石下 洋平

Sound frequency and duration are essential auditory components. The brain perceives deviations from the preceding sound context as prediction errors, allowing efficient reactions to the environment. Additionally, prediction error response to duration change is reduced in the initial stages of psychotic disorders. To compare the spatiotemporal profiles of responses to prediction errors, we conducted a human electrocorticography study with special attention to high gamma power in 13 participants who completed both frequency and duration oddball tasks. Remarkable activation in the bilateral superior temporal gyri in both the frequency and duration oddball tasks were observed, suggesting their association with prediction errors. However, the response to deviant stimuli in duration oddball task exhibited a second peak, which resulted in a bimodal response. Furthermore, deviant stimuli in frequency oddball task elicited a significant response in the inferior frontal gyrus that was not observed in duration oddball task. These spatiotemporal differences within the Parasylvian cortical network could account for our efficient reactions to changes in sound properties. The findings of this study may contribute to unveiling auditory processing and elucidating the pathophysiology of psychiatric disorders.

The action observation network (AON) has been extensively studied using short, isolated motor acts. How activity in the network is altered when these isolated acts are embedded in meaningful sequences of actions remains poorly understood. Here we utilized intracranial electrocorticography to characterize how the exchange of information across key nodes of the AON-the precentral, supramarginal, and visual cortices-is affected by such embedding and the resulting predictability. We found more top-down beta oscillation from precentral to supramarginal contacts during the observation of predictable actions in meaningful sequences compared to the same actions in randomized, and hence less predictable, order. In addition, we find that expectations enabled by the embedding lead to a suppression of bottom-up visual responses in the high-gamma range in visual areas. These results, in line with predictive coding, inform how nodes of the AON integrate information to process the actions of others.

BACKGROUND: We previously found that vagus nerve stimulation (VNS) strengthened stimulus-evoked activity in the superficial layer of the sensory cortex but not in the deep layer, suggesting that VNS altered the balance between the feedforward (FF) and feedback (FB) pathways. Band-specific oscillatory activities in the cortex could serve as an index of the FF-FB balance, but whether VNS affects cortical oscillations along sensory pathways through neuromodulators remains unclear. HYPOTHESIS: VNS modulates the FF-FB balance through the cholinergic and noradrenergic systems, which modulate stimulus gain in the cortex. METHODS: We investigated the effects of VNS using electrocorticography in the auditory cortex of 34 Wistar rats under general anesthesia while presenting click stimuli. In the time-frequency analyses, the putative modulation of the FF and FB pathways was estimated using high- and low-frequency power. We assessed, using analysis of variance, how VNS modulates auditory-evoked activities and how the modulation changes with cholinergic and noradrenergic antagonists. RESULTS: VNS increased auditory cortical evoked potentials, consistent with results of our previous work. Furthermore, VNS increased auditory-evoked gamma and beta powers and decreased theta power. Local administration of cholinergic antagonists in the auditory cortex selectively disrupted the VNS-induced increase in gamma and beta power, while noradrenergic antagonists disrupted the decrease in theta power. CONCLUSIONS: VNS might strengthen the FF pathway through the cholinergic system and attenuate the FB pathway through the noradrenergic system in the auditory cortex. Cortical gain modulation through the VNS-induced neuromodulatory system provides new mechanistic insights into the effect of VNS on auditory processing.

Gamma oscillations are physiological phenomena that reflect perception and cognition, and involve parvalbumin-positive γ-aminobutyric acid-ergic interneuron function. The auditory steady-state response (ASSR) is the most robust index for gamma oscillations, and it is impaired in patients with neuropsychiatric disorders such as schizophrenia and autism. Although ASSR reduction is known to vary in terms of frequency and time, the neural mechanisms are poorly understood. We obtained high-density electrocorticography recordings from a wide area of the cortex in 8 patients with refractory epilepsy. In an ASSR paradigm, click sounds were presented at frequencies of 20, 30, 40, 60, 80, 120, and 160 Hz. We performed time-frequency analyses and analyzed intertrial coherence, event-related spectral perturbation, and high-gamma oscillations. We demonstrate that the ASSR is globally distributed among the temporal, parietal, and frontal cortices. The ASSR was composed of time-dependent neural subcircuits differing in frequency tuning. Importantly, the frequency tuning characteristics of the late-latency ASSR varied between the temporal/frontal and parietal cortex, suggestive of differentiation along parallel auditory pathways. This large-scale survey of the cortical ASSR could serve as a foundation for future studies of the ASSR in patients with neuropsychiatric disorders.

