Atsushi Kodabashi

Dysfunctional Cortical Connectivity During the Auditory Oddball Task in Patients with Schizophrenia

Background: We studied the imaginary coherence (IC) of gamma frequency oscillations between brain regions of male schizophrenia patients during an auditory oddball task using magnetoencephalography (MEG) and electroencephalography (EEG). Methods: Subjects were 10 right-handed male schizophrenia patients, evaluated by the positive and negative symptom scale (PANSS), and 10 healthy controls. Functional connectivity during the auditory oddball task was reconstructed in low (30-50 Hz) and high (50-100 Hz) gamma bands, and represented by imaginary coherence (IC) based on significant oscillatory power changes. We calculated correlations between PANSS scores and IC. Results: In the high gamma band, IC between left occipital and right prefrontal lobe areas during the time window 750-1000 ms from stimulus onset showed negative correlations with total negative scores, total positive scores, the sum of positive and negative scores in PANSS, conceptual disorganization, and social avoidance scores. In the low gamma band, IC between the same areas from 250-500 ms also showed a negative correlation with the conceptual disorganization score. In the same time window, IC between left occipital and right frontoparietal lobe areas in the low gamma band showed a positive correlation with hallucinatory behavior; IC between right temporal pole and left prefrontal lobe areas showed a positive correlation with delusion scores, although these ICs were decreased relative to controls. Conclusions: Functional disconnection of high and low gamma bands in auditory oddball task may play an important role in the auditory processing in schizophrenia patients.

Changes in Event-Related Desynchronization and Synchronization during the Auditory Oddball Task in Schizophrenia Patients

Objective: We studied differences in the spatiotemporal dynamics of cortical oscillation across brain regions of patients with schizophrenia and normal subjects during the auditory oddball task using magnetoencephalography (MEG) and electroencephalography (EEG). Methods: Ten right-handed male schizophrenia patients were studied. We used a newly developed adaptive spatial filtering algorithm optimized for robust source time-frequency reconstruction of MEG and EEG data, and obtained consecutive images in functional maps of event-related desynchronization (ERD) and synchronization (ERS) in theta, lower alpha (8–10 Hz), upper alpha (10–13 Hz), and beta bands. Results: Beta ERD power at 750–1000 ms in patients was significantly increased in large right upper temporal and parietal regions and small upper portions of bilateral dorsal frontal and dorsal-medial parietal regions. Theta ERS power in schizophrenic patients during the oddball task was significantly increased in the left temporal pole at 250–500 ms, and was significantly increased in dorsal, medial frontal, and anterior portions of the anterior cingulate cortex in both hemispheres, and the left portion of lateral temporal regions at 500–750 ms, compared to the control group (family-wise error correction p<0.05). Lower alpha ERS power was significantly decreased in the right occipital region at 500–750 ms and in the right midline parietal and bilateral occipital regions at 750–1000 ms. Upper alpha ERS power was significantly decreased in right midline parietal and left occipital regions at 750–1000 ms. Conclusions: ERD/ERS changes were noted in the left temporal pole and midline frontal and anterior cingulate cortex in theta ERS, occipital lobe in alpha ERS, and right temporal-frontal-parietal, midline frontal, and anterior cingulate cortex in beta ERD. These findings may reflect disturbances in interaction among active large neuronal groups and their communication with each other that may be related to abnormal cognitive and psychopathological function. Significance: Study of ERD and ERS by time-frequency analyses using MEG is useful to clarify data processing dysfunction in schizophrenia.

Temporal activities during P3 components on the working memory-related brain regions: N-back ERP study

In recent cognitive neuroscience, many studies have been conducted on the human working memory. However, the temporal activities in the working memory-related brain regions are not clear yet. To elucidate the temporal activities of the working memory-related brain regions, we studied the EEG P300 activities during n-back tasks with a source analysis. We elicited two P3 components in the P300 activities; the early P3 and late P3, respectively. Those appeared approximately at 300 ms and 360 ms in our n-back ERPs with the scalp EEG data. The amplitudes of the corresponding peaks showed changes in according with the working memory load. Then, we created a source model in our analysis to evaluate the temporal activities in the P3 components. This source model was defined by the sources seeded from fMRI meta-analysis of the n-back tasks, the additional sources in the orbitofrontal cortex and the visual cortex estimated with the late P3 and the P100 components. It has provided a valuable insight into the temporal brain activities at the positions of the sources. The early P3 was mainly induced by the dorsolateral prefrontal cortex, the ventrolateral prefrontal cortex, the inferior parietal lobule, the medial posterior parietal and the visual cortex. The late P3 was mainly induced by the medial premotor, the lateral premotor, the frontal pole and the orbitofrontal cortex. The contribution of the frontal pole and the orbitofrontal cortex had a peak approximately at 390 ms which appeared after the late P3 component. In this study, we have described our method to evaluate the temporal activities in the working memory-related brain regions during the n-back tasks. Our results elicited a contribution of a network in the brain regions including the prefrontal association area and the parietal association area in the P300 components of the n-back working memory task.

