Fiber dissection study is an old technique originating in the 17th century and reached its apex with the sophisticated atlas of Ludwig and Klingler in the mid 20th century. Recent advancements in neuroscience, however, have once again highlighted the macroscopic anatomy of the brain, seeking a more precise and detailed map of the cortices and white matters from a new perspective where the brain is organized into a complex network of multiple distinct neural circuits, working more like a dynamic network with plasticity, as opposed to the traditional rigid and localizationistic view. The neural basis of language had once been considered as a simple model consisting of the Broca’s area, the Wernicke’s area, and the arcuate fasciculus connecting the above two cortical areas. However, it has grown to be understood as a larger and more complex model, in which language is processed through two distinct pathways, the dorsal stream and the ventral stream. The superior longitudinal fasciculus/the arcuate fasciculus make up the backbone of the dorsal stream and are associated with phonological processing. The ventral stream consists of a network supported by the inferior fronto-occipital fasciculus and intratemporal pathways and is associated with semantic processing. The frontal aslant tract is a deep frontal tract connecting the supplementary motor area and the Broca’s area and it is associated with the driving of language. It is necessary for every neurosurgeon to have a basic knowledge of the neural basis of language, including both the anatomical and functional aspects for safer surgical planning, and preservation of language.

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  Diffusion of water is based on the principle that water molecules show random motion. In diffusion studies on magnetic resonance imaging using a motion proving gradient, a signal decrease which is caused by molecular diffusion in the tissue provides information about tissue structure and physiological status. Diffusion-weighted images play a very important role in brain related diagnosis, especially for acute infarctions, and have become an essential tool in clinical practice. Diffusion tensor imaging using the Gaussian distribution model also has made strides in evaluating anisotropic water diffusion in the white matter in which water diffusion is restricted by macromolecules, membrane, and myelin. Diffusion tensor imaging is based on a mathematical model of an ellipsoid. Thus principal directions of diffusion and the magnitude of diffusion along those directions can be calculated. Diffusion tensor tractography is an innovative application of the diffusion tensor method which can access the pathways of neuronal fibers. However, neuronal tissue is a highly heterogeneous structure on various scales and the Gaussian distribution has only been adapted for free diffusion in a fluid that is uniform and sufficiently large. Complicated wall structures exist in the neuronal tissue, and the Gaussian distribution model does not reflect the existence of a large number of compartments and nerve tracts, particularly in the central nervous system. Therefore, instead of a simple Gaussian distribution model, measurement of the probability distribution of a detailed water molecule is necessary. One method is q-space imaging (QSI). QSI is performed by measuring a large amount of diffusion encoding and can provide the probability density function of individual water molecules. Although QSI is theoretically superior to conventional Gaussian distribution analysis, one limitation of QSI is the long acquisition time due to the large sampling number. The concept of kurtosis is another method to evaluate non-Gaussianity. Kurtosis is a quantity that reflects a gap between the diffusion distribution of a water molecule in vivo and the Gaussian distribution, and can be calculated from datasets of relatively few diffusion encoding elements compared to QSI. Thus, a rather short acquisition time is required for kurtosis. Recently, other innovative applications of non-Gaussian diffusion have been introduced including neurite orientation dispersion and density imaging (NODDI) which is a model-based diffusion technique that allows for the quantification of specific microstructural features directly related to neuronal morphology. These novel techniques will provide useful information on tissue microstructure not only in the scientific research but also in the clinical practice.

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  The preservation of brain function during and after surgery still poses a challenge for neurosurgeons. High-frequency electrical stimulation techniques have been established in order to map the intraoperative brain function and preserve the eloquent areas during surgery. In addition to this functional cortical mapping, the subcortical fibers related to eloquent function have been extensively investigated by using high-frequency electrical stimulation. However, these cortical- and subcortical high-frequency electrical stimulation methods are only able to identify the local function (i. e., stimulus site). Even during awake craniotomy, no monitoring methods have as yet been established to preserve the integrity of the language network during surgery, as opposed to the monitoring methods utilizing motor evoked potentials for the motor network.
  We have recently developed an in vivo electrical tract tracing method using cortico-cortical evoked potentials (CCEPs). In an extraoperative setting for presurgical evaluation of epilepsy surgery, single-pulse electrical stimulation was applied directly to the cortex, and CCEPs were recorded from the adjacent and remote cortices through cortico-cortical connections. In an extraoperative setting, this method has successfully probed eloquent brain functional networks such as the language and motor networks. Because of the high reproducibility and reliability, CCEP technique could be applicable in an intraoperative setting to identify and monitor functionally eloquent networks.
  In our pilot intraoperative CCEP study, using CCEP connectivity patterns, we were able to map the anterior and posterior perisylvian language areas. Combined single-pulse and high-frequency electrical stimulation to the removal cavity (white matter) delineated both the function and cortical terminations of the dorsal language pathway. Although further case studies are necessary to establish a clear cut-off value to prevent language dysfunction, intraoperative CCEP monitoring is clinically useful for evaluating the integrity of the dorsal language network.

