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Background: The aim of this study was to investigate whether default mode network (DMN) connectivity and brain white matter integrity at baseline were associated with severe cognitive impairments at baseline and poor cognitive outcomes after shunt placement in patients with idiopathic normal pressure hydrocephalus (iNPH).Methods: Twenty consecutive patients with iNPH whose symptoms were followed for 6 months after shunt placement and 10 healthy controls (HCs) were enrolled. DMN connectivity and brain white matter integrity in patients with iNPH at baseline were detected by performing resting-state functional magnetic resonance imaging with independent component analysis and by using diffusion weighted imaging with tract-based spatial statistics, respectively. Performance on the neuropsychological tests for memory and executive functions and gait test was assessed in patients with iNPH at baseline and 6 months after shunt placement.Results: The mean DMN connectivity in the iNPH group was significantly reduced compared with that in the HC group and was significantly positively correlated with the scores of the Rey auditory verbal learning test (RAVLT) immediate recall and the frontal assessment battery (FAB). The mean fractional anisotropy of the whole-brain white matter skeleton in the iNPH group was significantly lower than that in the HC group. We divided the patients with iNPH into relatively preserved and reduced DMN connectivity groups using the indexes of DMN connectivity and white matter integrity. The reduced DMN connectivity group showed significantly worse performance on RAVLT at baseline and significantly worse improvement of RAVLT immediate recall and FAB scores compared with the preserved DMN connectivity group. Moreover, the RAVLT immediate score/the FAB score ratio highly distinguished the patients with relatively preserved DMN connectivity from those with relatively reduced DMN connectivity.Conclusions: Our findings indicated that iNPH patients with relatively reduced DMN connectivity in comparison to the severity of brain white matter involvement are associated with severe memory deficits at baseline and poorer cognitive outcomes after shunt placement. In addition, DMN connectivity/brain white matter integrity and RAVLT immediate score/FAB score ratios are useful predictors of poor cognitive outcomes after shunt placement.

A 14-year-old boy suffered from daily epileptic seizures originating from the left polymicrogyric occipital cortex. Visual activation positron emission tomography (PET) was used to map the function of the occipital cortex presurgically. Loss of visual function in the left occipital cortex was suggested by both visual activation PET and electrical cortical stimulation. Left occipital lobectomy resulted in a completely seizure-free status without deterioration in the visual function. Preoperative evaluation of the visual function in the epileptogenic occipital cortex by activation studies using PET or functional magnetic resonance imaging is the key to the successful surgical treatment of occipital lobe epilepsy.

The positions of the bilateral N100m sources of the auditory evoked magnetic fields (AEFs) were measured in relation to the central sulcus (CS) using an MRI-linked whole head magnetoencephalography system in 20 right-handed normal male subjects. The location of the N20m source of the median nerve-stimulated somatosensory evoked magnetic fields (SEFs), in the left hemisphere was 3.9+/-5.4 mm (mean+/-SD) posterior to that in the right hemisphere (P0.005). The crossing point (CP) between the CS and Sylvian fissure in the left hemisphere was 4.3+/-4.8 mm posterior to that in the right hemisphere (P0.001). The N100m sources were posterior to the CP in both hemispheres. The left hemispheric N100m source was 9.4+/-6.4 mm posterior to that on the right (P0.0001) in absolute position. The relative distance between CP and the N100m source was 22.7+/-8.5 mm in the left hemisphere and 17.7+/-5.3 mm in the right hemisphere (P0.01). Comparison of positions of the AEF sources and the CS as defined by the SEF demonstrated functional asymmetry of the human temporal lobe and possible source extension of the AEF-N100m beyond the Heschl gyrus over the planum temporale.