Determination of hemispheric language dominance using functional magnetic resonance imaging and the Shiritori (Japanese word chain) task in patients with epilepsy: Comparison with the Wada test

PURPOSE The Wada test has been the gold standard for determining hemispheric language dominance (HLD) in the presurgical evaluation of patients scheduled for neurosurgical procedures. As it poses inherent risks associated with intra-arterial catheter techniques and as it occasionally fails to indicate language dominance, an alternative reliable test is needed. We quantitatively assessed the results of functional magnetic resonance imaging (fMRI) using the Shiritori task, a Japanese word chain, to identify the threshold for correctly predicting HLD. METHODS The subjects were 28 patients with intractable epilepsy scheduled to undergo the Wada test and focus resection. We set the region of interest (ROI) on the bilateral Brodmann areas 44 and 45 (BA 44 and 45). To compare the functional activity at both ROIs we calculated the language laterality index (LI) using the formula: [VL-VR]/[VL+VR]×100, where VL and VR indicated the number of activated voxels in the left and right ROIs, respectively. RESULTS As 2 patients were excluded due to the lack of activation in either ROI, the final study population consisted of 26 patients. By the Wada test, HLD was left in 20, right in 3, and equivocal in 3. At a cut-off of LI+50, the predictive sensitivity and specificity for left HLD were 85% (17/20) and 100%; right HLD was predicted in a single patient (sensitivity 33.3%, specificity 100%). CONCLUSION The fMRI using the Shiritori task showed good activation in ROI of BA 44 and 45. At a cut-off of LI+50, LI of BA 44 and 45 predicted HLD identified by the Wada test with high specificity.

Females with schizophrenia have abnormal functional cortical connectivity in the gamma frequency during an auditory oddball task using magnetoencephalography

We studied differences in imaginary coherence (IC) of the gamma band between brain regions of female schizophrenia patients during the auditory oddball task using magnetoencephalography (MEG). Subjects were 12 right-handed female schizophrenia patients, who were evaluated by the Positive and Negative Syndrome Scales (PANSS). Functional connectivity during an auditory oddball task was reconstructed in low gamma (30 - 50 Hz) and high gamma (50 - 100 Hz and 100 - 150 Hz) bands, and represented by IC using seeds determined by the significant oscillatory power changes obtained by event-related synchronization (ERS) and event-related desynchronization (ERD) power measurements. Gamma ERS (30 - 50 Hz) power was decreased in the left precuneus at 500 - 750 ms and in the right precuneus at 750 - 1000 ms. IC in the gamma band (50 - 100 Hz) was decreased between the right precuneus (seed) and right paracentral lobule (target) and between the right precuneus and right hypothalamus at 0 - 250 ms. IC in the gamma band (100 - 150 Hz) was increased between the left precuneus and right cuneus (Brodmann area 7) at 250 - 500 ms, between the left precuneus and right culmen at 500 - 750 ms, and between the left precuneus and right cuneus (Brodmann area 17), between the left precuneus and right posterior cingulate cortex, and between the left precuneus and right caudate nucleus at 750 - 1000 ms. In the high gamma band (50 - 100 Hz) at 0 - 250 ms, significant positive correlations were shown between IC and conceptual disorganization in PANSS scores, between IC and unusual thought content score, and between IC and positive scale score. IC within the high gamma band in female schizophrenia patients showed two types of functional disconnection, intrahemispheric and interhemispheric. IC between the right or left precuneus and other specific cortical areas showed dysfunction, suggesting that the parietal lobe plays an important role in dysfunction in connectivity in the gamma band during the oddball task.

Modification of Motor Evoked Potentials Caused by Electrical Peripheral Nerve Stimulation in Transcranial Magnetic Stimulation

Somatosensory cortex receives afferent inputs from skeletal muscles and joints while a voluntary movement is conducted. Although this sensory feedback may regulate the efferent motor control signals generated in the motor cortex, the relationship between the afferent sensory signals and the efferent motor signals is still unclear. In this study, we investigated the relationship between the afferent signals elicited by an electrical stimulus of a peripheral nerve and the efferent signals produced by a transcranial magnetic stimulation (TMS) of the motor cortex. The changes of motor evoked potentials (MEPs) elicited by TMS following an electrical stimulus of a median nerve were observed. The results showed that the MEPs were significantly attenuated when the inter-stimulus interval (ISI) between the electrical stimulus and the TMS was 20 ms, and that the MEPs were significantly enhanced when the ISI was longer than 35 ms. Furthermore, the brain condition which affected the MEPs was evaluated with the somatosensory evoked fields (SEFs) measured with magneto-encephalography (MEG). It was suggested that the activation and direction of the current dipole in the primary somatosensory cortex was related to the effect of the afferent signals on the motor function.

