Kensuke Kawai

Niigata University, Niahi-niigata, Niigata, Japan

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Publications (87)228.38 Total impact

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    ABSTRACT: Objective Resective surgery for mesial temporal lobe epilepsy (MTLE) with a correspondent lesion has been established as an effective and safe procedure. Surgery for temporal lobe epilepsies with bilateral hippocampal sclerosis or without correspondent lesions, however, carries a higher risk of devastating memory decline, underscoring the importance of establishing the memory-dominant side preoperatively and adopting the most appropriate procedure. In this study, we focused on high gamma activities (HGAs) in the parahippocampal gyri and investigated the relationship between memory-related HGAs and memory outcomes after hippocampal transection (HT), a hippocampal counterpart to neocortical multiple subpial transection. The transient nature of memory worsening after HT provided us with a rare opportunity to compare HGAs and clinical outcomes without risking permanent memory disorders.Methods We recorded electrocorticography from parahippocampal gyri of 18 patients with temporal lobe epilepsy while they executed picture naming and recognition tasks. Memory-related HGA was quantified by calculating differences in power amplification of electrocorticography signals in a high gamma range (60–120 Hz) between the two tasks. We compared memory-related HGAs from correctly recognized and rejected trials (hit-HGA and reject-HGA). Using hit-HGA, we determined HGA-dominant sides and compared them with memory outcomes after HT performed on seven patients.ResultsWe observed memory-related HGA mainly between 500 and 600 msec poststimulus. Hit-HGA was significantly higher than reject-HGA. Three patients who had surgery on the HGA-dominant side experienced transient memory worsening postoperatively. The postoperative memory functions of the other four patients remained unchanged.SignificanceParahippocampal HGA was indicated to reflect different memory processes and be compatible with the outcomes of HT, suggesting that HGA could provide predictive information on whether the mesial temporal lobe can be resected without causing memory worsening. This preliminary study suggests a refined surgical strategy for atypical MTLE based on reliable memory lateralization.
    Epilepsia 08/2014; 55(10). DOI:10.1111/epi.12764 · 4.58 Impact Factor
  • K. Kamada · N. Kunii · K. Kawai · N. Saito
    Clinical Neurophysiology 06/2014; 125:S103. DOI:10.1016/S1388-2457(14)50342-2 · 2.98 Impact Factor
  • Clinical Neurophysiology 06/2014; 125:S147-S148. DOI:10.1016/S1388-2457(14)50484-1 · 2.98 Impact Factor
  • Japanese Journal of Neurosurgery 01/2014; 23(4):296-305. DOI:10.7887/jcns.23.296
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    ABSTRACT: How visual object categories are represented in the brain is one of the key questions in neuroscience. Studies on low-level visual features have shown that relative timings or phases of neural activity between multiple brain locations encode information. However, whether such temporal patterns of neural activity are used in the representation of visual objects is unknown. Here, we examined whether and how visual object categories could be predicted (or decoded) from temporal patterns of electrocorticographic (ECoG) signals from the temporal cortex in five patients with epilepsy. We used temporal correlations between electrodes as input features, and compared the decoding performance with features defined by spectral power and phase from individual electrodes. While using power or phase alone, the decoding accuracy was significantly better than chance, correlations alone or those combined with power outperformed other features. Decoding performance with correlations was degraded by shuffling the order of trials of the same category in each electrode, indicating that the relative time series between electrodes in each trial is critical. Analysis using a sliding time window revealed that decoding performance with correlations began to rise earlier than that with power. This earlier rise time was replicated by a model using phase differences to encode categories. These results suggest that activity patterns arising from interactions between multiple neuronal units carry additional information on visual object categories.
    NeuroImage 12/2013; 90. DOI:10.1016/j.neuroimage.2013.12.020 · 6.36 Impact Factor
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    ABSTRACT: Recognition of faces and written words is associated with category-specific brain activation in the ventral occipitotemporal cortex (vOT). However, topological and functional relationships between face-selective and word-selective vOT regions remain unclear. In this study, we collected data from patients with intractable epilepsy who underwent high-density recording of surface field potentials in the vOT. "Faces" and "letterstrings" induced outstanding category-selective responses among the 24 visual categories tested, particularly in high-γ band powers. Strikingly, within-hemispheric analysis revealed alternation of face-selective and letterstring-selective zones within the vOT. Two distinct face-selective zones located anterior and posterior portions of the mid-fusiform sulcus whereas letterstring-selective zones alternated between and outside of these 2 face-selective zones. Further, a classification analysis indicated that activity patterns of these zones mostly represent dedicated categories. Functional connectivity analysis using Granger causality indicated asymmetrically directed causal influences from face-selective to letterstring-selective regions. These results challenge the prevailing view that different categories are represented in distinct contiguous regions in the vOT.