Primary central nervous system lymphoma (PCNSL) is a rare form of non-Hodgkin lymphoma, but its diagnosis is challenging in some cases. A brain biopsy is the gold standard for diagnosing PCNSL, but its invasiveness can be problematic. Thus, noninvasive imaging examinations have been developed for the pre-surgical diagnosis of PCNSL, including gadolinium-enhanced magnetic resonance imaging (MRI), 123I-N-isopropyl-p-iodoamphetamine single-photon emission computed tomography (123I-IMP SPECT), and positron emission tomography with 18F-fluorodeoxyglucose (18F-FDG PET). Here, we report the case of a 71-year-old woman with negative imaging findings for PCNSL, but who was diagnosed with PCNSL by a brain biopsy and histological analysis. Her imaging results were negative for gadolinium-enhanced cranial MRI, with low uptake in 123I-IMP SPECT and hypometabolism in 18F-FDG PET. However, a stereotactic brain biopsy from an abnormal lesion revealed that many round cells had infiltrated into the brain. Moreover, many infiltrating cells were positive for cluster of differentiation (CD)20 and CD79a, and proliferation marker protein Ki-67-positive cells accounted for nearly 80% of all cells. Based on these results, our final pathological diagnosis was PCNSL. The present case highlights the possibility of a PCNSL diagnosis even when all imaging-related examinations display negative results.

Epilepsy surgery should be aggressively considered for the cases of drug-resistant intractable epilepsy, especially earlier in infant and child because persistent epileptic seizures adversely affect on their psychomotor development. To achieve postoperative seizure free, it is required to identify epileptogenic zone and resect epileptic focus completely. Although radical resection of epileptic focus located on eloquent area possibly cause severe neurological complications, relatively good neurological outcomes can be expected because of neural plasticity of childhood brain. Furthermore, it is another reason for deciding surgical indication that long-term administration of anti-epileptic drug causes unfavorable effects on cognitive function of children. On the other hand, the surgical impacts on post-surgical intelligent quotient or coexisting neuropsychiatric disorders are still controversial. Here, we present the most appropriate timing for performing pediatric epilepsy surgery, showing our own clinical examples and literature considerations.

An epileptic seizure during the course of driving can result in a serious car accident. However, basic data on how epileptic seizures actually affect driving performance is significantly lacking. To understand the relationship, it is crucial to conduct not only behavioral but also electroencephalogram (EEG) analysis during epileptic seizures. Therefore, we developed a mobile driving simulator which makes it possible to record driving-related parameters time-lined with video-EEG. We report a case in which behavioral and EEG changes were successfully recorded during ictal periods of focal impaired awareness seizure in a patient engaged with the system. With the current lack of objective data describing how seizures impair driving performance, such an accumulation of information could improve personalized medical management, influence legal adjudication and assist in the development of driving support systems for people with epilepsy.

Auditory mismatch negativity (MMN) is an electrophysiological response to a deviation from regularity. This response is considered pivotal to understanding auditory processing, particularly in the pre-attentive phase. However, previous findings suggest that MMN is a product of N1 adaptation/enhancement, which reflects lower-order auditory processing. The separability of these two components remains unclear and is considered an important issue in the field of neuroscience. The aim of the present study was to spatiotemporally differentiate MMN from N1 adaptation using human electrocorticography (ECoG). Auditory evoked potentials under the classical oddball (OD) task as well as the many standards (MS) task were recorded in three patients with epilepsy whose lateral cortices were widely covered with high-density electrodes. Close observation identified an electrode at which N1 adaptation was temporally separated from MMN, whereas N1 adaptation was partially incorporated into MMN at other electrodes. Since N1 adaptation occurs in the N1 population, we spatially compared MMN with N1 obtained from the MS task instead of N1 adaptation. As a result, N1 was observed in a limited area around the Sylvian fissure adjacent to A1, whereas MMN was noted in wider areas, including the temporal, frontal, and parietal lobes. MMN was thus considered to be differentiated from N1 adaptation. The results suggest that MMN is not merely a product of the neural adaptation of N1 and instead represents higher-order processes in auditory deviance detection. These results will contribute to strengthening the foundation of future research in this field.