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  Functional neuroimaging techniques such as PET and functional MRI have been enhanced with a subtraction method allowing us to examine changes in brain activity associated with task performance. An implicit assumption of this method was that the brain is regarded as an input-output system driven by interaction with the external world. However, based on observations of spontaneous brain activity, or activity present even in the absence of task performance or stimuli, brain function can also be conceptualized as an operating-on-its-own system driven intrinsically, with external factors modulating rather than determining the operation of the system. Resting state network analysis with functional MRI is based on this conceptualization. Now this approach is being extended to across-brain network analysis to depict the neural representation of online social interaction. During a dyadic social interaction, two individuals can share visual attention through gaze, directed either to each other (eye contact) or to a third person or an object (joint attention). Eye contact and joint attention are tightly coupled to generate a state of shared attention across individuals. Hyperscanning fMRI in pairs of adults conducting joint attention tasks revealed the existence of an inter-individual neural synchronization in the right inferior frontal gyrus, after all the task-related effects were modeled out. We further conducted a two-day hyperscanning functional magnetic resonance imaging study in which pairs of participants performed a real-time mutual gaze task followed by a joint attention task on the first day, and mutual gaze tasks several days later. The joint attention task enhanced eye-blink synchronization, which is a behavioral index of shared attention. When the same participant pairs underwent mutual gaze without joint attention on the second day, enhanced eye-blink synchronization persisted, and this was positively correlated with inter-individual neural synchronization of the right inferior frontal gyrus. Thus, hyperscanning fMRI showed that the shared attention, a critical element of social interaction, is represented and retained by pair-specific neural synchronization that cannot be reduced to the individual level. The future perspective of this “we-mode” in neuroscience is discussed.

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  Clinical neuropsychology has analyzed various symptoms and signs after brain lesions seeking to understand the brain mechanisms underlying a wide range of cognitive functions. This type of semiology mainly deals with subacute to chronic pathophysiology, while the findings produced by electrical stimulation during awake surgery reflect the (hyper) acute modulation of brain functions. In recent neuropsychology trends, classical semiology has been reconciled with newly emerging approaches utilizing advanced imaging technology (e.g. functional imaging and tractography) and the findings taken during awake surgery, resulting in a paradigm shift in neuropsychological theories from localizationist models to neural network models. For example, an acute cognitive dysfunction resulting from a localized lesion is not always long lasting, which reflects the underlying redundancy of the neural network that takes part in the corresponding function. For resection of gliomas, the extent should be determined to achieve a favorable quality of life about a month post-surgery but not to prevent acute deficits. It is very important to revisit the vast accumulation of neuropsychological knowledge and to know the size and location of a lesion in order to ascertain how best we may secure a favorable recovery. The present review aims to provide such information focusing on the neural networks of language and spatial attention.

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  Cadaveric or radiological studies around the petrous apex structure have been reported. We assessed the bony ridge over Meckel’s cave and the superior petrosal sinus (SPS) and Dorello’s canal by 3D-CTA and MRI (CISS). Fifty-seven cases (male 18, female 39, mean age 57.8 years old) were evaluated basically on their normal side. Those included 29 meningiomas, 21 schwannomas, and 7 others. We classified these into 4 types concerning the bony structure over Meckel’s cave : No ridge ([none] type) in 56%, partial continuous ridge ([partial] type) in 24%, uncontinuous ridge ([free] type) in 7%, bony Meckel’s cave ([canal] type) in 11%. The SPS was also classified in 4 classes : No SPS ([none] type) 50%, [superior] route in 37%, [inferior] route in 9%, and both sides ([around] type) in 2%. Dorello’s canal was classified into 2 classes : it’s porus portion was inside of the sinus ([inside] type) in 71% and outside of the sinus ([outside] type) in 28%. We should also know that bony structure surrounds Meckel’s cave in 42%, the SPS passes under Meckel’s cave in 11%, and no venous sinus outside of Dorello’s canal is found in 28%. Understanding and utilizing this information could provide for much safer anterior petrosectomy procedures.

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  A solitary fibrous tumor (SFT) is a rare spindle-cell mesenchymal neoplasm, which frequently occurs in the pleural cavity and rarely in extrapleural sites. SFT of the central nervous system was first reported in 1996, and since then, more than 200 cases have been reported in the literature. We herein report a case of intracranial SFT extending supra/infratentorially. There are only ten similar cases reported in the literature.
  A 49-year-old female with a two-month history of disequilibrium was referred to our hospital. Contrast-enhanced magnetic resonance imaging (MRI) showed a right tentorial tumor extending supra/infratentorially, which was homogeneously enhanced. Right external carotid angiography showed intense tumor staining fed by the occipital artery. Under a preoperative diagnosis of tentorial meningioma, the tumor was removed with combined right suboccipital/occipital craniotomy after embolization of the feeding artery. The histopathological diagnosis was SFT. The patient’s postoperative course was uneventful, and her symptoms were completely resolved.
  Although intracranial SFT is poorly recognized and its preoperative diagnosis is still challenging, SFT should be included in the differential diagnosis of extra-axial tumors extending supra/infratentorially.

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