    Cerebral Cortex 11/2013; 25(5). DOI:10.1093/cercor/bht319 · 8.67 Impact Factor
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    ABSTRACT: Object Meningiomas treated by subtotal or partial resection are associated with significantly shorter recurrence-free survival than those treated by gross-total resection. The Simpson grading system classifies incomplete resections into a single category, namely Simpson Grade IV, with wide variations in the volume and location of residual tumors, making it complicated to evaluate the achievement of surgical goals and predict the prognosis of these tumors. Authors of the present study investigated the factors related to necessity of retreatment and tried to identify any surgical nuances achievable with the aid of modern neurosurgical techniques for meningiomas treated using Simpson Grade IV resection. Methods This retrospective analysis included patients with WHO Grade I meningiomas treated using Simpson Grade IV resection as the initial therapy at the University of Tokyo Hospital between January 1995 and April 2010. Retreatment was defined as reresection or stereotactic radiosurgery due to postoperative tumor growth. Results A total of 38 patients were included in this study. Regrowth of residual tumor was observed in 22 patients with a mean follow-up period of 6.1 years. Retreatment was performed for 20 of these 22 tumors with regrowth. Risk factors related to significantly shorter retreatment-free survival were age younger than 50 years (p = 0.006), postresection tumor volume of 4 cm(3) or more (p = 0.016), no dural detachment (p = 0.001), and skull base location (p = 0.016). Multivariate analysis revealed that no dural detachment (hazard ratio [HR] 6.42, 95% CI 1.41-45.0; p = 0.02) and skull base location (HR 11.6, 95% CI 2.18-218; p = 0.002) were independent risk factors for the necessity of early retreatment, whereas postresection tumor volume of 4 cm(3) or more was not a statistically significant risk factor. Conclusions Compared with Simpson Grade I, II, and III resections, Simpson Grade IV resection includes highly heterogeneous tumors in terms of resection rate and location of the residual mass. Despite the difficulty in analyzing such diverse data, these results draw attention to the favorable effect of dural detachment (instead of maximizing the resection rate) on long-term tumor control. Surgical strategy with an emphasis on detaching the tumor from the affected dura might be another important option in resection of high-risk meningiomas not amenable to gross-total resection.
    Journal of Neurosurgery 09/2013; 119(6). DOI:10.3171/2013.8.JNS13832 · 3.15 Impact Factor
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    ABSTRACT: Vagus nerve stimulation (VNS) is a palliative treatment for intractable epilepsy. Therapeutic mechanisms of VNS have not been elucidated. In this study, we measured the local field potential (LFP) with high-spatial resolution using a microelectrode array in adult rats, and analyzed VNS-evoked phase modulation at a local network level. Eight adult Wistar rats (270 - 330 g) were used. Each rat underwent implantation of VNS system (Cyberonics, Houston, TX., USA) under 1.5% isoflurane anesthesia. One week after implantation, right temporal craniotomy was performed under the same as previous anesthesia. Subsequently, a microelectrode array was placed in the temporal lobe cortex, and LFP was recorded with sampling rate of 1000 Hz. Phase-locking value (PLV) between all pairs of electrodes in varied frequency bands was calculated in order to evaluate the effect of VNS in terms of synchrony of neuronal activities. PLV was calculated both in a normal state and in an epileptic state induced by kainic acid. VNS increased PLV in a normal state, particularly in high-γ band. In an epileptic state, VNS increased PLV in high-γ band, and decreased in d and low-β bands. VNS modulates synchrony in a band-specific and state-dependent manner. VNS might keep cortical synchrony within the optimal state.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 07/2013; 2013(6):5348-5351. DOI:10.1109/EMBC.2013.6610757
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    ABSTRACT: BACKGROUND:: There has been a growing interest in clinical single-neuron recording, to better understand epileptogenicity and brain function. It is crucial to compare this new information, single-neuronal activity, with that obtained from conventional intracranial electroencephalographyduring simultaneous recording. However, it is difficult to implant microwires and subdural electrodes during a single surgical operation, since the stereotactic frame hampers flexible craniotomy. OBJECTIVE:: We describenewly designed electrodes as well as surgical techniques to implant these with subdural electrodes that enable simultaneous recording from hippocampal neurons and broad areas of the cortical surface. METHODS:: We designed a depth electrode that does not protrude into the dura and pulsates naturally with the brain. The length and the tract of the depth electrode were determined preoperatively between the lateral subiculum and the lateral surface of the temporal lobe. A frameless navigation system was used to insert the depth electrode. Surface grids and ventral strips were placed before and after the insertion of the depth electrodes, respectively. Finally, a microwire bundle was inserted into the lumen of the depth electrode. We evaluated the precision of implantation, the recording stability, and therecording rate with microwire electrodes. RESULTS:: Depth-microwire electrodes were placed with a precision of 3.6mm. The mean successful recording rate of single- or multiple-unit activity was 14.8%, which was maintained throughout the entire recording period. CONCLUSION:: We achieved simultaneous implantation of microwires, depth electrodes and broad-area subdural electrodes. Our method enabled simultaneous and stable recording of hippocampal single-neuron activities and multi-channel intracranial electroencephalography.