Objective: Temporo-parietal theta activity (TPTA), often detected in hemispheres with internal carotid (ICA) or middle cerebral artery (MCA) occlusive lesions, is more clearly separated from occipital alpha activity by magnetoencephalography (MEG) than electroencephalography. The present study investigated whether TPTA is correlated with misery perfusion, a surgically correctable type of hemodynamic impairment. Methods: Awake MEG was measured in 56 patients with ICA or MCA occlusive lesions. Regional cerebral blood flow (rCBF) and regional cerebrovascular reactivity (rCVR) to acetazolamide were measured in the MCA territory by xenon-133 single-photon emission computed tomography. MEG was repeated in 10 patients after vascular reconstruction surgery. Results: Fourteen patients showed TPTA in the lesion hemisphere (n = 13) or bilaterally (n = 1). The presence of TPTA was significantly correlated with both reduced rCBF and reduced rCVR (P = 0.0009). After surgery, TPTA disappeared in 7 of the 10 studied patients. Conclusions: The presence of TPTA suggests misery perfusion, which is characterized by reduced rCBF and reduced rCVR. Significance: MEG can detect the presence of reversible and surgically remediable cerebral ischemia before the development of complete infarction.

Rhythmic theta activity detected by electroencephalography (EEG) may be correlated with cerebrovascular brain diseases. Magnetoencephalography (MEG) has higher sensitivity and spatial resolution than conventional scalp EEG, so may be a better method to detect theta rhythm in patients with internal carotid artery (ICA) occlusive disease. Simultaneous EEG and MEG were performed in the awake state in 48 patients with unilateral ( n = 42) or bilateral ( n = 6) stenotic lesions (more than 60% occlusion) of the ICA ( n = 47) or middle cerebral artery ( n = 7), and in 27 age-matched healthy normal subjects. No subject had severe neurological deficits. MEG detected the theta rhythm (6–8 Hz) in 14 of 48 patients: ipsilateral to the stenotic or occluded side in 13 hemispheres and bilaterally in one patient with unilateral lesion. The source of the MEG theta rhythm was estimated in the dorsolateral temporo-parietal area, regardless of the location of infarct foci or the stenotic portion of the ICA system. The temporo-parietal theta rhythm was separated from the occipital alpha rhythm by frequency and distribution in MEG. The theta rhythm was found in only two patients by EEG, as well as by MEG. MEG provided better separation of this theta rhythm from the occipital alpha rhythm. Neither MEG nor EEG detected this theta rhythm in the normal subjects. Unilateral temporo-parietal theta rhythm is correlated with the hemisphere with ICA occlusive disease. This rhythm may indicate mild or subclinical abnormalities in the ICA system. MEG is superior to EEG for the detection and localization of theta rhythm.

A 16-year-old girl suffering from intractable temporal lobe epilepsy presented with a pilocytic astrocytoma, which occurred in an area of nodular heterotopia located in the white matter of the temporal lobe. The pilocytic astrocytoma appeared to be covered by an area of gliosis, which contained numerous Rosenthal fibers, while in the lesion the pilocytic astrocytoma occupied a small area. The gliosis eventually became a tumor-like lesion. The white matter around the mass was composed of gliosis with nodular heterotopia. Temporal developmental malformation, which was a basic lesion of the patient, might therefore be a precursor lesion of pilocytic astrocytomas.

Pattern reversal stimulus is most frequently used for clinical application of visual evoked potentials (VEPs). Half-field stimulus has been employed to separate the left and right hemispheric responses. In the partial-field stimulus, however, subjects have to fix their eyes on a given point during the entire procedure; if the visual fixation is not strict, bilateral occipital responses may interfere with each other. In a clinical applications, therefore, the partial-field stimulus may not be suitable for inexperienced patients.

Due to excellent spatio temporal resolution and noninvasive nature of the measurements, magnetoencephalography (MEG) becomes a powerful tool for clinical application. This is especially the case in evoked MEG applied for presurgical diagnosis of the patients who suffered brain diseases. However, in spontaneous activity such as epileptic discharges, applicability is not so simple. This is because, for spontaneous waves, several brain activities or noises were superimposed on the detected signal, and separation for target activity is generally difficult. Small array of sensing coils also restricted the spatial resolution and sometimes brought erroneous results simply because they could not cover the entire brain at once. The appearance of whole-head MEG directly linked to magnetic resonance imaging (MRI) reduces data acquisition time, patient fatigue and localization error. It also provides objective information about patients which is essential for correct diagnosis. Spontaneous MEG studies used to be concentrated to epileptic spike activity. However, slow wave activity, typically observed by electroencephalography (EEG), is quite common in stroke, tumor, epilepsy, cerebrovascular disease, or head injury. Earlier investigations of slow wave activity with MEG [1–3] were restricted to small (1 to 37) channel system. Here we present the results of whole head MEG and source analysis of a slow wave activity.