Auditory contextual processing has been assumed to be based on a hierarchical structure consisting of the primary auditory cortex, superior temporal gyrus (STG), and frontal lobe. Recent invasive studies on mismatch negativity (MMN) have revealed functional segregation for auditory contextual processing such as neural adaptation in the primary auditory cortex and prediction in the frontal lobe. However, the role of the STG remains unclear. We obtained induced activity in the high gamma band as mismatch response (MMR), an electrocorticographic (ECoG) counterpart to scalp MMN, and the components of MMR by analyzing ECoG data from patients with refractory epilepsy in an auditory oddball task paradigm. We found that MMR localized mainly in the bilateral posterior STGs, and that deviance detection largely accounted for MMR. Furthermore, adaptation was identified in a limited number of electrodes on the superior temporal plane. Our findings reveal a mixed contribution of deviance detection and adaptation depending on location in the STG. Such spatial considerations could lead to further understanding of the pathophysiology of relevant psychiatric disorders.

Restoration of speech communication for locked-in patients by means of brain computer interfaces (BCIs) is currently an important area of active research. Among the neural signals obtained from intracranial recordings, single/multi-unit activity (SUA/MUA), local field potential (LFP), and electrocorticography (ECoG) are good candidates for an input signal for BCIs. However, the question of which signal or which combination of the three signal modalities is best suited for decoding speech production remains unverified. In order to record SUA, LFP, and ECoG simultaneously from a highly localized area of human ventral sensorimotor cortex (vSMC), we fabricated an electrode the size of which was 7 by 13 mm containing sparsely arranged microneedle and conventional macro contacts. We determined which signal modality is the most capable of decoding speech production, and tested if the combination of these signals could improve the decoding accuracy of spoken phonemes. Feature vectors were constructed from spike frequency obtained from SUAs and event-related spectral perturbation derived from ECoG and LFP signals, then input to the decoder. The results showed that the decoding accuracy for five spoken vowels was highest when features from multiple signals were combined and optimized for each subject, and reached 59% when averaged across all six subjects. This result suggests that multi-scale signals convey complementary information for speech articulation. The current study demonstrated that simultaneous recording of multi-scale neuronal activities could raise decoding accuracy even though the recording area is limited to a small portion of cortex, which is advantageous for future implementation of speech-assisting BCIs.

Objective: Cortico-cortical evoked potential (CCEP) has been utilized to evaluate connectivity between cortices. However, previous reports have rarely referred to the impact of volume-conducted potential (VCP) which must be a confounding factor of large potential around the stimulation site. To address this issue, we challenged the null hypothesis that VCP accounts for the majority of the recorded potential, particularly around the stimulation site. Methods: CCEP was recorded with high-density intracranial electrodes in 8 patients with intractable epilepsy. First, we performed regression analysis for describing the relationship between the distance and potential of each electrode. Second, we performed principal component analysis (PCA) to reveal the temporal features of recorded waveforms. Results: The regression curve, declining by the inverse square of the distance, fitted tightly to the plots (R-2: 0.878-0.991) with outliers. PCA suggested the responses around the stimulation site had the same temporal features. We also observed the continuous declination over the anatomical gap and the phase reversal phenomena around the stimulation site. Conclusions: These results were consistent with the null hypothesis. Significance: This study highlighted the risk of misinterpreting CCEP mapping, and proposed mathematical removal of VCP, which could lead to more reliable mapping based on CCEP. (C) 2017 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