    Neurosurgery 04/2013; DOI:10.1227/01.neu.0000430327.48387.e1 · 3.03 Impact Factor
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    Kensuke Kawai · Michiharu Morino · Masaki Iwasaki
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    ABSTRACT: Delalande's vertical hemispherotomy is an innovative evolution of hemispherectomy in minimizing brain resection. We report our modification for this surgical procedure. We modified the original procedure in two aspects for the purpose of less brain resection and confirmation of the complete disconnection. Firstly, all procedures were done via an interhemispheric route instead of a transcortical route. Secondly, we set the anterior disconnection plane as the one that connects the anterior end of the choroidal fissure to the anterior end of the foramen of Monro, instead of the former to the subcallosal area. We applied this modified vertical hemispherotomy to 7 cases. Four cases were children with hemimegalencephaly and other 3 were adults with ulegyric hemisphere. Surgical procedure was completed without complication in all cases. There was no case that required CSF shunting. Seizure outcome was Engel's class I in 6 and class IV in 1. Postoperative MRI revealed complete disconnection of the affected hemisphere in all patients. We reported our modification of vertical hemispherotomy. Although these are minor modifications, they further minimized brain resection and may serve for less invasiveness of procedure and improvement in completeness of disconnection and its confirmation during surgery.
    Brain & development 02/2013; 36(2). DOI:10.1016/j.braindev.2012.12.013 · 1.54 Impact Factor
  • Japanese Journal of Neurosurgery 01/2013; 22(3):178-184. DOI:10.7887/jcns.22.178
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    ABSTRACT: Vagus nerve stimulation (VNS) is a surgical treatment for intractable epilepsy. Although VNS has been used to treat more than 60,000 patients, the precise therapeutic mechanism of action has not been elucidated. Here, we hypothesize that VNS modulates the local synchronization of cortical activities and thus inhibits seizures. In order to verify this hypothesis, we mapped local field potentials (LFPs) with high‐spatial resolution using a microelectrode array from the temporal cortices of adult rats and analyzed VNS‐induced phase modulation at the local network level. VNS significantly increased the phase locking value (PLV), an index of synchronization, specifically at the gamma band. The optimal stimulation pulse of VNS was 0.5 mA delivered at 10 Hz. This PLV modulation was most effective when the interelectrode distance was about 1.6 mm. Gamma‐band PLVs within the auditory cortex increased more significantly than those between the auditory and nonauditory cortices, while alpha‐ and low‐beta PLV exhibited more synchronization between the auditory and nonauditory cortices. These results demonstrate that VNS modulates cortical synchronization in a band specific manner, and has some implications for the mechanism of action of VNS.
    IEEJ Transactions on Electronics Information and Systems 01/2013; 133(8):1493-1500. DOI:10.1541/ieejeiss.133.1493
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    ABSTRACT: Despite the recent advances in microsurgical techniques, reconstruction of extensive skull base defects using free flaps in pediatric patients presents a surgical challenge, and reports on skull base reconstruction in infants is quite limited. We present a case of reconstruction of an extensive anterior skull base defect using a rectus abdominis (RA) myocutaneous flap in a 1 year-old (14 months) infant. Sufficient coverage of the intracranial contents, good aesthetic results, and minimal growth disturbance at the donor site were achieved by the muscle-sparing RA flap transfer. To the best of our knowledge, this was among the youngest case of skull base reconstruction using a free flap. The feasibility of free flap transfer and flap selection in pediatric skull base reconstruction is discussed. © 2012 Wiley Periodicals, Inc.