It is critical to preserve eloquent cortices during surgery of cerebral arteriovenous malformations (AVMs). Although MRI scans may identify “anatomical” central suclus, it is controversial whether the “functional” central sulcus can be shifted due to AVMs. Cortical recording of somatosensory evoked potentials (SEPs) can be used to recognize the central sulcus during open surgery. However, the cortical SEPs are not available during surgery for large AVMs, intravascular surgery, or stereotaxic radiosurgery. In the present study, somatosensory evoked fields (SEFs) were measured to localize the “functional” central sulcus non-invasively in cases with AVM adjacent to the central sulcus.

Visual image is supposed to be processed by parallel pathways that analyze different properties of vision such as form, depth, motion, and color. Positron emission tomography (PET) studies of functional specializations of the human visual system have demonstrated that the fusiform gyrus is playing a role in color processing[1],[2]. Poor time resolution of PET, however, gave no information about the time course of the activity in the brain. Although visual evoked potentials (VEPs) studies with dipole source analysis [3],[4] supplemented PET results, no direct comparison with the anatomy of the visual cortex of subjects was made. This is because spatial resolution of source localization in VEPs is low[4]. We have been investigating visual evoked magnetic fields (VEFs), which in principle have much better spatial resolution than VEPs, and found that the most prominent response (P100) evoked with pattern-reversal stimulation was located in the primary visual cortex[5].

Auditory evoked potentials have been measured in patients with several temporal lobe diseases. The N100 responses disappear in patients with lesions on bilateral superior temporal gyrus[1]. However, separation of a unilateral abnormality in evoked potentials, is difficult due to the spearing effect by tissue layers with inhomogeneous electric conductivities. Activity on the normal hemisphere may interfere with abnormal activity on the diseased hemisphere. Magnetoencephalography (MEG) is known to be less influenced by the inhomogeneous head conductivity. We have found that the whole head MEG is especially suitable to identify differences in bilateral cerebral function [2–4].

The “cruciform model” of the visual cortex suggests that the P100 generators of the visual evoked responses to pattern reversal (PR) stimuli are located throughout the entire striate cortex, including the interhemisphere surface and calcarine fissures. Our recent studies of visual evoked fields (VEFs) to PR stimuli [1–3] have localized the P100m sources near the lateral end of the calcarine fissures. We suggested that a smaller part of the striate cortex contributes to the P100m response than in the cruciform model. In the present study, we measured PR-VEFs in patients with homonymous hemianopsia due to unilateral occipital lobe lesions, to demonstrate the correlation between PI00m patterns and occipital lesions.

✓ The N100m wave response of the auditory evoked magnetic field originates in the posterior part of the bilateral superior temporal planes for either contra- or ipsilateral ear stimulus. Cortical auditory function was evaluated in 14 patients with temporal lobe tumors using a magnetic resonance (MR) imaging—linked whole-head magnetoencephalography (MEG) system. Before surgery, seven patients had normal N100m latency (within the range of the mean ± 2 standard deviations of 37 normal volunteers) in both normal hemispheres and in those with lesions, and MR imaging indicated no tumor invasion or edema in the posterior one-third of the superior temporal planes, even when the sylvian fissure was shifted upward due to the mass effect. Seven patients had prolonged N100m latency or absence of N100m in the hemisphere containing the lesion, and the posterior portion of the superior temporal plane was involved by the tumor or perifocal edema. Prolonged N100m latency recovered to the normal range after removal of tumors in two of four patients investigated postoperatively. The MEG system can be used to evaluate cortical auditory function noninvasively before and after surgical treatment of temporal lobe tumors.