using Functional MR Imaging: Quantitative Evaluation of Paradigms

OBJECTIVE: Functional magnetic resonance imaging (fMRI) is frequently used to localize language areas in a non-invasive manner. Various paradigms for presurgical localization of language areas have been developed, but a systematic quantitative evaluation of the efficiency of those paradigms has not been performed. In the present study, the authors analyzed different language paradigms to see which paradigm is most efficient in localizing frontal language areas. METHODS: Five men and five women with no neurological deficits participated (mean age, 24 years) in this study. All volunteers were right-handed. Each subject performed 4 tasks, including fixation (Fix), sentence reading (SR), pseudoword reading (PR), and word generation (WG). Fixation and pseudoword reading were used as contrasts. The functional area was defined as the area(s) with a t-value of more than 3.92 in fMRI with different tasks. To apply an anatomical constraint, we used a brain atlas mapping system, which is available in AFNI, to define the anatomical frontal language area. The numbers of voxels in overlapped area between anatomical and functional area were individually counted in the frontal expressive language area. RESULTS: Of the various combinations, the word generation task was most effective in delineating the frontal expressive language area when fixation was used as a contrast (p<0.05). The sensitivity of this test for localizing Broca's area was 81% and specificity was 70%. CONCLUSION: Word generation versus fixation could effectively and reliably delineate the frontal language area. A customized effective paradigm should be analyzed in order to evaluate various language functions.

Functional MRI Study for Phonological and Semantic Language Processing in Strongly Right-Handed Korean Twenty Year Olds / 대한간질학회지

OBJECTIVE: Using functional magnetic resonance imaging, cerebral language areas were determined during a series of language tasks in normal strong right-handed subjects. METHODS: Twelve normal right-handed volunteers were examined on a 1.5T MR unit. Language task paradigms included two phonological tasks involving meaningless letters and sentences, and four semantic tasks using different types of words. Each language task was examined using a separate scan consisted of three blocks separated by rest periods. BOLD (blood oxygenation level dependent) signals during language tasks were compared using 24 sec alternating rest periods during which subjects concentrated on a plus symbol. After preprocessing and statistically analyzing individual data, group analysis (p<0.001, k=50) was performed using SPM99 software. RESULTS: Meaningless letter reading was more efficient than sentence reading, in terms of delineating brain regions related to phonological processing, we found significant regions in the left inferior frontal gyrus (IFG), left thalamus, bilateral cingulate gyri, right anterior superior temporal gyrus (STG), right IFG, and left inferior parietal lobule (IPL). During semantic tasks, left IFG, left posterior middle temporal gyrus, left IPL, bilateral medial frontal gyrus, right posterior STG, right parahippocampal, and fusiform gyri were found to be activated. CONCLUSION: During the two phonological tasks, normal strongly right-handed people more actively used the left IFG, right anterior temporal lobe, and right IFG than during semantic processing, whereas during the four semantic tasks, these subjects more actively used the bilateral posterior temporal and right medial temporal lobes.