Sex Differences in Gamma Band Functional Connectivity Between the Frontal Lobe and Cortical Areas During an Auditory Oddball Task, as Revealed by Imaginary Coherence Assessment

We studied sex-related differences in gamma oscillation during an auditory oddball task, using magnetoencephalography and electroencephalography assessment of imaginary coherence (IC). We obtained a statistical source map of event-related desynchronization (ERD) / event-related synchronization (ERS), and compared females and males regarding ERD / ERS. Based on the results, we chose respectively seed regions for IC determinations in low (30-50 Hz), mid (50-100 Hz) and high gamma (100-150 Hz) bands. In males, ERD was increased in the left posterior cingulate cortex (CGp) at 500 ms in the low gamma band, and in the right caudal anterior cingulate cortex (cACC) at 125 ms in the mid-gamma band. ERS was increased in the left rostral anterior cingulate cortex (rACC) at 375 ms in the high gamma band. We chose the CGp, cACC and rACC as seeds, and examined IC between the seed and certain target regions using the IC map. IC changes depended on the height of the gamma frequency and the time window in the gamma band. Although IC in the mid and high gamma bands did not show sex-specific differences, IC at 30-50 Hz in males was increased between the left rACC and the frontal, orbitofrontal, inferior temporal and fusiform target regions. Increased IC in males suggested that males may acomplish the task constructively, analysingly, emotionally, and by perfoming analysis, and that information processing was more complicated in the cortico-cortical circuit. On the other hand, females showed few differences in IC. Females planned the task with general attention and economical well-balanced processing, which was explained by the higher overall functional cortical connectivity. CGp, cACC and rACC were involved in sex differences in information processing and were likely related to differences in neuroanatomy, hormones and neurotransmitter systems.

Current Dipole Estimation in MEG by Spatial Interpolation of Magnetic Sensors

In this study, a method for current dipole estimation with spatial interpolation of measured magnetic fields in magnetoencephalogram (MEG) is proposed. This method applies virtual magnetic (M v ) sensors uniformly interpolated in the surface comprised of MEG (M r ) sensors. Orientations and output signals of the virtual magnetic sensors are calculated by a spatial linear interpolation based on those of real magnetic sensors. For determining an optimal value of regularization parameter (α) in minimum norm inverse solutions, M v sensors are divided into some groups randomly. Quantities of magnetic field (b k ) at the M r sensors are calculated by estimated dipoles with each group of M v sensors. α is determined by minimization of the total sum of differences between b k and the output signals measured by M r sensors. In order to confirm the validity of the proposed method, we estimated source distribution of N20m components of unilateral and bilateral somatosensory evoked fields (SEFs) measured by a 160-channel axial SQUID gradiometer system, when subject’s right and/or left median nerve was electrically stimulated. The proposed method was able to estimate source distribution in the primary somatosensory cortex (S1). Furthermore, the source distribution estimated by the proposed method tended to be more confined than that estimated by a cross validation error method. These results indicate that the virtually improved spatial resolution of MEG data can estimate more confined source distribution.

Effect of Picture Appearance in the TMT on Fmri Activated Areas

In this study, attention and memory functions were evaluated during two types of TMT: the ordinary random pattern (TMT-random), and the test which eventually revealed the figure (TMT-figure). Using fMRI, the areas significantly activated by the TMT-figure compared with TMT-random were BA18, BA13, BA6 (attention-related), and hippocampus (memory-related). The TMT-figure may be more suitable for examination of the relationship between attention and memory functions.

Examination of appropriate stimuli to attention inducement

The aim of this study is to consider the appropriate element of the stimulation for subjects by observation of fMRI. The stimulus is used for suggesting the direction to the people. In this study, we have attempted to observe the brain activation during different kind of visual stimulus such as doll (teddy bear), arrow and Japanese character (Hiragana), and auditory stimulus. Twelve normal subjects consented to participate in this study. While the subject was watching the visual stimulus or hearing the auditory stimulus, the brain activity was examined through fMRI. As results, the activation of cerebral cortex by the visual stimuli was less than by the auditory stimuli and the simultaneous stimuli. Therefore, it is suggested that the visual stimuli is appropriate when it is necessary to quickly select the direction. Additionally, among the visual stimuli, the reaction time of the arrow was the smallest standard deviation (SD), and activated cerebellum as well as supplementary motor area. The teddy bear had activated dorsolateral prefrontal cortex and frontal pole, but it took time to react. Therefore, it was suggested that the arrow was appropriate when it was necessary for various people to select the direction, and that the teddy bear was appropriate when it is necessary to impress.