An 83-year-old woman was admitted with a diagnosis of transient symptoms with a left hemisphere infarction due to atherosclerosis. Despite the best medical treatments, her neurological symptoms gradually deteriorated. The color Doppler ultrasound (CDUS) and digital subtraction angiography (DSA) demonstrated a near occlusion of the left cervical internal carotid artery. Because the intracranial internal carotid artery (ICA) seemed patent on DSA, although CDUS also suggested that the intracranial ICA was also occluded, carotid endarterectomy was performed. However, magnetic resonance angiography performed immediately after the operation showed distal occlusion of the ICA. A superficial temporal artery-middle cerebral artery (MCA) bypass was performed immediately to rescue the region that was perfused by the MCA. The neurological symptoms stabilized after the operation. It is often difficult to assess the patency of the intracranial ICA by DSA if distal ICA flow is slow and faint. Although the pulsed Doppler waveform can be affected by the site of the distal occlusion, CDUS would be a good addition to the preoperative evaluation. And if the patency of the ICA distal to the stenosis cannot be confirmed, especially in emergent settings, a superficial temporal artery-MCA bypass can be a good treatment option.

OBJECTIVE: To present indications, surgical techniques, and outcomes of extracranial-intracranial (EC-IC) graft bypass. METHODS: Between January 1996 and June 2011, 38 patients with large or giant internal carotid artery (ICA) aneurysms were treated using graft bypass, employing the radial artery (RA) or the saphenous vein (SV) as a graft. Preoperative balloon test occlusions were not performed in any of the cases. In 17 patients, the external carotid artery (ECA)-RA-M2 segment of the middle cerebral artery bypass was used for treatment, and ECA-SV-M2 bypass was used in 21 patients. RESULTS: All aneurysms were completely trapped, and there were no subarachnoid hemorrhages or recanalizations of aneurysms during the follow-up period (8-170 months). Of the 38 bypasses, 36 (94.7%) remained patent, and there were no permanent neurologic deficits. Hyperperfusion syndrome was not experienced in this series. There were 2 temporary neurologic deficits. In 1 case using the RA, graft vasospasm occurred, and kinking occurred in 1 case using the SV. Another patient with a SV graft had to undergo an emergent revision of the graft 8 hours after the initial operation. One patient with a SV graft underwent a second operation to control an epidural abscess. CONCLUSIONS: Universal EC-IC graft bypass is a safe and effective method for treating large or giant ICA aneurysms.

BACKGROUND: The treatment of unclippable vertebral artery (VA) aneurysms incorporating the posterior inferior cerebellar artery with parent artery preservation is among one of the most formidable challenges for cerebrovascular microsurgery and endovascular surgery. We propose that intracranial VA reconstruction using an extracranial VA-to-intracranial VA (VA-VA) bypass with a radial artery graft or an occipital artery graft may be an additional technique in the armamentarium to treat these formidable lesions. The rationale, surgical technique, and complications are discussed. METHODS: Three illustrative cases are described, in which the lesions were a VA dissecting aneurysm with ischemic lesions, bilateral asymptomatic unruptured VA aneurysms, and a VA giant aneurysm with subarachnoid hemorrhage. RESULTS: The partial extreme lateral infrajugular transcondylar approach was used. Computed tomographic angiography was useful for preoperative evaluation of the depth of the distal aneurysmal neck. A VA-VA bypass was performed in two patients. Because there was another ipsilateral aneurysm at the V2 segment in one patient, an external carotid arteryeVA bypass was performed. Although two patients were discharged with good clinical results, one patient with subarachnoid hemorrhage died because of brainstem infarction. CONCLUSIONS: The VA-VA bypass using a radial artery graft or an occipital artery graft is an option that can be considered in the strategy for treating VA aneurysms to preserve the normal anatomic vascular configuration in the posterior circulation.

Whether to provide surgical intervention within 24 hours of intravenous recombinant tissue plasminogen activator (rt-PA) treatment is a subject of controversy. In this study, we report a case in which neurological deterioration was prevented by urgent bypass surgery performed shortly after rt-PA treatment.