    Microsurgery 11/2012; 32(8). DOI:10.1002/micr.22025 · 2.42 Impact Factor
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    ABSTRACT: BACKGROUND: Vagus nerve stimulation (VNS) is a palliative treatment for drug resistant epilepsy for which the efficacy and safety are well established. Accumulating evidence suggests that ascending vagal signals modulate abnormal cortical excitability via various pathways. However, there is no direct evidence for an ascending conduction of neural impulses in a clinical case of VNS. OBJECTIVE: We recorded and analyzed the short-latency components of the vagus nerve (VN) evoked potential (EP) from the viewpoint of determining whether or not it is a marker for the ascending neural conduction. METHODS: EPs within 20 ms were prospectively recorded simultaneously from a surgical wound in the neck and at multiple scalp sites during implantation surgery in 25 patients with drug-resistant epilepsy. Electrical stimulation was delivered using the clinical VNS Therapy system. A recording was made before and after a muscle relaxant was administered, when changing the rostrocaudal position of stimulation, or when stimulating the ansa cervicalis instead of the VN. RESULTS: The short-latency components consisted of four peaks. The early component around 3 ms, which was most prominent in A1-Cz, remained unchanged after muscle relaxation while the later peaks disappeared. Rostral transition of the stimulation resulted in an earlier shift of the early component. The estimated conduction velocity was 27.4 ± 10.2 m/s. Stimulation of the ansa cervicalis induced no EP. CONCLUSIONS: The early component was regarded as directly resulting from ascending neural conduction of A fibers of the VN, probably originating around the jugular foramen. Recording of VN-EP might document the cause of treatment failure in some patients.
    Brain Stimulation 10/2012; 6(4). DOI:10.1016/j.brs.2012.09.007 · 5.43 Impact Factor
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    ABSTRACT: High gamma activity (HGA) has been shown to be positively correlated with blood oxygenation level-dependent (BOLD) responses in the primary cortices with simple tasks. It is, however, an open question whether the correlation is simply applied to the association areas related to higher cognitive functions. The aim of this study is to investigate quantitative correlation between HGA and BOLD and their spatial and temporal profiles during semantic processing. Thirteen patients with intractable epilepsy underwent fMRI and electrocorticography (ECoG) with a word interpretation task to evoke language-related responses. Percent signal change of BOLD was calculated at each site of ECoG electrode, which has power amplification of high gamma band (60-120Hz) activity. We transformed locations of individual electrodes and brains to a universal coordination using SPM8 and made the quantitative comparisons on a template brain. HGAs were increased in several language-related areas such as the inferior frontal and middle temporal gyri and were positively correlated with BOLD responses. The most striking finding was different temporal dynamics of HGAs in the different brain regions. Whereas the frontal lobe showed longer-lasting HGA, the HGA-intensity on the temporal lobe quickly declined. The different temporal dynamics of HGA might explain why routine language-fMRI hardly detected BOLD in the temporal lobe. This study clarified different neural oscillation and BOLD response in various brain regions during semantic processing and will facilitate practical utilization of fMRI for evaluating higher-order cognitive functions not only in basic neuroscience, but also in clinical practice.
    NeuroImage 09/2012; 65. DOI:10.1016/j.neuroimage.2012.09.059 · 6.36 Impact Factor
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    ABSTRACT: We compared electrocorticography (ECoG) with invasive intracranial noninvasive functional MRI using language-related tasks. Twenty patients underwent bilateral implantation of subdural electrodes (more than 80 channels) for diagnosing intractable epilepsy. Before implantation of the electrodes, language-related fMRI was performed, and the fMR images were superimposed on individual brain images. Brain mapping with electrocortical stimulation was performed on the basis of the fused fMR and brain MR images, and the specificity and sensitivity of language-related fMRI was calculated. For careful interpretation of spatial and temporal ECoG changes with semantic tasks, we developed a software to visualize semantic-ECoG dynamics in the brain. Semantic-ECoG was recorded during word, figure, and face recognition as well as memory tasks. The raw ECoG data were processed by averaging and time-frequency analysis, and the functional profiles were projected onto the individual brain surface. Acquired ECoG was classified using Support Vector Machine and Sparse Logistic Regression to decode brain signals. Because of variations in electrode locations, we normalized the ECoG electrodes by using SPM8. Although fMRI has 90% sensitivity, its specificity is only up to 50%. The basal temporal-occipital cortex was activated within 250 ms after visual object presentation. Compared to other stimuli, face stimulation evoked significantly higher ECoG amplitudes. Among different brain regions, the hippocampus was predominantly activated during the memory task. The prediction rate of ECoG classification was 90%, which was sufficient for clinical use. Semantic-ECoG is a powerful technique to detect and decode human brain functions.
    Brain and nerve = Shinkei kenkyū no shinpo 09/2012; 64(9):1001-12.
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    ABSTRACT: OBJECTIVE: This study aims to elucidate differences in preoperative cerebral glucose metabolism between patients who did and did not become seizure free after unilateral mesial temporal lobe epilepsy (mTLE) surgery. We hypothesized that regional glucose metabolism on preoperative fluorodeoxyglucose positron emission tomography (FDG-PET) in patients with seizure-free outcomes differed from that in patients who were not seizure free after appropriate epilepsy surgery for unilateral mTLE. In this study, we compared preoperative FDG-PET findings between these two patient groups by applying a statistical analysis approach, with a voxel-based Asymmetry index (AI), to improve sensitivity for the detection of hypometabolism. METHODS: FDG-PET scans of 28 patients with medically refractory mTLE, of whom 17 achieved a seizure-free outcome (Engel class 1 a-b) during a postoperative follow-up period of at least 2 years, were analyzed retrospectively. Voxel values were adjusted by the AI method as well as the global normalization (GN) method. Two types of statistical analysis were performed. One was a voxel severity analysis with comparison of voxel values at the same coordinate, and the other was extent analysis with comparison of the number of significant voxels in the anatomical areas predefined with Talairach's atlas. RESULTS: In the voxel severity analysis, significant hypometabolism restricted to the ipsilateral temporal tip and hippocampal area was detected in the postoperative seizure-free outcome group as compared to controls. No significant area was detected in the non-seizure-free group as compared to controls (family-wise error corrected, p < 0.05). With extent analysis using a low threshold, the extents of hypometabolism in the ipsilateral hippocampal, frontal and thalamic areas were larger in the seizure-free than in the non-seizure-free group (p = 0.01, 0.03 and 0.01, respectively.) On the other hand, in the contralateral frontal and thalamic areas, extents of hypometabolism were smaller in the seizure-free than in the non-seizure-free group (p = 0.01 and 0.01). CONCLUSIONS: We found the preoperative distribution of hypometabolism to differ between the two patient groups. Severe hypometabolism restricted to the unilateral temporal lobe, with ipsilateral dominant hypometabolism including mild decreases, may support the existence of an epileptogenic focus in the unilateral temporal lobe and a favorable seizure outcome after mTLE surgery.
    Annals of Nuclear Medicine 07/2012; 26(9). DOI:10.1007/s12149-012-0629-9 · 1.51 Impact Factor
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    ABSTRACT: OBJECTIVE: We developed a novel technique of spatial normalization of subdural electrode positions across subjects and assessed the spatial-temporal dynamics of high-gamma activity (HGA) in the dominant hemisphere elicited by three distinct language tasks. METHODS: The normalization process was applied to 1512 subdural electrodes implanted in 21 patients with intractable epilepsy. We projected each task-related HGA profile onto a normalized brain. RESULTS: The word interpretation task initially elicited HGA augmentation in the bilateral fusiform gyri at 100ms after stimulus onsets, subsequently in the left posterior middle temporal gyrus, in the left ventral premotor cortex at 200ms and in the left middle and left inferior frontal gyri at 300ms and after. The picture naming task elicited HGA augmentation in few sites in the left frontal lobe. The verb generation task elicited HGA in the left superior temporal gyrus at 100-600ms. Common HGA augmentation elicited by all three tasks was noted in the left posterior-middle temporal and left ventral premotor cortices. CONCLUSIONS: The spatial-temporal dynamics of language-related HGA were demonstrated on a spatially-normalized brain template. SIGNIFICANCE: This study externally validated the spatial and temporal dynamics of language processing suggested by previous neuroimaging and electrophysiological studies.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 07/2012; 124(1). DOI:10.1016/j.clinph.2012.06.006 · 2.98 Impact Factor
  • 06/2012; 73(S 02). DOI:10.1055/s-0032-1314399
  • 06/2012; 73(S 02). DOI:10.1055/s-0032-1314246

Publication Stats

805 Citations
228.38 Total Impact Points


  • 2013
    • Niigata University
      Niahi-niigata, Niigata, Japan
  • 1997–2013
    • The University of Tokyo
      Tōkyō, Japan
    • Teikyo University
      • Department of Neurosurgery
      Edo, Tōkyō, Japan
  • 2012
    • Asahikawa Medical University
      • Department of Neurosurgery
      Asakhigava, Hokkaidō, Japan
  • 2006–2011
    • Tokyo Medical University
      • Department of Neurosurgery
      Edo, Tōkyō, Japan
  • 2002
    • University Hospital Medical Information Network
      • Department of Neurosurgery
      Tokyo, Tokyo-to, Japan
  • 1997–2001
    • Teikyo University Hospital
      Edo, Tōkyō, Japan
  • 1995
    • National Institutes of Health
      • Branch of Stroke and Ischemia
      Maryland, United States